Brazilian virus-resistant beans

posted in: Science | 11

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?

Feijoada

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.

Golden Mosaic Virus symptoms

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 viral rep gene, which leads to the synthesis of an essential protein for the replication of the virus. Consequently, without this protein, replication of the virus is compromised and the plants become resistant to the disease.

The virus-resistant GE bean plants are on the top. The original susceptible bean is on the bottom. Look at the difference a single transgene makes!

Safety and the way from research to seed market

Safety precautions for modern agricultural biotechnologies start at the very beginning of the research at the lab, and continue through the different phases of the development. Only when detailed scientific assessments determine it to be innocuous is the new development considered for commercial use. Prior to the submission for the commercial release, a comparison between the virus-resistant beans and its parental conventional/non-modified variety in all the ecosystems where the beans are cultivated in Brazil had been conducted by a consortium of 10 research centers over several years. Results showed that the transgenic beans do not differ in the environmental impact compared to its non-engineered parent beans. Additionally, the transgenic beans offer the advantage of reducing insecticides that have being used to kill the whiteflies that transmit the golden mosaic virus during the past decades. The new virus resistant beans are also considered as safe for consumption as the currently cultivated beans. On that ground, CTNBio, the multidisciplinary commission responsible for making science-based, technical assessments for the safety of genetically engineered products approved the beans for commercial release.

Approvals by CTNBio may be followed by an examination from the National Biosafety Council (CNBS) on the socio-economic convenience and opportunities of national interest.

There are in any case, further steps to be pursued on the way to market the seeds, such as the incorporation of the trait into cultivars suited to the different local conditions, the registration of the variety and production of the seeds. The following step is the law inspired by the UPOV Convention (International Union for the Protection of New Varieties of Plants), legislation that came with the intend of protecting the rights of developers of plant varieties, no matter if obtained through conventional breeding or modern biotechnology, while encouraging investment in research and development. According to the legislation, any plant variety with a minimum of clearly new distinguishable characteristics goes through a process to be registered.  After the approval of registration the new variety enters the fields of seed production. Farmers will probably have to wait another 2 to 3 years to see the virus-resistant beans.

For more information

Do you want to know more about the virus resistant beans? See for example: Kenny Bonfim et al; RNAi-Mediated Resistance to Bean golden mosaic virus in Genetically Engineered Common Bean (Phaseolus vulgaris); MPMI Vol. 20, No. 6, 2007 (Link) and Aragão and Faria, First transgenic geminivirus-resistant plant in the field, Nature Biotechnology Vol. 27, 1086-1088, 2009 . (link)

Do you want to know more about the Brazilian legislation on biosafety? See: CTNBio webpage (http://www.ctnbio.gov.br/index.php/content/view/12840.html )

I am thankful to Dr. Francisco Aragão for reviewing the text.

Editor’s Note: You will find these fantastic virus-resistant beans added to the rotating header images on our blog!

Follow Lucia de Souza:

Lúcia de Souza, Ph.D. is a biologist with extensive experience in teaching and has been actively involved in biosafety for several years. Since 2005, she is the vice-president of the Brazilian National Biosafety Association (ANBio). She is also the deputy executive secretary of the Public Research and Regulation Initiative (PRRI).

Latest posts from