Pawpaw Production
1. Introduction
Pawpaw is also known in English as Papaw or Papaya (The name papaya originated from Spanish). Pawpaw is a popular garden fruit crop in Tanzania, grown for home consumption and for sale of fresh fruits. In Arusha region, pawpaw was at one time grown as a plantation crop for the production of papain. It is a higher potential cash crop, particularly for the export market.
2. Botanical description
2.1 Classification
Family: Caricaceae (a family with 24 known species)
Genus: Carica (a genus with 7 species)
Species: papaya
Hence the botanical name for pawpaw is Carica papaya L. This is the only species of major economic importance in family Caricaceae . Other species exist mainly as wild fruit plants.
These include:
- C. candamarcensis HOOK. F. or C. cundinamarcensis J. LINDEN. The species is commonly known as the mountain papaya.
- C. chrysopetala HEILB or C. pentagona HEILB
- C. quercifolia BENTH
- C. microcarpa JACQ. or C. cauliflora JACQ.
- C. gracilis SOLMS.
- C. erythrocarpa LINDEN and ANDRE.
2.2 Plant characteristics
2.2.1 Stem
The pawpaw is a small soft wooded tree that is rarely naturally branched. It is therefore constituted by only a single axis – the trunk. It grows to a height of 3 to 10m. The trunk is marked with prominent scars of fallen leaves. It is hollow; from the median portion up to the apex, at which it holds a crown of large leaves.
2.2.2 Leaves
the leaves are large, with long hollow petioles. The leaf blades are lobed in 5-7 lobes, each traversed with thick venation. The leaves are arranged in a 2/5 spiral.
2.2.3 Flowers
The plant is normally dioecious. However, hermaphrodite (bisexual) flowers and trees do exist. Female flowers are large (3-5cm long), born in the axils of leaves, singly or in groups of 2-3 in the apical region of the stem. They carry 5 fan-shaped stigmas on the top. Male flowers are born on long branched and hanging panicles. They have 10 stamens. Hermaphrodite or bisexual flowers resemble female flowers. They are born singly in groups of 2-3, but have 5-10 stamens.
Pawpaw is consequently essentially a cross pollinated plant, though self-pollination occurs in hermaphrodite plants. The different types of plants are distinguished at flowering. In male plants sex reversion may take place when (old) tree are cutback or damaged.
2.2.4 Fruits
The fruit is a large fleshy hollow berry. The central cavity is filled with small black seeds, which are covered with mucilage. The fleshy is thick (2-3cm) and juicy. Its color ranges from yellow, orange to reddish. The fruit weighs 300g to 2kg or more depending on the variety.
The size and shape of the fruit differ also with the sex of the plant. Female plants generally produce large ovoid fruits with a large number of seeds. Female type plants are high yielding, precocious and have high quality flesh. They are ideal for growing in home gardens. Bisexual plants produce ellipsoidal or cylindrical fruits with thick flesh and few seeds. The fruit are more of uniform and medium size. These fruits types are ideal for the fresh fruit market as well as for papain production. Latex production is higher from oval fruit types than from long or round fruits.
2.2.5 Roots
The roots are shallow, dense and extensive. In good soils, the roots will penetrate deeply, while in wet or compact soils they will remain very superficial.
3. Uses and composition
Pawpaw is considered to be one of the excellent fruits nutrition-wise. The fruit’s most important nutritive value results from its high vitamins content. It is as rich in vitamin C as the orange, but it is the richest of all fruits in Vitamin A.
The unripe pawpaw fruit produces latex from which papain is extracted. Papain contains proteolytic enzymes, which aid in digestion. Papain is consequently used as a meat tenderizer and for medical and industrial purposes.
4. Origin and distribution
Pawpaw is a native of tropical America, notably in Mexico. It is generally grown in the lying region between 32ºN and S of the equator, i.e., in the tropics and the warm subtropics. The major producing countries are Brazil, Indonesia, India, Mexico and Zaire. The World production stands at around 2,000 tonnes per year.
Tanzania was in the 1960s – 1970s the main producer of papain. It has now been overtaken by Asian countries, particularly Thailand.
5. Plant growth and development
The plant is said to be fast growing, characterized by continuous fruiting. Depending on the variety and ecological conditions, fruiting starts after a short juvenile period ranging from 4-8 months, while the economic lifespan ranges from 3 to 5 years.
Since the plant is unbranched, fruits are born axilliary (in the leaf axils) on the truck. The number of fruits produced per plant is therefore determined by the number of leaves formed. It is estimated that, under favorable conditions, after germination of the seed, leaf emergency occurs at constant rate of 2 leaves per week, while flowering starts on average at the 32 nd leaf axil. If fruits were to be set in all leaf axils, a yield of 100 fruits per tree per year could therefore be expected. Although the tree remains in prime condition for 3-5 years, its economic life (for commercial production) comes to an end when the fruits are born so high that they cannot be picked profitably.
6. Ecology and physiology
6.1 Climate
Temperature: Optimum temperature is 26-32 ° C.
Rainfall: Well distributed rainfall of 1500 – 2000mm per year.
Light: Does well under conditions of full sunlight.
Under hot and very dry conditions growth is retarded, leading to the formation of very short internodes. As a result, fruits are densely set (crowded), and become severely deformed as they mature. The latex tends to dry on the tapped surface of the fruit and becomes difficult to collect. Low temperatures retard the vegetative and reproductive growth thereby reducing the yield. Although a high level of moisture is desirable for papain production, the plant does not thrive under water logged conditions. Lower rainfall conditions would be suitable provided adequate cultural practices are adopted to conserve soil moisture through mulching and addition of large quantities of organic matter.
