Effects of Cropping History, Cultivar, and Sampling Date on the Internal Fungi of Soybean Roots. J. D. Mueller, Former Graduate Research Assistant, Department of Plant Pathology, University of Illinois at Urbana-Champaign, Urbana 61801. B. J. Shortt, Former Graduate Research Fellow, and J. B. Sinclair, Professor, Department of Plant Pathology, University of Illinois at Urbana-Champaign, Urbana 61801. Plant Dis. 69:520-523. Accepted for publication 14 December 1984. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/PD-69-520.

The incidence of fungi and bacteria occurring in the roots of six soybean (Glycine max) cultivars growing in fields cropped the previous 3 yr to either corn (Zea mays) or soybeans was determined at 2-wk intervals throughout the 1980 growing season. Incidence of fungi increased up to 96 days after planting, then decreased until harvest. Roots were colonized early by Chaetomium spp., two groups of Fusarium spp., Gliocladium roseum, Penicillium spp., and Trichoderma spp. Recovery of Chaetomium and Penicillium spp. declined rapidly, and only trace amounts were recovered after the sample at 82 days. Fusarium and Trichoderma spp. were recovered less often than G. roseum throughout the growing season. Macrophomina phaseolina and Phomopsis spp. are considered pathogenic, and their recovery differed among cultivars. Recovery of nonpathogenic early-season colonizing fungi did not differ among cultivars. Cropping history affected the recovery of M. phaseolina, Phomopsis spp., and Trichoderma spp. but not Fusarium spp. or G. roseum. Incidence of recovery from plants following soybeans was greater than from corn for Phomopsis spp. and nearly twice as great for M. phaseolina. Recovery of Trichoderma spp. was greater following corn than following soybeans.

Keyword(s): pod and stem blight.