1 Introduction
1.1 Economic and social impact of the Pawpaw crop
1.2 World trade
1.3 Primary product
1.4 Preparation and uses
1.5 Alternative products from pawpaw
1.6 Benefits of Pawpaw
1.7 Requirements for export and quality assurance
1.8 Consumer preferences

1 Introduction

The pawpaw (Carica papaya L.) is the most economically important fruit in the Caricaceae Family. In some parts of the world, specially Australia and some islands of the West Indies, it is known as papaw, or pawpaw, names which are better limited to the very different, mainly wild Asimina triloba Dunal, belonging to the Annonaceae. While the name pawpaw is widely recognized, it has been corrupted to kapaya, kepaya, lapaya or tapaya in southern Asia and the East Indies. In French, it is papaye (the fruit) and papayer (the plant), or sometimes figuier des Iles. Spanish-speaking people employ the names melón zapote, lechosa, payaya (fruit), papayo or papayero (the plant), fruta bomba, mamón or mamona, depending on the country. In Brazil, the usual name is mamao. When first encountered by Europeans it was quite naturally nicknamed "tree melon". (Morton, 1987).

Production areas are located in most tropical and sub-tropical countries (CRFG, 1998) (Fig. 1 Pawpaw mayor producing countries).

Fig. 1 Pawpaw mayor producing countries

The percentage composition of typical pawpaw is: seed (8.5 %), skin (12 %) and pulp (79.5 %) (Fig. 2 Typical pawpaw, maradol variety; and Fig. 3 pawpaw maradol variety % composition). As a dual- or multi-purpose, early-bearing, space-conserving, herbaceous crop, it is widely acclaimed, despite its susceptibility to natural enemies.

Fig. 2 Typical pawpaw maradol variety

Fig. 3 Pawpaw Maradol variety % composition

a) Origin
The pawpaw is believed to be native to southern Mexico and neighboring Central America. It is currently cultivated in Florida, Hawaii, Eastern British Africa, South Africa, Sri-Lanka, India, Canary Islands, Malaysia and Australia. It is now present in every tropical and subtropical country. Pawpaw 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. The history of pawpaw spread was initiated approximately in 1500, when the Spanish conquerors carried seeds to Panama and Dominican Republic. 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 y 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, pawpaw 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 variety were introduced into Mexico in 1978, through CONAFRUT, in Xalapa, Veracruz (CRFG, 1998).

b) Taxonomy
Morphology and taxonomy

Family: Caricacea.

Order: Parietals.

Species: Carica papaya.

SCIENTIFIC NAME: Carica papaya L.

c) Botanical description

Plant: It is a fast growing arborescent herb, with short life, it has single straight or sometimes branched stem reaching 2-10 m height (Fig. 4 Pawpaw tree), the stem is cylindrical spongy-fibrous, loose, hollow, gray or gray-brown colour, 10-30 cm diameter and toughened by large and protuberant scars caused by fallen leaves and flowers.

Fig. 4 Pawpaw tree

The pawpaw is a polygamous species. 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 give a maximum number of fruitful trees of the desired type. This can't be do 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. Accordingly, the grower must hand pollinate to obtain the desired combination of flower types. This is done covering an unopened flower, either bisexual or pistillate, with a paper bag until it opens and then transferring the desired pollen onto the receptive pistil. Pollination studies have shown that: 1) pistillate flowers pollinated by staminate flowers give equal numbers of male and female progeny; 2) pistillate flowers pollinated by pollen from bisexual flowers give an equal number of female and bisexual progeny, 3) bisexual flowers either self or crossed-pollinated with other bisexuals give a ratio of one female to 2 bisexual, 4) bisexual flowers pollinated by staminate ones produce equal numbers of female, male and bisexual progeny. It is evident that the second and third combinations will produce the maximum number of fruit-bearing plants (Malo, 2001).

Radicular system: Highly superficial, which conditions soil work.

Leaves: Alternate, bundled at the apex between stem and branches, long petioles; widely evident, 25-75 cm diameter, smooth, moderately palm shape with thick middle irradiant veins, the base is deeply string shape with overimposed lobes; from 7-11 large lobed, each with a wide base or slightly constrained and sharp-pointed, and sharp apex. The bundle of leaves is dark green to yellow-green, bright, visibly marked by the off-white nerves embedded and reticulated veins; the underneath surface is pale green-yellow and opaque with visibly prominent vascular structures; the petioles are round and yellow-green, with sporadic purple or violet stains, fistulous form, fragile, 25-100 cm length and 0.5-1.5 cm thick. (Fig. 5 Pawpaw leaves).

Fig. 5 Pawpaw leaves

Flowers:  Six types of flowers are known in pawpaw plant.
a) Typical female flower. It is a rather large flower of conical shape when closed, when open, its five petals spread from the base. The ovary is large with circular and smooth or slightly ondulated. Fruits produced by this flower are spherical or ovoid in shape. (Fig. 6 Typical female flower, De Los Santos, et al., 2000).

Fig. 6 Pawpaw typical female flower

b) Similar to the above when closed, but this type has five short anthers, which correspond in their orientation with the five petals that also spread from the base. The ovary has five deep longitudinal grooves that remain until maturity. Fruit develop a form from globular to egg-shaped.

c) Hermaphrodite intermediate flower. The organization is undefined, petals may be fused up to two thirds of their length or free from the base. The number of anthers ranges from two to ten; the carpels range from five to ten, with different degrees of fusion. This type of flower produces irregularly-shaped fruit known as carpelodic (cat face), with little commercial value. These flowers appear more frequently when ambient temperatures are 24.5 °C during the day and 15.5 °C at night.

d) Hermaphrodite elongated flower. Petals of this type of flower are fused from one fourth to three fourths of their total length; ten anthers are observed, five long and five short (Fig. 7 Hermaphrodite elongated flower, (De Los Santos, et al., 2000). The ovary is long and when it contains five or more carpels, the form of the fruit varies from cylindrical to pear-shape. From the different types of hermaphrodite flowers, this is the most commercially important. (Fig. 7 Pawpaw hermaphrodite elongated flower, De Los Santos, et al., 2000).

Fig. 7 Pawpaw hermaphrodite elongated flower

e) Hermaphrodite sterile flower. It is a flower that resembles the former, but does not develop an ovary and hence it is sterile, warm temperatures or water stress. Due to the fact that it produces pollen only, it may be considered a functional male flower (Fig. 8 Pawpaw hermaphrodite sterile flower, De Los Santos, et al., 2000).

Fig. 8 Pawpaw hermaphrodite sterile flower

f) Typical male flower. This type of flower have a long and thin corolla contain anthers in two series of five; one series longer than the other. They have a rudimentary pistil no stigma and are non-functional. (De Los Santos et. al. 2000).

The leaves are spirally arranged in a terminal cluster, simple, on petioles 30-70 cm long. The leaves are rounded in outline, 60-90 cm in diameter, palmately 7-9 lobed. The margins of the lobes are very variable, and range from entire to undulate to deeply lobed (University of Cornell, 2000).

In nature, these plants are dioecious: male and female flowers are found on separate plants. Male flowers are morphologically distinct from female flowers. Male inflorescences are borne in many-flowered panicles of cymes on horizontal or pendent stalks to 1 m long. The flowers are yellowish, 2-4 cm long. The petals are fused into a long tube, have 10 fertile stamens, and a rudimentary, non-functional ovary. Female inflorescences are much shorter --only 3-4 cm long-- and have fewer flowers. Female flowers are larger, usually white or cream in colour, with five free petals. There are no stamens, but a large ovary with 5 fan-shaped stigmas.

In cultivation, there are many intermediate forms, including bisexual flowers. At least 15 different flower forms have been named (e.g. Pentandria--5 stamens and a functional ovary) and, because they are correlated with different fruit characteristics, some forms, have been selected by breeders. Environmental factors may also influence sexual expression, and the sexuality of a plant may change seasonally or over the course of its lifetime. Thus the sexuality of any one plant in cultivation depends on a complex mix of genetic, developmental, and environmental factors (University of Cornell, 2000).

Female flowers have a calyx formed by a crown or five-pointed star easy to differentiate. On top of the calyx, the ovary is located by five yellowish sepals (when young, they show a purple coloration and are lose. There are five round-shaped yellow stigmas. Fruits from this flower are usually large and balloon-like.

Hermaphroditic flowers have both sexes and the tree bearing these has three different types of flowers. One is called pentandria, resembling a female flower, but when petaks are taken apart 5 anthers are seen and the ovary is lobed. Fruit are balloon-shaped and lobed. A second type of flower is called elongata and bears 10 anthers, arranged in two sets, the flower is elongated and cylindrical as the ovary and produce elongated fruits. The last type is intermedia or irregular, which is not a well-constituted flower and produces malformed fruit. (Fig. 9 Pawpaw hermaphrodite flower).

