School Science Lessons
2019-06-03
Please send comments to: J.Elfick@uq.edu.au

Papaya Project
Websites: Papaya, paw paw

Table of contents
Preface

1.0 Papaya plant

17.5 Chemicals in papaya

1.1 Crop diary

2.0 Prepare planting

3.0 Seed nursery

3.1 Seed mixes

3.2 Planting seeds

4.0 Germination

5.0 Prepare land

6.0 Before transplanting

8.0
Transplanting

9.0 Flowers

10.0
Variation

11.0 Care

12.0 Pollination

13.0 Pests

14.0 Harvesting

15.0 Profit

16.0 Uses and recipes

16.0 6.20.0 Records


11.1 Grafting
17.4 Growing papaya at home in the subtropics
13.1
Boron deficiency
17.3
Commercial papaya seed
17.2 Genetics of papaya
17.0 Papaya varieties, "Paiola"
17.1 Papaya varieties, Babaco, mountain papaya

13.0 Pests and diseases
13.1 Planning to treat pests and diseases
13.2 Papaya pests and diseases
13.3 Fungus diseases
13.4 Phytophthora diseases
13.5 Virus infections
13.6 Mites
13.7 Papaya yellow crinkle disease
13.8 Boron deficiency

Aim
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 their diet.
These teaching notes tell you 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:
1. The 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 marrow and pumpkin.
It can be made into a tasty jam.
2. These teaching notes can be used to teach how to look after a papaya crop in the modern way, i.e. to increase the yield by
controlling energy loss.
You can do this by paying careful attention to selection of seed, where and how you plant seed, plant nutrition, pests and diseases,
looking after the papaya garden, and harvesting the crop.
3. Although most people have seen papayas growing, they may not understand the plant that has a very interesting structure and life
history, so study of this plant will broaden knowledge of their natural environment.

1.0 The papaya plant
| See diagram 58.1: Papaya with fruit
| See diagram: Red papaya
| Papaya varieties, Daley's Fruit Trees
1. The papaya (Australia: pawpaw), Carica papaya, is a member of an unusual perennial dicotyledon plant family, Caricaceae, that
comes from South America.
| Papayas are grown in most tropical countries.
Also, Asimina triloba, American pawpaw, Eastern USA, Annonaceae.
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 and 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, 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.
See 17.1 Babaco, Carica pentogona.

1. You need a ripe papaya fruit in the classroom.
Cut it in half lengthways.
Also you need male and female papaya trees growing near by.
2. Keep one half, then cut up the other half and eat it.
Note the structure of the half papaya fruit.
The fruit can be eaten fresh when ripe, or boiled when still green and eaten when unripe like a marrow.
Some people eat the young leaves and flowers as a vegetable and eat the seeds for medicine.
The white milky latex in the unripe fruit and leaves contains an enzyme call papain that can digest meat.
It is like the action of pepsin in your stomach, so meat can be cooked in papaya leaves to make it more tender.
3. See the separate male and female papaya trees growing near by.
See the male or female flowers are on separate plants.
Male flowers occur in dangling racemes.
Usually only the female plants produce fruit, close to the trunk, from small clusters of flowers.
Sometimes the male flowers become bisexual and produce some long thin fruit.
There are some bisexual dwarf varieties, e.g. variety Solo from Hawaii.
4. Bisexual fruit is thin, long and has a smaller hole in the centre so professional growers prefer them because they give more weight,
but they are also more tropical so they will not perform in a colder climate, whereas the female is more cold tolerant.
They also have a different flower.
For the backyard, it is better to have one bisexual and two females so you can hand pollinate the plants.
5. The plant has shallow roots, a succulent hollow stem of soft tissues, big palmately-lobed leaves, and grows to 8 m.
It should be grown in well drained moist soil.
It should be sheltered from strong winds.

1.1 Crop diary
Keep a crop diary and record the following:
3.1 When planting seed, germination, transplanting, culling, hand fertilizing, picking
3.2 When and how much harvest, cost of seed, fertilizer, materials for a nursery
3.3 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 iron tin cans.
If you think that this is too big, cut the number of seeds planted and mature plants by half to provide 2 rows, each with 5 trees.
In Queensland, with 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 1850 to the hectare.
The amount of seed required is 50 grams per acre or 125 grams per hectare.
With 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 tin can.
4. Use an opened tin can or beverage can with four holes punched in the bottom.

