Harish Damodaran

Patancheru, AP, Oct. 14

YET another genetically-modified (GM) crop is in the offing, and this time for controlling aflatoxin levels in groundnut, the country's largest produced oilseed.

Scientists at the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) here have developed groundnut varieties incorporating chitinase genes from rice that are resistant to Aspergillus flavus, the aflatoxin-producing fungal pathogen.

"We have introduced the rice chitinase genes in popular local varieties such as TMV-2 and JL-24. The transformed varieties have undergone the T-2 stage (corresponding to the third generation) of glasshouse laboratory trials. We will now seek approval from the Department of Biotechnology's Review Committee on Genetic Manipulation (RCGM) for conducting contained greenhouse field trials from the next kharif season," Dr Farid Waliyar, ICRISAT's Global Theme Leader for Biotechnology, told Business Line.

He said parallel work was going on to similarly incorporate glucanase genes from peas (matar) in groundnut. These `foreign' genes (drawn from plant species/genus outside that of groundnut) basically code for enzymes that degrade the cell walls of the fungi, leading to their incapacitation. "We expect the new aflatoxin-resistant GM groundnuts to hit the market within the next five years," Dr Waliyar said.

Aflatoxin contamination in groundnut is seen as both a major health and economic problem. Besides being a cancer-causing toxin (particularly in the liver), aflatoxin is also known to suppress the human body's natural immune response to invasion by foreign substances. One particular metabolite, called aflatoxin M1, is found in milk as well, which originates from the contaminated groundnut cattlefeed (obtained after crushing the shelled seed and separating the oil). The problem is less serious in groundnut oil, as the refined oil is devoid of protein matter.

While the presence of aflatoxin has not deterred domestic sales — thanks to lack of awareness among farmers, oil millers and consumers here — the issue has, however, acquired importance on the export front.

During 2003-04, the country exported 1.77 lakh tonnes (lt) of shelled groundnuts (kernel), valued at Rs 544 crore. In addition, export of groundnut extractions (meal) amounted to 1.30 lt (about Rs 100 crore).

India is currently the world's No. 1 exporter of groundnut meal and second largest in kernels, after China. Exporters perceive aflatoxin contamination as a significant non-tariff barrier, especially in the European Union, which does not permit import of groundnut with aflatoxin content above 6 micrograms per kg (parts per billion). As against this, it is not usual for groundnut grown in many parts of the country to have aflatoxin levels of 50-100 parts per billion.

According to Dr Waliyar, aflatoxin levels in groundnut are particularly high in the semi-arid areas of Andhra Pradesh, Karnataka, Maharashtra and Gujarat, which receive erratic rainfall. Aspergillus infection occurs mainly when the plant experiences severe moisture stress 75-80 days after sowing, by which time the pod and kernel formation has already taken place. The fungal spores (seeds) present in the soil and air are always looking for water and a host medium to germinate. And since the soil roots and other vegetative portions are rendered dry, the spores go to the more fleshy nuts, where they draw moisture from the pods and the seeds.

Infestation is also possible at the post-crop season stage, if the pods suffer mechanical damage at the time of harvest or the groundnut is stored under humid environs. These create conditions for the spores to make further ingress and `colonise' the whole kernel and subsequently produce the toxin.

`A practical, affordable option for farmers'

CONTROLLING Aspergillus flavus infestation in groundnut is relatively easy when the crop is grown under assured irrigation conditions. The farmer has to mainly ensure that the crop gets adequate water and does not face end-of-season drought conditions.

The moisture retention capacity of the soil can further be enhanced with liberal application of organic manure or through technologies such as plastic mulching. The latter involves using a planter to lay a thin extruded polyethylene film to cover the field after seed and nutrient application.

But these are options beyond the reach of farmers in the country's semi-arid groundnut growing tracts. Compounding the problem is the very narrow genetic base of aflatoxin-resistant varieties within the groundnut species or genus, which places limitations on conventional breeding methods.

"We see genetically modified (GM) groundnut as the most practical and affordable recourse for resource-poor farmers," said Dr Kiran K. Sharma, Principal Scientist at ICRISAT's Genetic Transformation Laboratory.

And here, it helps that groundnut, like all legumes, is a self-pollinating crop that farmers can themselves multiply and use over generations. In fact, it is precisely because groundnut is a closed flower that the private seed companies have preferred to work in crops such as cotton or bajra, which are naturally amenable to hybridisation and offer in-built protection of intellectual property. "When it comes to groundnut or other legumes, the responsibility of making available the fruits of modern biotechnology lies on public sector institutions like ICRISAT. We don't expect the private sector to develop GM groundnut varieties," Dr Sharma added.

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