Bacterial wilt of cucurbits: Ecology, genetics, and management
Bacterial wilt of cucurbits is an economically important disease that impacts most Cucurbitaceae species. The pathogen, Erwinia tracheiphila, is a vascular-inhabiting bacterium overwintered and transmitted by cucumber beetles. Disease management relies on controlling cucumber beetles, mainly through insecticide applications. However, the ecology and biology of E. tracheiphila are poorly understood. A better understanding of this pathosystem is critical for the development of effective and less insecticide-intensive management strategies.
Six field experiments were carried out to accomplish the following objectives: 1) assess efficacy of delayed removal of spunbond row covers for suppressing bacterial wilt on muskmelon, and 2) compare costs and returns of row cover treatments. Delayed removal of row covers significantly decreased bacterial wilt incidence. The economic analysis indicated that when bacterial wilt was present, average annual returns were much higher for the delayed-removal strategies than the controls. In the absence of disease, all row cover treatments were less profitable.
Growth chamber and laboratory experiments were conducted with the following objectives: 3) evaluate E. tracheiphila survival on muskmelon leaves under different environmental conditions, and 4) investigate the genetic diversity of E. tracheiphila strains. Growth chamber experiments consisted of spray-inoculated muskmelon seedlings incubated at different temperature and moisture regimes. Survival of E. tracheiphila on muskmelon leaves depended on temperature, and presence of leaf wetness significantly impacted survival. Results demonstrate that epiphytic populations might serve as a reservoir of inoculum for infections. Genetic variability of 69 E. tracheiphila strains was investigated by rep-PCR. Fingerprint profiles were associated with host-plant genus. Cross-inoculation of 12 different strains onto cucurbit seedlings demonstrated that fingerprint profiles were consistent with pathogenicity. Wilting occurred significantly faster when seedlings were inoculated with strains that originated from the same crop host genus. My results provide the first evidence of genetic diversity within E. tracheiphila and suggest that strain specificity is associated with plant host.
Finally, a pedagological research objective was the development of a case study to challenge students to solve a disease management situation in the context of real world decision-making. The case was run live with students and instructors, who provided feedback that was integrated into the manuscript.