Fig. 9 Pawpaw hermaphrodite flower

Male flowers grow along peduncles measuring over half a meter length and at the end there are bundles formed by 15-20 small flowers. These flowers are constituted by a long tube formed by fused petals, inside which there are 10 anthers, arranged in two sets of five. The flower has a small rudimentary pistil and has no stigmas. No fruit are usually produced, or if formed these are elongated and of low quality.

Fruit: Generally, the fruit is melon-like, oval to nearly round, somewhat pyriform, or elongated club-shaped, 6 to 20 in (15-50 cm) long and 4 to 8 in (10-20 cm) thick; weighing up to 20 lbs (9 kg). Semi-wild (naturalized) plants bear miniature fruits 1 to 6 in (2.5-15 cm) long. The skin is waxy and thin but fairly tough. When the fruit is green and hard it is rich in white latex. As it ripens, it becomes light- or deep-yellow externally and the thick wall of succulent flesh becomes aromatic, yellow, orange or various shades of salmon or red. It is then juicy, sweetish and somewhat like a cantaloupe in flavor; in some types quite musky. Attached lightly to the wall by soft, white, fibrous tissue, are usually numerous small, black, ovoid, corrugated, peppery seeds about 3/16 in (5 mm) long, each coated with a transparent, gelatinous aril (Morton, 1987). (Fig. 10. a) Typical maradol, b) wax and c) sunrise "solo" pawpaw varieties, De Los Santos, et al., 2000).

Fig. 10a Typical pawpaw maradol variety

Fig. 10b Wax pawpaw variety

Fig. 10c Sunrise "solo" pawpaw variety

An ovoid-oblong berry pyriform or almost cylindrical, large, fleshy, juicy, grooved along the upper longer side, green yellow to yellow or yellow-orange colour when ripen, single cell of orange or redish internal colour with many parietal seeds and a length of 10-25 cm or longer and 7-15 cm or more of diameter. Seeds are black, round or ovoidal shaped and enclosed inside a transparent aryl; subacid, cotyls are ovoid-oblong, flattened and white (Infoagro, 2002).

d) Cultivars
There are many strains and varieties of this melon-like fruit and the variation in size, form and colour is great.

Because of its complex genetic make-up, there are few, if any, true cultivars of pawpaw which are as uniform in horticultural characters as the cultivars of other herbaceous crops. When seed results from open pollination, it is impossible, in most cases, to obtain selections, which are reasonably uniform in flower type and fruit characteristics. Despite the lack of recognized cultivars, growers can maintain satisfactory strains by controlled pollination of selected plants as described under Propagation. Parent plants should be carefully selected for early and heavy fruit production and should have fruit of desirable shape and size.

A group of Hawaiian pawpaw s referred to as Solo comes closer to deserving cultivar rank than any other types. Originally from Barbados (W. I.), Solo owes its constancy in character expression to a high degree of natural self pollination of its bisexual flowers. This, in addition to continuous selection of pear-shaped fruit produced by bi-sexual plants, has maintained Solo relatively unchanged over the years. Improved selections, such as Sunrise Solo, have resulted from rigorous breeding work. Unfortunately, the Solo group is not well adapted to Florida conditions (Malo, 2001).

The mountain pawpaw (C. candamarcencis Hook. f.), is native to Andean regions from Venezuela to Chile at elevation between 6,000 and 10,000 ft (1,800-3,000 m). The plant is stout and tall but bears a small, yellow, conical, 5-angled fruit of sweet flavor. It is cultivated in climates too cold for the pawpaw, including northern Chile where it thrives mainly in and around the towns of Coquimbo and La Serena at near-sea-level. The fruit (borne all year) is too rich in papain for eating raw but is popular cooked, and is canned for domestic consumption and for export. The plant grows on mountains in Srilanka and South India; does well at 1800 ft (549 m) in Puerto Rico. Its high resistance to pawpaw viruses is of great interest to plant breeders there and elsewhere.

The babaco, or chamburo (C. pentagona Heilborn), is commonly cultivated in mountain valleys of Ecuador. The plant is slender and no more than 10 ft (3 m) high, but the 5-angled fruits reach a foot (30 cm) in length. Usually seedless, or with only a few seeds at most, the fruits are locally eaten only after cooking. The plant is not known in the wild and botanists have suggested that it may be a hybrid. It is propagated by cuttings and is grown on a small scale in Australia and New Zealand primarily for export (Morton, 1987).

e) Growth habit
Pawpaw are well adapted to many soil types (Fig. 11 Soil type for Pawpaw), like to be warm with both sunshine and reflected heat, so the hottest place against the house where nothing else seems happy is an ideal location. They also like to be as free from wind as possible, although this is not as critical as their need for sun. Pawpaw can be grown successfully in shade, but the fruit is rarely sweet. They are best planted in mounds or against the foundation of a building where water can be controlled (CRFG, 1998).

Pawpaw need a light, well-drained soil. They are easily killed by excess moisture. The soil needs to be moist in hot weather and dry in cold weather. Since this is the opposite of California's rain pattern, in addition to good drainage, plastic coverings to prevent over-wetting in winter may also be worthwhile. Pawpaw do not tolerate salty water or soil (CRFG, 1998).

Requires a well drained soil with high organic matter. Does not tolerate flooding even for short duration. Recommended in regions with well distribution rainfall throughout the year without flash floods, water-logging and strong winds (Agrolink, 2002).

While doing best in light, porous soils rich in organic matter, the plant will grow in scarified limestone, marl, or various other soils if it is given adequate care. Optimum pH ranges from 5.5 to 6.7. Overly acid soils are corrected by working in lime at the rate of 1-2 tons/acre (2.4-4.8 tons/ha). On rich organic soils the pawpaw makes lush growth and bears heavily but the fruits are of low quality (Morton, 1987).

It is recommended that no herbicides used due to the little woodyness of the pawpaw tree stem which may end up damaged.

Usually weeding is performed manually or mechanically-aided, deep soil disturbances can damage the root system. It is advisable to use black polyethylene film on the surface to avoid weed growth (Infoagro, 2002).

Fig. 11 Soil type for Pawpaw

f) Cultural practices
Seeds retain their viability for 2-3 years when kept air-dry in airtight containers. Seeds may be sown in cold frames or boxes during January or in the open in March. Early planting is much to be desired to make a vigorous plant before the beginning of following winter. Seeds germinate in 2-3 weeks. When 2 or 3 true leaves have formed, seedlings should be transplanted, spacing them 5-7.5 cm apart in seedbed. When plants are 7.5-10 m tall, they can be set in their permanent places in the field. Usual planting distance is about 3-4 m apart each way, giving about 1750 trees to the hectare. In selecting plants for field planting, the more vigorous growing plants are usually the males and may be safely discarded except for a few. By planting 2 or 3 plants in a hill, there is a chance for further selection and elimination of excessive males when first flowers appear, about one male plant to each 25 or so females is sufficient. Transplants must be watered and shaded. Mulch gives much better results than clean culture, keeping down weeds, preserving moisture, shading the soil from hot summer sun, and preventing the burning out of humus and nitrates in the top soil layer. Heavy applications of stable manure or commercial fertilizers can often be used with profit. Attempts at grafting and rooting shoots have not been successful on a commercial scale (Morton, 1987).

Culture: Seeds may be planted directly in the field, or seedlings raised in beds or pots may be transplanted when 6 weeks old or even up to 6 months of age, though there must be great care in handling and the longer the delay the greater the risk of dehydrated or twisted roots; also, transplanting often results in trunk-curvature in windy locations.

Small bottom perforated plastic containers can be used for seed germination (Fig. 12 Perforated plastic seed germination containers).

The small holes in the bottom of plastic containers avoid the humidity inside of the containers.

The fertilizer is added to the containers with pawpaw seeds in order to obtain the germination. This kind of containers offers advantages like: easy handling, easy release of the plant and recycle containers.

Fig. 12 Perforated plastic seed germination containers

Soil preparation and fumigation for seed germinatio. This operation consists of mixing 4 parts of ground, 2 of dry manure and one of sand. The mixture must be disinfested from fungi, weeds or insect larvae. A bed of 1 m width for 20-25 cm height and depth is prepared and its length is varied according to the number of plants needed. Chemicals that can be used are methyl bromide or sodium methane (Vapam); before their application the bed must be watered during three consecutive days to promote weed germination and hence the small plants may be destroyed by the chemicals.

Seed germination:
a) Seeding: This is the traditional method for pawpaw seeding and although some producers have found alternative methods, it is still been used in several producing areas. In the bed described above, grooves are marked with separations of 10-12 cm; then each groove receives from six to eight seeds every 10 cm. Seeds are placed 1-1.5 cm deep and covered with dirt. After seeding profuse watering must be made.

