Evaluation of soybean, dry bean, and sunflower for resistance to Sclerotinia sclerotiorum

Many inoculation methods have been used to evaluate resistance of different crops to Sclerotinia sclerotiorum (Lib.) de Bary. Only a few of these methods have been used to evaluate more than one crop. This study compared disease evaluations of soybean [Glycine max (L.) Merr.], dry bean (Phaseolus vulgaris L.), and sunflower (Helianthus annuus L.) inoculated in the greenhouse (cut stem inoculation method) to field evaluations. In one experiment, stems of two soybean cultivars, Williams 82 (susceptible) and NKS19-90 (partially resistant), were severed and inoculated with a colonized mycelial plug of S. sclerotiorum placed on top of the plant at the cut point of the stem. Stem lesion lengths on these two cultivars were used to determine what effect plant age and post-infection temperature had on disease development. There was a significant (P < 0.05) difference in lesion lengths between inoculated 5-wk-old plants compared with 6- or 7-wk-old plants within each cultivar. At different post-infection temperatures, lesions developed at 25degreesC but not at 30degreesC. In another experiment, disease rating of 15 soybean cultivars evaluated in the greenhouse and field had significant (P < 0.05) correlation coefficients from 0.53 to 0.79. In addition to soybean, two experiments were completed on dry bean and sunflower. There were significant (P < 0.05) differences in lesion lengths among 14 genotypes within dry bean and sunflower. The correlation between greenhouse and field evaluations of dry bean and sunflower were 0.74 and 0.50 (P < 0.05), respectively. In summary, disease assessments from the cut stem inoculation compared favorably with disease assessments in the field for soybean, dry bean, and sunflower.