Papaya Cultivation; Chapter 4 - Disease & Pest

Papaya ring spot virus is a well-known virus within plants everywhere. The first signs of the virus are yellowing and vein-clearing of younger leaves as well as mottling yellow leaves. Infected leaves may obtain blisters, roughen or narrow, with blades sticking upwards from the middle of the leaves. The petioles and stems may develop dark green greasy streaks and in time become shorter. The ring spots are circular, C-shaped markings that are darker green than the fruit itself. In the later stages of the virus, the markings may become gray and crusty. Viral infections impact growth and reduce the fruit's quality. One of the biggest effects that viral infections have on papaya is the taste. Right now, the virus is uncontrollable.

The papaya mosaic virus is very destructive because it completely destroys the plant until only a small tuft of leaves are left. The virus affects both the leaves of the plant and also the fruit itself. Leaves show thin, irregular, dark-green lines around the borders and clear areas around the veins. The more severely affected leaves are irregular and linear in shape. The virus can infect the fruit at any stage of its maturity. Fruits as young as 2 weeks old have been spotted with dark-green ring spots about 1 inch in diameter.

Rings on the fruit are most likely seen on either the stem end or the blossom end. In the early stages of the ring spot, the rings tend to be many closed circles, but as the disease develops the rings will increase in diameter consisting of one large ring. The difference between the ring spot and the mosaic viruses is the ripe fruit in the ring spot has mottling of colors and mosaic does not. There are few more disease caused by Root rot virus, Collar rot virus, Cucumber mosaic virus etc.

Fungi Anthracnose is known to specifically attack papaya especially the mature fruits. The disease starts out small with very few signs, such as water-soaked spots on ripening fruits. The spots become sunken, turn brown or black and may get bigger. In some of the older spots, the fungus may produce pink spores. The fruit ends up being soft and having an off flavor because the fungus grows into the fruit. 

The fungus powdery mildew occurs as a superficial white presence on the surface of the leaf in which it is easily recognized. Tiny, light yellow spots begin on the lower surfaces of the leaf as the disease starts to make its way. The spots enlarge and white powdery growth appears on the leaves. The infection usually appears at the upper leaf surface as white fungal growth. Powdery Mildew is not as severe as other diseases. 

The fungus phytophthora blight causes damping-off, root rot, stem rot, stem girdling and fruit rot. Damping-off happens in very young plants by wilting and death in plant. The spots on established plants start out as water-soaked lesions at the fruit and branch scars. These spots can get bigger and cause the death of the plant. The roots can be severely and rapidly infected, causing the plant to rapidly brown and wilt away collapsing within days. The most dangerous feature of the disease is the infection of the fruit because it cause harm to people who consume it. The biggest evidence that the fungus is present are the water-soaked marks that appears first along with the white fungus that grows on the dead fruit. After the fruit dies it shrivels and falls to the ground.

Pests The papaya fruit fly is mainly yellow with black marks. The female papaya fruit fly has a very long, slender abdomen with an extended ovipositor that exceeds the length of its body. The male papaya fruit fly looks like the female with the differences of a hairy abdomen and no ovipositor. Long slender eggs are laid inside of the fruit by the female papaya fruit fly. The larva is white and looks very much like the regular fruit fly larvae. The female is capable of lying up to 100 or more eggs and are laid during the evening or early morning in groups of ten inside young fruit. They usually hatch within 12 days of being in the fruit where they’ll feed on the seeds and interior parts of the fruit. When the larvae mature (usually 16 days after being hatched) they eat their way out of the fruit, drop to the ground, and pupate just below the soil and emerge within one to two weeks as mature flies. The flesh of the papaya must be ripe in order for the fly to migrate towards the surface of the fruit because unripe papaya juice is fatal to them. The papaya will turn yellow and drop to the ground if it is infected by the papaya fruit fly. 

The two-spotted spider mite is a 0.5 mm long brown or orange-red but a green, greenish yellow translucent oval pest. They all have needle-like piercing-sucking mouthparts and feed by piercing the plant tissue with their mouth parts usually the underside of the plant. The spider mites spin fine threads of webbing on the host plant and when they remove the sap, the mesophyll tissue collapses and a small chlorotic spot forms at the feeding sites. The leaves of the papaya fruit turn yellow, gray or bronze. If the spider mites aren’t controlled it can cause the death of the fruit.

