As we all know papaya is delicious, commands a good sale price, and has many excellent nutritional and medicinal properties. Growing organically is much the better for health, but as I was warned by Cergio Mai of BAHA Plant Health, “this will be a challenge!” due to the fact that papaya is susceptible to many diseases and pests. I can testify to that as we have found on our farm in Cayo. So I wanted to find out how we could be more successful growers of papaya.

This article is about Carica papaya, the specie that is grown in Belize. In Australia and some parts of the Caribbean papaya is known as pawpaw but in his book, Fruits of Warm Climates, J. Morton says pawpaw is better suited to very different, mainly wild Asimina triloba Dunal, which belongs to the family Annonaceae (1).  Papaya is native to both southern Mexico and neighboring Central American countries (1).

Papaya Flowers

This is complicated! Papaya plants grow in three sexes: male, female, and hermaphrodite (in which flowers contain both male stamens and female ovaries). But there may even be plants with both male and female flowers. Others at certain times of the year produce male flowers, but at other times, hermaphrodite flowers. This change of sex may occur temporarily during high temperatures. In addition, male or hermaphrodite plants may change completely to female plants after being beheaded (1).  The male plant has flowers which are clustered, growing at the end of long branching stalks. The buds are thin and shaped like an elongated spoon. They have bright orange anthers. The female flowers on the other hand, are considerably larger and fatter, on very short stalks. They are puffed out by a fat ovary and branching yellow stigma, where the pollen from a male or hermaphrodite lands. The hermaphrodite flower is thinner than the female flower, having a tubular shape. It has orange male anthers, and also a cylindrical ovary, but with no branching on top. The male produces only pollen, never fruit; the female produces small, inedible fruits unless pollinated by wind or insects. The fruits from female flowers are round or oval, and thin-walled.  The hermaphrodite flower, however, is able to self-pollinate. The fruits from these are usually cylindrical or pyriform, with a small seed cavity and a thick wall of firm flesh which withstands handling well (1). See what I mean about being complicated?

Almost all commercial papaya orchards contain only hermaphrodites. BAHA Plant Health advise planting out only hermaphrodites.

Cultivars

Two kinds of papaya are commonly grown. One has sweet red or orange flesh; the other, yellow flesh. Large red fleshed “Maradol”, Maradona”, “Sunrise” and “Caribbean Red” are commonly grown in Mexico and Belize. In Orange Walk, the papaya exporters favor the Tainung variety. (C. Mai, personal communication, 30.1.22)

Diseases and Pests Affecting Papaya in Belize.

•       Papaya mosaic virus

•       Papaya ringspot virus (PRSV)

•       Papaya Meleira virus

•       Bunchy top disease (involves a bacterium belonging to the genus Rickettsia, and most likely the vector is the leafhopper Empoasca papayae )

•       Anthracnose (a group of fungal diseases)

•       Phytophthora (these resemble fungi but in fact they are not. They are most often referred to as water molds.)

•       Mealy bugs

•       Snails

•       White flies

•       Leaf hoppers

•       Aphids

•       Mites

Seeds

Papaya are generally grown from seed. You need to start with certified seeds in order to grow healthy papaya. There is no hybrid papaya seed that is 100% hermaphrodite; generally the range is 50-90%. East West Seeds in Benque sells hybrid and non-GM seeds; the agent sells only in bulk (www.eastwestseed.com).  Agric-Pric in Cayo also sells papaya seeds. A recommended seed is the Tainung cultivar, developed in Taiwan, which ranked highest in extensive trials in Orange Walk. It has an excellent brix number (sweetness); it is less hollow than other varieties and fares well on handling. Certified Tainung seeds may be available in bulk from the papaya exporter in Indian Creek, in Orange Walk. Papaya tolerant to bunchy top disease have been found and bred, but production is limited to areas with a low disease pressure. Also testing well is the Red Lady variety. (C. Mai, personal communication, 30.1.22)

Saving Your Own Non-GMO Papaya Seeds

Interestingly enough, you can obtain your own true-to-type seeds from hermaphrodite plants grown from F1 certified seeds. This is done by (1) selecting the best trees which are healthy, (2) carefully covering unopened flowers with paper bags (stamp collectors semi-transparent envelopes are ideal), (3) stapling the ends closed to prevent other pollen getting in, and (4) marking with a tag the point where the bud attaches to the tree, as the bag will burst as the fruit grows. (www.hawaiihomegrown.net 2014 Rachel Laderman)

Harvest the fruit at the color break stage, and collect the seed from the fruit. The plants from these seeds should then grow true to type and be vigorous because the hermaphrodite flower can self- pollinate, so the seeds are replicas of the parent. The seeds should be dried to moisture levels of 9-12% for long term storage, as seeds harvested fresh can have variable germination (3).