Frequency of further watering are dependent on moisture conditions of the seeding daily or every other day watering may be needed. It is advisable to cover the seeding with mulch during the period of seeding and plantule emergence, in order to avoid excessive water loss by evaporation produced by the sun (Fig. 13 Pawpaw seeding establishment). The mulch is removed when the pawpaw plantules bloom and five plantules are left per site. (De Los Santos, et al., 2000).

Fig. 13 Pawpaw seeding establishment

Experiments in Hawaii indicate that direct seeding results in deeper tap-roots, erect and more vigorous growth, earlier flowering and larger yields. In Puerto Rico, it is customary to set 2 plants per hole. In El Salvador planters place 5 to 6 seeds, separated from each other, in each hole at a depth of 3/8 in (1 cm). When the plants bloom, 90% of the males are removed, preferably by cutting off at ground level. Pulling up disturbs the roots of the remaining plants. If the plantation is isolated and there is no chance of cross-pollination by males, all the seed will become female or hermaphrodite plants. Fruits should mature 5 to 8 months later.

In India, seeds are usually treated with fungicide and planted in beds 6 in (15 cm) above ground level that have been organically enriched and fumigated. The seeds are sown 2 in (5 cm) apart and 3/4 to 1 1/8 in (2-3 cm) deep in rows 6 in (15 cm) apart. They are watered daily and transplanted in 2 1/2 months when 6 to 8 in (15-20 cm) high. Transplanting is more successful if polyethylene bags of enriched soil are used instead of raised beds. Two seeds are planted in each bag but only the stronger seedling is maintained. Transplanting is best done in the evening or on cloudy, damp days. On hot, dry days, each plant must be protected with a leafy branch or palm leaf stuck in the soil. After flowering, one female or hermaphrodite plant is retained, the other two removed. But one male is kept for every 10 females. 'Coorg Honey Dew' and 'Solo' are planted one to a pit and no males are necessary. Watering is done every day until the plants are well established, but over watering is detrimental to young plants. Double rows of Sesbania aegyptiaca are planted as a windbreak.

The installation of constant drip irrigation (12 gal per day) has made possible pawpaw cultivation on mountain slopes on the relatively dry island of Maui, which averages 10 in (25 cm) of rain annually.

Pawpaw plants require frequent fertilization for satisfactory production. In India, best results have been obtained by giving 9 oz (250 g) of nitrogen, 9 oz (250 g) of phosphorus, and 18 oz (500 g) potassium to each plant each year, divided into 6 applications.

Because of the need to expedite growth and production before the onslaught of diseases, Puerto Rican agronomists recommend treating the predominantly clay soil with a nematicide before planting, giving each plant 4 oz (113 g) of 15-15-15 fertilizer at the end of the first week, and each month thereafter increasing the dose by 1 oz (28 g) until the beginning of flowering, then applying 227 g per plant as a final treatment. In trials, this program has permitted 6 harvests of green fruits for processing, each over 1 lb (1/2 kg) in weight, spanning a period of 13 months. The roots usually extend out beyond the leaves and it is advisable to spread fertilizer over the entire root area.

In late fertilizer applications of a crop destined for canning, nitrogen should be omitted because it renders the fruit undesirable for processing. High nitrate content in canned pawpaw (as with several common vegetables) removes the tin from the can. To avoid nitrogen deficiency at the beginning of flowering for the next crop, 1 or 2% urea sprays can be applied.

In southern Florida, on oolitic limestone, experts have prescribed liquid fertilizer weekly for the first 10 weeks and then 1 lb (1/2 kg) of 4-8-6 dry fertilizer mixture (with added minor elements) per plant weekly until flowering. Here, a heavy organic mulch is desirable to conserve moisture, control weeds, keep the soil cool, and help repel nematodes.

Mechanical cultivation between rows is apt to disturb the shallow roots. Judicious use of herbicides is preferable.

Overcrowded fruits should be thinned out when young to provide room for good form development and avoid pressure injury. Cold weather may interfere with pollination and cause shedding of unfertilized female flowers. Spraying the inflorescence with growth regulators stops flower drop and significantly enhances fruit set. After the first crop, the terminal growth may be nipped off to induce branching, which tends to dewarf the plant and facilitates harvesting. However, unless the plants are strong growers, fruiting branches may need to be propped to avoid collapse (Morton, 1987).

It is better to seed manually when two year old trees are been substituted, since older trees are too high and make fruit harvest or latex collection more expensive; in addition fruit production is diminished.

Female trees are better for latex production, because fruit are bigger. Fruit intended for fresh consumption are better produced from hermaphroditic trees because fruit are smaller and suitable for commercial handling.

It is necessary to perform self-pollination or cross-pollination between female and hermaphroditic plants or between hermaphroditic plants, since the male plants are no productive and represent an economic burden for commercial pawpaw production. Both female and hermaphroditic trees are selected, which flowers are well developed. With the help of a brush or a feather the pollen is carried to the stigmas. Later the pollinized flowers are covered with a bag until the fruit is set. With this practice more seeds are produced that will induce female and hermaphroditic plants avoiding male plants (Infoagro, 2002).

Cultivation: To grow pawpaw successfully, the grower should make sure that the following requirements are met.

1. The seed should preferably come from controlled crosses (female x bisexual or bisexual selfed), or from bisexual trees known to have a high degree of self-pollination under field conditions. The type of seed used is most important since it determines production potential and thus restricts or enhances the value of other cultural methods (Fig. 14 Pawpaw seed).

Fig. 14 Pawpaw seed

2. The soil should have good drainage. Pawpaws are very sensitive to even short periods of flooding. If not killed, they lose their vigor and regain it very slowly. (Fig. 15 Cultural practices of Pawpaw).

3. Irrigation should be provided during dry spells because a fluctuating water supply may cause growth retardation, flower abortion, and dropping of young fruits.

4. Pawpaws are fast growing plants, which require an abundant supply of nutrients if they are to be highly productive. Supplemental fertilization is particularly important in infertile soils. Nitrogen and phosphorus are especially important. In Florida, young plants should be started with 1/2 lb of a 10-10-10-5 mixture (with 30% of the nitrogen from natural organic sources) at planting time or shortly after. This amount of fertilizer is applied every 2 weeks and should be increased gradually to 1 1/2 lb until the plants are 7 to 8 months old. Thereafter, monthly applications should be sufficient, unless unusually hard rains occur. Fertilizer should be reapplied under these conditions.

Fig. 15 Cultural practices of Pawpaw

Cultivars : Because of its complex genetic make-up, there are few, if any, true cultivars of pawpaw, which are as uniform in horticultural characters as the cultivars of other herbaceous crops. When seed results from open pollination, it is impossible, in most cases, to obtain selections, which are reasonably uniform in flower type and fruit characteristics. Despite the lack of recognized cultivars, growers can maintain satisfactory strains by controlled pollination of selected plants as described under Propagation. Parent plants should be carefully selected for early and heavy fruit production and should have fruit of desirable shape and size. A group of Hawaiian pawpaws referred to as Solo comes closer to deserving cultivar rank than any other types. Originally from Barbados (W. I.), Solo owes its constancy in character expression to a high degree of natural self pollination of its bisexual flowers. This, in addition to continuous selection of pear-shaped fruit produced by bi-sexual plants, has maintained Solo relatively unchanged over the years. Improved selections, such as Sunrise Solo, have resulted from rigorous breeding work. Unfortunately, the Solo group is not well adapted to Florida conditions (Malo, 2001).

g) Planting and Climate
The pawpaw is a tropical and near-tropical species, very sensitive to frost and limited to the region between 32º north and 32º south of the Equator. It needs plentiful rainfall or irrigation but must have good drainage. Flooding for 48 hours is fatal. Brief exposure to 32 ºF (-0.56 ºC) is damaging; prolonged cold without overhead sprinkling will kill the plants.

h) Fertilization
In late fertilizer applications of a crop destined for canning, nitrogen should be omitted because it renders the fruit undesirable for processing. High nitrate content in canned pawpaw (as with several common vegetables) removes the tin from the can. To avoid nitrogen deficiency at the beginning of flowering for the next crop, 1 or 2% urea sprays can be applied (Morton, 1987).

Fertilization: The fast-growing pawpaw requires regular applications of nitrogen fertilizers but the exact rates have not been established. Feed monthly and adjust according to the plant's response. They can take fairly hot organic fertilizing such as chicken manure if used with deep irrigation after warm weather has started. Phosphorus deficiency causes dark green foliage with a reddish-purple discoloration of leaf veins and stalks (CRFG, 1998).

Fertilizer ( Dose): For the first year, a compound fertilizer consisting of nitrogen, phosphate and potassium in the ratio of 15:15:15 can be given in three applications followed by ratio of 12:12:17:2 with some trace elements (:2) applied in the fertile period (Agrolink, 2002).

Foliar fertilization. It is recommended to fertilize plantations through the leaves to supplement the soil, if enough moisture was retained by the soil and the fertilizer may be taken up by the plant.

i) Soil improvement and fixing nutritional deficiencies

Acidity and alkalinity correction of the soil. Yield of pawpaw decrease when the soil is too acid (pH values below 5.5) because this condition produces nutritional deficiencies in nitrogen, phosphorus, potassium, calcium and magnesium. To correct for this acidity, either calcium carbonate or lime is added to the soil.

