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Project experiments for 1998/1999

Table 1: Bitter melon links

Species: Momordica charantia L.

Family: Cucurbitaceae

Crop status: Established

The immature fruit of bitter melon is valued for its bitter flavour, considered to bring out the flavour in other ingredients. It is usually eaten fresh (stuffed and/or sliced) but can also be pickled, and has been canned in brine. Young shoots and leaves are also eaten (Vinning 1995). Leaves are packed into 5 kg mixed produce boxes and sold to Melbourne and Sydney as a medicinal plant (Peter McLaughlin 1999, pers. comm.).

Varieties

Producers from Darwin region source open pollinated seed from vegetable wholesalers (Lim 1998), friends and previous crops. There is a large amount of undesirable shape and quality variation within these varieties (Kevin Blackburn 1998, pers. comm.).

Peter McLaughlin (Murwillumbah) has been conducting a selection program in bitter melon for 7 years, based primarily on size, shape, colour and taste as judged by Chinese chefs. Original stock was a cross between varieties supplied by Dr Vong Nguyen and Minara Seeds (Peter McLaughlin 1998, pers. comm.). Vong Nguyen has done his own work on varieties.

Popular varieties in the Philippines include open pollinated: Sta Rita, Makiling and their F1 hybrids: Jade Star A and B (Reyes et al. 1994).

Agronomic trials

Variety x season trials are planned in 1999 by the Northern Territory DPIF , Peter McLaughlin (NSW) and Agriculture Western Australia . Peter is also looking at fertiliser regimes.

Production

Cultural practices are similar to those of cucumber (Reyes et al. 1994). It is grown commercially in NSW, Vic, Qld and NT (Lee 1995). Trials have been conducted by the agricultural departments in each of these states.

Weed: Weedy forms of bitter melon have escaped ornamental cultivation and become a problem in citrus groves of Florida (Robinson and Decker-Walters 1996).

Climate: It is tolerant to a range of environments (Lim 1998) and can be grown in tropical and subtropical climates (Reyes et al. 1994). Two crops are produced each year in Florida (Lamberts 1992).

Temperature: A minimum temperature of 18° C during early growth is preferred (Larkcom 1991), with 24-27° C being optimum (Desai and Musmade 1998). This range has been confirmed at Murwillumbah, with prolific growth occurring at day / night temperatures of 28-35 / 20-25° C and severe reduction in growth at night temperatures of 16° C (Peter McLaughlin 1998, pers. comm.). It requires more heat than the other gourds to produce maximum yield (Larkcom 1991), but is also more resistant to low temperatures. (Desai and Musmade 1998).

pH: Optimum is 6.0-6.7 (Desai and Musmade 1998). If lime is applied, it should be done well before the initial fertiliser application (Peter McLaughlin 1998, pers. comm.).

Soil type: Bitter melon grows best in a well drained sandy loam, rich in organic matter, but will tolerate many soils (Cantwell et al. 1996 , Reyes et al. 1994).

Soil preparation: It is preferable to grow on raised beds or ridges (Lim 199). Chicken manure may be dug in and watered 2-4 weeks before transplanting or sowing (Peter McLaughlin 1998, pers. comm.).

Germination: Seeds rapidly lose viability, so pre-germinating is recommended for all but very fresh seed. Soak for 24 hours and wrap in damp paper towelling, then keep in a plastic bag at 26-29 ° C for germination within a couple of days (Larkcom 1991). Germination ceases outside the range of 10-50° C (Singh 1991). Germination percentage can be increased by soaking in 1% KNO 3 (Devi and Selvaraj 1994). Sow germinated seeds into pots, or directly in the field if the temperature is warm (Larkcom 1991). Seedlings emerge 5-7 days after sowing (Reyes et al. 1994). They require protection from wind, chill and excessive sun, and water should be prevented from puddling nearby (Desai and Musmade 1998).

Seed weight: Varies between 6 000 (Desai and Musmade 1998) and 17 000 seeds/kg (Reyes et al. 1994).