Germination

Firstly remove the gelatinous layer by rubbing. Place on wet paper or blanket, cover and leave to germinate. (C. Mai, personal communication 30.1.22) An alternative protocol is to soak the seeds in a container filled with clean water for 48 hours. They should be completely covered with water. Change the water every 8 hours. After 36 hours, remove the seeds that float. East West Seeds recommends that during the last 8 hours of soaking, you should add 1/4 teaspoon (1.25 ml) of gibberelic acid per 4 1/4 cups (1 l) of water. This is a natural product extracted from the Gibberella fujikuroi fungus that is found on rice plants. However, other growers say adding gibberellic acid is not necessary. (C. Mai, personal communication, 30.1.22) It is advised to keep the seed for two days between two cotton sheets (boiled and disinfected) while keeping the humidity constant to avoid dehydration.

Sow the seeds in seedling trays at a depth of 1/2 inch (12.7 mm) against sun, wind and rain i.e. in protected structures. Regulate the humidity well to avoid root rot and fungal attacks.

Preparing the Soil

Papaya generally do poorly on land previously planted with papaya, a result of soil infestation by Pythium aphanidermatum (a water mold which causes damping off of seeds and seedlings, and root rot) and Phytophthora palmivora (1).  Root rot of papaya seedlings, caused by P. palmivora, in replant fields can be controlled with the virgin soil technique. Virgin soil (soil in which papaya has never been grown in before) is placed in planting holes about 12 inches (30.5 cm) in diameter and  4 inches (10.2 cm)deep, with a mound about 1.5 inches (3.8 cm) high. Roots of papaya plants are protected by the virgin soil during the susceptible stage, and become resistant to the pathogen when they extend to the infested soil.

Planting Out

Plant out from 6 weeks onwards (up to 6 months). The site must be free of volunteer papaya and host plants, especially in respect of viral diseases. Raised beds and properly drained land are ideal for the prevention of Phythophora.  It is important to do soil sampling of your intended sites prior to planting to determine the fertility and availability of nutrients, so that organic inputs can be customized.

Plant 6 seedlings per site, and then sex the plants at flowering. Due to being a dominant trait, hermaphrodites are the most common sex, followed by females and lastly males. It is best to plant 7 feet (2.2 m) apart, and 12 feet (3.6 m) between rows; about 3,000 plants per acre (1200 per hectare).  The best time of year to plant out is from May onwards excepting December.  The issue is slow yields in certain months. (C. Mai, personal communication 25.1.22)

Disease and Pest Control Treatments

The treatments should be Integrated Pest Management (IPM) based. The following are useful:

•       The use of plant barriers: sunflowers and sugar cane.

•       Weed control.

•       Colored insect traps; sticky insect traps.

•       Diatomaceous earth, sprinkled around the plants. Reapply after rains.

•       Neem.

•       EM 0.5 (effective micro-organisms with neem); and EM Agriculture, a concentrated mother culture of naturally occurring beneficial micro-organisms for growing plants.

•       For viruses in general: “roguing”: identifying and clearing out of diseased and undesirable plants, once a field is infected. This means that the control of pests that transmit them is crucial.

•       The cleaning of equipment and tools.

•       For bunchy top disease: in addition to measures to combat leafhopper vectors; removal of infected treetops at a point below where the latex flows freely on wounding can result in healthy shoots from the trunk.

•       Large net houses (as in Taiwan) to keep out disease-carrying non–persistent aphid vectors.

The following biological control agents (with the possible exception of Metarhizium) are difficult to source in Belize and in any case, usage should be guided by an entomologist.

•   Metarhizium (a fungus in spore form which is a natural pesticide against locusts)

•   Chysopa spp. (green lacewing insects; their larvae feed on aphids.)

•   Timorex Gold (an organic fungicide based on a plant extract)

•   Mealybug destroyer (Cryptolaemus montrouzieri, a ladybird species, which is a biological control against mealybugs and other scale insects)

•   Beauveria bassiana (a fungus which protects against insect pests)

•   Parasitic wasps (C. Mai, personal communication, 30.1.22)

Harvesting

Studies in Hawaii have shown that flavor is at its peak when the skin is 80% colored. However, for shipment, the first indication of color is permissible. The fruits must be handled with great care to avoid scratching and subsequent leaking of latex which would stain the fruit skin. Home growers can twist the fruit to break the stem, but commercial operations prefer the use of a sharp knife to cut the stem. The fruits are best packed in single layers and padded to avoid bruising.

