PAPAYA TECHNICAL


Introduction

Papaya (Carica papaya L.), is a table fruit in most of the tropical countries cultivated mainly for fresh fruit consumption. It is consumed as a part of breakfast dessert and as fruit salad. It is also used in soft drinks, jams, ice-cream flavouring, crystallised fruit and also sold as canned cubes and juice in some countries. In India it is mostly consumed as a table fruit. Papaya research during the last 5 decades encompassed both basic and applied areas. Research work concentrating mainly on crop-production technology, areas suitable for different agroclimatic regions of the country had been carried out at different agricultural universities and ICAR institutions. Systematic papaya breeding work for development of improved varieties was initiated at the TNAU and the IARI in early sixties and subsequently at the GBPUAT and the IIHR in the seventies.

The first improved cultivar of papaya Coorg Honey Dew was identified in 1959 at the Citrus Experiment Station, Chethalli. Interdisciplinary research programme on crop improvement, production technology and plant protection is presently under implementation at the centres at Coimbatore, Pusa, Pune, Jalgaon, Rahuri and Bhubaneshwar with the support under the All-India Co-ordinated Research Project on Tropical Fruits of the ICAR, and through ad-hoc projects under ICAR AP Cess Fund Scheme.

 
Varieties

15 high-yielding varieties of papaya have been developed in India, out of which 9 are widely adopted. Some successful hybrids have also been developed and heterosis has also been noticed with a wide range of breeding materials. Some of the common varieties in India include Coorg Honey Dew, Pusa Dwarf , Pusa Giant, Pusa Majesty, Pusa Delicious, CO.1, CO.2, CO 3, CO.4, CO.5 and CO.6. Varietal improvement work for frost tolerance, disease resistance and improved fruit quality is under progress.

 
Varietal Improvement

According to the Department of Agricultural Research and Education, ICAR, Government of India, in 1999-2000, the Pink Flesh Sweet variety recorded maximum fruit weight, whereas Red Indian maximum TSS (13.0 Brix). Hybrid Surya having medium-sized fruits (600-800 g), red flesh, high TSS (14 Brix) and low cavity (20%) with good keeping quality was identified to be released. The Indian Institute of Horticultural Research, Bangalore and developed a hybrid variety of papaya, `Surya, which is a cross between `Sunrise Solo and `Pink Flesh Sweet. It produces medium size fruits of 600-800 gram with red pulp about 3.0-3.5 cm thick and a smaller fruit cavity. The hybrid is gynodioecious and does not require male plants for pollination. The seedlings for planting. If planted at a spacing of `6x6 may yield 48-58 tonnes papaya per acre.

 
Propagation

Papaya is usually propagated by seeds. Germination of seeds takes place 2-3 weeks after sowing. Seeds treated with thiourea (100-200 ppm) and gibberellic acid (GA3 at 200 ppm) germinated better. Seed germination is highest at an optimum temperature of 35C. Storage of seeds at 10C was found to be the best for retention of seed viability. Viability of papaya seed can be maintained for 9 months of room temperature when stored in air-tight containers. Patch budding has been reported to be quite successful (90%) in papaya but it is not practiced commercially. Tissue-culture technique has been standardized for papaya micro-propagation. It has been reported that plants raised through tissue-culture technique yielded more fruit in Pusa Delicious when compared with the seedlings. Young papaya seedlings form callus profusely in Murashige and Skoog medium supplemented with auxins (NAA). Callusing was obtained from stem segments, roots and leaf tissue. Callus readily differentiated into leafy shoots in medium containing high ratio of kinetin and NAA (2.0 : 0.2 mg/litre), while root formation was favoured by a low kinetin: NAA ratio (0.2 : 0.5 ml/litre). Shoot tip culture from seedlings and lateral buds from female plants of Coorg Honey Dew variety was found to be successful. The tissue-culture plantlets measuring 5.5 to 9.5 cm and hardened in plastic chamber survived better when planted in the field. The available information indicates that tissue-cultured papaya plantlets can be used with added advantage of uniformity in plant type.