1. Papaya plants selected for seed.
The best papaya seed comes from a large smooth fruit growing nearby.
Select a papaya from group of trees that all have good fruit.
2. 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.
3. You can plant seed as follows:
3.1. in a seed bed 15 cm apart and 1 cm deep and,
3.2. in jam tins, fish tins, steel 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 tin cans may be the best method.
4. Line the tin cans with paper or leaves.
Fill the tin 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
1.1 Spades, forks, hoes, bush knife, rake, string, tape measure.
1.2 Fresh papaya seeds.
1.3 Uprights, sticks and palm leaves for a nursery.
2. If you want to use fertilizer, bring tin can of mixed fertilizer or superphosphate, a matchbox and a spoon.
3. The papaya seeds will take 3-4 weeks to germinate, and be ready for transplanting in 10 - 12 weeks.
4. See the arrangement of seeds planted in the seed bed.

1. Select a small piece of land about 2 x 1 metres, with good topsoil, in a well drained position.
2. 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.
3. Fill the tin cans with a mixture of clean sand and crushed dried leaves.
Water the tin cans well.
Scratch your name on the jam tin can.
4. 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 tin cans well.
5. Build four uprights, cross sticks and a light shade of palm leaves.
6. Water the seeds in the seed bed or tin 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.
7. 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 can.

3.1 Seed mixes for pots or tin cans
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"), 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.

Decide whether to plant the papaya seeds into a seed bed or into containers, e.g. as tin cans.
Plants in a seed bed are easy to look after but the plants may die after transplanting.
Plants in tin 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 tin cans to compare the results as in an experiment.
You will need the following:
2.1 Large ripe papayas for seed
2.2 About 20 kg of lime or dolomite if your soil is very acid, ask the agriculture field staff.
The soil pH should be 6.0-6.5.
Some people also use Epsom salts to give increased magnesium to the plants.
If you wish to add fertilizer, you will need:
2.3 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.
2.4 About 10 kg of urea or ammonium sulfate, or potassium sulfate.
2.5 If the leaves are yellowing, use a spray of 1 g / litre of boron on the leaves and soil.

4.0 Percentage germination calculation
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 tin cans and 47 germinate to form seedlings then the percentage germination is as follows:
47 / 50 100 = 94% in jam tin cans.
From this calculation, the conclusion is that it is better to plant in tin cans to get good germination.

1. Examine the germinated seeds in the nursery and count them as follows
1.1 Number germinated in seed bed,
1.2 Number germinated in the jam tin cans.
Dig up germinated seeds from the seed bed, but not from the jam tin cans.
Keep the dug up seedlings wet.
2. Number of seeds germinated seed bed, tin cans percentage germinated:
Number germinated in seed bed x 100 = (call this "percentage seed bed")
Number planted in seed bed
Number germinated in tin cans x 100 = (call this "percentage tins")
Number planted in tin cans Is there any difference between percentage seed bed and percentage tins?

5.0 Chose and prepare the land
9.14.0: Composting
1. Use bush knives, hoes, forks, spades, string, tape measure or rule, sticks.
2. Go to a place where old papayas are growing, a second place where the soil is badly drained or it is windy, and a third place that
you have selected as suitable for the papaya garden.
3. Dig a hole in the place you have selected to show the soil profile.

1. At the first place, ask them whether it is a good place to grow papayas.
At the second place, ask the same question.
At the third place, ask why it is a good place for a papaya garden.
Examine the soil profile.
The soil must be well drained.
2. 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.
3. Put wood ashes or 1 tin 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. Diagram F 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 Prepare to transplant
See diagram 58.7: Positions of transplants in papaya garden
1. Plants are ready for transplanting when they are more than 10 cm high.
2. Transplanting experiment: seed bed or tin 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 tin cans.
Papayas may die after transplanting and this experiment will show which is the best method.
3. Transplant on a dull wet afternoon.

1. Sequence for transplanting:
1. Dig four transplanting holes around each fertilizer hole and fill them with water.
2. Water plants in nursery.
3. Select plants from nursery.
4. Do not damage roots when transplanting.
5. Level of soil up the stem in a papaya garden should be no higher than in a nursery.
6. Remove one leaf from each transplant to reduce water loss through leaves.
Why do you transplant four plants quite close around each fertilizer hole? [Because you will be keeping only 1 plant of each four when
you select the largest male or female plant.]

8.0 Transplanting
1. Use: Trowels or spades, watering can.
If you want to fertilize you will need about 3 tin cans of ammonium sulfate or urea.
2. To develop interest in these plants, make a transplanting map:
3. Have some mulch ready.

1. Dig four transplanting holes around each fertilizer hole in the papaya garden and fill them with water.
2. Water plants in nursery
3. 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.
4. When planting around the T holes, select four tin cans with healthy plants.
Take the tin cans to the garden.
Open the bottom of the tin can.
Plant no deeper than in the tin can.
5. Water all 80 transplants in the garden.
6. Place mulch around each plant, but not touching the plants.
7. If you want to use fertilizer, put 3 matchboxes of ammonium sulfate or urea in each fertilizer hole.