On the other hand, if pH of the soil is on the alkali side (pH values above 8.0), deficiencies in magnesium, manganese, iron, zinc, copper and boron, occur that need to be corrected; in this case by addition of sulfur. The type and amount of product must be defined by a laboratory based on physical and chemical analyses of the soil to test for pH values, texture and Ca, Mg and S availability.

Foliar diagnosis . In order to evaluate the nutritional status of the plantation, a foliar analysis is performed. This analysis includes sampling of leaves at the beginning of the flowering period, the most recently matured petiole (usually the third or fourth counting downward) is cut off and the leave is discarded.

Correction of Boron deficiency . Boron deficiency is frequent in sandy soils. When this is detected, borax and sodium tetraborate may be applied. These two compounds are readily available boron sources. (De Los Santos et al., 2000).

j) Pollination
If a pawpaw plant is inadequately pollinated, it will bear a light crop of fruits lacking uniformity in size and shape. Therefore, hand-pollination is advisable in commercial plantations that are not entirely bisexual.

Bags are tied over bisexual blossoms for several days to assure that they are self-pollinated. The progeny of self-pollinated bisexual flowers are 67% bisexual, the rest being female.

To cross-pollinate, one or 2 stamens from a bisexual flower are placed on the pistil of a female flower about to open and a bag is tied over the flower for a few days. Most of such cross-pollinated blooms should set fruit. Resulting seeds will produce 1/2 female and 1/2 bisexual plants.

By another method, all but the apical female flower bud are removed from a stalk and the apical bud is bagged 1-2 days before opening. At full opening, the stigma is dusted with pollen from a selected male bloom and the bag quickly resealed and it remains so for 7 days.

Plants from female flowers crossed with male flowers are 50-50 male and female. Bisexual flowers pollinated by males give rise to 1/3 female, 1/3 bisexual and 1/3 male plants.

South African growers have long been urged to practice hand-pollination in order to maintain a selected strain and, in breeding, to incorporate factors such as purple stem, yellow flowers and reddish flesh so that the improved selection will be distinguishable from ordinary strains with non-purple stems, white flowers and yellow flesh (Morton, 1987).

k) Germplasm
Reported from the Middle American Center of Diversity, pawpaw, is reported to tolerate drought, high pH, insects, mycobacteria, slope, and virus (Duke, 1978). Pawpaw trees differ from each other in that some are either male (staminate) or female (pistillate), whereas others are perfect, having both male and female flowers on same plant. When the sexes are separate, fruits set on the female plant only when pollen is carried from male plants. One male tree is needed for each 25 or so female plants, but one cannot determine the male trees until they flower, about 12 months after germination. (Morton, 1987).

l) Propagation
Pawpaws are normally propagated by seed. To start a plant, extract the seeds from ripe pawpaws and wash them to remove the gelatinous covering (Fig. 16 Propagation of maradol pawpaw). They are then dried, dusted with a fungicide and planted as soon as possible (the seeds loose their viability rapidly in storage). Plant the seeds in warm (80° F), sterile potting mix. Seeds should be planted in sterile soil as young pawpaw seedlings have a high mortality rate from damping off. Potting soil can be sterilized by mixing 50-50 with vermiculite and placing in an oven at 200° F for one hour. Under ideal conditions the seeds may germinate in about two weeks, but may take three to five weeks. Gibberellic acid can be used to speed up germination in some seasons. Seedlings usually begin flowering 9-12 months after they germinate.

Fig. 16 Propagation of maradol pawpaw

Seedling pawpaw do not transplant well. Plant them in large containers so the seedlings will have to be transplanted only once, when they go into the ground. Transplant carefully, making sure not to damage the root ball. To prevent damping off, drench the potting mix with a fungicide containing benomyl or captan. Set the plants a little high to allow for settling. A plastic mulch will help keep the soil warm and dry in wet winter areas, but remove it as soon as the weather becomes warm. Plant at least three or four plants to insure yourself of having females or plant hermaphroditic plants.

Pawpaw plants can also be grown from cuttings, which should be hardened off for a few days and then propped up with the tip touching moist, fertile soil until roots form. Semi hardwood cuttings planted during the summer root rapidly and should fruit the following year (CRFG, 1998).

Pawpaw is propagated by seeds sown in sand beds or they can be sown directly in polythene bags. The soil mixture used is 50% sand for good drainage, 25% organic manure and 25% top soil. The seedlings are ready for transplanting after about 2 to 3 months old. The planting distance is 2.5m x 3m square and the planting holes are about 30cm x 30cm x 30cm. After the holes are dug, some organic matter with phosphate fertilizer and limestone is added to the soil before the seedlings are placed in the holes (Agrolink, 2002).

To reproduce the characteristics of a preferred strain, air-layering has been successfully practiced on a small scale. All offshoots except the lowest one are girdled and layered after the parent plant has produced the first crop of fruit. Later, when the parent has grown too tall for convenient harvesting the top is cut off and new buds in the crown are pricked off until offshoots from the trunk appear and develop over a period of 4 to 6 weeks. These are layered and removed and the trunk cut off above the originally retained lowest sprout, which is then allowed to grow as the main stem. Thereafter the layering of offshoots may be continued until the plant is exhausted.

Rooting of cuttings has been practiced in South Africa, especially to eliminate variability in certain clones so that their performance can be more accurately compared in evaluation studies. Softwood cuttings made in midsummer rooted quickly and fruited well the following summer. Cuttings taken in fall and spring were slow to root and deficient in root formation. The commercial cultivar 'Honey Gold' is grown entirely from cuttings. Once rooted, the cuttings are planted in plastic bags and kept under mist for 10 days, and then put in a shade house for hardening before setting in the field.

Hawaiian workers have found that large branches 2-3 ft (60-90 cm) long rooted more readily than small cuttings. Planted 1 ft (30 cm) deep in the rainy season, they began fruiting in a few months very close to the ground.

In Hawaii, 'Solo' grafted onto 'Dwarf Solo' was reduced in vigor and productivity, but 'Dwarf Solo' grafted onto 'Solo' showed improved performance.

In recent years, the potential of rapid propagation of pawpaw selections by tissue culture is being explored and promises to be feasible even for the establishment of commercial plantations of superior strains.

Efforts have been made to determine the sex of seedlings in the nursery, Indian scientists making colorimetric tests of leaf extracts have had 87% success in identifying seedlings as female; 67% in classifying males/bisexuals grouped together (Morton, 1987).

Vegetative propagation is not practical, although it may be desirable to preserve good selections. Both grafting and rooting of cuttings are easily accomplished but are too laborious to justify their commercial use. In contrast, seeds are produced abundantly and germinate readily (in 10 to 15 days) and uniformly. Under suitable growing conditions fruit can be harvested in 8 to 10 months. Seeds should be obtained from ripe fruit, washed to remove the gelatinous aril, planted in small pots, and germinated under full sunlight. Peat pots are ideally suited for this, since they can be set directly in the field without removing the plants from individual containers. Two to three seeds are sown per pot to compensate for low germinations, damage by insects, and removal of male plants. Planting distance depends on soil fertility, irrigation facilities, and location. The home owner should space his plants 8 to 10 feet apart. The use of machinery in commercial operations requires rows to be 12 to 15 feet apart, but plants should be 6 to 8 feet apart in the row. Seedlings are set in the field when 6 to 8 inches tall. They begin flowering after 5 months, and only one vigorous bisexual or female plant is allowed to grow, in each site all others being removed. In south Florida, if plants are set in the field in February or March, it is possible, with good care, to harvest fruit in October or November. This requires starting seedlings in a greenhouse or under plastic, and protecting them against frosts by heating or sprinkler irrigation. In cooler areas of the state, May and June are better months for field planting, and good yields cannot be expected before the following April or May (Malo, 2001).

1.1 Economic and social impact of the Pawpaw crop

Brazil is the main producer and trader of pawpaw in the world. As trade has increased new producers have appeared in the international market. With the development of better cultivation and post-harvest technologies, pawpaw is becoming a new star in the world tropical fruit market.

a) Production and export
In 1998 the FAO reported an estimate of 5.1 millions of metric ton. that were harvested in the world, representing twice the harvest of 1980.

The main consumer markets are usually supplied by one major supplier; in the case of the US market, most of the fruit is supplied by Mexico, whereas for Europe, Brazil is the main exporter, and Japan's demands are covered by the US via Hawaii. (Table 2).

In general, pawpaw crops have shown a continuous and stable growth and importers are confident of the future of this market. The key for a successful prospect for pawpaw lies on development of new varieties, better crop handling and post-harvest technologies. (Medinillla, 2000).

