Evaluation of Cucurbita Moschata Accessions for Crown Rot Resistance to Floridian Isolates of Phytophthora Capsici

Phytophthora capsici causes several disease syndromes on squash and pumpkins (Cucurbita spp.) including crown rot, foliar blight and fruit rot, which can cause yield loss as high as 100%. Currently, there are no Cucurbita cultivars with resistance or tolerance to this pathogen. The objective of this study was to evaluate a select group of C. moschata accessions, from the USDA germplasm collection, for sources of resistance or tolerance to crown rot caused by P. capsici. A collection of 119 C. moschata accessions, representing 39 diverse geographic locations, were evaluated for response to inoculation with a suspension of three highly virulent P. capsici isolates from Florida. Eight plants per accession along with a susceptible control were inoculated at their crown with a 5 mL P. capsici suspension of 2 x 10⁴ zoospores/mL. Twenty-one days post-inoculation, the plants were visually rated on a scale ranging from 0 (no symptoms) to 5 (plant death). Mean disease rating scores (DRS) of the C. moschata collection ranged from 1.4 to 5. Accessions with low, intermediate, and high mean DRS were rescreened. Potential sources of resistance or tolerance were identified in the C. moschata collection. PI 458740, PI 442266, PI 442262, and PI 634693 with a mean DRS < 1.0 were the most promising. Selections from these accessions can be made to develop Cucurbita breeding lines and cultivars with resistance or tolerance to crown rot caused by P. capsici.