The development of postharvest handling technology for selected tropical tree fruits

• Thailand Institute of Scientific and Technological Research, Thailand
• Chiang Mai University, Thailand
• Horticultural Research Institute, Thailand
• Kasetsart University, Thailand

Under traditional handling systems in the ASEAN region, postharvest loss of fruit and vegetables between the field and retail markets may be 20-40%. ACIAR Project 8356 investigated such losses: it primarily concerned mangoes, but also included initial studies on several other tropical fruits, and the present project has resulted from direct requests from Thai institutions for assistance to expand on its results.

In Thailand, fruit and vegetable production comprises about 15% of the agricultural GDP, with exports increasing significantly since 1983. Six of the fruit crops studied in this project - mango, lychee, rambutan, longan, mangosteen and durian - currently account for about 62% of Thailand's horticultural export earnings. All are important throughout South-East Asia, with lychee and longan also being significant in China, as are mango and lychee in Australia. (The seventh crop, coconut, is important in ASEAN and South Pacific countries.)

For these six main crops, the project will establish commercially applicable harvesting indices that can be used to regulate market quality and ensure maximum storage potential. It will further refine controlled-atmosphere storage recommendations for mango and define optimum cool-storage and CA storage regimes for the other five crops.

A wide range of pathogens cause side lesion and stem-end rots on all six fruits and research teams will investigate the precise identity, relative importance and infection mechanisms of the organisms, and gather detailed information on the effects of environment and fruit maturity on disease development as well as establishing disease-control measures. Results will form the basis of permanent reference culture collections and plant-disease herbaria in Thailand, to allow future monitoring of changes in pathogen importance and fungicide tolerance.

While seeking alternative technology to sulfur dioxide fumigation for postharvest disease control in lychee, longan, rambutan, mangosteen and durian, the scientists will also develop the present fumigation technology for use with the first three crops (including devising measures to limit loss of skin colour in lychee and rambutan in storage) and for the control of external browning in trimmed green coconuts.

Additional work on mangoes will seek better commercial control measures against stem-end rot (Dothiorella spp., Lasiodiplodia theobromae), as current technology is only about 80% effective, and control measures against alternaria rot (Alternaria alternata), a disease now known to be a significant problem in long-term storage. Sapburn, a surface disorder of the fruit, causes significant loss in quality during commercial harvesting in Australia and recent work has indicated that a specific oil fraction in the sap is responsible. The present project will examine the susceptibility of Thai varieties, and try to identify the specific chemicals involved and to develop handling practices to eliminate sapburn.

The research will initially investigate specific aspects for each crop and then combine the findings into composite postharvest handling recommendations for testing on a semi-commercial or commercial scale. Although individual institutions will conduct specific subprojects, particular combinations of them will conduct replicated studies, complementary studies and joint investigations. Since Thailand and Australia have complementary cropping seasons the scientists have the benefit of two crops per year. Research activities can thus be accelerated by moving the research team from one country to the other every six months.

The project will significantly improve the level of research facilities and expertise in Thailand, while establishment of culture collections and disease herbaria should enhance pathogen identification and disease management. Application of results should significantly reduce postharvest wastage and, in the medium to long term, greatly increase Thailand's tropical fruit exports.

Advances in tropical fruit production will also have relevance for Australia, with considerable potential for exports to Southeast Asian neighbours. Complementary cropping seasons will enable Thailand and Australia to supply the markets year-round, rather than the present situation of seasonal abundance followed by no supplies for the rest of the year.