From 1992 pawpaw world trade increased as much as twice of that in 1995. Certainly the appreciation for the fruit as well as the attractive prices have been the main causes for the increase in exports. The list of exporting countries has been expanding, but five are considered the most important: Malaysia, South Korea, Brazil, US and Jamaica. These five countries contribute together over 80% of total world exports. Out of these countries, Jamaica has shown the most dynamic trend in exports; between 1992 and 1998 export sales were doubled. Next, South Korea appeared in the export market in 1995, with a concomitant increase. For the period 1995-1998 sales toped 30,000 MT with represented 19.6% of the world total. Current average sales of Malaysia are near 40,000 MT, with is twice the amount reported in 1992. (Claridades Agropecuarias, 1999).

The main actors in the international trade market for pawpaw are presented in Table 3. There were included countries with reported production exceeding 1,000 MT/year.

1.2 World trade

a) World Trade in Fresh Pawpaw

North and Latin América
US production is concentrated in the Hawaian islands. In 1994, 256 agricultural operations produced 28,000 MT of pawpaw, of which ca. 90% is used for fresh marketing directed to domestic markets as well to Japan and Canada. In 1998 US produced 18, 140 MT, the drop been attributed to the ring spot virus (RSV). Mexico is the largest producer of the region with 498,000 MT in 1998, it is also the main exporter of pawpaw to the US and Canada. Costa Rica produced in the same year 22,000 MT aimed mostly to the US and Dutch markets (Medinilla, 2000).

Brazil has become the main producer in the world, with most of the fruit been sent to European countries. In 1998 the country reported 35,000 ha's devoted to pawpaw production, with an average yield of 48.6 Ton/ha.

Asia and Africa
Nigeria is the main producer in the African continent with 751,000 MT, with a 90,000 ha's devoted to the crop, and together with South Africa, Mozambique and Congo are the most important producers, but none of them reports any export activity.

Just after Brazil, India is the second world producer with 40,000 ha's and a total production of 400,000 MT and a yield of de 11.25 Ton/ha. Other important producers include: Indonesia with 336,068 MT, China with 149, 163 MT and Phillipines with 67,000 MT ((Medinilla, 2000).

b) Market price
The acceptance of pawpaw fruit in the world has produced a wide range of prices for the different varieties. However, there are markets so important that are worth analyzing in detail, since these sometimes define the prices for other, geographically distant markets. Such is the case of the US, in which it is possible to find different prices for pawpaw varieties (red and strawberry pawpaw) all year long. (Table 4).

General prices for pawpaw as supplied either internally or imported from Jamaica, Brazil, Costa Rica and Belize, have been defined by the Baltimore market with an average price of $2.68/kg through 1998; in Los Angeles the average prices was $3.58/kg; in Miami $2.20/kg and San Francisco $3.06/kg. The strawberry variety was found mainly in Los Angeles and supplied by Hawaii; however, pawpaws from Brazil, Costa Rica and Jamaica were found in lesser amounts. Average price was $3.58/kg.

In addition to tge US market, Toronto and London have prices for pawpaw all year long as well. The main suppliers for Toronto are Jamaica and Brazil, while the London market is supplied almost solely by Brazil and only marginally by Jamaica. The long distance between Brazil and England makes the product more expensive as compared to other American markets. Thus, pawpaw from Brazil in London was $3.26/kg, compared to $2.36/kg in Toronto. (Claridades Agropecuarias, 999).

1.3 Primary product

Importers require fruit at specific stages of ripeness for optimum sales; this varies between 50 and 70% yellow colour depending on the importer, the market and the time of year. For fruit to arrive in the importing country at the correct colour stage, attention has to be paid to the maximum and minimum colour stages on departure from the pack house, the length of the shipment period (24 hours when considering UK, Canada and USA, and 48 hours for Holland) and the temperature in the importing country. Thus, colour stages on departure from the packhouse for air shipment can vary from 20% to 50%, and the selections are generally more rigid during the summer months due to the rapid rates of ripening on arrival in importing countries. Fruit exported too green (less than 20% yellow colour) will fail to ripen adequately when temperatures in importing countries are low, particularly in winter months.

Sea-shipment of pawpaw is possible when fruits are shipped at the optimum harvest maturity, with one or two yellow streaks. Shipments should be made at 10° to 12°C and 85 to 95% relative humidity, in refrigerated holds or refrigerated containers. Post-harvest disease control is critical with sea-shipment, particularly anthracnose and Phytophthora. Colour development during sea-shipment usually increases from 10% to 40% during 10 days at 12°C, and will develop further during the customs, clearance and delivery period on arrival. (Medlicott, 2001).

Commercial pawpaws are normally harvested 9 to 10 months after being transplanted from nurseries. Fruit should be harvested when skin colour changes from dark green to light green and when one yellow streak begins developing from the base of the fruit upward. Fruit in this condition will continue to ripen normally after harvest. If harvested before or after this stage, however, pawpaws will either fail to ripen completely (if picked too early) or become more susceptible to damage and bruising during handling (if picked too late). Because their ideal stage of maturity is so short-lived, pawpaws are usually harvested three or four times a week. Leaving fruit as long as five to seven days between harvests can lead to its rejection as over-ripe.

Pawpaws are harvested by hand alone or with knives or specialized tools, depending on the size and age of the tree. When harvesting pawpaw by hand or with knives, harvesters snap or cut the stem directly adjacent to the tree and immediately trim it flush against the top of the fruit. To reach fruit at the top of tall trees, harvesters use a long pole with a small hoop and a small, mesh bag at the end. Above the hoop sits a horizontal blade, which the harvester positions below the stem of the fruit and moves upward to detach the pawpaw from the tree and catch it in the mesh bag below. Two or three fruits are collected at a time in this manner. Bags should be shallow to prevent overfilling and should be made of a soft material to prevent damage to the pawpaw skin.

After harvest, the fruit are placed gently —never thrown or dropped— in single layers in shallow, light-colored plastic field crates, preferably with a foam layer for cushioning. Mesh bags, sacks, or baskets are unacceptable for pawpaw transport because of the fruit's high susceptibility to bruising. Care should be taken during transport to minimize jostling of the fruit, and all stems should be trimmed to ensure that no stem-to-fruit rubbing occurs. Prior to collection, field crates and fruit should be left in shaded conditions, protected from the sun and rain. Grading and packing should be carried out as soon as possible after harvest, normally within three hours, after which time the fruit should be kept at ambient tropical conditions (25°C to 28°C) to continue ripening, or cooled and stored at 10°C to 12°C. Standard packing house design and operations apply for pawpaw grading and packing. Operations can be carried out with basic equipment, including water tanks, field crates, and grading tables, or with automated washing and weight-grading or separation systems. All tanks and grading tables should be covered with foam to protect fruit from exposed edges; the skin of the pawpaw is delicate, and scratches will result in latex exudation and staining. Similarly, if the fruit is dropped, it will easily develop bruises as it ripens. (Market. A.G, 2002; Smith et al., 1992).

a) Food for humans
Excellent quality fruit, high in vitamin A. Ripe fruit is consumed fresh as a breakfast or dessert fruit and with honey. Green fruits are grated in salads or boiled like squash. (Fig. 17 How to eat a pawpaw 1, Fig. 18 How to eat a pawpaw 2, Fig. 19 How to eat a pawpaw 3, Fig. 20 How to eat a pawpaw 4, Fig. 21 How to eat a pawpaw 5, Fig. 22 How to eat a pawpaw 6, Fig. 23 How to eat a pawpaw 7).

Fig. 17 How to eat a pawpaw 1

Fig. 18 How to eat a pawpaw 2

Fig. 19 How to eat a pawpaw 3

Fig. 20 How to eat a pawpaw 4

Fig. 21 How to eat a pawpaw 5

Fig. 22 How prepare a pawpaw 6

b) Food for livestock
Foliage is sometimes used as a feed source in fish ponds (herbivorous Tilapia, etc.).

c) Other Uses:
The green fruit is the source of the enzyme papain, which is used in commercial meat tenderizers. In the Philippines, meat is wrapped in young leaves to tenderize it (Smith, et al., 1992).

Various parts of the pawpaw plant are used for medicinal purposes in various parts of the world. For example, as a treatment for intestinal parasites (Smith, et al., 1992, University of Purdue, 2000).

1.4 Preparation and uses

Green, or unripe, pawpaws may be cooked like winter squash. Ripe pawpaws are terrific eaten plain or with a dollop of yogurt. Simply cut in half and remove the seeds; the flesh is tender enough to be scooped out with a spoon. Although pawpaw skin is not edible, its seeds are. Pawpaw seeds resemble large peppercorns and also have a peppery taste. They may be crushed and sprinkled on salads in the same way as crushed peppercorns. Left whole, they make an interesting garnish for a fruit salad. Add pawpaw to fruit salads or pouree into a thick juice (Healthnotes, Inc, 2001).

