Location: Subtropical Plant Pathology Research2013 Annual Report
1a. Objectives (from AD-416):
1. Determine and compare acquisition and transmission characteristics and efficiencies of whitefly- and thrips-transmitted vegetable viruses including Squash vein yellowing virus (SqVYV) and Groundnut ringspot virus (GRSV), respectively. 2. Analyze feeding behavior with electrical penetration graph (EPG) monitoring to determine when during feeding process the viruses are transmitted. 3. Develop and determine effect of vector management strategies on virus transmission.
1b. Approach (from AD-416):
Laboratory, growth chamber and greenhouse experiments will be used with whole plants and leaf discs to determine and compare acquisition and transmission efficiencies for SqVYV and GRSV. These experiments will show how similar (or different) SqVYV and GRSV transmission is by their respective vector, and thus the likelihood of a single, common management strategy being effective for control of both viruses. Multiple species of thrips will be examined for their ability to transmit GRSV to determine which are likely the key vector species. EPG monitoring will be used to analyze feeding behavior. Vector management strategies will be developed for the key vector species and tested for their effect on virus transmission. Such strategies will include repellants, oils and insecticides.
3. Progress Report:
This research relates to inhouse project objectives 1). Characterize ecology, biology, epidemiology, molecular genetics, and vector and host (crop and weed) interactions of domestic, exotic, newly emerging, and re-emerging pathogens, 2). Develop/refine rapid, sensitive reliable detection/sampling methods for pathogens, and 3). Develop or improve comprehensive integrated disease management strategies. A second set of experiments was conducted to determine acquisition of SqVYV by the whitefly Bemisia tabaci biotype B after mechanical and/or whitefly inoculation of the host plant. Results were consistent with previous experiments that showed that, at a low level, SqVYV can be acquired as early as two days post inoculation of the source plant and successfully transmitted by whiteflies to a new healthy host. After eight days, the transmission rate was high. A manuscript has been prepared and is about to be submitted for publication. Whitefly population data collected during two years in watermelon field trials was analyzed. Results showed a stratified distribution of the different life stages of whiteflies along the watermelon vines. Oviposition and hence, egg distribution occurred mainly in the distal third of the watermelon vine. As the plant grows older, small nymphs are concentrated in the second third of the plant and large nymphs in the older third of the plant. Preliminary results were presented as a talk at the 2012 combined Southeastern/Southwestern Branch meeting of the Entomological Society of America in Little Rock, AR. Further analysis of the data has been conducted to elaborate a sampling plan for whiteflies in watermelon in Florida, which will help with management decisions. A manuscript is being prepared for publication. Currently, the EPG (electrical penetration graph) technique is being used to study the feeding behavior of whiteflies on watermelon plants. This technique allows us to monitor the pathway of the whitefly’s stylets within the plant. Different waveforms correspond to different behaviors, beginning with probing of the epidermis and ending with committed feeding in the phloem. We are using EPG to determine the effect of SqVYV infection and the effect of mixed infections of PRSV-W and SqVYV on whitefly feeding behavior and transmission of SqVYV by whiteflies. These studies will be continued this coming year. Studies of whole-insect behavior in choice tests between non-infected and infected plants show differences depending on the host plant used (watermelon or squash). A cucurbitaceous weed, Melothria pendula, can serve as a host for SqVYV. We are evaluating this plant as a source of virus, both within the species and for watermelon. Our preliminary results suggest that, when infected, it is an excellent source of virus for whiteflies, which then can transmit the virus to watermelon.