Plant density: 50 cm between plants and 2-3 m between rows. Optimum plant density varies with cultivar, from 6 500 to 11 000 plants/ha (Reyes et al. 1994) or 20 000 plants/ha (Huyskens et al. 1992). Producers in the Northern Territory have just 1 m between rows (Lim 1998).

Transplanting: It may be necessary to grow the first plants of the season in a hot bed to ensure enough warmth for immediate germination, and then transplant them at the 4-6 leaf stage (Peter McLaughlin 1999, pers. comm.).

Trellising: Grown on 2 m high fence trellising in Darwin (Lim 1998) but the Chinese gourd trellis, with a 2 m high 'roof', may provide greater yields. Remove lateral branches until the runner reaches the top of the trellis, and then leave 4-6 laterals. Cut the tip of the main runner to induce early cropping (Peter McLaughlin 1998, pers. comm.). Removal of lateral branches in the first ten nodes has a positive effect on total yield. Without pruning, most of the female flowers occur between the 10 th and 40 th nodes, or at 0.5 - 2 m height (Rasco and Castillo 1990). Higher yields are obtained with 2 m than 1 m high trellises (Abusaleha and Dutta 1994) and the crop is more accessible. Vertical (fence) trellising may reduce the proportion of marketable fruit (Huyskens et al. 1992). This occurs because laterals keep matting and leaves push to the outside, causing an impenetrable barrier for bees and pollinating insects, and creating a dark, moist environment ideal for pathogens (Peter McLaughlin 1998, pers. comm.).

Grafting: Luffa provides an excellent root stock for bitter melon, and grafting can increase yields subtantially in Taiwan, mainly through the control of Fusarium wilt (Lin et al. 1998). Luffa rootstock is also more resistant to flooding (Liao and Lin 1996 ).

Nutrition: If soil is highly fertile and prepared with enough organic matter, further feeding may not be necessary (Larkcom 1991). Otherwise, fertigate weekly. Add Nitrofoska until the plant reaches trellis height, then potassium nitrate until flowering. Reduce nitrogen application during fruit set. The addition of calcium nitrate improves shelf life, possibly by strengthening the epidermis and reducing ethylene production (Peter McLaughlin 1998, pers. comm.). However, nitrate is also known to suppress flowering in many species. N:P:K applications of around 100:50:50 kg/ha are recommended by Robinson and Decker-Walters (1996).

Water: Plenty of water is needed throughout growth (Larkcom 1991). Irrigate at least weekly, beginning from the day of sowing (Desai and Musmade 1998), and water well past the root area to induce root growth (Peter McLaughlin 1998, pers. comm.). The plant is intolerant to flooding (Reyes et al. 1994), with 4 days of flooding producing significant changes in morphology (Liao and Lin 1994).

Flowering: Bitter melon will first flower at 45-55 days after sowing if conditions are optimal, and continue throughout a season of usually 6 months (Reyes et al. 1994). Hand pollination can be avoided either by introducing bee hives or by blowing pollen around with an unloaded mister. Bees don't work in prolonged wet overcast conditions, and pollen can only be blown when it is dry (Peter McLaughlin 1998, pers. comm.). Pollen loses viability as the day advances and may be fully inviable by midday (Desai and Musmade 1998). The stigma is usually receptive for one day either side of flower opening, after which it turns brown and dries (Rasco and Castillo 1990). Flowering behaviour varies among cultivars and climatic conditions (Deshpande et al. 1979).

Male/female flower ratio: Long days cause the male flowers to bloom up to 2 weeks before the female flowers, while short days have the reverse effect (Huyskens et al. 1992 and references within). Spraying with 50 mg/L dikegulac at the 6-8 leaf stage increases female flower numbers and may double the number of fruit (Basu et al. 1994). Gibberellic acid at 25-100 mg/L has a similar effect, and can last for up to 80 days (Wang and Zeng 1996). Treatment with 2,4-D, maleic hydrazide and Cycocel (chlormequat) has also increased female flowers and yields, but reduced vine length and leaf area (Kabir et al. 1989). Pruning lower laterals increases the total number of flowers per plant by increasing the number of flowers on higher laterals (Rasco and Castillo 1990).

