DOMESTIC, EXOTIC, AND EMERGING DISEASES OF CITRUS, VEGETABLES, AND ORNAMENTALS (DEED)
Location: Subtropical Plant Pathology Research
Title: Epidemiological Analysis of Multi-Virus Infections of Watermelon in Experimental Fields in Southwest Florida
Submitted to: International Plant Virus Epidemiology Symposium
Publication Type: Abstract Only
Publication Acceptance Date: April 1, 2010
Publication Date: June 15, 2010
Citation: Turechek, W., Kousik, C.S., Webster, C.G., Stansly, P., Roberts, P., Adkins, S.T. 2010. Epidemiological Analysis of Multi-Virus Infections of Watermelon in Experimental Fields in Southwest Florida. International Plant Virus Epidemiology Symposium.
Interpretive Summary: Whitefly-transmitted Squash vein yellowing virus (SqVYV), Cucurbit leaf crumple virus (CuLCrV), and Cucurbit yellow stunting disorder virus (CYSDV) have had serious impact on watermelon production in southwest and west-central Florida in recent years. We monitored the progress of all three viruses and the density of whiteflies in a 2.5 acre experimental field of ‘Fiesta’ in which whiteflies were not controlled, located at SWFREC in Immokalee, FL over the course of 5 growing seasons. Symptoms of CuLCrV were generally found before SqVYV and were present as soon as 5 weeks after planting (wap). Symptoms of SqVYV appeared about 7 wap in nearly all seasons and the plants fully collapsed from SqVYV infection by 12 wap. Both viruses appeared in 4 of the 5 seasons but were conspicuously absent in the spring 2009 season. Weather-related phenomena are suspected as the cause of the absence of viruses in this season. In our experiment, CYSDV was first found 6 wap in the 2009 fall season although its presence in the region has been known since 2008. The largest number of whiteflies was typically found midway through the season, just prior to the rapid collapse of plants. Preliminary analyses indicated that the degree of association between SqVYV and CuLCrV was not greater than would be expected from random arrangement of the two viruses, and that SqVYV was distributed randomly at low incidences, but became more aggregated as disease increased. These results are an indication that the viruses are being introduced independently by whiteflies, although the whiteflies may be emigrating from the same source, with secondary spread being dominated by within-field populations of whiteflies. This pattern is supported by other results showing that the two viruses were generally spatially separated within individual watermelon plants. Additional studies are in progress to verify and extend these findings.
Whitefly-transmitted Squash vein yellowing virus (SqVYV) and Cucurbit leaf crumple virus (CuLCrV), and aphid-transmitted Papaya ringspot virus type W (PRSV-W) have had serious impact on watermelon production in southwest and west-central Florida in recent years. Tissue blot nucleic acid hybridization assays were developed for simple, high throughput detection of these three viruses as well as the more recently introduced Cucurbit yellow stunting disorder virus (CYSDV). To determine virus distribution within plants, we collected 80 entire plants randomly, 20 each on four different dates, from a commercial watermelon field showing symptoms of SqVYV, CuLCrV and PRSV-W, and possibly CYSDV. This was followed by a smaller sampling of five plants in a different commercial planting. Tissue prints were made from cross sections of watermelon plants from the crowns through the tips at 0.6 m intervals on nylon membranes and nucleic acid hybridization assays were used for virus detection. Results from testing of crown tissue showed that SqVYV, CuLCrV and PRSV-W were present in approximately 37%, 43.5% and 54%, respectively, of the 80 plants from the first field. For individual vines diagnosed with SqVYV, the distribution of SqVYV in vine tissue decreased proportionately with distance from the crown. The probability of detecting SqVYV was 70% at the base of the vine, compared to 23% at the tip of the vine, In contrast, CuLCrV tended to be more evenly distributed throughout the plant with a slightly higher probability of detection at the growing tip. The distribution of PRSV-W resembled that of SqVYV, but with a slightly greater probability of detection at the tip of the vine. Similar trends were detected in the smaller sampling; however, CYSDV was also detected in these plants. Overall, our results indicate that SqVYV, CuLCrV, and PRSV-W are distributed differently in watermelon plants, and this difference has implications for sample collection, and may affect vector acquisition and transmission of these viruses.