Unripe and mature pawpaw fruits
Pawpaw fruits should be harvested when the colour of the skin changes from dark green to light green and when one yellow streak begins development from the base upwards (Fig. 23. One-quarter ripe pawpaw). Fruits in this condition will continue to ripen normally after harvest. Those fruits harvested before this stage will fail to show complete ripening, and those harvested after, are more susceptible to damage and bruising during handling (Medlicott, 2001).

Fig. 23 One-quarter ripe pawpaw

Selection and Care : Softening is the key to ripeness. Pawpaws that are one-quarter to one-half ripe should keep 1-2 weeks. The development of a yellow blush is associated with ripening when the fruit ripens at 65 °F, or over. At lower temperatures the colour process may stop and the fruit soften without changing colour. For this reason pawpaw should be stored at room temperature until ripe (soft). Ripening can be slowed by chilling at 60 °F. or stopped at 50 °F. Chilling below 50 °F will damage fruit. Chill a pawpaw once it is completely or almost ripe, not before. Serve within a day or two, or it loses flavor (UFL, 2000).

The most common use of pawpaw is fresh in slices or chunks and in fruit compotes. A thick juice can be prepared by blending diced pawpaw with a little water. Pawpaw can also be sliced and dried. Green pawpaw is sometimes cooked and eaten like squash. Pawpaw is a prime source of papain enzyme (meat tenderizer), so green fruit chunks and leaves can be wrapped around meat or fowl before cooking to enhance tenderness and flavor (Aggie Horticulture, 2002).

1.5 Alternative products from pawpaw

1.5.1 Medicinal uses

In tropical folk medicine, the fresh latex is smeared on boils, warts and freckles and given as a vermifuge. In India, it is applied on the uterus as an irritant to cause abortion. The unripe fruit is sometimes hazardously ingested to achieve abortion. Seeds, too, may bring on abortion. They are often taken as an emmenagogue (agent that promote the menstrual flow) and given as a vermifuge. The root is ground to a paste with salt, diluted with water and given as an enema to induce abortion. A root decoction is claimed to expel roundworms. Roots are also used to make salt.

Crushed leaves wrapped around tough meat will tenderize it overnight. The leaf also functions as a vermifuge and as a primitive soap substitute in laundering. Dried leaves have been smoked to relieve asthma or as a tobacco substitute. Packages of dried, pulverized leaves are sold by "health food" stores for making tea, despite the fact that the leaf decoction is administered as a purgative for horses in Ghana and in the Ivory Coast it is a treatment for genito-urinary illness. The dried leaf infusion is taken for stomach troubles in Ghana and they say it is purgative and may cause abortion (Morton, 1987).

1.5.1.1 Folklore, medicinal and non-food uses

A. Milky latex may cause dermatitis.

B. Hypoglycemic activity has been shown experimentally.

C. Toothache relief - the inner bark is used for this in Samoa.

D. Amebicide - latex and seeds used in Central America to kill Entamoeba histolytica which causes dysentery and liver abceses.

E. Cosmetics - pawpaw fruit pulp is the basic component of many facial creams, salves, and shampoos.

F. Papain - is one of two proteolytic enzymes (the other is chymopapain) found in pawpaw latex.

Papain is extremely useful since it retains proteolytic activity over a wide pH range, unlike other proteases. Papain is used during surgical procedures to disolve ruptured spinal discs; it is referred to as "nature's scalpel" because it preferentially degrades dead tissue. Latex is extracted on a commercial scale in East Africa and Sri Lanka. The green fruit are "tapped" by making incisions on the fruit surface in the morning, and catching the latex in a container hanging beneath. The latex is dried, ground into powder, and packed in tin containers. One thousand average-sized fruits will yield one pound of papain.

The most popular use is a meat tenderizer. Columbus, on one of his voyages to the Caribbean, noted that natives could consume a large amount of fish and meat without getting indigestion if unripe pawpaw was eaten after the meal. Green pawpaw can be rubbed onto a piece of meat, cooked with it, crushed leaves can be wrapped around meat, or a commercial tenderizer preparation sprinkled on the surface. Beef cattle are sometimes injected with papain 1/2-h before slaughter to tenderize them. Meat treated with papain should not be cooked "rare", as the enzyme will not have been inactivated. Additional uses include: beer clarification, wool and silk treatment before dyeing, de-hair hide before tanning, tuna liver oil extraction, treatment of ulcers, diphtheria, swelling, and fever, relief of gas and sour stomach.

G. Folk medicine - Fresh latex can be smeared on boils, warts or freckles to remove. Latex is smeared on the uterus to cause abortion in India, or sometimes the unripe fruit and/or seeds are eaten to induce abortion (The University of Georgia, 2002).

1.5.1.2 The healing power of the tropical Medicine Tree

Nutrition for the Skin Vitamins were first used and applied through the skin after the Second World War. Ex-prisoners with severe vitamin deficiency, who were unable to take them orally, were treated through the skin with successful results. Dermatologists have often recommended hormonal creams to post menopausal women that are applied to the skin. The extracts from plants in the form of essential oils can also be absorbed through the skin. Tests have been conducted on animals where essential oils have been found in their urine, half an hour after application. A clove of garlic rubbed onto the soles of the foot of a baby could be smelt on its breath ten minutes later. Over the last decade the skin has been used more and more for taking in medication.

Vitamins can be applied to the surface of the skin, either from a capsule or mixed into creams, oils, ointments, herbal infusions or fruit juices. Here are just a few of the commonly applied skin benefactors:

Vitamin A - has been successfully used in treating dry aging skin and acne. It accelerates the formation of new cells, it protects the external layers of the skin.

Vitamin D - has a healing effect on the skin, it is often used in ointments for burns, acne and pimples.

Vitamin E - is a natural anti-oxidant. It promotes the formation of skin cells, improves blood circulation and nourishes the skin and assist in healing and minimizes scarring.

Vitamins C- is an anti-oxidant, it also strengthens and builds capillaries. (Kneipp Cure Pty Ltd, 2000).

1.5.2 Pawpaw Tropical Skin Food Products

* A unique range off 100% Australian made products.
* Based on all natural ingredients and anti-oxidants to strengthen and nourish the skin.
* Unique formulas based on the ancient art of Aromatherapy and Herbalism.
* All products are "Skin Food Based" and environmentally friendly which are tested on humans only.

1.6 Benefits of Pawpaw

Pawpaw is used in skin products for a natural 'face lift' and rejuvenation. The green fruit and leaves are used in cosmetics as it contains papain, and other enzymes. Pawpaw is beneficial for skin care and repair. Pawpaw contains vitamin A which accelerates the formation of new cells, it protects the external layers of the skin, vitamin C is an anti-oxidant, and builds capillary strength, the skin can be benefited with improved smoothness, softness, and resiliency. Pawpaw reduces the signs of premature aging and eliminates dead skin cells. Pawpaw tea and fruit contains an enzyme that dissolves surface cell debris making it a great facial peel. Beta-carotene, protects the skin and provides elasticity.

1.6.1 Essential Oils

Essential oils are the volatile or end product of the plant metabolism. They are generated and stored by the plant in special cells and are extracted by steam distillation, cold pressing or effleurage - a form of extraction using fats. Scent globules can be found in different parts of the plant and this will influence the method of extraction such as flowers-rose, jasmine, neroli, roots-angelica, vetiver, seeds-anise, coriander, caraway, leaves-sage, geranium, thyme, bark-cinnamon, fruit rind- citrus oils an resin-sandalwood, frankincense. Essential oils can be used to help correct the imbalances represented by the skin types. The oils can be used to reduce the amount of sebum being produced, and control the bacteria, which thrive on the surface of the skin. Many essential oils stimulate the generation of new cells, which preserves the health and beauty of the skin.

1.6.1.1 Essential Oils used in Pawpaw Skin Care

Lavender (Lavandula vera) all skin types, minimizes scarring.

Geranium (Pelargonium graveolens) oily, acne, mature skin, sluggish congested skin. It also has a balancing effect on the sebaceous glands.

Orange (Citrus aurantium) combination skin, soothing to dry, irritated, or acne prone skin Frankincense (Boswellia thurifera) rejuvenating for mature skin, balances oily skin.

Sandalwood (Santalum album) oily, dry and mature skin, cracked or damaged skin, dehydrated skin, itching or inflammation of the skin.

Neroli (Citrus aurantium) sensitive, dry and mature skin, broken capillaries, all skin types, stimulates cellular activity and growth.

Rose Moroc (rosaceae) mature skin, promotes cell renewal, ideal for all skin care, broken capillaries (Kneipp Cure Pty Ltd, 2000).

