Identification of Resistance to Acidovorax avenae subsp. citrulli among Melon (Cucumis spp.) Plant Introductions

Bacterial fruit blotch (BFB) caused by the bacterium Acidovorax avenae subsp. citrulli (Aac) is a seed-borne disease that threatens most cucurbit crops. Although limited resistance has been found in a small number of Plant introductions (PIs) in watermelon ( Citrullus spp.), there are no reports of high levels of resistance in germplasm lines of Cucumis spp. In this study, 332 Cucumis spp. PIs were screened for resistance to Aac using a newly developed seed vacuum–infusion assay. Significant differences in the reaction of the PI to BFB were observed. The majority of lines were found to be extremely susceptible to the disease. However, several PIs with lower levels of resistance were also identified. Variability in the reaction of plants within each PI was also observed. Of the 332 PI tested, 16 were selected for additional evaluation using a standard spray inoculation tests. PI 353814, PI 381171, PI 536573, and PI 614401, all belonging to C. melo , and PI 504558 ( C. ficifolius ) were found to have significantly greater levels of resistance than susceptible control cultivars or other PIs in two independent spray inoculation tests. Germplasm lines developed from these PIs may be useful as sources of resistance to BFB in Cucumis breeding programs.