Growing Papaya in San Antonio

Rene Tzib, pesticide-free farmer in San Antonio, grows hybrid papaya successfully from F1 certified seed. (R. Tzib, personal communication, 4.11.21). His regime is:

•   Plant seedlings out at 3 months, then sex the plants at flowering at 4 months. Plant out only 5 male plants out of 100.

•   Phyton to protect against fungus: use it as you plant out; then spray the leaves and soil every 4 weeks.

•   EM Agriculture: apply when planting in a hole, then again every two weeks.

•   Sulphate (or cow or pig manure) and white marl mixture: use for preparing seedlings against fungus and ants; spray plant tops every month.

•   White lime: mix with water and put in the hole when planting; this counteracts ants and worms.

Pruning

After fruiting at 6 months, Rene cuts the big branches, and then the smaller branches give a second crop. The plant dies at around 1 year 6 months.

Nutritional Value

Papaya is regarded as a fair source of iron and calcium; a good source of vitamins A, B; and an excellent source of vitamin C. The carotenoid content is low compared with mango, carrot and tomato. (1)

Food Uses

Ripe papaya - Papaya is commonly eaten ripe, fresh, peeled, seeded and cut into wedges or chunks. Often it is served with a wedge of lime to squeeze the juice over the papaya. Sometimes it is shaped with a melon baller and served with other fruit. Firm-ripe papaya can be seasoned and baked like a vegetable. Ripe flesh can be made into a sauce for shortcake or ice cream or swirled through ice cream before freezing. (1)  Papaya can also be cooked in a pie, pickled, or preserved as a jam. (1)

Papaya juice - In Hawaii, papaya are pureed, and sucrose added to retard gelling; the puree is then frozen for use locally, or in mainland USA in fruit juice blending or for making jam. (1)

Unripe (raw green) papaya - This is never eaten raw because of its latex content. However it is used in Thai and Vietnamese cooking; in salads it is peeled, deseeded, boiled until tender, then chilled. Green papaya is boiled and served as a vegetable. (1)

Papain - The latex of the papaya plant and its green fruits contain two proteolytic enzymes, of which papain is the most potent.  This property makes it especially useful as meat tenderizer: pieces of green papaya can be rubbed on meat to make it palatable. However, papain treated meat should never be eaten “rare”; it should be cooked enough to inactivate the enzyme. Papain has other practical applications: it is used to clarify beer, to treat wool and silk before dyeing, and to de-hair hydes before tanning, to mention a few. (1).

Medicinal Uses 

The handbook of action Natural Medicine in the Tropics (4), lists 17 different medicinal uses. This NGO was founded by Hans-Martin Hirt, a German pharmacist working in DRC, Congo. It should be noted that it is not advisable for pregnant women to eat papaya seeds.

Papaya Allergy

Skin irritation of papaya harvesters, due to papaya latex, is well documented. In sensitized individuals, even the pollen of papaya flowers can cause severe respiratory reactions. Following this, such individuals can display a contact reaction to any part of the plant, and to eating papaya or meat tenderized with papaya.

Hybrid Papaya Seed and Metarhizium Sources in Belize

The Seed Agent, located at 4 George Price Blvd, Benque (cell: 636 3678.), sells East West Maradona F1 seeds.

Agro-Pric (Carlos Herrera) in Cayo, cell: 607 5058, sells hybrid papaya seeds.

George Thiesen, Papaya exporter in Indian Creek, Orange Walk. Cell: 674 4807. He will haveTainung seeds available for sale from March.

The Sugar Industry Research and Development Institute (SIRDI) sells Metarhizium. (Bz 25 which covers 1 hectare)

Procer sells Phyton.

Mile 25 Hummingbird Highway, Stann Creek sells white marl, white lime and sulphate.

References

1.  Morton, J. 1987. Papaya. P 336-346. In: Fruits of Warm Climates. Miami, Fl. Available free from: https://hort.purdue.edu/newcrop/morton/index.html

2.     East West Seeds (www.eastwestseed.com)

3.     Paull, RE., Duarte O. 2011. Tropical Fruits volume 1. P. 311. Second edition. UK. MPG Books Group.

4.     Hirt, HM and Pia, B. 2001. Natural Medicine in the Tropics. Second edition. Winnenden. Druckerei Bauer.