9.0 Study the flowers
See diagram 58.9: Papaya flower
1. Papaya plants are unusual because most of them produce either male, female or hermaphrodite flowers.
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.

10.0 Study variation between plants
See diagram 58.10: Papaya stem and leaf
1. There are 3 reasons why plants are different from each other:
1.1 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.
1.2 They may be growing in different environments that affect their growth, e.g., different climates, soils, methods of crop management.
1.3 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. In agriculture you 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.
3.1 Old axillary buds above the leaf scars and axillary buds in the terminal cluster.
3.2 A stem is not branching unless the terminal bud has been cut off.
3.3 Wood is spongy or hollow.
3.4 The lamina of the leaf has tooth shaped lobes
3.5 The petiole of leaf is long and hollow.

4. You can produce better papayas by controlling pollination.
This can be done by:
4.1 finding a group of healthy papaya trees producing good fruit,
4.2 deciding which male plants fertilized them,
4.3 cutting down all other male trees,
4.4 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.
Studying variation in plants is important 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.
7.1. Draw and label a stem.
7.2. Draw and label a leaf.
7.3. 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.
7.4. Draw and describe some characters of the plants selected for study in the classroom.
They should be different from the plants in your project.

The characters could be:
9.1 Fruit, diameter of middle fruit in bunch, diameter of largest fruit, number of fruit on tree, taste, colour, diseases
9.2 Habit, size of tree after 3 years, any branching
9.3 Stem, colour, diameter, any diseases
9.4 Leaves, shape, number in spiral, number in terminal cluster, diseases
9.5 Flowers, shape, colour, size and number of parts of male / female / bisexual flowers.
9.6 Root, depth, diseases.
9.7 Consumer preference, which fruits do people like and why.

10.0. Are there are other kinds of papayas growing near by or in the villages?
What are the characters of these papayas and why do people like them?

11.0 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.

1. Always keep the garden free of weeds and rubbish.
2. 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.
3. 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.

11.1 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.
For example of this W graft of a Sunrise Solo bisexual papaw weighing five kg of apex on a male rootstock, the apex was taken
from an 8 years old, 5 metres tall papaw and was grafted on a 13 cm in diameter male rootstock.
Since then the apex grew by one metre.

12.0 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.

1. Check the wind direction.
Cut down all male trees except two so that wind can blow pollen from the two towards the female plants.
2. Cut down excess female trees to height of 60 cm.
3. Pick some male flowers still in the bud - peel back the petals and brush the pollen on to the female flowers.
4. Draw a plan of the 20 plants left in the papaya garden in their notebooks and show where the male and female plants are.
5. 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 especially
males.
Insects are also good pollinating agents.

13.1 Planning to treat pests and diseases
1. 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 the local office of the Department of Agriculture and ask about the pests and diseases of papaya in you region and the
recommended control measures, especially which pesticides and fungicides are recommended and allowed for use in school gardens.
Papaya is sensitive to some fungicides that may cause phtotoxicity, 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 the Department
of Agriculture before using any fungicides.
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.
3. Garden visit
Visit another papaya garden and look for any signs of disease.
Take notebooks to the garden and write reports there.
When some pests or diseases are found, draw and describe the disease.

13.2 Papaya pests and diseases
Papaya pests and diseases include the following:
Insect pests
False spider mite (Brevipalpus sp.), Yellow peach moth (Conogethes punctiferalis), Queensland fruit fly (Bactrocera tryoni)
Two-spotted mite (Tetranychus urticae), Oriental scale (Aonidiella orientalis), Fruit-spotting bug (Amplypelta nitida),
Fruit-piercing moth (Eudocima sp.), Papaya mealybug (Paracoccus marginatus), Scale insects (Pseudaulacaspis pentagona),
Spiralling whitefly (Aleurodicus dispersus).
4. Diseases
4.1 Fungus infections
Anthracnose (Colletotrichum gleosporoides), Black rot (Mycosphaerella caricae), Black spot (Asperisporium caricae),
Cercospora black spot (Cercospora papayae ), Powdery mildew (Erisiphe sp.).
4.2 Bacteria infections
Bacterial canker (Erwinia), Bacterial leaf spot (Xanthomonas campestris), Bunchy top (Rickettsia sp.),
Internal yellowing (Enterobacter cloacae),
4.3 Virus infections
Papaya ringspot, Papaya rindspot virus, type P PRSV-P (PRV)
4.4 Oomycota, oomycetes infections (not a fungus)
Phytophthora fruit rot, Phytophthora stem rot (Phytophthora sp.)
Phytophthora root rot (Phytophthora cinnamomi)
4.5 Phytoplasma infections
Dieback, Yellow crinkle, Papaya mosaic
When starting from the top, the leaves become shrivelled and fall off.