When light is limiting, the internodes become excessively elongated, thus producing too widely spaced fruits and consequently reduced plant lifespan and yield
6.2 Soil
Since pawpaw roots are very susceptible to water logging conditions, heavy clayey soils with poor drainage are unsuitable. Very shallow soils where water easily accumulates are also unsuitable. Well-drained soils with a pH of 6-6.5 and a depth of at least 1m are ideal for pawpaw.
6.3 Wind
Pawpaw has a hollow weak stem, which will easily break due to strong prevailing wind. Strong wind increases transpiration, reduces latex yield and damages the foliage.
7. Varieties
Varieties in the real terms; ie, well defined and fixed, do not exist. What is available are in fact regional and temporary types. Nevertheless, many varieties have been recognized. The most important pawpaw breeding work is done in Hawaii. The most well known in trade include:
- Solo types (solo, solo sunrise, solo sunset, solo low bearing). Produce fruits which are oblong shaped for hermaphroditic and round for the female. The fruit flesh is yellow to orange colored and red for sunrise. The fruits weigh between 300 and 400g.
- Waimanalo: Has yellow firm flesh, small cavity, weighing between 500g to 1kg.
- Amazon red: With bright red flesh fruits weighing 300 – 400g.
- Colombo: Pink fleshed, big more round shaped fruits of 700g to 1kg.
8. Cultural practices
8.1 Propagation
Pawpaw is propagated from seeds. Certified seeds of self-pollinated blooms bagged against inopportune pollination are recommended. When none selected seeds are used, varietal alterations usually occurring.
Own seeds can be collected from high yielding disease free mother plants. These should preferably be from hermaphrodite types, which rarely produce male plants and do also undergo self-pollination (fertilization). Ripe fruits are harvested and seeds extracted. The seeds are washed to remove the gelatinous cover around them. This is easily achieved by immersing the seed in water for about 4 days, so that the gelatinous material ferments. Washed seeds are dried under shade before sowing. Under ideal storage conditions, seeds will retain viability for more than a year.
the seeds are started off in a nursery preferably in polyethylene bags. Three seeds are sown per bag at a depth of 1-2cm. The seedlings are transplanted in the field when they attain a height of about 20cm. Sowing at stake is also practiced. With this practice, 8-15 seeds are sown per hill. In general, 125 – 250g of seeds will be required per ha.
8.2 Spacing and planting density
The planting density varies from 1000 – 2500 plants per ha, at a spacing ranging from 4 x 4m, 3 x 2.5m, 3 x 2m, 2.5 x 2m to 2 x 2m.
Wide spacing (low planting density) is commended for fruit production while close spacing (high planting density) is suitable for papain production.
8.3 Management practices
8.3.1 Thinning
At flowering stage male plants are removed. One vigorous female or hermaphrodite plant is retained per planting site. For pollination purposes, where necessary, one male plant per 50 female plants may be kept in the orchard.
8.3.2 Fertilization
From 1 – 6 months apply 50g NPK (6:18:20) and 20g CAN per plant. From 7 – 8 th month double the amount.
8.3.3 Pest and diseases
There are no major pests of economic importance. However, mites can be a problem. They will attack the stem and fruits. The mites will cover the fruits, which besides the damage due to the sucking effects make the fruits look dirty.
Occurrence of the papaya ring spot disease has been reported in the Lake Victoria areas and in the Coast regions, particularly in Tanga. Affected plants exhibit severe leaf distortion with at times high leaf size reduction and narrowing. The disease is viral, leading to the formation of numerous ring spots on the fruit. The fruit appears hard and malformed. Elsewhere, the disease is known to be a serious problem in Mexico, Hawaii, Brazil, Thailand and Jamaica.
Orchards should be kept weed free. When weeding, avoid wounding the plant stems and roots
9. Harvesting, yield and post harvest practices
9.1 Harvesting
The fruits are harvested when change in color (yellow / red tinge) appears at the blossom end, implying that ripening has started. If the fruits are harvested too early (before ripening) they will shrivel, will not ripen post-harvest. Conversely, if they are too ripe picked, they are difficult to keep and transport.
The fruits are harvested by twisting and pulling. By so doing the fruits snap very easily. Bruising of and dropping the fruits should be avoided.
9.2 Yield
Yield varies from 40 to 60 tons of fruits per ha per year, with each plant bearing 30 to 50 fruits per year.
Papain is extracted by tapping mature fruits. Yield of papain is dependent on fruit yield. At the above average fruit yield, it is estimated to range from 60 to 100kg per ha per year. It is estimated moreover that 4kg of wet latex gives 1kg of sun-dried latex.
9.3 Fruit grading and packaging
Fruits weighing over 800g are not imported into Europe. The most popular sizes are the 300 to 400g range, which allows a reasonable unit price. In reference to the classification of pineapple degree of ripeness, a similar system has been devised for the pawpaw. The classes are:
· M1: Green fruit with a yellow / red tip
· M2: Fruit one third yellow / red
· M3: Fruit half yellow / red or more
Pawpaw fruits are packed in boxes in a single layer with a protective lining in the base. Inserts are not used. The fruits are often individually wrapped and raid diagonally in the box. Size grades are expressed in terms of the number of fruits per box and are 6, 8, 10, 12, 14 and 16 for weights of 3, 4 and 5kg.
9.4 Storage
For short periods of storage the recommended store temperature is +15 – 16ºC, with a relative humidity of 85 to 90%. For longer periods 2 – 3 weeks, the best temperature is + 8.5 ° C at the same relative humidity. Temperatures of below 7º easily harm the fruit.
10. References
1. COLEACP, 1986. The papaya.
2. Samson JA, 1986. Tropical fruits. Tropical Agriculture series. Longman Scientific and Technical. Singapore, 332p.
3. UNDP / FAO, 1981. Pawpaw cultivation and processing (Papain production). Technical bulletin 7, 12p.
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