School Science Lessons
2024-04-18
Papaya Project
(ProjPap)
Contents
Preface
Aim
Pawpaw
1.0 Papaya plant
1.1 Crop diary
2.0 Prepare to plant seed
3.0 Make a seed nursery
3.1 Seed mixes for pots
3.2 Planting seeds
4.0 Percentage germination calculation
5.0 Chose and prepare the land
6.0 Study the plant before transplanting
7.0 Transplanting
8.0 Papaya flowers
9.0 Care for the papaya garden
10.0 Culling and pollination
11.0 Harvesting
12.0 Harvest and profit
13.0 Papaya uses and recipes
14.0 Pests and diseases
Records
Other papaya topics
15.1 Babaco, Mountain papaya, (Carica pentagona)
15.2 Chemicals in papaya
15.3 Commercial papaya seed
15.4 Genetics of papaya
15.5 Growing papaya at home in the subtropics
15.6 Papaya varieties, "Paiola"
16.1 Grafting papaya
16.2 Papaya propagated by marcotting
16.3 Papaya research
16.4 Tissue culture
16.5 Variation between plants
Asimina triloba, American pawpaw, pawpaw, Eastern North America, Annonaceae
Aim of Papaya Projec
The aim of this Papaya Project is to teach how to grow papayas as a managed crop to provide a regular supply of fresh fruit or cooked vegetable in the diet.
These teaching notes explain how to start a Papaya Project and how to look after the papaya plants to get plenty of fruit to eat.
Most people have seen papayas growing and they may ask why they should study them at school.
There are three reasons:
* Papaya is a useful addition to the diet, because a ripe fresh papaya contains lots of vitamin A and some vitamin C.
If picked when hard and green, it can be cooked like pumpkin and it can be used to make into a tasty jam.
* These teaching notes explain how to increase the yield of papaya by controlling energy loss.
* Papaya has a very interesting structure and life history.
Pawpaw
1. The common pawpaw, (Asimina triloba), is a temperate fruit tree, native to eastern North America.
2. The mountain pawpaw, (Vasconcellea pubescens), is a fruit tree, native to South America.
3. The papaya, (Carica papaya), is a widely cultivated tropical fruit tree.
In Australia, a papaya, (Carica papaya), plant or fruit, is commonly called a "pawpaw".
1.0 Papaya plant
See diagram 58.1: Papaya with fruit
See diagram: Red papaya
Broad Leaf Papaya, Daleys Fruit Tree Nursery
Dwarf Papaya 'Southern Red', Carica papaya, Daleys Fruit Tree Nursery
Dwarf Papaya Torpedo, Daleys Fruit Tree Nursery
1. (Carica papaya), papaya, paw paw, a tall evergreen herb; with large, yellow, melon-like fruit; is used fresh and for juice, is propagated from seeds and by grafting; is a herbal medicine, and comes from Tropical America; Family Caricaceae.
(Carica) was the first fruit tree to have its genome recorded.
The papaya fruit has a thickened orange to orange-red ovary wall containing carotene pigments, sugars, but no starch.
Ripening starts at the centre then moves outwards.
It is a low acid fruit with a delicate smell, caused by terpenes.
The many small, black seeds are not usually eaten, but they can be dried and used for seasoning.
Unripe papaya can be used for salads and pickling.
Some people eat it raw, in very thin slices, as a digestive.
The green fruit has a milky latex, containing the proteolytic digesting enzyme | Papain |, which is used in some meat tenderizers.
Male papaya flowers are good source of papain.
(Carica pubescens) is not as sweet, but contains Lycopene, so is more reddish in colour.
1.1 Crop diary
Keep a crop diary and record the following:
* When planting seed, germination, transplanting, culling, hand fertilizing, picking
* When and how much harvest, cost of seed, fertilizer, materials for a nursery
* When recording income from selling papayas.
2.0 Prepare to plant seed
1. Select a papaya that has a good size and shape, growing in a group of trees that all have good fruit.
Leave this papaya on the tree until the day before you want to use it.
2. The papaya garden planned in these will have 20 mature trees at 2 metres x 2 metres - a total area of 48 square metres.
This will require 50 seeds planted at 15 cm and 50 seeds planted in 50 metal beverage cans.
In Queensland, when planting dioecious varieties, growers generally plant 4 seedlings to the site, thinning sites to 1 male site to 10 female sites.
Planting density varies between growers, but on average is 750 sites to the acre, or 1,850 to the hectare.
The amount of seed required is 50 grams per acre or 125 grams per hectare.
When planting bisexual varieties, growers generally plant 2 or 3 seedlings to the site, thinning to 1 bisexual tree per site.
Some growers market the female fruit of the bisexual plant, although the flesh is not as thick.
Seed required is 40 grams per acre or 100 grams per hectare.
3. If you want to add fertilizer, you will need five matchboxes of NPK 12-15-10 or 9-25-25 or 9-25-25,
or phosphate sprinkled over the seed bed, and a teaspoon of fertilizer in each steel can.
4. Use an opened steel can or beverage can with four holes punched in the bottom.
5. The best papaya seed comes from a large smooth fruit growing nearby.
Select a papaya from group of trees that all have good fruit.
6. Papaya seed must be used fresh, or cleaned then sealed in an airtight jar.
Put copper oxychloride in the jar to protect the seed from attack by fungus.
7. You can plant seed as follows:
* in a seed bed 15 cm apart and 1 cm deep and.
* in steel cans, fish tins, jam tins, beverage cans.
Both methods of planting need shade.
Papayas are often attacked by nematode worms in the soil, so planting seed in clean sand in steel cans may be the best method.
8. Line the steel cans with paper or leaves.
Fill the steel cans with a mixture of clean sand and dried crushed leaves or grass.
3.0 Make a seed nursery
See diagram 58.3: Papaya nursery
1. You will need the following
* Spades, forks, hoes, bush knife, rake, string, tape measure.
* Fresh papaya seeds.
* Uprights, sticks and palm leaves for a nursery.
* If you want to use fertilizer, bring steel can of mixed fertilizer or superphosphate, a matchbox and a spoon.
2. The papaya seeds will take 3-4 weeks to germinate, and be ready for transplanting in 10 - 12 weeks.
See the arrangement of seeds planted in the seed bed.
3. Select a small piece of land about 2 x 1 metres, with good topsoil, in a well drained position.
4. Dig up the soil to make a fine even seed bed.
Improve the soil of the seed bed by adding sand and crushed dry leaves.
Water the seed bed well.
5. Fill the steel cans with a mixture of clean sand and crushed dried leaves.
Water the steel cans well.
Scratch your name on the steel can.
6. Plant the seeds in the seed bed, 1 cm deep, in rows 15 cm apart, and cover the seeds with sand and dried leaves.
Water the seeds again.
Press down on the seed bed with a flat board.
Plant one seed in each jam tin, one centimetre deep.
Water the steel cans well.
7. Build four uprights, cross sticks and a light shade of palm leaves.
8. Water the seeds in the seed bed or steel cans every day.
The plants will germinate in 3-4 weeks.
They will remain 10-12 weeks in the nursery, before they are big enough for transplanting, when more than 10 cm high.
9. If fertilizer is to be used, add five matchboxes of mixed fertilizer or superphosphate to the seed bed, or a teaspoon of fertilizer to each jam tin.
3.1 Seed mixes for pots
1. Use: 20 litres peat moss, 20 litres vermiculite (Grade 3), 120 g superphosphate (ground to a powder)
2. Use: 90 g lime or dolomite, 27 g sulfate of ammonia (ground to a powder), 7 g trace elements nix, 9 g sulfate of iron
Organic potting mixes
3. Use: 20 litres peat moss, 20 litres vermiculite (Grade 3), 70 g guano, 60 g dolomite
4. Use: 10 g organic potassium (ground to a powder), 1 litre blood and bone fertilizer
Sterilize pots before use with a 3:1 water/chlorine solution.
Wet the mixture in a bucket before filling pots.
Soak seed in water for 24-36 hours.
Change the soaking water as it discolours.
Soaking allows faster germination, replacing the moisture removed in the drying process when the seeds were stored
Place pots in a shade house with 30%-40% shade cloth
Plants seeds in pots < 10 mm depth.
Use mesh bench tops for good air circulation around pots.
To rain proof a shade house, purchase builders film and fix it under the shade cloth with wire.
Seedlings must not be too wet to avoid infection by Pythium and Phytophthora, so water in the mornings.
Fertilizer in conventional mix should last 4 weeks.
If the seedlings appear a yellow, use a soluble fertilizer, e.g. Thrive.
3.2 Planting seeds
1. Sterilize pots need with 3:1 water : chlorine solution.
Put pots in a shade house having 30%-40% shade cloth and use mesh bench tops to allow air circulation around pots.
2. Soak seed in water for 24-36 hours.
Changing water as it discolours.
Plant seed in pots < 10 mm depth.
To discourage infection by Pythium and Phytophthora, seedlings should be damp, not wet, so one watering each morning is sufficient.
The fertilizer in seed mixes 1. and 2. should last 4 weeks.
However if the seedlings appear a yellow then apply a soluble fertilizer, "e.g. Thrive".
3. Bisexual plants, e.g. Red Lady papaya, "RB5", form both bisexual and female seed.
The thin bisexual flower is about 8 cm long.
The short and rounded female flower is about one centimetre long.
Bisexual fruit is thin, long and has a smaller hole in the centre.
If you have one bisexual plant and two female plants you can hand-pollinate the plants.
Bisexual papaya may be affected by "carpellody" ("cat-facing", carpelliod fruits), caused by the fusing of the ovary and stamens during bad weather.
Cat-facing fruit becomes deformed and hard to sell.
So bisexual varieties are not normally grown in sub-tropical areas.
Plant 2-3 seedlings to the site, and later thin to 1 bisexual tree per site.
The seed required is 100 g per hectare.
4. Hybrids are formed by crossing two "fixed" (stable) parent lines.
They are more vigorous than their parents, produce more fruit and are less susceptible to disease.
Also, they are very consistent in fruit shape and size if grown in stable conditions.
The hybrid seeds for sale are only the first cross of the parent lines, i.e. F1 hybrids.
However, further hybrids grown from seed collected from F1 fruit will be inconsistent in shape, size and yield.
5. For dioecious plants (male and female flowers on different plants), plant 4 seedlings to the site and later thin sites to one male site to ten female sites.