1.7 Requirements for export and quality assurance

a) Export grading
Grading should be carried out as soon as possible after harvest, and fruit left under ambient conditions to continue ripening or placed at 10° to 12°C for cooling and storage. On arrival in the packing facility, fruit should be washed in water to remove latex and debris then treated in a 0.05% Thiabendazole solution for anthracnose control. Washing, treatment and grading can be carried out using mechanized or manual systems (Fig. 24 Washer and disinfectant container for pawpaw fruits.), depending on the volumes of fruits. Grading in each carton is required in terms of size, sex (shape) and stage of ripeness. Female and hermaphrodite fruit cannot be mixed in the same carton; all fruits must be of a similar size in each carton resulting in a range of counts, and separations must be made for the degree of ripeness. Carton net weight is dependent on the importer, ranging from 3.5 to 5 kg (8 to 11 lbs), and must not be overfilled during packing (Medlicott, 2001).

Fig. 24 Washer and disinfectant containers for pawpaw fruits

Quality Criteria: Pawpaw should be exported with the required size and stage of ripeness (as defined in the market specifications) with sufficient yellow peel and orange or red pulp coloration, free from bruises, blemishes, insect and spray damage and uniform in size and ripeness within each carton (Medlicott, 2001).

Export Criteria: Pawpaws intended for export are carefully graded by size and stage of ripeness. Fruit should be uniform in size and ripeness and be free from bruises, blemishes, and insect damage. Most importers also require that pawpaws be mostly yellow and have a uniform softness; a smooth, unblemished skin; and a minimum sugar content of 12 °Brix.

When harvested, pawpaws are green with a stripe of yellow at their base; they ripen during transport or are commercially ripened on arrival. As pawpaw ripens, skin colour changes from green to yellow, and the fruit becomes softer and develops a fruity aroma. Pawpaws are normally sold to consumers when they are at least one-quarter ripe. Optimal ripeness occurs at the three-quarter stage, when the fruit bears a yellow-orange peel and an orange-red pulp. Peel colour may vary from yellow to reddish-orange, depending on the variety of pawpaw.

Three Hawaiian varieties —Solo Sunrise, Kapoho, and Waimanalo— are the most popular, and Solo Sunrise is the most important in world trade. Pawpaws of all three varieties are relatively small, normally weighing from 250 to 500 grams. Some countries are beginning to produce and export several Taiwanese varieties, which tend to be larger than those from Hawaii. Some markets require very large, local varieties of pawpaw. In the Latin market in the United States, for example, pawpaws weigh about 3 kilograms.

Fruit shape is not a function of variety but of the sex of the plant the fruit grows on. Round fruit comes from a female plant, and traditional pear-shaped fruit comes from a hermaphrodite plant. Because the market prefers pear-shaped fruit, female plants are normally removed from production as soon as their sex is known.

Pawpaws are harvested by hand alone or with knives or specialized tools, depending on the size and age of the tree. When harvesting pawpaws by hand or with knives, harvesters snap or cut the stem directly adjacent to the tree and immediately trim it flush against the top of the fruit. To reach fruit at the top of tall trees, harvesters use a long pole with a small hoop and a small, mesh bag at the end. Above the hoop sits a horizontal blade, which the harvester positions below the stem of the fruit and moves upward to detach the pawpaw from the tree and catch it in the mesh bag below. Two or three fruits are collected at a time in this manner. Bags should be shallow to prevent overfilling and should be made of a soft material to prevent damage to the pawpaw skin.

After harvest, the fruit are placed gently —never thrown or dropped— in single layers in shallow, light-colored plastic field crates, preferably with a foam layer for cushioning. Mesh bags, sacks, or baskets are unacceptable for pawpaw transport because of the fruit's high susceptibility to bruising. Care should be taken during transport to minimize jostling of the fruit, and all stems should be trimmed to ensure that no stem-to-fruit rubbing occurs. Prior to collection, field crates and fruit should be left in shaded conditions, protected from the sun and rain.

Grading and packing should be carried out as soon as possible after harvest, normally within three hours, after which time the fruit should be kept at ambient tropical conditions (25°C to 28°C) to continue ripening, or cooled and stored at 10°C to 12°C.

Standard packing house design and operations apply for pawpaw grading and packing. Operations can be carried out with basic equipment, including water tanks, field crates, and grading tables, or with automated washing and weight-grading or separation systems. All tanks and grading tables should be covered with foam to protect fruit from exposed edges; the skin of the pawpaw is delicate, and scratches will result in latex exudation and staining. Similarly, if the fruit is dropped, it will easily develop bruises as it ripens (Market. A.G, 2002, Smith et al., 1992).

b) Market requirements
Storage and Transportation Importers require fruit at specific stages of ripeness for optimum sales; this varies between 50 and 70% yellow colour depending on the importer, the market and the time of year. For fruit to arrive in the importing country at the correct colour stage, attention has to be paid to the maximum and minimum colour stages on departure from the pack house, the length of the shipment period (24 hours when considering UK, Canada and USA, and 48 hours for Holland) and the temperature in the importing country. Thus, colour stages on departure from the pack house for air shipment can vary from 20% to 50%, and the selections are generally more rigid during the summer months due to the rapid rates of ripening on arrival in importing countries. fruit exported too green (less than 20% yellow colour) will fail to ripen adequately when temperatures in importing countries are low, particularly in winter months.

Sea-shipment of pawpaw is possible when fruits are shipped at the optimum harvest maturity, with one or two yellow streaks. Shipments should be made at 10 to 12°C and 85 to 95% relative humidity, in refrigerated holds or reefer containers. Post-harvest disease control is critical with sea-shipment, particularly anthracnose and Phytophthora. Colour development during sea-shipment usually increases from 10% to 40% during 10 days at 12°C, and will develop further during the customs, clearance and delivery period on arrival.

Importers require fruit at specific stages of ripeness for optimum sales; this varies between 50 and 70% yellow colour depending on the importer, the market and the time of year. For fruit to arrive in the importing country at the correct colour stage, attention has to be paid to the maximum and minimum colour stages on departure from the packhouse, the length of the shipment period (24 hours when considering UK, Canada and USA, and 48 hours for Holland) and the temperature in the importing country. Thus, colour stages on departure from the packhouse for air shipment can vary from 20% to 50%, and the selections are generally more rigid during the summer months due to the rapid rates of ripening on arrival in importing countries. fruit exported too green (less than 20% yellow colour) will fail to ripen adequately when temperatures in importing countries are low, particularly in winter months.

Fruit harvested and placed to ripen at the recommended harvest stage (one yellow stripe) will ripen to 60 to 70% yellow coloration within four to six days under ambient tropical conditions (25° to 28°C). Fruit transferred to low temperature storage (10° to 12°C), when harvested at the one-stripe stage, will store successfully for 14 to 21 days if post-harvest disease incidence can be controlled. When harvested at more advanced stages of ripening, the storage life will be significantly reduced (Medlicott, 2001).

1.8 Consumer preferences

a) Characteristics of pawpaw fruits
Pawpaws have a creamy, custard-like flesh with a complex combination of tropical fruit flavors. They are most commonly described as tasting like banana combined with mango, pineapple, melon, berries, or other fruit. There is a considerable variety of flavors among wild pawpaws, ranging from awful to sublime. Most pawpaws taste good, some are truly wonderful, and a few are better for throwing than for eating. All of the named cultivars produce tasty fruit, and different people will have different preferences. Ripe pawpaws usually give off a powerful fruity aroma, as well. Color change is generally not a reliable indicator of ripeness.

b) Varieties
Despite the great variability in size, quality and other characteristics of the pawpaw, there were few prominent, selected and named cultivars before the introduction into Hawaii of the dioecious, small-fruited pawpaw from Barbados in 1911. It was named 'Solo' in 1919 and by 1936 was the only commercial pawpaw in the islands. 'Solo' produces no male plants; just female (with round, shallowly furrowed fruits) and bisexual (with pear-shaped fruits) in equal proportions. The fruits weigh 1.1 to 2.2 lbs (1/2-1 kg) and are of excellent quality. When the fruit is fully ripe the thin skin is orange-yellow and the flesh golden-orange and very sweet.

'Kapoho Solo' or 'Puna Solo' was discovered and became popular with growers on Kauai before 1950. In 1955 a 'Dwarf Solo' (a back-cross of Florida's 'Betty' and 'Solo') was introduced to aid harvesting, and this became the leading commercial pawpaw on the island of Oahu. It was, up to 1974, the only export cultivar. It is pear-shaped, 14 to 28 oz (400-800 g) in weight in high rainfall areas, and has yellow skin and pale-orange flesh.

'Waimanalo' (formerly 'Solo' Line 77) was selected in 1960 and released by the Hawaii Agricultural Experiment Station in 1968 and soon superseded Line 8' Solo' on Oahu for the fresh fruit market because of its firmness and quality, but there it is usually too large for export. It has long storage life and is recommended for sale fresh and for processing. Since 1974 this cultivar has been produced commercially on the low-rainfall island of Maui where it ripens at a greener colour than on the island of Hawaii and is exported to cities in the northwestern and central USA. The growers raised only bisexual plants; they say that the fruits of female plants are too rough in appearance.