Plant maintenance: Vines producing whitish fruit should be discarded as they are genetic throwbacks and may cross pollinate Peter McLaughlin 1998, pers. comm.).

Harvest: It typically takes about 15-20 days after fruit set (90 days from planting) to reach marketable age (Reyes et al. 1994), but bitter melon can be harvested at any stage before. Fruit should be light green, thick and juicy (Lim 1998), and the seeds should be soft and white (Huyskens et al. 1992). Harvest every 2-3 days as the fruit ripens quickly (Desai and Musmade 1998). It accumulates bitterness with time, due to a build up of the alkaloid momordicine, and then loses the bitterness during ripening (Cantwell et al. 1996). The stem should be cut cleanly with a sharp knife (Reyes et al. 1994). If fruit is becoming too dark (and hence more bitter), a paper bag can be used to protect it from the sun and insects before harvesting (Larkcom 1991).

Yield: 20-30 t/ha is common (Reyes et al. 1994), and yields over 50 t/ha have been reported (Huyskens et al. 1992 and Kuang et al. 1997). Yields of 61-108 t/ha were achieved in Taiwan with plastic housing and grafting (Liao and Lin 1996).

Postharvest

There is currently an HRDC project looking at cool chain management from grower to retailer. Postharvest changes in pigmentation was studied by Tan et al. (1999) .

Storage temperature: Pick early morning and dip in chilled water (not below 6° C) to remove heat rapidly, then get fruit to a refrigerated packing shed as quickly as possible (Peter McLaughlin 1998, pers. comm.).

• Optimal storage temperature for fruit is 10-12.5° C (Zong et al. 1995), but the optimum temperature for setting refrigeration will be lower, and is different for each set of transport/storage conditions. If air circulation is low, heat will build up in the cartons causing fruit temperature to be higher than air temperature. Fruit can also sustain short periods (days) below 10° C without developing chilling injury and while this should be avoided, it is probably better to err on the side of colder rather than warmer. Temperature settings of 5-7° C have been quoted by suppliers.
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• Lower temperatures cause chilling injury, evident as pitting, decay and discolouration, and as higher ethylene production (faster ripening) when temperature is later raised to 15° C (Zong et al. 1995).
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• Higher temperatures cause ripening. Maturer fruit (slightly soft but still green) will rapidly begin to ripen if the temperature is too high, risking the entire batch, but maturity has less effect on postharvest life when fruit is stored at the correct temperature (Zong et al. 1995).
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Storage humidity: Store at 85 - 90% humidity. Fruit is quite resistant to water loss (Cantwell et al. 1996). Humidity is achieved by lining boxes with plastic which reduces movement of all gases, including water vapour. This causes problems with bitter melon in Australia because maturer fruit produce ethylene, risking the entire box when ventilation is low. Paper lining is thus preferable at the moment to allow ventilation, but plastic may become preferable with better cultivars. Ethylene production is highly cultivar dependent and can be very low (Zong et al. 1995), and it is likely that maturity levels in a box can be kept more homogeneous with hybrid varieties.

Shelf life: A life of 2-3 weeks is possible with good varieties stored under good conditions. Field heat, maturity at harvest and mode of transportation are all critical in determining shelf life (TK Lim 1998, pers. comm.). Common quality defects include ripening and yellowing, and scuffing of the peel (Zong et al. 1992).

Packaging: Pack 10 kg into a 13 kg banana box with wet paper between each layer, so that the box is not quite full, and ventilate to remove ethylene (Peter McLaughlin 1998, pers. comm.). Fruit wrapped individually in low density polyethylene film and stored at 5-7° C was still marketable after 21 days. The film delayed appearance of chilling injury as well as other symptoms of quality loss (Mohammed and Wickham 1993).