With planting density of 1850 sites to the hectare, the seed required is 125 g per hectare.
6. Decide whether to plant the papaya seeds into a seed bed or into containers, e.g. as steel cans.
Plants in a seed bed are easy to look after, but the plants may die after transplanting.
Plants in steel cans can be easily transplanted, but they are harder to look after, because they must be watered regularly for 10-12 weeks.
Use both seed bed and steel cans to compare the results as in an experiment.
7. You will need the following:
* Large ripe papayas for seed
* About 20 kg of lime or dolomite if your soil is very acid, ask an agriculture extension officer.
The soil pH should be 6.0-6.5.
Some people also use Epsom salts to give increased magnesium to the plants.
8. I you wish to add fertilizer, you will need:
* About 10 kg mixed fertilizer with a high content of phosphorus, e.g. NPK 12-15-10 or NPK 9-25-25 or NPK 10:3:6 superphosphate.
* About 10 kg of urea or ammonium sulfate, or potassium sulfate.
* If the leaves are yellowing, use a spray of 1 g / litre of boron on the leaves and soil.
4.0 Percentage germination calculation
1. If you plant 50 seeds in the seed bed and 42 germinate to form seedlings then the percentage germination is as follows:
42 / 50 100 = 84% in seed bed.
If you plant 50 seeds in the steel cans and 47 germinate to form seedlings then the percentage germination is as follows:
47 / 50 100 = 94% in jam tins.
From this calculation, the conclusion is that it is better to plant in steel cans to get good germination.
2. Examine the germinated seeds in the nursery and count them as follows
Number germinated in seed bed.
Number germinated in the jam tins.
Dig up germinated seeds from the seed bed, but not from the jam tin.
Keep the dug up seedlings wet.
2. Number of seeds germinated seed bed, steel cans percentage germinated:
Number germinated in seed bed x 100 = (call this "percentage seed bed")
Number planted in seed bed
Number germinated in steel cans x 100 = (call this "percentage tins")
Number planted in steel cans Is there any difference between percentage seed bed and percentage tins?
5.0 Chose and prepare the land
1. Use bush knives, hoes, forks, spades, string, tape measure or rule, sticks.
2. Go to a place where:
a. old papayas are growing,
b. where the soil is badly drained or it is windy,
c. which you have selected as suitable for the papaya garden.
3. Dig a hole in the place you have selected to show the soil profile.
4. Mark out the land, 6 metres 8 metres, and mark the four corners with sticks.
Then clear the land and hoe and fork it lightly.
Mark each 2 metres 2 metres position with a stick then dig a hole next to the stick.
5. Put wood ashes or 1 steel can of mixed fertilizer or superphosphate in each hole.
6.0 Study the plant before transplanting
See diagram 58.6: Young plant before transplanting
1. Dig up some smaller plants, wash the roots and bring them to the class.
2. The diagram represents the general arrangement of parts of a plant before transplanting.
Be able to draw accurately from a living specimen using the diagram as a guide to understanding the structure.
The shoot is the stem, buds and leaves.
The axil is the angle between the stem and the leaf.
The terminal bud may increase the length of the stem or form flowers.
The axillary bud may remain quiet or it may form a lateral shoot (a branch or it may form flowers.
The thickened parts of the stem called nodes produce leaves and axillary buds.
The smooth parts of the stem between the nodes are called the internodes.
3. Note length of plant, the number of nodes and internodes, and the internode distances.
7.0 Transplanting
See diagram 58.7: Positions of transplants in papaya garden
1. Plants are ready for transplanting when they are more than 10 cm high.
Transplanting experiment: seed bed or steel cans.
Plant around 10 holes in the papaya garden from plants in the seed bed and plant around 10 holes from plants in the container steel cans.
Papayas may die after transplanting and this experiment will show which is the best method.
Transplant on a dull wet afternoon.
2. Sequence for transplanting:
* Dig four transplanting holes around each fertilizer hole and fill them with water.
* Water plants in nursery.
* Select plants from nursery.
* Do not damage roots when transplanting.
* Level of soil up the stem in a papaya garden should be no higher than in a nursery.
* Remove one leaf from each transplant to reduce water loss through leaves.
* Transplant four plants quite close around each fertilizer hole, because you keep only 1 plant of each 4, when you select the largest male or female plant.
3. Transplanting method
* Use: Trowels or spades, watering can.
* To develop interest in these plants, make a transplanting map:
* Have some mulch ready.
* Dig four transplanting holes around each fertilizer hole in the papaya garden and fill them with water.
* Water plants in nursery
* When planting around the S holes, select four plants each from the seed bed, dig them up very carefully and transplant them no deeper than in the nursery.
* When planting around the T holes, select four steel cans with healthy plants.
Take the steel cans to the garden, and open the bottoms of the steel can.
Plant no deeper than in the steel can.
* Water all 80 transplants in the garden.
* Place mulch around each plant, but not touching the plants.
* If you want to use fertilizer, put 3 matchboxes of ammonium sulfate or urea in each fertilizer hole.
8.0 Papaya flowers
See diagram 58.9: Papaya flower
1. Papaya plants are unusual, because the sex type is female flower or hermaphrodite flower or male flower.
You cannot tell which sort of flower will be formed until the immature flowers have formed.
2. Female plants produce the large female flowers only, near the trunk close to the base of the hollow leaf stalk.
In the female flower each petal is separate and there are no stamens.
3. Male plants produce only male flowers.
Many small flowers are found hanging down on long branches.
Some plants, e.g. a variety from Hawaii called Solo, are bisexual having male and female parts.
4. The genetics of sex are as follows:
M1 dominant for maleness, M2 dominant for hermaphrodite, m recessive for female.
All combinations of M1 and M2 are sterile.
M1m are male, M2m are hermaphrodite and mm are female.
The cross mm X M2m give half plants female with round fruits and half plans hermaphrodite with cylindrical fruits.
5. The sex of a male papaya tree may sometimes be changed by cutting it down to about one metre off the ground.
It may send out two strong shoots below the top that bear female flowers and fruits.
9.0 Care for the papaya garden
1. Make regular visits to the papaya garden to see how the plants they transplanted are growing.
Record anything unusual.
2. Give an extra lesson on the need for careful observations.
Give a prize for the first report of flowers forming!
3. To get good flavour in your papayas feed them monthly.
When they are young with no fruit, use a high nitrogen fertilizer.
When they start to fruit, use "Dynamic Lifter" or "Organic Xtra", + a handful of sulfate of potash.
4. Papaya need 100 gm of sulfate of potash per month, i.e. about 42 g of potassium.
If papaya fruit is not sweet, they need more potash.
They also require nitrogen, so use poultry pellets if the leaves do not have a healthy green look.
5. Always keep the garden free of weeds and rubbish.
6. When the first flowers appear cut down excess male plants and female plants leaving 2 male and 18 females, each 2 metres apart.
Two males should be on a windy side of the garden.
Extra female plants can be cut back to height of 60 cm and left for a reserve if bigger ones die.
7. You can pollinate female flowers if you open the buds of male flowers and brush pollen on to the stigmas.
This is called hand pollination.
When stigmas go brown and die, pollination is successful and fruit will form.
10.0 Culling and pollination
1. Culling refers to cutting down the unwanted male and female plants.
Unwanted plants should not be pulled out unless diseased.
They should either be cut across at ground level if no longer wanted or cut across 60 cm above the ground to be kept as replacement plants.
2. First select two male plants on the windy side of the papaya garden so that the pollen can blow over all the female plants.
Later, you can pollinate by hand to make sure that all the female flowers will produce fruit.
Papaya are easily cross pollinated.
Even at 10 kilometres distance if the wind direction is favourable.
Insects are also good pollinating agents so avoid using insecticides.
3. Then cut across at ground level all the remaining male plants.
Leave only the tallest female next to each fertilizer hole.
Cut the other females down to 60 cm.
4. Cut down all the other male plants in the school grounds.
5. You will need axes or bush knives.
6. If tree grows too tall, cut the top off in the dry season and it will form branches.
You will need to prop up the branches.
7. Check the wind direction.
* Cut down all male trees except two so that wind can blow pollen from the two towards the female plants.
* Cut down excess female trees to height of 60 cm.
* Pick some male flowers still in the bud - peel back the petals and brush the pollen on to the female flowers.
* Draw a plan of the 20 plants left in the papaya garden in their notebooks and show where the male and female plants are.
* Papaya are easily cross pollinated, even at 10 kilometres distance, if the wind direction is favourable, papaya flowers if ready can be fertilized from other trees.
Also, insects are also good pollinating agents.
13.2.1 Bacterial soft rots, Erwinia spp.
Bacterial canker Erwinia sp.
Papaya dieback, (Erwinia papayae)
Black rot, (Erwinia cypripedii)
Erwinia decline (Erwinia sp.)
Erwinia mushy canker (Erwinia sp.)
Purple stain (Erwinia herbicola)
Bacterial soft rots, (Erwinia carotovora, E. chrysanthemi, E. herbicola, E. amylovora, E. papayae).
The pathogen attacks the top of the leaf stalk causing yellowing and then browning.
The leaf collapses and will turn brown.
If the tip of the plant is infected the whole plant will rot and die.
Symptoms can look like Phytophthora infection, but split the stem, because Phytophthora usually starts at the bottom and other infections start at the top of the tree.
Black rot, (Erwinia cypripedii)
Purple stain, (Erwinia herbicola)
Internal fruit infection, (Erwinia herbicola), Postharvest disease
Internal fruit infections, (Enterobacter cloacae), Postharvest disease
Water-soaked areas on base of leaf stalks and crown of papaya infected with (Erwinia papayae).
Fruits infected by (Erwinia papayae), flesh with water-soaked areas.
Erwinia decline, Erwinia mushy canker, (Erwinia sp.)
Papaya dieback, (Erwinia papayae), occurs in Malaysia.
The disease may have been spread by human activity and possibly birds and insects.
By the end of 2006 it had caused the destruction of approximately 1 million trees.
Early symptoms included yellowing and necrosis along leaf edges followed by water-soaked areas on the bases of leaf stalks, crowns and along leaf midribs.
Fruit symptoms included dark spots on the skin and water-soaked flesh.
Later, necrotic and water-soaked areas developed on stems and spread to the internal tissues, followed by secondary fungal infections.
