Response of Sweet Spanish Onion Cultivars and Numbered Hybrids to Basal Rot and Pink Root. M. K. Thornton, Parma Research and Extension Center, University of Idaho, Parma 83660. S. K. Mohan, Parma Research and Extension Center, University of Idaho, Parma 83660. Plant Dis. 80:660. Accepted for publication I March 1996. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-0660.

Yellow sweet Spanish onion cultivars and numbered hybrids were evaluated for disease resistance, bulb yield, and bulb size in field trials on a soil heavily infested with the pathogens that cause pink root and basal rot. Hybrid lines exhibited lower incidence of basal rot and pink root than named cultivars in both 1990 and 1991. Resistance to basal rot was not closely related to level of pink root infection. Hybrids that exhibited a low level of pink root infection had the healthiest roots and produced the highest bulb yields. Extensive replacement of infected roots with healthy new roots was a common characteristic of pink root-resistant hybrids. Adoption of numbered onion hybrids resistant to pink root and basal rot could reduce the current dependence on fumigation as the primary control method for these soilborne diseases.