 
Plant Density

A spacing of 1.8 m x 1.8 m is normally followed in most of the places. Field trials conducted indicates that a spacing of 1.8 m x 1.8 m for varieties like CO. 1, CO.2 and Solo, and 2.1 m x 1.2 m (3.968 plants/ha) for Coorg Honey Dew variety was optimum for Bangalore conditions. The spacing of 1.4 m x 1.4 m or 1.6 m x 1.4 m is ideal for CV Pusa Delicious under sub-tropical conditions of Bihar. For the dwarf variety Pusa Nanha a closer spacing of 1.25 m x 1.25 m has been found satisfactory. For papain production a spacing of 1.6 m x 1.6 m was recommended based on field trials conducted in Tamil Nadu. In West Bengal under a spacing of 1.5 m x 1.5 m (4, 444 plants/ha) fruit yield of 98.7 tonnes/ha could be recorded with papaya variety Ranchi.

 
Nutrition

The CO. 1 papaya plant revealed significant uptake of nutrients like N, P, K, Ca and Mg at the flowering and the nutrients were removed by the whole plant at harvest were 305, 103, 524, 327 and 183 kg of N, P, K, Ca and Mg/ha respectively. Thus the ratio of N:P:K removed was 1:0.33:1.71. The lack of N and P causes reduction in growth of the papaya plant, while absence of K and Ca induces pronounced foliar symptoms. Among the micronutrients, B followed by Fe, Cu, Zn and Mo are considered important for proper growth and development. Deficiency of B and Zn in field conditions causes considerable yield loss. The NPK requirements of papaya have been determined by conducting large number of fertilizer trials at different regions of the country. Field trials showed that 140-350 g N, 200-300 g P2O5 and 200-300 g K2O/plant/year are optimum, depending on the cultivars and soil-climatic conditions. The applied nutrients to leaf showed optimum concentration of NPK in leaf petiole as 1.52% nitrogen, 0.14% phosphorus and 4.42% potash. Organic manures like farmyard manure (FYM), sheep manure, wood ash and bone-meal improved yield and quality of fruits of papaya. Inorganic fertilizers @ 200-250 g each of N, P2O5 and K2O/plant are generally recommended for obtaining high yield in papaya. The N @ 200 g/plant was found optimum for fruit yield at Pusa (Bihar), but papain yield increased with doses up to 300 g/plant at Coimbatore (Tamil Nadu). Some of the important fertilizer recommendations emerged from field trials conducted at different parts of the country are as follows:

  1. A dose of 250 g N, 250 g P2O5 and 500 g K2O/plant/year applied in 6 bimonthly intervals was found the best for Coorg Honey Dew variety and gave estimated fruit yield of 186.8 tonnes/ha in 28 months crop cycle at a plant spacing of 2.4 m x 2.4 m (1, 736 plants/ha).
  2. A dose of 350 g N, 250 g P2O5 and 200 g K2O/plant year applied in 6 split doses was best for Solo variety spaced at 2 m x 2 m (2,500 plants/ha) under Bangalore (Karnataka) conditions.
  3. At Coimbatore, a dose of 200 g each of N, P2O5 and K2O/plant in 4 split doses during 1, 3, 5 and 7 months after planting resulted in higher yield of papaya variety CO. 1. For papain production from CO.2 variety a dose of 250 g N/plant/year in 6 split doses at biomonthly intervals commencing from the second month after planting was found the best.

  4. A fertilizer dose of 200 g N, 300 g P2O5 and 600 g K2O/plant gave highest fruit (110 tonnes/ha) yield in papaya variety Ranchi under West Bengal conditions. For maximum papain yield 94.45 g/fruit), fertilizer dose of 200 g N, 300 g P2O5 and 400 g K2O was found optimum.