In advanced stages bending of water-soaked leaf stalks occurs, leading to dieback, and death of trees.
Infection of the main trunk.
Note the ooze from the centre of the lesion (with maggots feeding on the ooze).
The outside of the plant rots away leaving the fibrous material inside.
13.2.2 Black rot, Bacterial spot, (Xanthomonas campestris pv. campestris)
Black Rot is a common name given to a variety of diseases caused by various fungal or bacterial pathogens and water moulds (oomycetes).
The symptoms vary depending on the pathogen type and host plant.
Black rot infection causes rot inside the young fruit, which then drop to the ground or form brown lesions on ripening fruit.
The fungus enter the fruit through wounds from contact with stems or leaves on a very windy day.
Treat black spot with fungicides or dip fruit in 50oC water for 20 minutes.
Collect and burn any fallen fruit and when harvesting do not put fruit on the ground.
13.2.3 Papaya Bunchy Top Disease
Papaya bunchy top disease is caused by a mycoplasma-like organism (MLO).
It occurs in the Caribbean region, Central and South America.
After mottling of upper leaves the laminae of become more chlorotic in interveinal areas, develop marginal necrosis, and become rigid.
The internodes become shortened, and petioles adapt a more horizontal position.
Oily spots appear in the upper parts of stems and in petioles.
Apical growth ceases and the shortening internodes give the plant a "bunchy top" appearance.
The plants may die or new shoots may appear from the lower parts of the stems.
Fruit of infected plants have a bitter flavour.
The disease is transmitted by leafhoppers, (Empoasca papayae) and (E. stevensi), and by grafting.
No papaya plants have complete immunity, but more tolerant cultivars do exist.
Control methods: Use leafhopper control, remove sources of inoculum by topping infected plants below where latex exudes, drench the soil with chlortetracycline.
Papaya bunchy top virus.
Irregular water-soaked marks at the base of the leaf stem.
Fruiting or latex discharge rarely occurs on severely infected trees.
Can be found with other symptoms on the younger leaves.
These two causes are extremely difficult to tell apart in the field.
Papaya Bunchy Top.
Candidatus phytoplasma carica.
Upper leaf mottling and yellowing between leaf veins, leaves are thickened and the edges may turn brown.
Tree leaves and leaf stalks are smaller (shorter internodes), giving a bunchy top appearance.
Fruits can become bitter and the entire tree may die.
Research report: Papaya bunchy top (PBT), a major disease of (Carica papaya) in the American tropics, was thought to be caused by a phytoplasma.
Bacteria detected were rod-shaped, their cell wall resembled that of Gram-negative bacteria.
The bacteria were consistently observed by light microscopy in expressed sap from fresh pawpaw petioles of plants with PBT symptoms.
All attempts to isolate the bacteria were unsuccessful.
If the bacterium causes PBT, it would be the first example of a leafhopper-transmitted, latex cell-inhabiting, plant pathogenic bacterium.
14.0 Pests and diseases
14.1 Planning to treat pests and diseases
14.2 Bacterial diseases
14.3 Fungus diseases
14.4 Insect pests
14.5 Mites
14.6 Nematodes
14.7 Virus infections
14.8 Abiotic fruit disorders
CABI = "Centre for Agriculture and Biosciences International"
14.1 Planning to treat pests and diseases
Papaya is a sensitive plant attacked by many pests and diseases, with only some specific to papaya.
Papaya fruit is easily damaged to allow extra infections before and after harvest.
Consult an agriculture extension officer and ask about:
* the pests and diseases of papaya in your region and the recommended control measures,
* which pesticides and fungicides are recommended and allowed for use in school gardens.
Papaya is sensitive to some fungicides that may cause phytotoxicity, injuries to leaves and skin of fruits, and even the death of plants.
The most commonly used fungicides are mancozeb (not USA), and chlorothalonil, but get advice from an agriculture extension officer.
Plants that are well looked after and healthy can withstand most of these pests and diseases.
Do not allow any diseased trees to remain in the school grounds and keep the papaya project clear of any fallen plant material.
14.2 Bacterial diseases
13.2.1 Bacterial soft-rots, (Erwinia spp.)
Bacterial soft-rots, Erwinia papayae).
Soft rot, watery fruit rot, (Rhizopus stolonifer)
13.2.2 Black rot, Bacterial spot, (Xanthomonas campestris pv. campestris)
13.2.4 Bacterial leaf spot: (Pseudomonas carica-papayae)
Maribo (Pseudomonas maribos)
Bacterial wilt: (Pseudomonas solanacearum)
13.2.5.Internal yellowing, (Enterobacter cloacae)
Internal yellowing Erwinia sp.
14.3 Fungus diseases
14.3.1 Alternaria fruit spot, (Alternaria alternata)
14.3.2 Angular leaf spot, Powdery mildew of cotton, (Leveillula taurica)
13.3.3 Anthracnose, (Colletotrichum gloeosporioides)
13.3.4 Black spot, (Asperisporium caricae)
14.3.5 Blossom spot, Choanephora fruit rot, (Choanephora cucurbitarum)
13.3.6 Black rot, (Mycosphaerella caricae), (Guignardia bidwellii)
13.3.7 Brown spot, Corynespora brown spot, (Corynespora cassiicola)
14.3.8 Collar rot, Cylindrocladium disease, (Cylindrocladium crotalariae), (Calonectria crotalariae)
13.3.9 Damping off, (Rhizoctonia solani)
14.3.10 Dry rot, (Phoma caricae-papayae)
Leaf spot of papaya, (Mycosphaerella caricae)
13.3.11 Foot rot, (Pythium spp.)
14.3.12 Fruit spot, (Cercospora mamaonis)
14.3.13 Fusarium fruit rot, Fusarium wilt (yellows), (Fusarium spp.)
14.3.15 Guignardia spot, (Guignardia dioscoreae), postharvest disease
Greasy spot, (Corynespora casiicola)
13.3.16 Grey Mould, (Botrytis cinerea)
14.3.17 Internal blight, (Cladosporium sp.),( Fusarium spp.),(Penicillium sp.)
14.3.18 Lasiodiplodia fruit rot, (Lasiodiplodia theobromae)
14.3.19 Leaf spot, (Alternaria sp.), (Asperisporium caricae), (Ascochyta caricae-papayae)
(Mycosphaerella caricae). (Phyllosticta sulata)
14.3.20 Petiole spot, Canker of tomato, (Didymella lycopersici)
Phytophthora fruit rots, (Phytophthora palmivora)
Phytophthora palmivora blight, (Phytophthora palmivora)
13.3.22 Powdery mildew, (Oidium caricae-papayae)
14.3.23 Rhizopus soft rot, (Rhizopus stolonifera)
13.3.24 Root rot, Black root rot, (Pythium spp.), (Phytophthora spp.)
14.3.25 Sclerotium blight, Sclerotium rot, (Sclerotium rolfsii)
14.3.26 Seedling blight, (Colletotrichum gloeosporioides)
Black-leg of seedlings, (Pythium ultimum)
14.3.27 Stem-end rot, (Mycosphaerella), (Botryodiplodia theobromae), (Stemphylium lycopersici), (Phomopsis sp.)
(Rhizopus stolonifer), (Lasiodiplodia theobromae), (Ascochyta caricae), (Alternaria alternata)
14.3.28 Stemphylium fruit spot, Grey leaf spot, (Stemphylium lycopersici)
14.3.29 Stem rot, (Fusarium sp. (Phytophthora palmivora), (Pythium spp.)
14.3.30 Target spot, Target leaf spot of tomato, Corynespora cassiicola), Phyllosticta caricae-papayae)
14.3.31 Verticillium wilt, (Verticillium dahliae)
14.3.32 Wet rot, wet fruit rot, (Phomopsis caricae-papayae)
13.3.3 Anthracnose, (Colletotrichum gloeosporioides)
Starts as a small pink spot, but progresses to cover a wide area.
It is prevalent in high humidity conditions and mainly attacks the maturing fruit, with mature fruit being more susceptible.
It causes small water-soaked spots that enlarge, turn brown or black and become darker.
The fungus grow into the fruit tissue, ruining it for consumption, resulting in softening of the fruit and an "off" flavour.
It causes small round, dark areas on ripe fruit which later enlarge into sunken lesions fruit will rot.
Post-flowering drop of 5- to 15-day-old pawpaw fruits by (Colletotrichum gloeosporioides) in Arunachal Pradesh, India.
Circular to oval, sunken, brown to black-coloured spots were observed on the surface of the dropped fruit or at the blossom and stalk ends.
In some cases, severely affected fruits did not drop off and remained attached to the plant as small, mummified fruits with a mass of fungal growth.
Seedling blight: (Colletotrichum gloeosporioides), (Colletotrichum dematium) (leaf spot), (Colletotrichum papayae)
Collectotrichum rot, fruit surface rot, anthracnose, (Glomerella cingulata), Postharvest disease
Round, water-soaked, sunken spots, can become as large as 50 mm diameter.
Turning pinkish orange, with fungal masses in the centre.
It is often present on over-ripe.
Small water-soaked spots appear on the fruit surface as ripening commences.
Circular sunken lesions with light brown margins form, with pink fungal masses in the centre.
Internal tissue is firm with a greyish white discoloration.
13.3.4 Black spot, (Asperisporium caricae)
Black spot infection causes circular brown lesions on older leaves, raised lesions on trunks and sunken lesions on fruit, the leaves turn brown and curl.
Treat black spot with fungicides.
Plants deficient in potassium, phosphorous and magnesium are more susceptible to attack by black spot and powdery mildew.
Increase potassium in the soil with sulfate of potash or lucerne mulch.
Increase phosphorous in the soil with rock phosphate or chicken manure.
Increaser magnesium in the soil with magnesium sulfate crystals (Epsom salts).
Papaya are most susceptible to black spot disease during the cooler months.
Spray with sulfur or copper-based compounds prior to the onset of the cool weather and water with liquid seaweed, e.g. "Seasol", to help reduce the severity of infestations.
Control: Spray from March to October with Mancozeb or Folicur, if an agriculture extension officer approves.
Cover fruit and cut off lower leaves.
Lesions start as water soaked spots that become necrotic (brown).
These develop into pale shallow circular lesions up to 10 mm diameter often surrounded by a chlorotic halo.
There is no tissue decay beneath.
The white zones in the photo are fungal parasites of the pathogen and not the pathogen itself.
