2018 ASHS Annual Conference

Verticillium dahliae is a soil-borne fungal pathogen that causes Verticillium wilt. Grafting has been widely used as part of an integrated disease management strategy for Verticillium wilt in cucurbits. Cucurbit rootstock seeds can be expensive and seeds of most rootstock cultivars are imported into the U.S. from seed companies that breed them. Verticillium resistant germplasm accessions from the USDA National Plant Germplasm System (NPGS) could potentially be used by researchers and seed companies as rootstocks or as parents in rootstock breeding programs to develop domestic rootstocks. NPGS accessions could thus reduce the cost of development and availability of rootstock seed. This study evaluated 56 NPGS cucurbit accessions from four species – Benincasa hispida, Cucurbita maxima, Cucurbita moschata and Lagenaria siceraria- for their resistance to Verticillium wilt. These four species are commonly used as rootstocks for watermelon. The evaluation was done at WSU Mount Vernon NWREC, in a certified organic field naturally infested with V. dahliae (10 cfu g-1 of soil). Seedlings were raised in the greenhouse and inoculated with V. dahliae microsclerotia (sand inoculum was adjusted to deliver 1.5 cfu per planting hole) at transplanting. Disease development was noted over five weeks, and AUDPC values were calculated for all accessions. Mean AUDPC values for germplasm accessions ranged from 9 to 297 and was 275 for ‘Sugar Baby’ (Verticillium susceptible control). Thirteen accessions with the lowest AUDPC values and no detectable V. dahliae colonies in a subsequent stem sap assays were identified. The selected accessions included L. siceraria (seven accessions) Lagenaria sp. (one accession) and Cucurbita (five accessions). These accessions will be used in a follow-up study, during which they will be used as rootstock for grafting watermelon and evaluated again for resistance to V. dahliae and grafting compatibility.