A homemade, high potential benefit-driven development from the public sector
Beans are an important food item, mostly in the developing world. Unfortunately, the golden mosaic virus infection is a serious constraint causing severe grain losses in Brazil and South America. The National Technical Commission on Biosafety (CTNBio) approved the genetically modified golden mosaic virus-resistant beans developed by the Brazilian public Agricultural Research Corporation (Embrapa) linked to the Ministry of Agriculture, Livestock and Supply. This work is an example of a public-sector effort to develop useful traits, such as resistance to a devastating disease, in an “orphan crop” cultivated by poor farmers throughout Latin America. It is a milestone as it is the first fully “publicly funded homemade” recombinant biotechnology crop improvement strategy that has reached this stage in a developing country.
Why are the virus-resistant beans so important?
Beans are highly nutritious and one of the most important legume consumed by over 500 million people in Latin America and Africa. In Brazil it is regularly an indispensable item of the everyday diet, often combined with rice and eaten by all social classes in all parts of the nation. They are found in a great variety of types with different sizes, colors and tastes consumed throughout the country. Perhaps, the most typical Brazilian dish is the ‘feijoada”, a black beans stew. The local consumption is around 16 kg per person every year. Given its high protein (15 to 33%) content besides B vitamins and minerals as iron, calcium and phosphorus, beans provide a high nutritional value meal. Moreover, beans are the major source of protein for the economically disadvantaged.
Currently Brazil is the largest producer, responsible for approximately 20% of the global production. It is estimated that the domestic production should reach 3.8 million tons in the 2010/2011 period. This is mostly an achievement of small farmers (less than 100 hectares) responsible for approximately 70% of the 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