Lesions start as water soaked spots that become brown.
These lesions develop into pale circular leaf spots up to 4 mm diameter often surrounded by a yellow ring.
Young leaves are not attacked, but severely damaged older leaves fall off and up to half of the leaves can fall off causing a reduced vigour.
Disease is favoured by wind and rain for dispersal.
Cercospora black spot, (Cercospora papayae), University of Hawaii
Black Spot Cercospora sp.
Tiny Black dots on fruit which enlarge to 3 mm across.
Spots are slightly raised and although indistinct on unripe green fruit.
Become visible on ripening to yellow; lesions on leaves are irregular in shape and grey-white in colour.
If infection is severe, leaves may turn yellow and die and drop from plant.
Stem rot of pawpaw, (Phomopsis caricae-papayae)
13.3.6 Black rot, Dry rot, (Mycosphaerella caricae)
Mainly attacks young fruits, usually at the point of contact with dead leaves.
Can affect ripening fruits through broken fruit stalks.
Small, dark, sunken, water-soaked regions, wrinkled fruits which may ooze sap.
13.3.7 Brown spot, Corynespora brown spot, (Corynespora cassiicola)
Pale yellow lesions with brown centres on upper leaf surface, 1-2 mm in diameter, but can join together into larger areas.
On lower leaf surface small light and water soaked brown spots with yellow halo, turning necrotic.
All lesions become brown and sunken with reddish margins.
Spores are more apparent on lower surfaces.
Lower leaves are particularly susceptible.
Brown rot, (Monilinia fructigena)
Chocolate spot, (Colletotrichum gloeosporioides)
13.3.9 Damping off fungus, Phytophthora
Water mould, Phylum Oomycota, Class Oomycetes, 1. Phytophthora group, (Phytophthora palmivora), (Phytophthora nicotianae). 2. Pythium group, 3. Downy mildews, 4. White blister rusts, ( Albugo sp.)
Phytophthora fruit rot, Phytophthora and stem rot.
The fungus-like Phytophthora causes lesions on unripe fruit that later ooze latex and cover the fruit with white mycelium.
Phytophthora lives in the soil and enters damaged plants.
Treat Phytophthora infection with mancozeb or copper sulfate.
Plant papaya in new soil that has never had Phytophthora infection.
Control: plant in raised beds or well-drained ground.
The diseases caused by this pathogen include damping-off of seedlings, root rot, stem-rot and fruit rot.
Papaya plants of all ages are susceptible to Phytophthora root rot, but seedlings up to 2 months old are most susceptible.
Leaves of affected plants turn yellow, wilt, and eventually drop prematurely.
Root rot generally originates as minor lesions on smaller lateral roots, which quickly develop into a major rot of the tap root, making trees unstable and prone to damage during high winds.
Phytophthora causes stem rot (trunk rot), following severe storms.
Brown sunken cankers occur on the stem and the upper portion of the plant will collapse due to the expanding rot.
Immature and mature green fruit infected with Phytophthora develop water-soaked lesions and the fruit become covered with off-white mycelium of the pathogen.
Infected fruit falling to the ground are a major source of the disease.
The pathogen is a soil-inhabiting water mould and requires water for spore production and fruit infection.
Cause is cool damp weather conditions.
Control with wettable sulphur @3.5g per litre. Bayfidan @20ml per 100 litres.
CABI names of Phytophthora species which infect Papaya
Stem and fruit rot of Capsicum, (Phytophthora capsici)
Phytophthora dieback, (Phytophthora cinnamoni)
Phytophthora blight, (Phytophthora infestans)
Black shank, (Phytophthora nicotianae)
Coconut budrot, (Phytophthora palmivora)
Damping Off, (Phytophthora spp.)
Shoots and roots are necrotic; seedlings necrotic with watery roots; seeds have watery rots.
If the plant is older, infections are not as lethal, but they can still have a significant impact on plant growth and yield, particularly in abnormally hot and windy weather.
13.3.11 Foot rot, (Pythium spp.)
Fruit rot initially appears as small, circular, water-soaked spots about 5-10 mm in diameter.
Large lesions, often forming first where the fruit touches the stem of the plant.
As the pathogen spreads within the fruit it becomes covered with whitish fungal growth and masses of Phytophthora sporangia.
Phytophthora diseases include damping-off of seedlings, root rot, stem-rot and fruit rot.
Phytophthora root rot, Phytophthora palmivora
Severely infected plants may die.
Plants with a heavy load of fruit may fall.
Papaya plants with rotten roots are susceptible to drought.
Fruit rots are difficult to control, because the fruit is usually infected when green and the rot develops when the fruit ripens.
Watch the fruit closely for signs of fruit rot and pick the fruit immediately any sign of rot appears.
Rotten fruit should be burned.
Some types of papayas are more easily attacked by fruit rot than others, so when visiting village gardens look out for papaya plants not affected by disease.
Anthracnose infections cause sunken round water-soaked lesions with brown margins in ripening fruit.
It is spread by wind and rain.
Treat anthracnose with fungicide or dip fruit in 50oC water for 20 minutes.
13.3.16 Grey Mould, (Botrytis cinerea)
An opportunistic pathogen that will attack weak and over-ripe fruit.
It will occur in times of high humidity and especially on damaged fruit.
A characteristic grey fluffy (fuzz) of spores will cover the rot which gradually spreads over all of the fruit.
13.3.22 Powdery mildew, (Oidium caricae-papayae)
(Sphaerotheca sp.), (Erisiphe sp.)
Lower leaf surfaces spotted with small water soaked yellow dots that become powdery patches of fungus and spores.
Patches are usually near the veins and are more clearly seen in humid conditions.
Yellow patches later become necrotic (brown) and scorched.
Leaves may curl and fall from trees early.
Powdery mildew starts as white powdery growth developing first in spots on the underside of leaves during cold winds and light grey areas on the skin of the fruit.
The spots later join up to form yellow patches and then the leaf looks burnt and dried out.
It is caused by the fungus (Oidium caricae-papaye) (formerly (Erisiphe cruciferarum))
It can be controlled with wettable sulfur dust or a weekly spray of 1 part full cream milk and 10 parts of water.
A scar on the fruit shows where the mildew has been.
Mildew on immature fruit begins as circular patches of white powdery material that join together and cover the entire fruit.
As the fruit ripens, the fungus may disappear leaving behind grey scars.
13.3.24 Root rot, Black root rot, (Pythium spp.), (Phytophthora spp.)
Browning of the inside of the roots.
Damage start at the ends of the secondary roots and progresses towards the inside of the primary roots.
Rot is at the base, but general wilting and stunting of the plant/tree from the top down.
Rapid browning and wilting of the plants, followed by total collapse within days
Young leaves wilt and matured leaves turn yellow and drop.
Root rot, collar rot and fruit rot have a foul odour
,
The leaves drop and plant will die, spray with metalaxyl
Root rot fungus can attack the roots in wet soils.
The leaves from the older leaves will collapse down and wilt and the plant dies.
This fungus can enter the roots easily when nematode worms attack the roots.
14.4 Insect pests
13.4.1 Castor capsule borer, Yellow peach moth, (Conogethes punctiferalis)
13.4.2 Citrus Mealybug, (Planococcus citri)
13.4.3 Cotton aphid, (Aphis gossypii)
13.4.4 Fruit-piercing moth, (Eudocima fullonia)
13.4.6 Fruit sucking moths, (Othreis fullonia)
13.4.7 Green peach aphid, (Myzus persicae)
13.4.8 Leaf hopper of papaya, (Empoasca papayae)
13.4.9 Empoasca papayae is capable of transmitting PMeV-Mx to C, Sticky disease virus, to papaya var. ‘Maradol’.
13.4.10 Mediterranean fruit fly, Ceratitis capitata)
13.4.11 Melon fly, (Bactrocera cucurbitae)
13.4.12 Oriental fruit fly, (Bactrocera dorsalis)
13.4.13 Oriental yellow scale, (Aonidiella orientalis)
13.4.14 Papaya fruit fly, (Toxotrypana curvicauda)
13.4.15 Papaya hornworm, (Erinnyis alope)
13.4.16 Papaya mealybug, (Paracoccus marginatus)
13.4.17 Papaya whitefly, (Trialeurodes variabilis)
13.4.18 Queensland fruit fly, (Bactrocera tryoni)
13.4.19 Snow Scale, (Unaspis citri)
13.4.20 Stevens leafhopper, (Empoasca stevensi)
13.4.21 Striped mealybug, (Ferrisia virgata)
13.4.22 Tobacco thrips, (Thrips parvispinus)
13.4.23 Tobacco whitefly, (Bemisia tabaci)
13.4.24 White peach scale, Mulberry scale, (Pseudaulacaspis pentagona)
13.4.25 Whitefly, (Aleurodicus dispersus)
13.4.1 Yellow peach moth, (Conogethes punctiferalis).
Control: nil. Cut tree out. Usually attacks unwell trees.
Feeds on the surface of fruit.
Leaves scarring, sometimes rots.
13.4.2 Citrus Mealybug, (Planococcus citri)
Adult female, pinky/white and covered in wax.
Females suck sap and cause wilting, yellowing and stunting.
The honeydew they produce often leads to sooty mould.
The little white fingers around the insect edge are more obvious than on the Papaya Mealybug.
13.4.4 Fruit-piercing moth, (Eudocima fullonia)
Only the adult form is the pest.
Moths feed at night by piercing the skin of the ripe or ripening fruit with their strong mouth parts.
Internal injury to papaya consists of a bruised, dry area beneath the skin.
Secondary roots develop at the feeding site.
Secondary-moth feeders often visit fermenting fruit, using the holes the fruit piercing moths have made.
Only the adult form is the pest.
Moths feed at night by piercing the skin of the ripe or ripening fruit with their strong mouth parts.
Internal injury to papaya consists of a bruised, dry area beneath the skin.
Secondary roots develop at the feeding site.
Secondary-moth feeders often visit fermenting fruit, using the holes the fruit piercing moths have made.
Other species are called "Fruit-piercing moth".
13.4.5 Fruit-spotting bug, Amblypelta nitida
Attacks growing point, upper stem and the petioles of the younger leaves.
Can cause severe damage.
13.4.6 Fruit sucking moths or fruit piercing moths
Control nil, because larvae feeds on the Stephania vine which is common on the coast.
Moths can be trapped, but it is hit and miss exercise.
