Evaluation of Squash (Cucurbita pepo L.) Genotypes for Resistance to Cucurbit Chlorotic Yellows Virus

Abstract

Cucurbit chlorotic yellows virus (CCYV), a Crinivirus transmitted by whiteflies, poses a significant threat to cucurbit crops globally. Summer squash (Cucurbita pepo L.), an important vegetable crop in the Southeastern United States, is particularly affected. The absence of commercially available resistant summer squash cultivars necessitates the exploration of resistant sources. Cucurbita germplasms with potential resistance to CCYV were previously identified through field screening. In this study, we describe the controlled greenhouse screening of these germplasm lines aimed at validating resistance to CCYV infection. The susceptible cultivar Gentry used as control exhibited early and severe symptoms in response to CCYV infection. In contrast, all the PI accessions tested, including PI 512749, PI 615141, PI 136448, PI 442312, PI 458731, and PI 420328, displayed delayed and less severe symptoms. Nevertheless, CCYV RNA accumulated in all the PI accessions. Lower symptom severity while harboring a considerable amount of CCYV indicates their inherent tolerance to the yellowing disease induced by CCYV. When comparing CCYV RNA accumulation in PI accessions with the commercial cultivar ‘Gentry’, lower virus titers were observed across all tested accessions. Specifically, PI 420328 and PI 458731 exhibited significantly reduced CCYV titers compared to the susceptible cultivar in both mass exposure and clip cage experiments. These accessions, displaying reduced symptoms and lower virus titers, hold promise as sources of resistance to CCYV in breeding programs. This study also highlights the importance of utilizing a reliable method to assay the resistance or tolerance of selected germplasm to infection by CCYV.