Application of phosphatic fertilizers reduces acidity, while potash normally increases the TSS and total sugar. When K was adequate, TSS did not lower even with high N fertilization. The fruit quality in papaya as indicated by TSS was significantly influenced by K and N x K interactions. Not many field trials have been conducted to determine the micronutrient requirements of papaya. The B-deficient plants normally develop bunchy top and deformed fruits. Foliar applications of Mn (0.25%) plus Cu (0.25%) at 60 and 90 days after transplanting helped in harvesting maximum fruit yield (94.7 tonnes/ha) with high quality fruits. Combined application of B (0.1%), Mn and Cu markedly improved fruit quality in papaya variety Ranchi under West Bengal conditions. Beneficial effects of mycorihiza have been observed in papaya. Association of vesicular arbuscular mycorrhiza (Glomus mosseae + Glomus fasciculatum + Gigaspore margarita) helped in saving 25% of P recommended for papaya.

 
Water Management

Papaya is susceptible to waterlogging and the orchard should have good drainage system, particularly in heavy soils experiencing high rainfall. Total water requirement of CO.2 variety of papaya is estimated to be of 1,800-1,900 mm and irrigation at 60-80% available soil moisture (ASM) depletion was found optimum for papaya. Plants receiving frequent irrigation with 100% evaporation replenishment maintained higher transpiration rate, lower diffusive resistance but gave significantly higher yields as compared to 50 and 25% evaporation replenishment. Evapotranspiration decreased with decreasing frequency of irrigation. Generally irrigation to grown-up plants at 7-10-day interval during hot summer months is recommended. Among various systems of irrigation, ring of furrow system of irrigation is preferred over the bed system. Bed system allows direct contact of irrigation water with the plant and thus predisposes plants to collar rot disease. Irrigation in widely spaced furrows of 100 cm resulted in significantly higher fruit yield as compared to basin and flood methods of irrigation under Bangalore condition. Drip system of irrigation helps in saving 50-60% water, and water use efficiency under drip is much higher.

 
Weed Management

Chemical weedicides like atrazine and simazine were found phytotoxic for papaya. Gramoxone at 1.0 litre/ha controlled weeds and gave maximum fruit yield in papaya (91 tonnes/ha) under West Bengal condition. Paraquat (1.0 litre/ha) applied twice at 90 and 180 days after transplanting caused maximum reduction of weeds, improved plant growth, advanced flowering and resulted in higher fruit yield. In field trials conducted at IIHR, Bangalore, Diuron 2 kg ai was found effective in controlling weeds without any adverse effect on papaya.

 
Disease Management

Various diseases, caused significant loss in yield and quality of papaya fruits every year. Some of the more common diseases and their recommended remedies are given below:

Name of the Disease Recommended Remedy
Stem rot or collar rot
  1. Good drainage
  2. Spraying of 1% Bordeaux mixture
Powdery mildew Bavistin (Carbendazim) at 0.1% applied twice at 15-day interval gave an effective control of the disease
Viral Diseases (leaf curl, mosaic, mild mosaic, distortion ringspot, ringspot and leaf crinckle)
  1. The spread of the disease could be minimized by controlling aphid vector through application of Malthion.
  2. Preliminary work on papaya showed that papaya could be protected from PRSV by pre-immunizing seedlings with milder strain of the virus.
  3. Growing of Disease resistant varieties
Nematode Diseases Application of 1 kg of neem-cake or Carbofuran @ 2 kg/ha.

