Project Number: 3607-22000-011-00
Project Type: Appropriated

Start Date: Jun 19, 2007
End Date: Jun 18, 2012

Objective:
Objective 1: Develop corn and soybean virus disease control strategies. ¿ Sub-objective 1.A. Characterize the nature of host resistance to virus disease. ¿ Sub-objective 1.B. Identify, map, and clone virus-resistance genes. ¿ Sub-objective 1.C. Determine the effect of combining quantitative virus resistance with insect resistance on virus disease severity. ¿ Sub-objective 1.D. Characterize insect vector/virus relationships. Objective 2: Identify and characterize emerging virus diseases in corn and soybeans. Objective 3: Develop virus-based gene vectors in corn. Soybeans and corn are the two highest value crops grown in the U.S. Although research from this laboratory and others has led to significant improvements in their management, virus diseases continue to be annual threats. Furthermore, history has shown that unanticipated, and often unknown, new virus disease problems can rapidly emerge at any time. In soybeans, the threat of virus diseases has increased even more following the introduction of the soybean aphid into the U.S. in 1999. This is the first soybean-colonizing aphid in the U.S., and the consequences for future virus disease problems in soybeans are unknown. A long-term objective of this program is to reduce corn and soybean losses attributable to virus diseases. Our strategy to do so is to identify corn and soybean viruses when they arise and to characterize their biology and epidemiology (Objective 2), and to then use this information develop practical, effective methods and strategies for minimizing crop losses (Objective 1). Our final objective (Objective 3) is to use our knowledge and expertise in maize virology to develop new tools for forward and reverse genetic analysis of maize gene function. We will develop gene silencing and expression vectors based on selected maize viruses, and use these vectors immediately to characterize the functions of candidate maize genes thought to be important for virus infection and/or resistance. Because reliable vectors are lacking for monocotyledenous plants such as corn, vectors developed under this objective would be of benefit both to corn geneticists and to those seeking to use corn for the production of non-endogenous materials.

Approach:
Our overall approach is to: 1) identify existing and emerging viruses; 2) understand their biology; and 3) develop effective disease control strategies. Known viruses will be identified using existing diagnostics. For previously uncharacterized viruses, we will culture them in healthy plants using mechanical or arthropod transmission, determine their characteristics, and develop diagnostic assays. This knowledge will be used to formulate disease control strategies, although, usually, the most effective and economic control strategy is to use virus-resistant crop varieties and cultivars. Therefore, a primary focus of this project is to identify, characterize, and map virus resistance in maize and soybean germplasm. To develop an understanding of how resistance genes work, they will be isolated and characterized, and their role in the molecular and biochemical changes associated with virus resistance will be examined. Also, factors affecting virus transmission by arthropod vectors will be characterized so that alternative disease control methods can be developed. Maize virus-based gene expression and silencing vectors will be developed to facilitate functional analysis of plant resistance genes using forward and reverse genetics. Such vectors should have broad impact as few are available for cereals. The impact of this research will be to advance our knowledge of virus diseases of corn and soybeans and provide vital information for the development of control strategies to reduce disease losses.