COMPARISON OF LABORATORY AND FIELD EVALUATIONS OF EVALUATIONS OF RESISTANCE IN SOYBEAN TO SCLEROTINIA-SCLEROTIORUM

Fifteen commercial soybean (Glycine max) cultivars were evaluated for resistance to Sclerotinia sclerotiorum in the laboratory, using an excised stem technique, and in the field during 1988 and 1989. In the laboratory tests, significant differences in the length of stem lesions among cultivars were observed. Maple Presto, McCall, and Clay were significantly more resistant to stem decay then Pride B152, Apache, Merit, and Portage. In the field, significant differences in the disease severity index among cultivars were observed. Portage, Maple Presto, and McCall were the most resistant, whereas Merit, Evans, and Simpson were highly susceptible. Evans, although highly susceptible in the field, did not differ significantly from Maple Presto in the laboratory tests. There was no correlation (P = 0.05) between laboratory evaluations and the 1988 and 1989 field evaluations. The lack of a correlation between field and laboratory evaluations suggests that a laboratory test measuring stem decay is unlikely to be a reliable method for identifying field resistance to S. sclerotiorum and, therefore, would have limited value in a breeding program.