The International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) has achieved another global first in agricultural research. Field trials have been launched for genetically modified pigeonpea that is resistant to the insect pest, the legume pod borer or Helicoverpa armigera.

The pod borer caused 50% of pest-induced losses for all crops in India during 1997/98 cropping season. It is estimated that the crop losses cost the country US$ 475 million, despite the use of insecticides worth $ 211 million.

According to ICRISAT Director General Dr William Dar, the successful genetic modification of pigeonpea, enabling the crop to resist Helicoverpa attack, signifies a major scientific breakthrough. “This is an important step that addresses the specific needs of the resource-poor farmers of the semi-arid tropics through an effective biotechnological intervention. Pigeonpea is an important crop that supports the livelihoods of the farm families living in these rainfed areas.”

A group of ICRISAT scientists led by Dr KK Sharma, at the Genetic Transformation Laboratory developed the technology for genetically transforming pigeonpea, and introduced the synthetic Bt Cry1Ab gene that offers resistance against lepidopteran insect pests like Helicoverpa armigera. The strategy included transferring the Cry1Ab gene and the soybean trypsin inhibitor through Agrobacterium tumefaciens-mediated genetic transformation. The Cry1Ab gene is extracted from the bacteria Bacillus thuringiensis.

After extensive molecular characterization of the transgenics and insect bioassays in the glasshouse, permission to carry out a field trial under controlled conditions was obtained from the Department of Biotechnology, Government of India.

The group's work provides a significant breakthrough in the fight against Helicoverpa armigera. The control for the pest is currently based on heavy insecticide use. However, Helicoverpa populations are seen to develop resistance to insecticides in several countries, thereby making insecticide application ineffective. Intensification of agriculture has aggravated the pest problem, and farmers are resorting to frequent use of more toxic insecticides.

Researchers have recognized that for intractable pest problems such as Helicoverpa no single tactic will suffice in itself to contain this pest. It has long been recognized that host plant resistance is the most effective management option.

According to Dr HC Sharma an Entomologist at ICRISAT, more than 14,000 pigeonpea accessions were screened for resistance to Helicoverpa armigera by the Institute and collaborating national agricultural research centers. However, these genotypes have not been used widely. The level of tolerance provided in these genotypes is low, and some of the lines are susceptible to the major fungal diseases.

Increased levels of plant resistance will significantly contribute to our efforts to manage this pest. Hence, development of genetically modified pigeonpea cultivars with resistance to Helicoverpa armigera will provide an effective complementary approach to control the pod borers. Resistant or less susceptible cultivars will also provide an equitable, environmentally sound, and sustainable pest management tool.

After this contained field trial, the transgenic pigeonpea crop will go through a second season of contained trial at the ICRISAT campus to generate more data on biosafety. Once successful, ICRISAT will collaborate with its national agricultural research partners to implement open field trials.

According to Dr Dar, ICRISAT's work on transgenic pigeonpea is a continuation of the process to biotechnologically improve the Institute's mandate crops. In 2002, ICRISAT announced the contained field trials of world's first transgenic groundnuts for resistance to the Indian peanut clump virus developed by Dr KK Sharma's group. After the success in the first season the transgenic groundnut trials are currently being repeated for the confirmation of the positive results.