The papaya whitefly lays yellow oval eggs that appear dusted on the undersides of the leaves. They eat the papaya fruits leaves therefore damaging the fruit. There, the eggs developed into flies in three stages called instars. The first instar has well-developed legs and is the only mobile immature life stage. The crawlers insert their mouthparts in the lower surfaces of the leaf when they find it suitable and usually don’t move again in this stage. The next instars are flattened, oval and scale-like. In the final stage as the pupal the whiteflies are more convex, with large conspicuous red eyes.

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Papaya Cultivation; Chapter 3 - Cultivation Process & Proceedures

Climate 

 

Papaya flourishes in the frost-free and humid areas of the tropics and subtropics. They may be damaged or die if exposed to prolonged frost, and prefer climates that are warm throughout most of the year. An average temperature of 25°C is optimum. Papaya trees are fast growing and have an upright growth pattern. In tropical conditions they flower within 6 months after planning and will continue flowering throughout the year. The plant requires rainfall between 1500-2000 mm, which needs to be spread throughout the year. Due to its soft wood and flat root system, the papaya is very susceptible to wind break, especially in mono-culture. Papaya trees do poorly in wet soil. If your climate is rainy, you may plant them on a mound of well-draining soil as described further on.

1.  Although a mature papaya tree can withstand a temperature of -2°C. Production is only recommended where the average daily minimum temperature during the midwinter never drops below 5°C.
2. Ideally, night temperature should not drop below 12°C.
3.  The optimum temperature range for papaya is between 25 and 28°C.
4. Temperature higher than 36°C and lower than 17°C for extended periods of time will adversely affect the growth of the trees.
5.  At average day temperature (+/- 23°C) it will take about 6 months from flowering for the fruit to mature.
6. The lower the temperature the longer it will take for the fruit to mature and the other way round. After the winter the trees are in recovering stage and few flowers are produced.
7. Production normally peaks from September to November.

Soil requirements 

Papayas grow and produce well on a wide variety of soil types. The tree often develops a fairly strong taproot shortly after planning. He root system can, under favorable conditions, penetrates the soil to a depth of 2 m, but most of the roots responsible for nutrient uptake are found in the top 500 mm of soil, with the largest concentration in the top 250 mm.

1. Drainage – Papaya grow best on soil with a slight slope, because it enables the runoff or drainage of excess water and therefore prevents water-logging. Papaya roots will die off in over-saturated and poorly drained soils such as depressions or basins as a result of a lack of aeration. Impermeable layers in the soil adversely affect growth and production of the plant and can lead to infection with root diseases.
2. Depth – Under irrigation, papaya grow optimally in soils with an unimpeded depth of more 1 m. However, if irrigation is well planned and manages, there should be no problem on with an unimpeded depth of 750 mm, provided that no drainage problems occur at that depth.
3. Texture – The ideal soil texture for papaya cultivation under irrigation is a sandy loam or loam soil (i.e. with clay content of 15 % to 30 %), butt soils with a clay content of up to 50 % are also suitable.
4. Soil structure – The ideal soil has fairly loose, brittles, crumbly structure. A compact or strongly developed soil structure will adversely affect water infiltration and root penetration. These soils are normally associated with very high clay content in the subsoil.
5. Soil pH – papaya grows best in soils with pH values of 6 to 6.5. If the soil exchangeable aluminum is not more than 30 ppm, soil with pH of 5.5 or higher may be used.

Fetilisation 

Papaya prefers a high soil-fertility. This should be considered when choosing a site. Additionally, a balanced mixed cultivation system with a substantial production of organic material, high turnover and plenty of soil activity is essential to a healthy papaya plantation. Well-rotted compost should be added to each seedling before covering. The compost can be mixed with the excavated soil. For a high yield of papaya per harvest, the following nutrients must be added annually per hectare.

Nitrogen (N)            : 100 kg

Phosphate (P)         :   40 kg

Potassium (K)          :   60 kg

Micronutrients are also very necessary part and play a significant role in production and quality of the fruits. Papaya plants with a boron deficiency have lumpy fruit, reduced fruit set and show poor growth. To prevent deficiency fertilization must be incorporated into the fertilization program from the onset. Similarly, all the other micronutrients like Zn, Mn, Mg, Fe, Ca, and S also require proper attention and application in various available forms (For detailed information about fertilizer selection and nutrient application please mail me personally).

