REACTION OF SOYBEAN CULTIVARS TO ISOLATES OF FUSARIUM-SOLANI FROM THERED RIVER VALLEY

Five isolates of Fusarium solani, originally isolated from diseased so ybean roots in the Red River Valley (RRV) of Minnesota and North Dakot a, were evaluated for their ability to cause symptoms on 10 geneticall y diverse soybean cultivars. Taproots of 2-week-old plants were inocul ated with F. solani-infested oat kernels, and 3 and 10 weeks later, pl ants were evaluated for root rot and foliar symptoms. At 3 weeks after inoculation, taproots of all cultivars had extensive reddish brown to black lesions; root rot severity (1-6 scale) ranged from 4.8 to 5.1, and 3.5% of the plants had died. Foliar symptoms were not observed. At 10 weeks after inoculation, all cultivars showed extensive decay of t aproots and >50% of lateral roots were necrotic; root rot severity (1- 4 scale) ranged from 2.7 to 3.7, and 42.5% of the plants had died. Fol iar symptoms were first observed between the R-l to R-6 growth stages (about 5 weeks after inoculation) on the lower leaves and consisted of chlorosis at the margins that progressed inward. Veins initially were green, but leaves eventually became chlorotic, then necrotic, and fel l with petioles still attached to the stem. In some cases, all of the foliage died. There was no significant (P = 0.05) isolate x cultivar i nteraction for root rot at 3 or 10 weeks after inoculation or for seve rity of foliar symptoms. Thirty-three cultivars commonly grown in sout hern Minnesota and the RRV were evaluated for reaction to one isolate of F. solani. Root rot severity ranged from 4.2 to 5.7 (1-6 scale) and 3.5 to 4.0 (1-4 scale), at 3 and 9 weeks after inoculation, respectiv ely, and >50% of the plants died by 9 weeks after inoculation. Severit y of foliar symptoms was low. These results indicate that isolates of F. solani from the RRV cause root rot and foliar symptoms on soybean a nd that cultivars grown in the region lack resistance to this pathogen . Foliar symptoms were not identical to those associated with sudden d eath syndrome.