Submitted to: Citrus and Vegetable Magazine
Publication Type: Popular Publication
Publication Acceptance Date: 12/15/2004
Publication Date: 12/30/2004
Citation: Roberts, P., Muchovej, R. M., Gilreath, P., McAvoy, G., Baker, C. A., Adkins, S. T. 2004. Mature Vine Decline and Fruit Rot of Watermelon. Citrus and Vegetable Magazine. Interpretive Summary: This popular press report documents progress towards identifying the cause of a vine decline of watermelon observed in Florida over the past several growing seasons. Numerous physical and biological factors have been explored. This report initiates a cooperative research effort between ARS, University of Florida and the Florida Cooperative Extension Service. It also provides a timely account of watermelon vine decline to growers, Extension personnel and state and Federal regulatory and research scientists.
Technical Abstract: In spring 2003 and 2004 in southwest Florida and fall 2003 in west-central Florida (Manatee County area), a severe watermelon vine decline occurred as the crop approached harvest or soon after the first harvest. Foliar symptoms included yellowing, wilting of the vines, scorched and brown leaves, and rapid mature vine collapse. Frequently, the interior fruit rind appeared greasy with a brown discoloration, rendering the fruit non-marketable. Disease progress was very rapid. In some fields, vine decline increased from 10% affected plants to greater than 80% within a week. Research is underway to determine the cause of vine decline in order to manage or avoid it in the future. Possible environmental and biological (pathogen) causes are being examined. Soil and plant tissue are being analyzed for deficiencies. In an attempt to link cultural practices to the onset and spread of the decline, growers were asked to provide information on all cultural practices performed at the farm. Various fungi and bacteria were recovered from symptomatic crown, root, foliar, and fruit tissue. In the laboratory, several fungal isolates caused watermelon seedling death following inoculation. Watermelons with decline symptoms were also examined for the presence of viruses and virus-like agents. Crude extracts of plant sap from these symptomatic watermelons were filtered to remove fungi and bacteria and used to inoculate greenhouse grown watermelon plants. The inoculated plants developed decline symptoms similar to those observed in the field and died. Papaya ringspot virus type W (PRSV-W), a pathogen commonly observed in south Florida watermelon fields, was identified in the declining plants. PRSV-W alone did not lead to the same symptoms of vine decline suggesting, along with other evidence, the possible presence of a second virus or virus-like agent that may be involved in vine decline. Research is ongoing to identify the other virus or virus-like agent present in field samples and determine the role it may play in vine decline. This fall, additional experiments were placed in previously affected watermelon fields to examine host susceptibility and other factors. Work is continuing to determine the causal agent and possible remedies.