The International Consortium on Agricultural Biotechnology Research (ICABR)
Value of Engineered Virus Resistance in Crop Plants and Technology Cooperation with Developing Countries
S. Flasinski1, V. M. Aquino2; R. A. Hautea3, W. K. Kaniewski1, N. D. Lam4, C. A. Ong5, V. Pillai5, K. Romyanon6
1Monsanto, 700 Chesterfield Parkway North, St Louis, MO 63198, USA; 2Institute of Plant Breeding, University of the Philippines at Los Banos, College, Laguna 4031, Philippines, 3ISAAA-SEAsia Center, c/o IRRI, MCPO Box 3127, 1271 Makati City, Philippines, 4National Center of Natural Science & Technology, Institute of Biotechnology, Hoang Quoc Viet, Caugiay, Hanoi, Vietnam; 5Malaysian Agricultural Research and Development Institute, Strategic, Environment and Natural Resources Research Center, MARDI, G.P.O. Box 12301, 50774 Kuala Lumpur, Malaysia, 6Plant Genetic Engineering Unit, Kasetsart University Kamphaengsaen, Nakhon Pathom 73140, Thailand
Plant viruses often cause considerable crop damage and significantly reduce yields in the absence of effective protection treatments. In cultivated crop plants the decrease in yield and crop value caused by virus infection is estimated at 60 billion US dollars per year. Virus infected crops are always of inferior quality, which reduces their market value. Modern biotechnology has significant potential to increase agricultural productivity to meet the demand for food from an increasing world population. Transformation of plants with viral genes has been proven in many cases to produce resistance to the virus from which the genes were derived. The development of transformation techniques broadens the possibility of using engineered virus resistance in plant breeding. There are many destructive virus diseases of crop plants worldwide, and biotechnology may be the fastest and most efficient way to produce resistant cultivars. From the original discovery of coat protein-mediated resistance in 1986 to the introduction in 1995 of squash and papaya resistant to different viruses, this technology has finally reached the market-place. Transgenic virus resistance, like genetic resistance, is of great value for modern agriculture and can create even greater savings for subsistence farmers, who cannot afford other measures of crop protection. Other than transgenic solutions, only breeding for virus resistance and vector resistance offer long term solutions to a virus disease problem; however, this process is lengthy and the resistance genes are not always available in the desired species. Genetic engineering offers an alternative in crops where no effective resistance gene(s) has been identified, or as a way of creating durable multiple resistance mechanisms by combining natural and transgenic resistance.
To obtain virus resistant transgenic plants, a strong constitutive promoter is needed to drive the gene, regardless of whether resistance is conferred by protein or by transgene RNA. Line (event) selection after transformation is critical for the development of resistant crop plants. Low accumulation of virus, together with the absence of virus symptoms and presence of a majority of non-infected individuals within a plant population, are good indications of a high resistance phenotype. The benefits of transgenic virus resistance include increased yield, reduced pesticide use to control the vectors transmitting viruses, and improved crop and food quality. In addition, transgenic virus resistance can eliminate or reduce the need for alternative measures of virus control, which may be less acceptable and more difficult to apply in developing countries.
The example of papaya ringspot virus (PRSV) was chosen to describe cooperative effort between the International Service for the Acquisition of Agri-biotech Application (ISAAA), Monsanto and developing countries in generation of resistant papaya. Papaya suffers from several diseases and pests, the most widespread and destructive of which is PRSV. The virus has significantly reduced papaya production in the SE-Asia region, causing substantial losses of income to farmers, a relative scarcity of the fruit in the market, and higher costs to consumers. Field resistance of transformed papaya to PRSV was demonstrated in Hawaii; however, commercial lines did not confer resistance to Asian isolates of PRSV. Transgenic papaya expressing the CP or replicase genes may be the optimal solution since no genetic resistance to PRSV has been identified. To address the problem of PRSV impact on Asian papaya production the Papaya Biotechnology Network was formed and is sponsored by five Southeast Asian (SE-Asian) countries (Malaysia, Thailand, Philippines, Vietnam and Indonesia) and by ISAAA with technical and financial support from Monsanto. A comprehensive plan was developed for genetic enhancement of papaya and technology cooperation with SE-Asia. The purpose of the papaya project is to accelerate the development and safe deployment of PRSV resistant local papaya cultivars, thereby benefiting small-scale farmers in SE-Asia. The project will allow SE-Asian countries to incorporate PRSV resistance into the most important local cultivars. As network members, participating national research institutes and Monsanto work individually and collectively to address the critical aspects of product development, effective biosafety and food safety regulations, product dissemination, and product acceptance by growers, consumers and the general public. Monsanto has chosen to participate in the Network and in the development of papaya resistant to PRSV because the company is committed to sharing, that is, bringing the knowledge and advantages of all forms of modern agriculture to benefit resource-poor farmers in the developing world to help improve food security and protect the environment. Private companies have a role to play in projects such as this one, that can bring the value and benefits of biotechnology to farmers and consumers, particularly in developing countries.
Scientists from respective Network laboratories produced three plant expression vectors containing genes from PRSV isolates from Thailand, Vietnam, Philippines and Malaysia during their research internships at Monsanto. PRSV sequence diversity in SE-Asia is much higher than in other locations. This justifies very well the use of genes from local virus isolates for the production of resistant transgenic papaya. Currently the vectors are being used in transformation of papaya somatic embryos as the first step in generation of transgenic papaya plants. Transgenic R0 plantlets are being produced and will be analyzed for the presence of transformation marker gene. Resistance tests will be done initially on segregating R1 progeny and confirmed on the homozygous R2 population. The line selection criteria will be based on virus resistance, the presence of an intact copy of transgene without any unnecessary sequences, proper R1 and R2 segregation, preservation of agronomic characteristics, and yield. Prior to commercialization, extensive field testing and regulatory approvals are required to address agronomic performance, preservation of cultivar characteristics, and food/environmental safety. If successful, the technology would improve the yield and quality of papaya fruit in SE-Asia.