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Papaya Cultivation; Chapter 2 - History & Origin

  

The history of papaya spread was initiated approximately in 1500, when the Spanish conquerors carried seeds to Panama and Dominican Republic. Papaya was first described in 1526 by the Spanish chronicler Oviedo, who found it first on Panamanian and Colombian coasts. The fruit was rapidly propagated in the tropics, most likely due to the abundant and highly viable seeds. The crop has adapted quite well to tropical areas with fertile soils and abundant rainfall. During the following century Spanish and Portuguese sailors took the seeds to the Phillipines, Malaysia and India. For 1600 the fruit had been produced in warm regions of South and Central America, Southern Mexico, the Antilles, Bahamas, Bermuda Florida. In the same century pawpaw seeds were taken from India to Naples in Italy. 

The crop reached Hawaii between 1800 and 1820. Until 1900, papaya seeds were taken to Florida, probably from Bahamas' plantations. The Solo variety has been cultivated in Hawaii since 1911, probably brought from Barbados and Jamaica. The first seeds of the Maradol 1 variety were introduced into Mexico in 1978, through CONAFRUT, in Xalapa, Veracruz.

 

Origin and Spread

1. The original home of the papaya is tropical America.

2. The studies in the areas of archaeology, history and

   etymology to trace the origin of papaya are limited.

3. Most of the evidence about its origin are based on the  

   species distribution, records of world travels and limited 

   etymology.

4. It is said to have been introduced into India by about the  

   middle of the 16th century.

5. The family Caricaceae as a whole was practically reported to 

   be restricted to continental America, though it was known in 

   the West Indies namely Jamaica at least in 1756.

6. Subsequently, Spanish and Portuguese sailors had 

   disseminated the papaya to other tropical and sub-tropical 

   countries.

7. Since the papaya seeds have a moderate period of longevity, 

   it is likely that the papaya spreads rapidly throughout the 

   tropics following the discovery and exploration of the new 

   world.

8. It has existed nearly everywhere in the tropics practically as 

   long as man has recorded the modern history.

    

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Papaya Cultivation; Chapter 1 - Introduction

Papaya is a fast growing arbore scent herb, with short life and very sensitive nature. It has single straight or sometimes branched stem reaching 2-10 m height (Papaya tree). When it reaches maturity usually after one year of production, new shoots appear at the lower trunk that develops into branches when the plant reaches it maximum high or when the main top stem is prune off. The stem is cylindrical spongy-fibrous, loose, hollow, gray or gray-brown color, 10-30 cm diameter and toughened by large and protuberant scars caused by fallen leaves and flowers. Papaya has approximately 31 varieties and can be cultivated throughout the India but there are few limitations.  

 

Papaya, with spirally arranged leaves confined to the top of the trunk. The lower trunk is conspicuously scarred where leaves and fruit were borne. The leaves are large, 50–70 cm (20–28 in) in diameter, deeply palmately lobed, with seven lobes. Unusually for such large plants, the trees are dioecious. The tree is usually unbranched, unless lopped. The flowers are similar in shape to the flowers of the Plumeria, but are much smaller and wax-like. They appear on the axils of the leaves, maturing into large fruit - 15–45 cm (5.9–17.7 in) long and 10–30 cm (3.9–11.8 in) in diameter. The fruit is ripe when it feels soft (as soft as a ripe avocado or a bit softer) and its skin has attained amber to orange hue. 

 

The plants may be classified into three primary sex types: 1) male (staminate), 2) hermaphroditic (bisexual), and 3) female (Pistillate). In addition, some plants can produce, at the same time, more than one kind of flower. Also, some produce flowers that are not of these basic forms, but exhibit different degrees of maleness and femaleness. This tendency to change in sexual expression seems to be triggered by climatic factors, such as drought and variable temperatures. The tendency to produce male flowers seems to increase at high temperatures. Since male trees are unfruitful and fruit from bisexual plants is preferred in some markets, it is very important to select seed which will produce fruitful trees of the desired type. This can't be done by simply saving seed from productive open-pollinated plants, but one can predict fairly accurately the progeny by knowing the source of pollen and the kind of flower the fruit came from. In the past few decades agriculture sector has increased drastically production wise and quality wise so there are so many companies all over the world which are providing hybrid seeds, in which the production, resistance to disease, quality etc. important factors are favorable.

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