'Higgins' (formerly Line 17A), the result of crosses in 1960, was introduced to Hawaiian growers in 1974. It is of high quality, pear-shaped, with orange-yellow skin, deep-yellow flesh, and averages 1 lb (0.45 kg) when grown under irrigation. In and territory or seasons of low rainfall, the fruit is undersized.

'Wilder' (formerly Line 25) is a cultivar admired for its uniformity of size, firmness and small cavity and it is now popular for export.

'Hortus Gold', a South African cultivar, launched in the early 1950's, is dioecious, early-maturing, with round-oval, golden-yellow fruits, 2 to 3 lbs (0.9-1.36 kg) in weight. From 200 female 'Hortus Gold' seedlings planted at the University of Natal's Ukulinga Research Farm in 1960, selections were made of the plants showing the highest yield. Of these, one clone having the best sugar content and disease resistance was chosen and named 'Honey Gold' in 1976. This cultivar has a slight beak at the apex, golden-yellow skin; is of sweet flavor and good texture but becomes mushy when overripe. It averages 2.2 lbs (1 kg) per fruit except for those at the end of the season, which are much smaller. It does not reproduce true from seed and is therefore propagated by cuttings. It is late in season and late-maturing (10 months from fruit set to maturity) and therefore brings nearly double the price of other cultivars.

'Bettina' and 'Petersen', long-standing cultivars in Queensland, Australia, were inbred for several generations to obtain pure lines. 'Bettina', a hybrid of Florida's 'Betty' and a Queensland strain, is a low, shrubby, dioecious plant producing well-coloured, round-oval fruits weighing 3 to 5 lbs (1.36-2.27 kg).

'Improved Petersen', of local origin, is dioecious, tall-growing, with fruits deficient in external colour and indifferent as to keeping quality but noted for the fine colour and flavor of the flesh. In 1947 'Bettina 100A' was crossed with 'Petersen 170' to produce the superior, semi-dwarf 'Hybrid No. 5', smooth, yellow, rounded-oval, 3 lbs (1.36 kg) in weight, thick-fleshed, of excellent flavor and prized for marketing fresh and for canning. It bore more heavily than either of its parents and remained a preferred cultivar for more than 20 years. 'Solo' and 'Hortus Gold' are often grown but most plantations are open-pollinated mixtures.

In Western Australia, after trials of 9 cultivars – 'Hybrid No. 5', 'Petersen', 'Yarwun Yellow', 'Gold Cross', 'Goldy', 'Hong Kong', 'Guinea Gold', 'Golden Surprise' and 'Sunnybank' – only 'Sunnybank' and 'Guinea Gold' were chosen as having sufficient yield and quality to be worth cultivating commercially.'Sunnybank' fruits average 1.39 lbs (0.63 kg), and ripen over 11 months. 'Guinea Gold' averages 2.4 lbs (a little over 1 kg) and ripens over a period of 18 months.

The Universidad Agraria, La Molina, Peru, began to assemble pawpaw strains in 1964, collecting 40 strains from various parts of the country and introducing 3 from Brazil, 1 from Puerto Rico, 3 from Mexico and 2 lines of 'Solo' from Hawaii, and embarked on an evaluation and breeding program and the creation of a germplasm bank.

In Ghana, dioecious cultivars such as 'Solo', 'Golden Surprise', 'Hawaii', and 'No. 5595', were introduced and commonly cultivated by farmers but they hybridized with local types and lost their identities after several generations. A number of types were collected at the Agricultural Research Station at Kade in Ghana, from 1966 to 1970 and classified according to sex type, fruit form, weight, skin and flesh colour, flesh thickness, texture and flavor, number of seeds, and various plant factors. It was determined that preference should be given female plants with short, stout stems, early maturing, and bearing heavily all year medium-size fruits of bright colour, thick-flesh and with few seeds.

The Instituto Colombiano Agropecuario, at Palmira, Colombia, began a pawpaw breeding program in 1963 by bringing together Colombian-grown cultivars – 'Campo Grande', 'Tocaimera', 'Zapote', 'Solo', –with some from Brazil– 'Betty', 'Bettina' and '43-A-3' –South Africa– 'Hortus Gold' –and Puerto Rico, and representatives of related species: C. candamarcensis Hook. F., C. pentagona Heilborn, C. goudotiana Tr. & Pl. (one type yellow with green peduncles and another red with purple peduncles), C. cauliflora Jacq. of Colombia and C. monoica Desf. and Jacaratia dodecaphylla A. DC. from Peru. The first two of these species were not suited to conditions at Palmira.

The progeny of crosses with C. cauliflora were the only hybrids showing some virus resistance but they were unfruitful when attacked. There were no viable seeds and 30% of the fruits were seedless. C. monoica proved well adapted to Palmira, bore small, yellow fruits, but succumbed to virus. The introductions from Brazil were by far the most promising. 'Zapote', with rich, red flesh is much grown on the Atlantic coast of Colombia.

In India, pawpaw breeding and selection work has been carried on for over 30 years beginning with 100 introduced strains and 16 local variations. A well-known cultivar is 'Coorg Honey Dew', a selection from 'Honey Dew' at Chethalli Station of the Indian Institute of Horticultural Research. There are no male plants; female and bisexual occur in equal proportions. The plant is low-bearing and prolific. The fruit is long to oval, weighs 4.4 to 7.7 lbs (2-3 1/2 kg); has yellow flesh with a large cavity, and keeps fairly well. 'Washington', popular in Bombay, has dark-red petioles and yellow flowers. The fruits are of medium size with excellent, sweet flavor. 'Burliar Long' is prolific, bearing as many as 103 fruits the first year, mostly in pairs densely packed along the stem down to 18 in (45 cm) from the ground. Seedlings are 70% females and bloom 3 months after transplanting.

In 1965, a program of pawpaw improvement was undertaken in Trinidad and Tobago utilizing promising selections from local types, including 'Santa Cruz Grant', a vigorous plant mainly bisexual (having both male and female flowers), very large fruits weighing 10 to 15 lbs (4.5-6.8 kg), with firm, yellow flesh of agreeable flavor. The fruit is too large for marketing fresh but is processed both green and ripe. 'Cedro' is dioecious, rarely bisexual, a heavy bearer and highly resistant to anthracnose. The fruits weigh from 3 to 8 lbs (1.37-3.6 kg) but average 6 lbs (2.7 kg); have firm, yellow, melon-like flesh and are suitable for sale fresh or for processing.

In 'Singapore Pink', the plants are mainly bisexual, producing cylindrical fruit. The minor are female with round fruit. Average weight of fruit is 5 lbs (2.27 kg) though there is variation from 2 to 7 lbs (1-3 kg). The flesh is pink. The fruit surface is prone to anthracnose in rainy periods, so, at such times, the fruits must be picked and sold in the green state. Two smaller-fruited types, 2 to 3 lbs (1-1.37 kg) in weight, with bright-yellow skin and thick, firm flesh, were selected for marketing fresh.

The 'Solo' of Hawaii has performed unsatisfactorily in Florida, producing low yields of small fruits. Scott Stambaugh, a pawpaw specialist, began his pawpaw breeding with a strain designated USDA Bureau of Plant Industry #28533 obtained from the then Plant Introduction Station in Miami. From off spring of this he made a selection which he named 'Norton'. When he acquired seed of a type called 'Purplestem'; later 'Bluestem', he crossed it with 'Norton' and the hybrid yielded fruits 10 lbs (4.5 kg) in weight and was named 'Big Bluestem'. The latter was crossed with 'Solo' and the hybrid was called 'Bluestem Solo' or 'Blue Solo'. The 'Blue Solo' has been well regarded in Florida for its low growth, dependable yields of good quality fruits, 2 to 4 lbs (1-2 kg) in weight, orange-fleshed and rich in flavor.

'Cariflora' is a new cultivar developed at the recently renamed Tropical Research and Education Center of the University of Florida at Homestead. It is nearly round, about the size of a cantaloupe, with thick, dark-yellow to light-orange flesh; tolerant of pawpaw ringspot virus, but not resistant to pawpaw mosaic virus or pawpaw apical necrosis virus. Yield is good in southern Florida and warm lowlands of tropical America but not at elevations above 2625 ft (800 m).

'Sunrise Solo' (formerly HAES 63-22) was introduced from Hawaii into Puerto Rico. The fruit has pink flesh with high total solid content. In Puerto Rican trials, seeds were planted in mid-November, seedlings were transplanted to the field 2 months later, flowering occurred in April and mature fruits were harvested from early August to January. Recent selections from Puerto Rican breeding programs are 'P.R. 6-65' (early), 'P.R. 7-65' (late), and 'P.R. 8-65'. Venezuelan pawpaws are usually long and large, ranging in weight from 2 to 13 lbs (1-6 kg) and mostly for domestic consumption or shipment by boat to nearby islands (Morton, 1987).

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