Field Screening for Onion White Rot Resistance

Abstract

Onion white rot disease (Sclerotium cepivorum) is a serious production problem throughout the world. Very low pathogen level in the soil can cause significant loss. Generic integrated pest management programs include clean seed, site selection, sanitation, crop rotation, biological and chemical controls, crop resistance to the pest, and other components. Onion white rot disease management currently does not have crop resistance as a component. The lack of resistant germplasm and/or the inability to identify and screen potentially resistant germplasm are primary reasons. Research was conducted to determine if field screening for resistance is feasible, to define field screening methodology, and to identify and/or quantify resistance. Disease incidence was inconsistent from year to year. In some years, disease expression was high; in others, disease was low. Uniform pathogen level and disease expression throughout the experimental field were required for successful screening. Results provide evidence that “resistant” or “tolerant” germplasm does exist, and that disease “resistance”, “tolerance”, or “susceptibility” can vary from slight to strong, suggesting multigenic involvement. “Resistance”/”tolerance” was identified in long-day yellow hybrids and inbreds. `Southport White Globe' selections and derivatives had much higher disease susceptibility than yellow or brown skin lines screened.