2007 Annual Report 1a.Objectives (from AD-416) The objective of this collaboration is to determine the biophysical and/or biochemical basis of resistance to whiteflies in cassava and to develop chemical and genetic markers for use in genetic improvement of cassava and other crops. 1b.Approach (from AD-416) CIAT has identified cassava gentotypes with high and stable levels of resistance to whiteflies, a major pest in tropical, subtropical, and temperate agricultural systems including a wide range of vegetable, fruit and legumes grown in Arizona, California, Florida and Texas. Such plant resistance is sufficiently rare to be of interest to breeders of horticultural crops. The objective of this collaboration is to determine the biophysical and/or biochemical basis of resistance in cassava and to develop chemical and genetic markers for use in cassava improvement and potentially in improvement of other crops. Initial work at CIAT will compare whitefly performance, feeding behavior, and feeding damage on susceptible and resistant cassava genotypes. CIAT will provide cassava germplasm to ARS for evaluation with the whitefly Bemisia tabaci biotype B at Ft. Pierce. 3.Progress Report This report on Project Number 6618-22000-030-02S, Understanding the Mechanism of Plant Resistance to Whiteflies, serves to document research conducted under a Specific Cooperative Agreement 58-6618-3-0121F between ARS and the International Center for Tropical Agriculture, Cali, Colombia. Additional details of research can be found in the report for the parent project 6618-22000-030-00D, Development of Biological Control and IPM Technology for Exotic Insect Pests. A selection of cassava genotypes described as highly resistant and susceptible to species of whiteflies common in South America were imported via tissue culture to USHLR. These were successfully transplanted and normal plants were grown at USHRL. The first trials with the silverleaf whitefly, Bemisia tabaci, were carried out during FY04. Initial results show a different response by B. tabaci to the cassava genotypes indicating an interaction between whitefly species and modality of insect resistance. Plants lost to hurricanes during FY05 were re-generated. Work at CIAT identified a highly resistant variety (MEcu 72) and 9 varieties with moderate resistance. Through SDS-PAGE and immunodetection, polymorphic protein bands unique to a resistant variety and absent from a susceptible check were identified. Methods will be optimized to study the involvement of these proteins in resistance to whitefly with the ultimate goal of identification and sequencing. Regenerated plants are now being screened to confirm resistance rankings to B. tabaci. Work at CIAT isolated high quality, total RNA of Mecu-72 and CMC40. The RNA concentration was measured using GENios™ specterfluorometer (TECAN). Poly A+ mRNA was isolated from 100 µg of total RNA from each pool to synthesize cDNA. Microarray expression profiling will be used to identify putative early-response, regulatory and/or signaling genes, and to test the function of selected candidate genes using real time PCR technology. Progress was monitored through email and telephone discussions of project plans, and reviews of submitted progress reports.