Make a cone from mosquito netting and a wire base, then place a small ripe fruit in the apex.
When disturbed or when they take off these moths fly straight upwards, thus getting caught in the top of the trap.
At night the moth eyes reflect brightly when caught in car headlights or in torchlight.
13.4.11 Melon fly, (Bactrocera cucurbitae)
It can attack flowers as well as fruit, and additionally, will sometimes attack stem and root tissue. with eggs being laid into unopened male and female flowers, and larvae even developing successfully in the taproots, stems and leaf stalks.
Treatment of Papaya Fruit for Bactrocera dorsalis and Bactrocera cucurbitae.
Vapour heat treatment (VHT) is used disinfest papaya fruits from oriental fruit fly, Bactrocera dorsalis, and melon fly, Bactrocera cucurbitae, which are major pests for papaya fruits.
It was found that when the papaya fruit core temperature increased to 47.2°C in 3 h, both fruit flies showed 100% mortality.
Both fruit quality and injury test results demonstrated insignificant differences in colour, appearance, soluble solids, or firmness of fruits before and after treatment.
Thus, VHT effectively disinfested papaya fruits against both fruit fly species, thus making it a viable quarantine treatment for papaya fruits prior to their export.
13.4.12 Oriental fruit fly, (Bactrocera dorsalis)
Brown and yellow fly; slightly smaller than a housefly.
Lays eggs below the skin of the fruit.
Larvae (maggots) hatch and feed inside the fruit almost immediately.
The fruit often falls off and the maggots leave the fruit to pupate in the soil.
This pest is not seasonal, it occurs continuously throughout the year in many areas.
Small puncture wounds with circular halos on the fruit surface; rotting of the skin.
The puncture holes often allow other diseases to attack the fruit, making the fruits difficult to sell.
13.4.14 Papaya fruit fly, (Toxotrypana curvicauda)
Very characteristic insect which lays its eggs through the papaya fruit into hole in the middle of the fruit.
The maggots feed on the developing seeds and fruit in the centre of the fruit.
The mature maggot tunnels out of the fruit and pupates in the soil.
Infested fruits turn yellow and fall early.
13.4.16 Papaya mealybug, (Paracoccus marginatus)
Body yellow, covered with wax, but this is not thick enough to hide body colour.
Heavy infestations cause distortion of new growth, leaf yellowing, leaf curl and early fall of fruit.
The honeydew they produce often leads to sooty mould.
Fruit may become completely covered by a layer of mealybugs and wax secretions.
Heavy infestations may cause early fruit fall.
When infested the fruit loses value or cannot be sold at markets.
13.4.18 Queensland fruit fly, (Bactrocera tryoni)
Control: Spray with Lepidex or Lebacid or Rogor, if approved by an agriculture extension officer.
Baits traps males only, but indicates quantity of flies present.
Use yeast- based baits set soon after winter for females.
Baits are very effective if timing is right.
Pick fruit in early stages of ripening to avoid stings.
13.4.19 Snow Scale, (Unaspis citri)
The young (nymphs) are ‘crawlers’, because this is the dispersal stage.
Nymphs are oval and bright yellow in colour and form a waxy armour.
The snow white armour of the immature male is the reason for the name.
The coat has three long ridges; one prominent centre ridge, and one either side.
Immature males are about 1 mm long.
13.4.24 White peach scale, (Pseudaulacaspis pentagona)
Causes leaf chlorosis and twig dieback.
Produces honeydew leading to sooty mould, which can reduce plant vigour and cause death of tree if severe.
Common on leaves and fruit.
Males and females look quite different and both are pests.
The adult female (shown) cannot move on the plant.
Small, circular insect (up to 2mm diameter).
Conical in shape there is a darkened tip to the cone.
Males are mobile and appear as tiny grains of rice.
It is a widespread and serious pest of papaya and is currently widely distributed in the Palearctic and Nearctic Regions.
It only lives indoors in colder countries and has started to spread northwards in Europe.
It is a polyphagous species and has between one and four generations per year in different parts of the world.
It overwinters in cold countries as adult females.
To control white peach scale in papaya in Hawaii using imported parasitoids,
Two parasitic wasps, Encarsia berlesei and E. diaspidicola have been imported into Hawaii for its biological control.
Heavy infestations on the bark of trees produce large, visible white colonies of female and male scales.
Obtaining scale-free nursery material is very important, because young plants can die very quickly after infestation. The removal of heavily infested parts of the trees and the cleaning of bark from infestation can improve the efficacy of chemical treatments.
Surrounding vegetation can be a source of re-infestation by pests and/or a refuge for natural enemies.
14.5 Mites
13.5.1 Broad Mite, (Polyphagotarsonemus latus)
13.5.2 Citrus red mite, (Panonychus citri), (upper surface of mature leaves)
13.5.3 False Spider Mite, (Brevipalpus phoenicis)
13.5.4 Red and black flat mite, (Brevipalpus phoenicis) (fruit)
13.5.5 Spider mites, (highly polyphagous, spread on wind, crop yield reduction)
13.5.6 Tuckerellid mites, (Tuckerella spp.), (trunks of old plants)
13.5.7 Texas citrus mite, (Eutetranychus banksii) (upper surface of mature leaves)
13.5.1 Broad Mite, (Polyphagotarsonemus latus)
There are various mites, tiny spiders, that may attack papaya plants.
If little red spider mites are found under the leaves, treat them with wettable sulfur spray.
Similarly the fruit spotting bug attacks the leaf stalks and young fruit causing the fruit to drop.
Edges of damaged young leaves usually curl.
The foliage often becomes rigid and stiff, it appears brown (bronzed) or scorched.
Leaves are very small and do not expand properly.
Mites are too small to be seen, even with a hand lens.
Broad mite, Polyphagotarsonemus latus (seedlings, young plants, lower surface of young leaves)
Control by spray with Kelthane @ 2ml per litre. Wettable sulphur @3.5g per litre with no wetter.
Only spray sulphur below 25oC.
Sulphur can burn the fruit.
13.5.3 False Spider Mite, (Brevipalpus phoenicis)
The mites scratch the surface of the developing fruit, which responds by producing sap (latex).
The milky white sap will dry on the surface of fruit leaving ugly dry scabs.
It is very small, flat reddish; moves around very quickly on the surface of leaves or fruit.
Hand lenses are needed to see it properly.
It can create marks, scarring and sometimes a mosaic on leaf and fruit skin.
It reduces plant vigour and affects the taste of the fruit.
It causes marks, scarring and sometimes a mosaic on leaves and fruit skin.
It reduces plant vigour and affects the taste of the fruit.
14.6 Nematodes
13.6.1 Lesion nematode,
(Pratylenchus spp.)
13.6.2 Reniform nematode Rotylenchulus spp.
13.6.3 Root-knot nematode, (Meloidogyne spp.)
13.6.4 Lesion nematode,
(Pratylenchus sp.)
13.6.5 Spiral nematode, (Helicotylenchus dihystera)
13.6.6. Xiphinema basiri
13.6.3 Root-knot nematode, (Meloidogyne javanica)
Lumps or galls of between 1 and 10 cm on the roots.
Heavily-galled roots may rot away.
Tree or plant growth stunted, starts to wilt, followed by a general chlorosis.
This can result in the death of the tree if severely infected roots are continually attacked.
Nematode worms are the small white S-shaped worms pointed at both ends.
There is no treatment for this disease except to drain the soil.
If the plant dies, pull it out with the roots and burn it, but do not replant.
14.7 Virus infections
14.7.3 Papaya ringspot virus, (PRSV)
14.7.4 Papaya lethal yellowing virus, PLYV
14.7.5 Papaya sticky disease, Papaya meleira virus (PMeV)
14.7.6 Papaya mosaic virus, PaPMV
14.7.9 Papaya sticky disease, Papaya meleira virus (PMeV)
14.7.10 Papaya yellow crinkle disease, Phytoplasma australasiae, Phytoplasma
Tobacco leaf curl virus
Tomato spotted wilt orthotospovirus (Tomato spotted wilt virus)
11.0 Harvesting
First harvest when the plants 9-12 months old.
Then can harvest for 4-6 years.
Harvest by cutting stalk with a sharp knife.
Do not bruise fruit or get white latex on the skin.
Harvest papaya when the colour of the skin changes from dark green to light green, and when one yellow streak develops from the base upwards.
These fruit will continue to ripen, but if harvested before this stage, they will fail to ripen completely.
After harvest, place the fruit in single layers in shallow crates, not on the ground.
Field crates may contain foam plastic for cushioning the fruit.
Trim stems off the fruit to prevent fruit rubbing during transport.
Papaya fruit should never be thrown, dropped, rubbed, cut or damaged, or left unshaded in the hot sun.
After transport fruit should be washed in hot water, treated for post harvest disease, and stored between 10oC and 12oC.
If store below 10oC fruit, will develop chilling injury, surface pitting, discoloration, poor flavour.
For further transport wrap dry fruit in paper and trim the peduncles and store peduncle down.
12.0 Harvest and profit
1. In modern agriculture you are very interested in measuring the yield of your crop so that you can know how to increase the yield and make more profit.
2. Harvest the crop in a regular way, e.g. every Tuesday afternoon.
Do the harvesting properly by cutting the fruit stalks with a short knife and throwing away and burning any bad fruit.
3. The harvested fruit should be counted, measured and weighed.
Sell some papaya so that you can estimate the returns for the whole crop.
4. Show how to harvest papayas correctly and what to do with bad fruit.
5. Records:
* Number of papayas harvested.
* Weight of papayas harvested.
* Estimated returns (money that could be received from selling harvest).
(If you do not actually sell the papaya you cans till calculate or estimate the returns as if all were sold.).
* Returns - production costs - establishment costs = Profit.
Calculate the value of estimated returns.
What is the value of establishment costs, e.g. tools?
What is the value of production costs, e.g. seed, fertilizer, insecticide, razor blades?
What is the estimated profit?
* In some countries the average commercial papaya plant produces 15-20 fruits each year weighing 75 kg.
What do your papaya plants produce?
13.0 Papaya uses and recipes
Papaya is usually eaten when ripe as fresh fruit.
Cooks may wrap meat in papaya leaves and cook by steaming over hot stones underground.
Papaya can also be cooked as a vegetable.
Try some of these recipes to show new ways of using this fruit.