Biocontrol: Use of Trichoderma sp. will suppress growth of Sclerotium rolfsii on fruit during storage and transport (Mukherjee and Raghu 1997).

Quality assessment

Should have a fresh appearance, of uniform colour and free from visual defects. Must be firm without excessive seed development. Common postharvest defects include over maturity, seed development, softening and ripening with internal or external colour changes, scuffing of the peel and chilling injury (Cantwell et al. 1996).

Pests and diseases

Foilage pests and diseases tend to be not much of a problem, due to the toxic compounds in the plant (Robinson and Decker-Walters 1996). Control of ants is important, as they farm the larvae of some insects. Thrift, which can devastate a crop, can be controlled by 2-3 applications of Roger per season. Fungal infections can occur during prolonged wet periods, and can be controlled with Mankozeb (Peter McLaughlin 1998, pers. comm.). Dissipation of mancozeb from the fruit was investigated by Beevi et al. (1996) .

Fruit fly ( Strumetia cucurbitae ) is a problem in the US, combated by covering fruit with paper protective bags (Cantwell et al. 1996). Fruit fly does not appear to be a problem in Queensland (Peter McLaughlin 1998, pers. comm.). Double layer paper bags may be used against melon fly in Taiwan, and are applied when fruit measure 2-3 cm in length (Fang and Chang 1987).

Domestic market

The Australian market appears to prefer dark green shiny fruit (Peter McLaughlin 1998, pers. comm.). It is mostly supplied from the Northern Territory, with Southern states producing during the summer and autumn months. Development prospects were rated as high for both fresh and processed bitter melon (Vinning 1995). There is also a potential for fresh cut format.

Prices at Flemington Markets, Sydney fell to around $1.50/kg in 1998 for the southern producers, who supply from December to May (Figure 2). This followed years of prices in the $2.00 to $2.50/kg range (Peter McLaughlin 1998, pers. comm.). The price in Darwin averaged $1.84/kg in 1994/5 and $2.06/kg in 1995/6 (Northern Territory Department of Primary Industries and Fisheries 1996 ) and production increased substantially (Figure 1). Northern Territory producers were accustomed to receiving from $2.00 to $3.50/kg (Lim 1998) but this has also dropped. Melbourne is supplied by Victoria and the Northern Territory. During summer, bitter melon leaves are also available for $1.50 to $3.00/bunch retail, sourced from Victoria. Melbourne prices were much higher in 1995 (Chew and Morgan 1996).

Pickled bitter melon is imported from India, Malaysia and the Philippines. As these are low cost producers, it is unlikely that Australia will be able to compete on this market (Vinning 1995).

Export market

(click here for exchange rates).

Bitter melon will remain an important vegetable crop in South East Asia and may gain popularity with the release of lower bitterness cultivars (Reyes et al. 1994). Major markets include the Philippines, Malaysia, Hong Kong and Taiwan, but trade data is scanty Vinning 1995). Ethylene problems make bitter melon difficult to export (Peter McLaughlin 1998, pers. comm.).

Filipino production rose to 18 000 tons in 1992 (Lim 1998). Retail prices rose markedly during the 1980's (Vinning 1995). It is one of the ten most widely grown vegetables (Rasco and Castillo 1990).

Malay production rose to 19 000 tons in 1994 (Lim 1998).

Taiwanese production climbed to 35 000 tons in 1993 (Lim 1998). Taipei wholesale prices are falling (NT$28/kg in 1994) but volumes are increasing (8000 tons in 1994). Prices peak in March and April (Vinning 199).

Thai production was 17 749 tons in 1994 (Lim 1998).

Sri Lankan production was 19 266 tons in 1987 (Lim 1998).

Chinese use it for a range of medicinal purposes (see Yang and Walters 1992).

