Evaluation of sunflower hybrids for resistance to Sclerotinia sclerotiorum

摘要

Ten sunflower hybrids were evaluated for resistance to Sclerotinia sclerotiorum in the Laboratory and in pot and field experiments during 1997 and 1998 seasons. Sunflower seedlings, three-weeks old, exposed to culture filterate of S. sclerotiorum showed symptoms of wilt on leaves and bleached lesions on stems, within 12 h of exposure, similar to naturally infected plants. Variations in the sensitivity to culture filterate of the pathogen were recorded among hybrids. Under pot conditions, sunflower hybrids differed in their reactions, from highly susceptible to less susceptible to S. sclerotiorum. In the field significant differences in percentage of plants that developed wilt symptoms, wilt severity index and basal stem lesion were recorded between hybrids. Only two hybrids, Pioneer 6480 and Pioneer 6479. were least susceptible to Sclerotinia wilt. However, all hybrids tested were susceptible to head rot and there were no significant differences among hybrids. A positive correlation between lesion length on stem base and wilt severity was determined. Thus, lesion length measure seems to be a simple and direct method for assessing resistance of sunflower against S. sclerotiorum. No differences between four hybrids for preinfectional phenol content were observed however, post-infectional phenol was higher in the least susceptible hybrids (Pioneer 6480 and Pioneer 6479) than in the most susceptible hybrid (Vidoc).