Certain other minor fungal diseases like Phytophthora; fruit rot, stem rot caused by Rhizoctonia solani; anthracnose caused by Colletotrichum gloeosporioides, leaf spot caused by Alternaria sp and Cercospora sp; and leaf blight caused by Helminthosporium rostratum have been reported in the country. Certain post-harvest diseases also cause great losses during transportation and storage of fruits. As most of the causal organisms are associated with fruits from the pre-harvest states, application of protective fungicides is most effective in reducing the losses. It is advised to frequently spray fungicides like Mancozel or Chlorothalonil at pre-harvest stages. Hot-water immersion of fruits after harvest at 42C for 30 min, followed by a 20 min immersion at 49C reduces the inoculum level substantially. The hot water-treated fruits receiving fungicide wax emulsion treatment are free from post-harvest decay and store well. A hot water (54C for 3 min) spray treatment is developed for effective control of decay caused by anthracnose and stem-end rots. Breeding work involving resistant species is in progress. Through repeated selection and back-crossing the population has reached to F7 generation and some degree of resistance to PRSV is also reported. The breeding work at Pune since 1968 has resulted in identifying a resistant line having small fruits (0.5 to 1.2 kg) with TSS ranging from 7 to 10Brix. At IIHR, Bangalore, hybrid progenies from crosses of C. papaya x C. cauliflora are tolerant to PRSV. Post-monsoon planting of papaya reduces the incidence of the disease under subtropical condition of north India. A ready-to-serve papaya juice drink has been developed at TNAU, Coimbatore. Papaya candy or tutti-fruitti is being produced at commercial scale in Coimbatore, Bangalore and Jalgaon. The product is in great demand in bakery and confectionery industry. According to DARE, Solo papaya recorded good growth and higher accumulation of boron. Fruit set increased by 20% either by soil application or foliar spraying. Application of boron increased Ca in fruits which is an important element to increase the shelf-life of papaya. Papaya plants receiving inorganic nutrients alone (200 g each of N, P2O5 K2O/plant/year) recorded highest yield, but inclusion of organic source of nutrient (farmyard manure/neem cake) produced better quality fruits. Drenching with Ridomil (0.2%) was most effective method to control root-rot.

 
Post Harvest Management of Papaya

Papaya fruits are sensitive to poor quality outturns and high post-harvest losses if harvesting, treatments and handling techniques are inadequate or inappropriate. From harvest, a shelf-life of four to six days under tropical conditions and up to three weeks at low temperature storage can be achieved with the correct harvest maturity, disease control measures, handling techniques and storage conditions.

Harvest Maturity

Papaya 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. 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.

Harvesting

Papaya is harvested manually depending on the size and age of the tree, using specialised tools, knives or by hand. When harvesting by hand or with knives, the peduncle is snapped or cut from next to the tree.. then immediately trimmed flush against the top of the fruit. The specialised implement for harvesting of fruit inaccessible by hand due to tree height, comprises of a long pole, a small circular hoop at the top, a small mesh bag attached to the hoop, and a horizontal blade above the hoop and the bag. The blade is positioned below the peduncle of the fruit and the pole moved upwards; the fruit is detached from the tree and then drops gently into the mesh bag below the hoop at the top of the pole. After harvest, the fruit are placed in single layers into shallow, light coloured field crates, preferably containing a foam layer for cushioning. All stems should be trimmed after harvest to ensure that no stem to fruit rubbing occurs during transport to the packing facilities. Fruit should never be thrown or dropped. Field crates containing the fruit should be left in shaded conditions protected from the sun and rain, while awaiting collection for delivery to a packing facility. Mesh bags, sacks or baskets are unacceptable for papaya transport due to the high susceptibility to bruising. Care should be taken during transport in field crates to minimise the movement of fruit.

Export Grading and Packing

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 12C 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% Thaibendazole solution for anthracnose control. Washing, treatment and grading can be carried out using mechanised or manual systems, 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.

Packaging

Single layer, one-piece self-locking or two-piece full telescopic fibre board carton; bursting strength 200 to 250 lb/in2. Internal packaging material should include shredded paper in the base of the carton and individual tissue wraps for each or alternate fruit. Individual labels can be attached to the fruit for appearance and recognition.
Carton internal dimensions:

  • 10.9 by 34 by 26.9 cm (4.3" by 13.4" by 10.6")
  • 10.2 by 43.2 by 27.9 cm (4" by 17" by 11")

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 packhouse, the length of the shipment period 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 papaya is possible when fruits are shipped at the optimum harvest maturity, with one or two yellow streaks. Shipments should be made at 10 to 12C 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 12C, and will develop further during the customs, clearance and delivery period on arrival. Fruit harvested and placed to ripen at the recommended harvest stage (one yellow stripe) will ripen to 60 to 70% yellow colouration within four to six days under ambient tropical conditions (25 to 28C). Fruit transferred to low temperature storage (10 to 12C), 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.

