P-138 - Screening of long-day onion cultivars for Stemphylium leaf blight tolerance.

Stemphylium leaf blight (SLB) is a common foliar disease affecting onion (Allium cepa L.) in the northeastern United States. Onion production in New York, especially in the muck areas, relies upon intensive fungicide use in the absence of cultivars with resistance to any of the main foliar diseases. No comprehensive evaluations of onion cultivars adapted to NY conditions assessing their susceptibility to foliar diseases such as SLB have been conducted. In this study, we conducted a replicated small plot trial to evaluate the susceptibility of long-day onion cultivars to SLB at Cornell AgriTech, Geneva, NY (2024). We tested eight onion commercially available cultivars including both yellow and red cultivars, different maturity groups, and storage capacity. The trial was established as a randomized block design with three replications. SLB severity was estimated twice per week and used to calculate the Area Under Disease Progress Curve (AUDPC). Yield, average bulb size (ABS), and average bulb weight (ABW) were also recorded for each cultivar. Onion cultivars differed significantly in their susceptibility to SLB with less disease progress in cultivars ‘SVNY1608’ and ‘Redwing’ compared to the most susceptible cultivar ‘Candy’. Yield, ABS and ABW were significantly higher in cultivar ‘SVNY1608’ than cultivars ‘Candy’ and ‘Red Spring’. These findings can assist in the design of integrated disease management strategies for SLB and underpin breeding programs for the evaluation of host resistance.