13.3 Fungus diseases
1. 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.
2. 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.
3. 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 which 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), and can be controlled with wettable sulfur
dust or a weekly spray of 1 part full cream milk and 10 parts water sprayed on.
A scar on the fruit shows where the mildew has been.
4. 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.
5. 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
6. 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.
7. 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.

13.4 Phytophthora infections
Phytophthora fruit rot, Phytophthora and stem rot, Oomycota, oomycetes, (not a fungus).
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

13.5 Virus infections
Papaya ring spot 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.

13.6 Mites
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.

13.7 Papaya yellow crinkle disease
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.

13.8 Boron deficiency
1.1.0 Boron deficiency
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".

14.0 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.

15.0 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.

1. Show how to harvest papayas correctly and what to do with bad fruit.
2. Record:
2.1. Number of papayas harvested.
2.2. Weight of papayas harvested.
2.3. Estimated returns (money that could be received from selling harvest).
(If you do not actually sell the papaya you can still calculate or estimate the returns as if all were sold.)
3. 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?
4. In some countries the average commercial papaya plant produces 15-20 fruits each year weighing 75 kg.
What do your papaya plants produce?

16.0 Papaya uses and recipes
Papaya is usually eaten when ripe as fresh fruit.
Sometimes people wrap meat in papaya leaves and cook by steaming over hot stones underground.
The 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.
Dried papaya may be sold as fruit chips, leaf and leaf powder.
Medical uses in Southeast Asia and Sri Lanka.
1. Dried fruit pulp used to reduce swellings.
2. Pounded leaves are applied to ulcers, swellings, boils and wounds.
3. Latex is used to expel intestinal worms, treat enlarged spleens and remove skin blemishes, e.g. freckles, warts and corns.
4. Latex is applied to snakebites.
5. Roots are used to treat uterine tumours, induce flow of urine and assist removal of stones from kidneys.
6. 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
1 large green papaya, cut in halves and seeds taken out to leave 2 shells
2 tablespoons of cooking oil
1cup finely chopped onions
1kg minced beef or 1 tin 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 tin can.
Put some boiling water into roasting tin 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 tbsp 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.
Eat with wedges of cabbage, or coconut rice.

4. Papaya jam
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.
Stir frequently with a large spoon.
When it is like a jelly pour into jars and seal.

5. Papaya chutney
1 green papaya
litre malt vinegar
1/4 kg sugar
cup raisins
1 teaspoon chopped ginger root
1 teaspoon chopped fresh chillies
5 teaspoons salt
Peel the papaya, discard seeds, cut into 2 cm cubes.
Place papaya and vinegar into a heavy saucepan.
Bring to boil and cook briskly for 10 minutes, stir occasionally.
Now stir in sugar, raisins, ginger, chillies and salt.
Simmer for 45 minutes until the papaya is tender.
When thick enough pour into jars and seal.

6. Papaya and pepper sauce
1cup of fresh chopped chillies
5 tablespoons chopped onions
2 tablespoons peeled finely chopped unripe papaya
1 teaspoon mustard
1teaspoon salt
3 tablespoons vinegar
Put chillies, onion, papaya, mustard, salt and vinegar into small saucepan.
Boil quickly and stir constantly.
Cool before using.
7.1 Pickled papaya
1 small green papaya, pealed and cut into 2 cm cubes
1cup of chopped chillies
1 piece of ginger 21
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.

7. Papaya and fish soup
This soup may be good for mothers breast feeding their children
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.

8. Use 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, they 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.

9. "Pawpaw delight", from Solomon Islands
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.

17.0 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.

17.1 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), 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, Daley's Fruit Trees

17.2 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 is an excellent system in which to
study the early events of sex chromosome evolution.
Over 95% male papaya trees produce some hermaphrodite flowers in spring and can set 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.

17.3 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.
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.
Germination of commercial seed should be tested before dispatch to guarantee a minimum germination rate of 50% for 50 days after
purchase date.

17.4 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 saved from single sex trees may be male or female, while seed from bisexual trees are more likely to 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.

17.5 Chemicals in papaya
| Antheraxanthin | Benzyl isothiocyanate, (BITC), C6H5CH2NCS, in seeds | Carotene epoxide | Carotene | Carpaine, C28H50N2O4
| Chymopapain | Chymopapain | Cryptoxanthin | Danielone | Glucotropaeolin | Mutatochrome | Papain | Papava peptidases A and B |
| Papavarine, C20H21NO4 |

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.
Also, 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

Preface
Before teaching this project, discuss the content of the lessons with a field officer of the Ministry of Agriculture 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 the local field officer of the Ministry of Agriculture.
If you cannot control insects by hand-picking, ask the Ministry of Agriculture 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.