Indonesia imported 2 t from Taiwan in 1992, then none from 1993-5 (Taiwanese official trade statistics)

Indian preferences are for a small, dark green, very bitter type (Lamberts 199).

Exported to Europe mainly from Kenya, with London being the largest market (Huyskens et al. 1992). Prices were US$8/kg in 1984 (Chang et al. 1998).

References

Ab usaleha and O. P. Dutta (1994). Performance of bittergourd (Momordica charantia) under different training systems. Indian Journal of Agricultural Sciences 64 (7): 479-481.

Basu, P. S., Banerjee, S. and Susmita, Das. (1994). Hormonal regulation of flowering and fruit development: effects of dikegulac on flowering, fruit setting and development of Momordica charantia L. and Luffa acutangula Roxb. Indian Journal of Plant Physiology 37 (4): 282-285.

Beevi, S. N., Gokulapalan, C., Reghunath, P. and Visalakshi, A. (1996). Dissipation of mancozeb residues in bitter gourd (Momordica charantia L.) fruits. Pesticide Research Journal 8 (2): 199-201.

Brunt, A.A., Crabtree, K., Dallwitz, M.J., Gibbs, A.J., Watson, L. and Zurcher, E.J. (eds.) (1996 onwards). `Plant Viruses Online: Descriptions and Lists from the VIDE Database. Version: 16th January 1997.'

Cantwell, M., X. Nie, R. J. Zong and M. Yamaguchi (1996). Asian vegetables: Selected fruit and leafy types. Progress in new crops. Ed.: Janick, J. Arlington, VA, ASHS Press: 488-495.

Chang, M. K., Chapital, D. C., Conkerton, E. J., Wan, P. J., Vadhwa, O. P. and Spiers, J. M. (1998). Comparison of the fruit from four cultivars of Chinese melon (Momordica charantia L.). Tropical Science 38 (3): 128-133.

Chew, M . and Morgan, W. (1996). Melbourne retail Asian vegetable survey. Melbourne, Agriculture Victoria 143 pp.

Desai, U. T. and Musmade, A. M. (1998). Pumpkins, squashes and gourds. In: Handbook of vegetable science and technology: production, composition, storage and processing. (Ed; Salunkhe, D. K. and Kadam, S. S.). New York, Marcel Dekker 273-298.

Deshpande, A. A., Venkatasubbaiah K., Bankapur V. M. and Nalawadi U. G. (1979). Studies on floral biology of bitter gourd (Momordica charantia L.). Mysore Journal of Agricultural Sciences 13 (2): 156-159.

Devi, J. R. and J. A. Selvaraj (1994). Effect of pre-sowing treatment on germination and vigour in bitter gourd (Momordica charantia L.) cv. Co.1. Seed Research 1996 (22: 1): 64-65.

Fang, M. N. and C. P. Chang (1987). Population changes, damage of melon fly in the bitter gourd garden and control with paperbag covering method. [Chinese]. Plant Protection Bulletin, Taiwan 29 (1): 45-51.

Huyskens, S., Mendlinger, S., Benzioni, A. and Ventura, M. (1992). Optimization of agrotechniques for cultivating Momordica charantia (karela). Journal of Horticultural Science 67 (2): 259-264.

Kabir, J., Chatterjee, R., Biswas, B. and Mitra, S. K. (1989). Chemical alteration of sex-expression in Momordica charantia . Progressive Horticulture 21 : 1-2.

Kuang, B. F., Xiao, C. H., Huang, Z. X. and Zheng, S. Q. (1997). Selection and breeding of early ripening variety Hengza Bitter Gourd No. 1. [Chinese]. Journal of Hunan Agricultural University 23 (4): 331-335.

Lamberts, M. (1992). Production trends for specialty Asian vegetables in Dade County, Florida. Acta Horticulturae 318 : 79-85.

Larkcom, J. (1991). Oriental vegetables: the complete guide for garden and kitchen. London, John Murray 232 pp.