The white juice in the skin of unripe papayas contains the enzyme papain that irritates the skin of some people.
Be careful to wash your hands after touching the white juice.
Chemical compounds include | cyangenic acid | glycoside | papain | Sinigrin glucosinolate |.
Dried papaya may be sold as fruit chips, leaf and leaf powder.
Medical uses in Southeast Asia and Sri Lanka.
* Dried fruit pulp used to reduce swellings.
* Pounded leaves are applied to ulcers, swellings, boils and wounds.
* Latex is used to expel intestinal worms, treat enlarged spleens and remove skin blemishes, e.g. freckles, warts and corns.
* Latex is applied to snakebites.
* Roots are used to treat uterine tumours, induce flow of urine and assist removal of stones from kidneys.
* Paw paw cream from health food shops used to treat dermatitis, eczema and psoriasis.
Recipes
1. Boiled papaya.
Cut a green papaya into pieces and cook with salt in the same way as cooking pumpkin or marrow.
2. Baked papaya with filling
Use 1 large green papaya, cut in halves and seeds taken out to leave 2 shells, 2 tablespoons of cooking oil, 1cup finely chopped onions, 1 kg minced beef or 1 steel can of fish, four tomatoes, peeled and chopped, 1 teaspoon of finely chopped fresh hot chillies, 1 teaspoon salt, pepper
Heat oven to temperature for baking
Heat cooking oil in large frying pan, drop in onions and cook for 5 minutes until soft, but not brown.
Stir in beef or fish and cook lightly until pink colour gone.
Stir in tomatoes, chillies, salt, pepper and cook quickly until mixture is about solid.
Spoon mixture into papaya shells.
Place shells in an oven in roasting steel can.
Put some boiling water into roasting steel can.
Bake for 1-1 hours until the papaya is soft.
3. Green papaya salad
Use 3 cloves peeled garlic, pinch of salt, 4 deseeded chillies, 1 tsp. roasted peanuts, 4 cherry tomatoes cut in halves, 1 cup of shredded green papaya, 2 tbsp brown sugar, 1 tbsp lime juice, 1 tbsp tamarind paste,
1 tbsp fish sauce.
Mix together in a mortar and pestle the garlic, salt and chillies, add peanuts and pound into a coarse paste.
Add cherry tomatoes and mash the mixture.
Add green papaya and eat with wedges of cabbage, or coconut rice.
4. Papaya jam
Use 2 small ripe papayas, 1 kg sugar
Cut papaya into 2 cm cubes, place in a heavy saucepan and add 3 tablespoons of water or lime juice.
Heat to boiling quickly then reduce heat to simmer for 30 minutes until most of the liquid is gone, while stirring frequently with a large spoon.
When it is like a jelly pour into jars and seal.
5. Papaya chutney
Use 1 green papaya, 1 litre malt vinegar, 1/4 kg sugar, 1 cup raisins, 1 tsp. chopped ginger root, 1 tsp. chopped fresh chillies, 5 tsp. salt
Peel the papaya, discard seeds, cut into 2 cm cubes.
Place papaya and vinegar into a heavy saucepan, and bring to boil and cook briskly for 10 minutes, stir occasionally.
Stir in sugar, raisins, ginger, chillies and salt, then simmer for 45 minutes until the papaya is tender.
When thick enough, pour into jars and seal.
6. Papaya and pepper sauce
Use 1 cup of fresh chopped chillies, 5 tablespoons chopped onions, 2 tablespoons peeled finely chopped unripe papaya, 1 tsp, mustard, 1 tsp. salt, 3 tablespoons vinegar.
Put chillies, onion, papaya, mustard, salt and vinegar into small saucepan, boil quickly, stir constantly and leave to cool before using.
7. Pickled papaya
Use 1 small green papaya, pealed and cut into 2 cm cubes, 1 cup of chopped chillies, 1 piece of ginger, 1 tablespoon of salt, 4 cups vinegar.
Place all ingredients into cold vinegar and leave in a jar with a tight cap for some days before eating.
8. Papaya and fish soup
This soup may be good for mothers breast feeding their children.
Use 1 whole fish, 1 green papaya, peeled and cut into 2 cm cubes, 1 small piece of ginger.
Place in large saucepan, bring to boil and simmer for up to hour.
9. Papaya seeds either dried or fresh.
Use dried in a peppercorn grinder as substitute for black pepper to replace pepper corns when making dill pickles.
Use fresh in a blender with vinegar and ground small then add other salad dressing ingredients.
Also, papaya seeds may act as a vermifuge to expel intestinal worms.
However, papaya seeds are said to can make men sterile and it is used as an abortifacient in some countries.
10. "Pawpaw delight", from Solomon Islands
Use 1 median papaya, 1/2 cup brown sugar, 2 tsp. chopped ginger, juice of 1 lemon, grated coconut, raisins or sultanas, short crust pastry.
Cook the papaya with the sugar, lemon juice and ginger.
Roll pastry, line a pie dish with it, and put in the cooked papaya.
Sprinkle with raisins or sultanas, and grated coconut, cover with pastry, bake in hot oven for 1/2 hour.
Serve with coconut cream.
11. Papaya meat tenderiser
Use papaya, (ripe or unripe), on tough cuts of red meat and the enzymes in the fruit will help break down the collagen, leaving a tender steak.
To use it, slice in half, scoop out the seeds and puree.
Spread it over the meat, chill for 30-40 minutes, longer for tougher cuts of meat, then scrape off the puree and cook.
To make and store papaya paste, use 2 medium-sized green papaya, half teaspoon of salt, one tablespoon of cooking oil
Wash and cut papaya in half, remove seeds.
Cut into small pieces, in a blender, add salt and cooking oil to ease the blending process.
Pour the raw papaya mixture into ice cube trays for freezing.
When frozen, place in zip-lock bags for storage.
Defrost and use two ice cubes per one kilo of meat.
Chymopapain, C6H4Na2O8S2, Protein
Chymopapain, sulfhydryl proteases similar to papain, isolated from the crude latex derived of the fruit of Carica papaya by squeezing the green papaya while on the plant prior to harvest, extracellular plant cysteine proteinase, was used for lumbar surgery, but use discontinued, because of serious side effects, used for wound healing and tenderising meat.
Papain, C9H14Na4O3S2 Vegetable Pepsin
Papaine, folded polypeptide chain of 212 residues, proteolytic enzyme, papaya proteinase, cysteine protease, inhibits peptidases, breaks peptide bonds, proteolytic enzyme, dissolves mucus, from latex in Carica papaya (papaya) latex, in Vasconcellea cundinamarcensis, (mountain papaya), the enzyme is found in the skin of papaya, and is used in food, pharmaceutical, textile, and cosmetic industries, used to treat infected wounds, aid sloughing, prevent adhesions.
Papain powder, enzyme mixture, white sap of (Papaya), meat tenderizer, breakdown of dietary protein, some people allergic especially if patient has latex sensitivity.
The name "papain" is used for a mixture of papain and chymopapain used for wound cleaning, antihelminth and tooth-whitening.
Papain inhibitor, C19H29N7O6, diaminomethylideneamino pentanoic acid, H-Cly-Gly-DL-Tyr-Arg-OH. inhibits peptidase activity of papain and is used in affinity chromatography
Papaya peptidases A and B, sulfhydral proteases, in Carica papaya latex
/> Papaya ringspot virus, (PRSV)
Control nil so cut out tree.
Mosaic manifests as a distinctive pale area on the fruit.
Interestingly if the pale area is pierced no latex flows.
Pierce an area on the same fruit outside the mosaic area and latex will flow.
Papaya ringspot disease, caused by Papaya ring spot virus, causes significant damage to papaya.
Symptoms include yellowing and vein-clearing of young leaves and distinctive ring spot patterns on fruit, concentric rings and spots, and C-shaped markings.
These markings persist during ripening and can darken to become orange-brown rings as the fruit matures.
Fruit set is usually reduced and as plant vigour declines, fruit quality, particularly flavour, is adversely affected.
Papaya ring spot disease is spread from plant-to-plant by aphids.
The movement of infected papaya plants is the most likely pathway for this disease to spread.
Papaya ringspot virus (PRSV)
Leaves develop prominent mosaic and chlorosis on the leaf lamina and water soaked oily streaks on the petioles and upper part of the trunk.
Severe symptoms often include a distortion of young leaves which also result in the development of a shoestring appearance that resembles mite damage.
Mottling and mosaic of leaves; leaf lobes are reduced, giving a shoe-string appearance.
This distortion becomes more obvious as the disease progresses.
Severely affected trees infected at a young age will not produce a good crop.
Fruit from infected trees have ring spots on the skin (they are not actual spots).
The ring spots can be very light at the beginning of the disease and gradually increase in number and colour.
Fruit is not produced on severely affected plants.
PRSV can be confused with Tomato spotted wilt virus.
14.7.4 Papaya lethal yellowing virus, PLYV
It is spreading every year, probably by infected plantlets and contaminated agriculture tools.
It is readily transmitted mechanically and by human actions, including contaminated hands, agricultural tools, contaminated soil, and irrigation water.
Healthy papaya plantlets can be infected if they are grown in contaminated soil, however, no biologic vector has been confirmed.
14.7.5 Papaya sticky disease, Papaya meleira virus (PMeV)
The disease causes fruit to weep watery latex that causes further cankers and makes the fruit unmarketable.
The papaya meleira virus (PMeV) responsible was detected in Australia in 2014.
Later, four umbraviras-like viruses were found to also cause this disease.
The Queensland Department of Agriculture and Fisheries has developed a test to detect all the viruses.
The disease is spread mechanically, so disinfection of tools with bleach is recommended to avoid spread between plants.
Empoasca papayae is capable of transmitting PMeV-Mx to C. papaya ‘Maradol’.
14.7.6 Papaya mosaic virus, PaPMV
Symptoms of infection include mild leaf mosaic and stunting.
No symptoms appear on leafstalks, stems or fruit.
Stunting is only obvious when healthy plants are present for comparison this disease is considered of little importance.
14.7.9 Papaya sticky disease, Papaya meleira virus (PMeV)
The disease causes fruit to weep watery latex that causes further cankers and makes the fruit unmarketable.
The papaya meleira virus (PMeV) responsible was detected in Australia in 2014.
Later, four umbraviras-like viruses were found to also cause this disease.
The Queensland Department of Agriculture and Fisheries has developed a test to detect all the viruses.
