 country’s production. In spite of this high domestic production, Brazil does not produce enough to meet its own needs.
The major threat to the farmer’s plants, causing losses of up to a 100%, is the golden mosaic virus, which is transmitted by the whitefly Bemisia tabaci in a persistent and circulative manner. That means that once the insect gets the virus it will transmit the disease to the crop its whole life. Only one to three whiteflies per plant in a field are enough to infect all plants. With the spread of the disease throughout Latin America, hundreds of thousands of hectares were either abandoned or could not be cultivated without heavy use of insecticides with limited efficacy. This kind of control has resulted in the development of insecticide resistance, adverse environmental effects, and health hazards to field workers throughout the region. In Brazil alone, annual losses vary between 90,000 and 280,000 tons. That would be enough to feed up to 18 Million adults in the country. There are 180 to 200 thousand hectares that are not suitable for cultivation.
The long way to develop the virus-resistant beans.
The search for bean varieties resistant to the golden mosaic virus (BGMV) begun in the 70’s. It was hoped to obtain plants immune to this disease through conventional breeding methods. Thousands of lines were evaluated for natural resistance or immunity to the disease, but the extensive screening of common bean germplasm found no genotypes with satisfactory level of resistance to BGMV. With the advent of genetic engineering new strategies have been employed in addition to conventional breeding. Finally a successful strategy was found. The strategy was the use of RNA interference (RNAi) that mimics natural silencing mechanisms. Infected plants naturally produce silencing mechanisms that interfere with the virus in the bean cells, unfortunately not effective enough against this disease. The new “vaccinated” variety produces small fragments of RNA that will activate its defense mechanism to silence the v