Lee, B. (1995). Audit of the Australian Asian vegetables industry. RIRDC Research Paper No. 95/13. Canberra, Rural Industries Research and Development Corporation 97 pp.

Liao, C. T. and C. H. Lin (1994). Effect of flooding stress on photosynthetic activities of Momordica charantia. Plant Physiology & Biochemistry 32 (4): 479-485.

Liao, C. T. and C. H. Lin (1996). Photosynthetic responses of grafted bitter melon seedlings to flood stress. Environmental & Experimental Botany 36 (2): 167-172.

Lim, T. K . (1998). Loofahs, gourds, melons and snake beans. The New Rural Industries. Ed.: K. W. Hyde. Canberra, Rural Industries Research and Development Corporation : 212-218.

Lin, Y. S., Hwang, C. H. and Soong, S. C. (1998). Resistance of bitter gourd-loofah grafts to Fusarium oxysporum f.sp. momordicae and their yield. [Chinese]. Chih Wu Pao Hu Hsueh Hui Hui K'An 40 (2): 121-132.

Mohammed, M. and L. D. Wickham (1993). Extension of bitter gourd (Momordica charantia L.) storage life through the use of reduced temperature and polyethylene wraps. Journal of Food Quality 16 (5): 371-382.

Mukherjee, P. K. and K. Raghu (1997). Trichoderma sp. as a microbial suppressive agent of Sclerotium rolfsii on vegetables. World Journal of Microbiology & Biotechnology 13 (5): 497-499.

Nguyen, V. Q. (1992). Growing Asian vegetables. Agfact, NSW Agriculture H8.1.37.

Northern Territory Department of Primary Industries and Fisheries (1996). PrimeStats. Rural and fishing industries in the NT 1995-96.

Rasco, A. O. and P. S. Castillo (1990). Flowering patterns and vine pruning effects in bittergourd (Momordica charantia L.) varieties 'Sta. Rita' and 'Makiling'. Philippine Agriculturist 73 : 3-4.

Reyes, M. E. C., Gildemacher, B. H. and Jansen, G. J. (1994). Momordica L. In: Plant Resources of South-East Asia: Vegetables. (Ed.: Siemonsma, J. S. and K. Piluek). Wageningen, The Netherlands, Pudoc Scientific Publishers 206-210.

Robinson, R. W. and Decker-Walters, D. S. (1996). Cucurbits. New York, CAB International 226 pp.

Singh, D. K. (1991). Effect of temperature on seed germinability of Momordica charantia L. cultivars. New Agriculturist 2 (1): 23-26.

Tan, X. P., Ueda, Y., Imahori, Y. and Chachin, K. (1999). Changes in pigments in pulp and aril of Balsam pear (Momordica charantia L.) fruit during development and storage [Japanese]. Journal of the Japanese Society for Horticultural Science 68 (3): 683-688.

Vinning, G. (1995). Market Compendium of Asian Vegetables. RIRDC Research Paper No. 95/12. Canberra, Rural Industries Research and Development Corporation 386 pp.

Wang, Q. M. and Zeng, G. W. (1996). Effects of gibberellic acid and Cycocel on sex expression of Momordica charantia . [Chinese]. Journal of Zhejiang Agricultural University 22 (5): 541-546.

Waters, C. T., Morgan, W. C. and McGeary, D. J. (1992). How to identify, grow and use oriental vegetables. Melbourne, Agmedia 128 pp.

Yang, S. L. and Walters, T. W. (1992). Ethnobotany and the economic role of the Cucurbitaceae of China. Economic Botany 46 : 349-367.

Zong, R. J., Cantwell, M., Morris, L. and Rubatzky, V. (1992). Postharvest studies on four fruit-type Chinese vegetables. Acta Horticulturae 318 : 345-354.

Zong, R. J., Morris, L. and M. Cantwell (1995). Postharvest physiology and quality of bitter melon (Momordica charantia L). Postharvest Biology & Technology 6 (1-2): 65-72.