The disease is spread mechanically, so disinfection of tools with bleach is recommended to avoid spread between plants.
Empoasca papayae is capable of transmitting PMeV-Mx to C. papaya ‘Maradol’.
14.7.10 Papaya yellow crinkle disease, Phytoplasma australasiae
Bacteria Phylum Mycoplasmatota Family Mycoplasmataceae Genus Mycoplasma
Yellow crinkle disease is caused by (Mycoplasma) sp.
At first, clear spots appear on the leaves.
Then the younger leaves at the top become yellow and curled.
This disease is probably carried from infected tomato plants by sucking insects.
The only cure for these virus diseases is to cut the tree down at soil level, burn it, and let one of reserve trees grow up.
Also, pull up and burn any nearby tomatoe plants affected with yellow crinkled young leaves.
Control: nil. Cut out tree.
Dieback, Yellow crinkle, Papaya mosaic
When starting from the top, the leaves become shrivelled and fall off.
14.8 Abiotic fruit disorders
Algal leaf spot Cephaleuros virescens Kunze
Bi-sexual-change to male
Mainly in hot weather, some trees change sex from hermaphrodite to male, producing male flowers and no fruit, but they revert to hermaphrodite when the weather cools.
Blistering on fruit
Control: nil.
Cause is internal pressure in fruit, usually occurs prior to fruit being picked.
Fruit presents with a pool of latex under skin
Bumpy fruit
The fruit of boron deficient papaya are deformed and bumpy due to the irregular fertilization and development of seeds within the fruit.
Opening is uneven and the developing fruit secrete pinkish white to brown latex.
Heavy premature shedding of deficient male tree flowers and impaired pollen tube development can lead to poor set in the fruit-bearing female trees.
Upper mature leaves are pale, stiff and brittle, and may die at the tip, curling downward to become claw-like in shape.
Growth ceases at the growing point and a white exudate flows from cracks in the upper trunk that becomes twisted.
The growing point and stubby terminal roots may die.
Treat with half a teaspoon of borax per plant / m2 or apply "OrganiBOR".
For boron deficiency, spread 15-20 milli grams of borax decahydrate around trees twice a year, or use a fertilizer with a reasonable amount of boron in it.
Bumpy fruit of papaya is associated with boron deficiency.
It is known to occur in many of the papaya growing areas of the world.
Deformity begins early, but symptoms appear to become more severe as the fruit gets older.
The bumpy appearance is a result of localized areas of the fruit being affected by the deficiency and cease to increase in size.
Adjacent unaffected tissue continues to increase and result in a misshapen, bumpy appearance.
The earliest symptoms usually occur in the young, developing fruits where bleeding of latex and initial deformation becomes evident.
Seeds in affected fruit are often aborted or poorly developed and vascular bundles are often darkened.
Under severe deficiency situations, height growth of trees may be affected causing a slight rosette effect and an associated stunting.
Boron deficiency is related to shallow, rocky soils and dry conditions.
Trees with deformed fruits typically have boron levels in petioles (dry weight basis) of about 20 ppm and below.
Normal boron levels in petioles are about 25 ppm and higher.
Foliar applications of 0.25% borax (Na2B4O7ù10H2O) and ground applications with 1-3 kg/ha elemental boron have been effective in raising petiole boron levels and the prevention of deficiency symptoms on fruits subsequently formed.
Shortage of Boron deficiency
Symptoms first appear in new growth.
The leaves appear brittle and distorted.
Affected fruit are seedless, ripen unevenly and are covered in lumps.
Affected trees can lose up to 100% of their fruits.
Boron toxicity
Boron toxicity occurred to these trees, because borax pentahydrate was used on the trees instead of borax decahydrate.
The lower the number, penta(5) instead of deca (10) the more soluble the boron is.
Hence using pentahydrate caused the trees to take up the boron quickly thereby causing toxicity.
Borax decahydrate is virtually insoluble thereby allowing the tree to take up the boron slowly.
Cat face
Carpoloidal (cat face fruit) on bi-sexual trees, control seed selection.
"Cat face" or carpellody is specific to papaya.
The appearance of carpellodic fruits can range from those that resemble female fruits to those that are severely deformed with longitudinal ridges or seams.
Carpellodic fruits are generally rounded rather than the more typical pyriform shape and are unmarketable.
Carpellody or "cat-face" fruits result when stamens develop abnormally into carpel-like fleshy structures.
Sex expression in hermaphroditic papaya trees is variable and is influenced by environmental factors.
The development of carpellodic fruits is favoured by low night temperatures in combination with high moisture and nitrogen levels.
Carpellody is an inherited trait thus careful seed selection can reduce its occurrence.
The "Solo" varieties, because of many years of inbreeding, have lower incidence of carpellody but it does occur occasionally under conditions described above.
Bisexual papaya are affected by a condition known as carpellody or"cat-facing" and is caused by the fusing of the ovary and stamens during adverse weather conditions.
This fruit is deformed and unmarketable.
Carpellody is one of the reasons bisexual varieties are not normally grown in sub-tropical areas.
Papaya dieback
Seasonal, occurs every few years.
At Yandina our heaviest loss was 30% of trees and at Redland 100%, (because of red soil?)
Papaya freckles
Freckles are initially noticed as small pinpoint spots on fruits that are half developed.
As the fruit matures, the spots slowly increase in size up to about 13 mm in diameter.
However, the spots usually do not increase beyond 14 mm in diameter.
The spots are brown in colour, have a reticulated pattern, and may have a water-soaked margin.
The centres of large spots may attain a grey colour.
Freckles are usually limited to the exposed surface of the fruit facing away from the stem.
They occur throughout the year, but appear to be more prevalent during seasons or periods when sunny days prevail.
Freckles are superficial and do not affect the flesh and are primarily a cosmetic disorder.
Freckles are common on most commercial papaya cultivars.
Numerous attempts to isolate pathogens and microscopic examinations of freckles have not linked any organism with this disorder.
Fruits that are covered with pollination bags soon after formed remain free of freckles at harvest.
A severe form of this disorder has been observed on the cultivar Sunrise Solo during the dry periods from Brazil, Hawaii and Fiji.
Affected fruits have large numbers of freckles that coalesce and cause the fruit surface to appear russetted.
Iron deficiency
Yellowing between the veins which appears as a green network of veins on leaves.
The symptoms are seen in the younger leaves first.
Fruit may be low in sugar.
Poor fruit set
Cause is low pH or poor pollination.
The pH needs to be 6.5 to neutral.
Coastal soils are naturally acidic, therefore an annual liming of 0.5-1.0 kg of lime per tree is usually necessary.
Damage in seedlings
A white powder can be seen on the petioles of affected trees.
Returning a tree
When a tree is too tall, cut tree off above suitable side shoot in spring or early summer.
Ripe fruit rot
Control tree selection.
Uneven ripening
Cause is rapid changes in air temperature.
Winter freckle
Occurs in winter, but has no affect on eating quality of fruit.
15.6 Papaya varieties, "Paiola"
Paiola is a papaya hybrid developed and promoted by the Malaysian Agrifood Corporation (MAFC).
"Paiola" is the commercial name for the hybrid from the word papaya and the expression of "oo la la" meaning "nutritional" in Polynesian.
Paiola variety is small, like the size of a palm, with golden yellow skin and sweet and deep crimson flesh.
It can also be kept a week longer than ordinary papayas.
15.1 Babaco, mountain papaya
Babaco, (Carica pentagona), champagne fruit, effervescent flesh of fruit, torpedo-shaped fruit, hybrid, Ecuador, Caricaceae
It is a naturally occurring hybrid of (Carica stipulata) and (Carica pubescens), from Ecuador.
It is grown commercially in New Zealand, Israel and southern California.
It has cream-coloured fruit that is slightly sour and has no seeds.
It grows in a cool frost-free subtropical climate.
The five-sided, rounded at the stem end and pointed at the apex fruit sets parthenocarpically, so it has no seeds.
However, the fruit is juicy, slightly acidic, low in sugar and with its own special flavour, and the skin is edible.
It keeps well and the plants are very productive and easy to grow.
It is so compact that it can be grown in a greenhouse.
The mountain papaya, (Carica pubescens), is a high altitude plant, has many seeds and is regarded as an inferior fruit, so is better cooked than fresh.
It is more cold tolerant than papaya.
Babaco, Daleys Fruit Tree Nursery
15.4 Genetics of papaya
Papaya is one of the rare species classified as trioecious, because its individuals exist as one of three sex types; female, male, and hermaphrodite.
Sex determination in papaya is controlled by a pair of recently evolved sex chromosomes with the genotype XX for female, XY for male, and XYh for hermaphrodite.
The difference between X and Y or Yh chromosomes is a small non-recombination region, called the male specific region of the Y chromosome.
The Y and Yh originated from an ancestral Y chromosome about 73, 000 years ago, so papaya used for study of the early events of sex chromosome evolution.
More than 95%of male papaya trees produce some hermaphrodite flowers in spring and canset from 5-25 fruit.
They are always a larger shape as are all hermaphrodite (bisexual)
fruit and are called "long toms".
The seeds of this fruit give 75% male and 25% female plants.
They are commercially used in breeding programs to produce a purer
female line as they result from inbreeding or self-pollination.
15.3 Commercial papaya seed
Commercial papaya seed is sold as both bisexual (hermaphrodite) seed and dioecious seed is offered.
Bisexual seed produces both bisexual (67%) and female (33%) trees.
Dioecious seed produces female (50%) and male (50%) trees.
Hybrid numbers are prefixed by B (bisexual) and D (dioecious) as well as Y (yellow fleshed) and R (red fleshed).
So the yellow hybrid "YD1B" indicates yellow fleshed dioecious Hybrid 1B, the most widely grown of all the hybrids in Australia, fruit is oblong, is very clean, flesh is firm, and is a medium yielding tree.
Red hybrids include RD2 is a dioecious red fleshed hybrid.
This is a very fast growing plant and will start picking 9 months after planting out as seedlings.
The fruit is roundish and slightly ribbed, with deep red flesh colour.
Also "Sunrise Solo" is a pink fleshed bisexual inbreed.
It is the most commonly grown papaya world wide.
The fruit is small, pear shaped with a very sweet musk flavour.
Hybrids are the result of crossing 2 "fixed" (stable) parent lines.
Hybrids are more vigorous than their parents, produce more fruit and are less susceptible to disease.
