Breeding for Resistance to aflatoxin Contamination in Groundnut
H D Upadhyaya, F Waliyar and S N Nigam
Groundnut (Arachis hypogaea L.) is an annual legume grown primarily for high quality edible oil (36 to 54 % on dry matter basis) and easily digestible protein (12 to 36 %) in its seeds. It is cultivated in 107 countries in tropical, sub-tropical and warm temperate regions of the world. The crop is grown on about 25.54 million ha world wide with an estimated total production of 35.09 million t in shell and an average productivity of 1.37 t ha-1 (Food and Agriculture Organization, 2001). In several countries of Asia, which accounts for 57.44% of world area and 66.69% of production and Africa, which accounts for 37.86% area and 24.54% of production, groundnut is an important cash crop. Over two-thirds of the global groundnut production occurs in seasonally rainfed regions where drought is a potential constraints for crop production. Beside low productivity which ranges from 0.7 to 0.8 t ha-1 in these regions, drought particularly the one which occurs at the end of season, predisposes crop with invasion by the aflatoxin-producing fungus Aspergillus flavus.
Groundnut is an important oilseed crop cultivated in 96 countries worldwide on 23.8 million ha with an annual production of 30.97 million t. It is an important cash crop in several countries of Asia, which accounts for 57.13% of world area and Africa, which accounts for 37.24% area.
Aflatoxin contamination of groundnut is a widespread serious problem in most groundnut-producing countries where the crop is grown under rainfed conditions. The aflatoxin contamination does not affect crop productivity but it makes produce unfit for consumption as toxins are injurious to health. The marketability of contaminated produce, particularly in international trade is diminished to nil due to stringent standards of permissible limits on aflatoxin contamination set by the importing countries. The aflatoxin-producing fungus, Aspergillus flavus and A. parasiticus, can invade groundnut seed in the field before harvest, during postharvest drying and curing, and in storage and transportation. The semi-arid tropical environment is conducive to preharvest contamination when the crop experiences drought before harvest, whereas in the wet and humid areas, postharvest contamination is more prevalent. Research on aflatoxin contamination is not regularly carried out by all the groundnut-producing countries because of the complex nature of the problem and lack of qualified personnel and appropriate infrastructure. Nevertheless, some countries have been regularly monitoring groundnut and its products for aflatoxin at different stages (farm, markets, and storage). Aflatoxin contamination can be minimized by adopting certain cultural, produce handling, and storage practices. However, these practices are not widely adopted particularly by the small farmers in the developing countries, which contribute about 60% to the world groundnut production.
One of the possible means of reducing aflatoxin contamination of groundnut is the use of cultivars resistant to seed invasion by aflatoxin-producing fungi or to aflatoxin production. These cultivars will be of great value to the farmers in both developed and developing countries as there is no cost input. Therefore, breeding for resistance to A. flavus and A. parasiticus and/or aflatoxin production can play a significant role in preventing aflatoxin contamination in groundnut and consequently associated economic losses and health hazards.
The alleviation of aflatoxin contamination through genetic manipulation has been attempted since mid-1970s. We have achieved significant progress; however, these efforts have not resulted in complete eradication of aflatoxin contamination. In this paper we have briefly discussed the status of research on finding a genetic solution to this problem.
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