2012 Annual Report 1a.Objectives (from AD-416): Evaluate exotic melon germplasm from India for potential new sources of resistance to CYSDV; Characterize host plant resistance to CYSDV in PI 313970 and TGR-1551, and select and introgress resistance to western U.S. shipping type background adapted to the desert southwest U.S.; Evaluate virus content in PI 313970, TGR-1551 and lines derived from these sources to determine ability of lines to suppress CYSDV accumulation; and develop antiserum for field diagnosis of CYSDV using an immunostrip format. 1b.Approach (from AD-416): Resistant, susceptible and segregating germplasm will be field tested for resistance to CYSDV in field trials and tested for virus by molecular method. Resistant and susceptible germplasm will be grown under controlled conditions, inoculated in standardized tests and screened for virus concentration and transmission efficiency by whiteflies. Virus protein will be expressed and antiserum developed for use in immunodetection of CYSDV. 3.Progress Report: This project relates to, Subobjective 4B, Characterization of new whitefly-transmitted viruses and their vectors, and identification of potential sources of resistance. Cucurbit yellow stunting disorder virus (CYSDV) emerged in the Southwest US during the fall of 2006, and is transmitted by the sweet potato whitefly, Bemisia tabaci biotype B. To generate an antibody for detection of CYSDV, collaborators at the University of California-Davis amplified CYSDV CP gene total RNA extracted from melon leaves infected with CYSDV using reverse transcription (RT)-PCR, and the product was cloned into a protein expression vector, sequenced, and transformed into E. coli. A protein was expressed in E. coli, purified and used to immunize two rabbits for antisera production. Antiserum was purified from each of the two rabbits by standard methods, and was confirmed by Western blot analysis for specificity in detection of CYSDV from infected plants. Additionally, CYSDV-infected melon samples were tested at the USDA-ARS Virology Lab in Salinas by a second serological method, enzyme-linked immunosorbent assay (ELISA) using the new antisera to determine if there were significant non-specific or background reactions to the antiserum and ability to confirm infection. Results demonstrated that the antisera effectively detected CYSDV in symptomatic plants, and had very low background reactivity even following overnight incubation of enzymatic detection reactions. Melon samples infected with CYSDV from a related project were collected from research plots at University of California- Desert Research & Extension Center for virus analysis by the ARS Virology Lab in Salinas. Both ELISA using the newly developed antiserum and quantitative RT-PCR assays were used to examine virus concentration in melon germplasm and correlation with symptom severity. Results of both detection methods yielded similar results, with virus concentration in melon corresponding with increasing disease severity in plants.