All papaya are affected by climatic changes, but when grown under stable conditions hybrids are very consistent in fruit shape and size.
Hybrid seed for sale is usually only the first cross of the parent lines, producing F1 hybrids.
Hybrids cannot be successfully grown from seed collected from F1 fruit and will be inconsistent in shape, size and yield.
Germination of commercial seed should be tested before dispatch to guarantee a minimum germination rate of 50% for 50 days after purchase date.
15.5 Growing papaya at home in the subtropics
Papaya are upright growers that do not take up much space, fruit in their first growing season, and can be less demanding than other fruit trees.
They hate the cold and frost common to inland regions and are plagued by disease in the subtropics.
Their versatile harvest can be eaten ripe or unripe in sweet, savoury and salad dishes and possess nutritional properties said to aid digestion and stomach upsets.
Plants may be male, female and bisexual trees.
Male trees produce small flowers on metre long stems, while female trees produce blooms on short stems close to the trunk.
One male tree will pollinate up to eight female trees.
Bisexual trees produce fat, robust flowers on short stems that are self pollinating, so just one tree will produce fruit.
Papaya are seed grown and can vary considerably in their genetic characteristics.
Single plants sold in pots are typically named bisexual varieties, while those sold three per pot are an unsexed, random mix, but not guaranteed to contain male and female plants.
If collecting and saving your own seed, choose a fresh, ripe, locally grown fruit that grows well in your region as it is most likely that the offspring will possess characteristics that make it well
adapted to local growing conditions.
There is no accurate way of predicting the sex of seed grown plants, prior to flowering, although male trees often grow more quickly.
Seed from single sex trees may be male or female, seed from bisexual trees usually produce bisexual offspring, but not all bisexual fruit contain seed.
Choose a full-sun position with perfectly well-drained soil.
A garden supported by a retaining wall or a mounded or raised kit-style garden bed is ideal.
Good air circulation is essential.
Positions that receive radiated or reflected heat and those close within the protected envelope of buildings often suffer less disease.
Prepare the soil a few weeks ahead of planting by incorporating plenty of manure-based compost and some complete organically-based fertilizer.
Papaya grow quickly and are very hungry feeders.
Add gypsum plus rock dust, soft rock phosphate and / or other slow release sources of trace elements prior to planting.
Plant singly or in groups where short on space.
Water in with liquid seaweed and / or worm juice and fertilize with fish-based liquid nutrients each fortnight until plants begin to show significant growth.
Tropical gardeners often treat papayas as an annual crop, favouring dry season planting and let nature takes it course over the monsoon season.
If root rot disease is an issue in your garden during summer, be sure to save seed from the best performing trees of your current crop.
15.2 Chemicals in papaya:
Antheraxanthin, Benzyl isothiocyanate, Carotenes, Carpaine, Chymopapain, Cryptoxanthin, Danielone, Glucotropaeolin, Mutatochrome, Papain, Papaverine.
16.1 Grafting papaya
See diagram 9.93: Bud graft, shield graft, saddle graft
See diagram 9.93.2: Budding and grafting
For papaya seedlings with 1-2 cm stem diameter, use the V top grafting.
For large tops up to 20 cm in diameter, use a W graft.
Cut 99% of the leaves, fasten grafts at 2-3 places with a plastic zipper strip, then spray with fungicides and bactericides.
To maintain humidity double cover with opaque plastic bags.
Match the diameter of the crown to the rootstock.
For huge crowns use a sharp long knife or a very thin blade hand saw.
Draw the cutting lines with similar complementary angles so that the 2 parts fit into each other.
16.3 Papaya research
The National Papaya Breeding Program, lead by Professor Rebecca Ford, is developing papaya that not only looks and tastes better than the current varieties, but is also easier for the farmers to grow.
They are using molecular and biochemical methods to breed plants that produce fruit lower to the ground for easier picking, have fruit that are shaped and taste sweet and flavorsome, according to market.
They use the following list of traits for evaluation for papaya fruit quality and tree productivity.
1. Tree age 5 months, Productivity traits
Sex type, Height to first marketable fruit, Number of side shoots, Tree circumference, Peduncle length.
2a. Tree age 10 months, Productivity traits
Tree circumference, Peduncle length, Saleable yield (number of saleable fruits), Yield Gap, Number of carpelled fruit, Fruit size (fruit length and fruit width), Cavity size (cavity length and cavity width).
2b. Tree age 10 months, Fruit quality traits
Skin gloss, Skin freckle, Skin colour, Fruit firmness, Fruit shape, Teat shape, Stalk insertion, Cavity shape, Flesh colour, Consistency in
flesh colour, Flesh thickness, Flesh texture, Flesh sweetness ("Brix").
3. Tree age 15months, same as 2a + 2b.
16.4 Tissue culture
Skybury Farms, in North Queensland, Australia. grows all papaya by tissue culture,
Dr Jose Josekutty, who runs the Skybury Farms tissue culture laboratory, reported in the Commercial Horticulture Journal from New Zealand, June/July issue, on considerable success with papayas.
Some of the lines going into production produce 300 papayas fruits in one year; each worth AUD 3.0 at the farm gate.
The papaya plants produce fruit six to eight weeks after being planted.
During the harvesting runs done every two weeks, only fruit about 1 kg weight or more are selected for picking.
The plants are removed and replace after two years, because the new fruit formed higher up the plant are too high to be picked from platforms.
The major advantages of tissue culture include that large number of new plants can be obtained quickly, using certified disease-free stock,
Also, when plants go into dormancy, the farm can keep propagating with tissue culture.
An anti-viral compound is used in the liquid media to limit the impact of:
16.2 Papaya propagated by marcotting, based on article by Julio P. Yap
Sowing the black seeds of the papaya fruit is not a guarantee for the farmers to attain a good yield, because some of the seeds may turn out to become a male papaya tree which will not bear fruits, thus, wasting the time and effort of the farmer.
The Central Philippines State University (CPSU) in Kabankalan City under the leadership of Dr. Aladino C. Moraca, developed and introduced the process of Papaya asexual propagation through marcotting.
Marcotted papaya grows faster and produces fruits earlier than those grown from seeds.
Marcotting, a type of vegetative plant propagation commonly known as air layering, involves rooting of a part of the stem while it is still attached to the parent plant.
In marcotting, the induction of root development is usually done by slitting the part of a plant to be rooted.
See diagram 58.8: Marcotting Papaya
This method can also be utilized by those living in the urbanized areas where the space to propagate a plant is a perennial problem, because a marcotted papaya tree can be grown in small containers like discarded pails or appropriate pots.
Chose a papaya plant with abundant leaves for marcotting.
The rooting medium should be a mixture of slightly moistened vermicompost (30 percent) and decomposed sawdust or cocodust (70 percent).
Watering should be done regularly with an interval of 2 to 3 days for the first month by using a syringe to maintain the moisture content of the rooting medium.
When plenty of roots have already developed after 10 to 15 days after marcotting, the marcotted papaya can then be severed from the parent plant and transferred to a pot or planting site.
16.5 Variation between plants
See diagram 58.10: Papaya stem and leaf
1. There are 3 reasons why plants are different from each other:
* They may have different genes.
These are messages carried in the pollen and ovules (in the ovary), which are combined when a seed is formed.
The genes tell the plant what characters to have, e.g. tall or short, white flowers or red flowers, large fruit or small fruit.
* They may be growing in different environments that affect their growth, e.g., different climates, soils, methods of crop management.
* They may be different ages or at different stages of maturity.
2. Plants that grow from seed that had unlike parents will be unlike.
These plants will have a mixture of the characters of the parents.
Plants that grow from seed that had like parents will be like each other and like the parents.
Plants that are like their parents and each other over many generations are called a pure line.
3. Look for good characters such as size of fruit, amount of fruit, resistance to disease, consumer preference,
and then try to produce a pure line that will have all the good characters.
* Old axillary buds above the leaf scars and axillary buds in the terminal cluster.
* A stem is not branching unless the terminal bud has been cut off.
* Wood is spongy or hollow.
* The lamina of the leaf has tooth-shaped lobes
* The petiole of leaf is long and hollow.
4. You can produce better papayas by controlling pollination.
This can be done by:
* finding a group of healthy papaya trees producing good fruit,
* deciding which male plants fertilized them,
* cutting down all other male trees,
* for the next generation cutting down all male and female trees not grown from the seed of good papayas.
5. Imported seeds in packets are pure lines, but they may not be suitable for tropical countries.
Locally produced seed will probably not be pure lines, but they will have good characters for tropical countries.
6. Study of variation means looking at the different characters of plants and deciding which are good and which are bad characters.
If you can find plants with good characters and use them only as parents you can start producing pure lines for tropical countries.
Do not let plants with good characters be fertilized by pollen from plants with bad characters.
Study variation in plants to allow us to describe accurately the different characters of plants and to decide which are good and which are bad characters.
7. Select some papaya plants outside the project for study in this lesson.
* Draw and label a stem.
* Draw and label a leaf.
* Draw the root of a small plant.
Label: primary root, lateral roots, note depth of roots, note depth of roots in the soil, note any damage by pests or disease.
* Draw and describe some characters of the plants selected for study in the classroom.
They should be different from the plants in your project.
8. The characters could be:
* Fruit, diameter of middle fruit in bunch, diameter of largest fruit, number of fruit on tree, taste, colour, diseases
* Habit, size of tree after 3 years, any branching
* Stem, colour, diameter, any diseases
* Leaves, shape, number in spiral, number in terminal cluster, diseases
* Flowers, shape, colour, size and number of parts of male / female / bisexual flowers
* Root, depth, diseases
* Consumer preference - which fruits do people like and why?
Preface
Before teaching this project, discuss the content of the lessons with an agriculture extension officer and get advice on planting material, planting distances,
site for planting, approved mulch, composting, and control of pests and diseases.
Use only the procedures, agricultural chemicals and insecticides recommended by an agriculture extension officer.
If you cannot control insects by hand-picking, ask an agriculture extension officer to recommend a chemical spray.
All insect sprays are dangerous.
Show the students how to use them safely.
Do not get the spray onto your hands.
Do not breathe in the spray.
Wash your hands well after using spray.
Keep the spray container in a safe place where students cannot get it.
Spray on a day of no wind, but if you must spray when there is a wind, spray down wind.
Make sure the spray does not blow on other people.