Potential Post-harvest Losses

Papaya is particularly susceptible to post-harvest losses as a result of high susceptibility to bruising and disease infection. Careful handling must be employed during harvesting, handling and shipping, and the relevant disease control measures employed. Mechanical Damage: Damage to the skin immediately after harvest, as a result of the harvesting implement, dropping into crates, over-filling of crates and excess movement of fruit during in-field transport, will result in latex staining, punctures, scars and bruises. During ripening, bruised areas will develop into dark soft regions, which become affected by secondary microbial infection. Similar effects can occur as a result of poor handling during washing, grading and packing. Damage can be reduced by taking protective measures throughout the handling procedures. Staff should be trained with harvesting techniques, foam should be included in the base of field crates and crates should contain only one layer of fruit. Stems are to be removed in the field to prevent puncturing or scratching of adjacent fruit. Vehicles used to transport the fruit from the field to packhouse should be driven slowly and with care. During handling in the packhouse, fruits should never be thrown or dropped and in automated operations, all machinery should be padded where possible. Palletised systems of produce movement in packhouse operations are preferable, both with field crates and with the final packed product. Pathological Factors: Anthracnose (Colletotrichum gloespoirides L.) disease is prevalent during long term storage and with humid orchard conditions, inappropriate pre-harvest disease control or poor orchard hygiene. The presence of the disease is characterised by small black or light brown spots, which gradually enlarge and may coalesce and sink. Anthracnose can be controlled or reduced by pre-harvest sprays. Post-harvest control where pre-harvest sprays are in operation should include a cold-water dip or spray containing 0.05% Thaibendazole and surfactant. Changing of chemical is required each four to five tonnes of fruit. Where no pre-harvest control is in operation and the disease is present in the orchard, the cold water treatment may have to be replaced with a hot-water Thaibendazole treatment. A treatment time of 20 minutes at 46C is required. Specialised equipment for temperature maintenance and water circulation is necessary as fluctuations in temperature will reduce the effectiveness of the treatment and may damage the fruit. Phytophthora: the disease can be prevalent during long-term storage at low temperature if orchard control systems are not in operation. Phytophthora is characterised by circular translucent lesions, which develop with grey surface mycelium, and is particularly apparent around the peduncle. Post-harvest control is achieved by treatment with 0.1% Previncur N. Low Temperature: Storage of unripe papaya below temperatures of 10C will result in chilling injury. The symptoms are indicated by surface pitting, discolouration of the peel and the flesh, incomplete ripening, poor flavour and increased susceptibility to disease incidence. Ripe papayas will store successfully at lower temperatures, but transport of ripe fruit (more than 50% yellow colour) is not recommended due to the susceptibility to mechanical damage and bruising.

Characteristics
for Export Markets

Yellow/green peel, deep orange/yellow flesh. Hermaphrodite fruit should be pear-shaped and female fruit uniformly round; all fruit should appear fresh with no shrivelling, discolouration or non-uniform ripening.
Size

Different sized fruit are separated and packed according to weight, resulting in different "counts". The following weight range is used for a 4 kg net weight carton, both for female and hermaphrodite fruit:

  • small: 12 to 15 count (260 to 330 g)
  • medium: 8 to 12 count (360 to 500 g)
  • large: 4 to 8 count (570 to 1000 g)

  • Condition
  • no latex stains or surface debris
  • no wounds from harvesting or handling, including punctures, scratches and bruises
  • no scars or residues from insect or spray damage
  • no fruit above the required colour stage for shipment

  • Market Requirements

    All markets: small and medium hermaphrodite fruit are preferred with 50 to 70% yellow colouration on arrival at the importer. Small female fruit are acceptable to some importers. Selected markets and importers require medium and large fruit, particularly for ethnic or catering markets. Hermaphrodite fruit are preferred due to the large cavity size and susceptibility to damage shown with large female fruits.
    Handling in Importing Countries

    For the maximum marketing period of papaya, the fruit should be stored at 10 to 12C. Temperatures below this range will cause chilling injury and rapid deterioration in fruit quality. To develop ripening in papaya, fruits should be stored at 18 to 25C and treated with ethylene gas at 100 ppm (0.01%) for 24 hours. Unripe papaya are sensitive to ethylene and will commence ripening if stored with ethylene-producing commodities. Similarly, ripe papaya produce ethylene and will cause deterioration in ethylene-sensitive crops.