A small, circular patch of soybean (Glycine max) showing symptoms consistent with sudden death syndrome (SDS) (2) was noted on July 25, 1998, in a producer's field in Jersey Shore, PA. Foliar symptoms included interveinal chlorosis and necrosis, leaf cupping, and leaf abscission. The vascular cylinder of roots and stems had areas of reddish-brown discoloration. A slow-growing Fusarium sp., which produced a bluish-purple color on potato dextrose agar, was isolated from the roots of several symptomatic plants. The fungus was identified as Fusarium solani by The Fusarium Research Center, The Pennsylvania State University. Koch's postulates were tested on soybean cultivars A2506, Stine 3171, Pioneer 9305 and 9306, and Jack. Five plants per cultivar were inoculated at growth stage V1 by pouring 35 ml of a 4 × 107 spores per ml suspension on the growth mix in each pot. Five plants per cultivar were treated similarly with sterile water. Foliar symptoms of SDS began to appear 3 weeks after inoculation. Seven weeks after inoculation, symptoms of interveinal chlorosis and/or necrosis, leaf cupping, and occasional leaf abscission were apparent on the inoculated plants and on several noninoculated plants. The percentage of the plant showing symptoms was recorded and converted to the 0 to 5 scale (in which 0 = 0%, 1 = 1--10%, 2 = 11--30%, 3 = 31--40%, 4 = 41--90%, and 5= 91--100% of the leaf area affected) used by Rupe (3). Regardless of the rating method, there was a significant difference (P = 0.0001) between inoculated and noninoculated plants. There were no significant differences among cultivars. Roots of the inoculated plants were frequently discolored, in contrast to those of the noninoculated plants. F. solani was isolated from the roots of 97% of the inoculated plants and 23% of the noninoculated plants. Fungus gnats were suspected of spreading the pathogen to the noninoculated plants (1). F. solani f. sp. glycines causes SDS in soybean and its identity is confirmed by the symptoms produced on soybean (2). The symptoms produced when soybean plants were inoculated in the greenhouse were consistent with those of SDS (2) and indicate that the F. solani isolate recovered from symptomatic plants in the field was F. solani f. sp. glycines. This is the first documented occurrence of SDS on soybean in Pennsylvania.
References: (1) D. W. Kalb and R. L. Millar. Plant Dis. 70:752, 1986. (2) K. W. Roy et al. Plant Dis. 81:1100, 1997. (3) J. C. Rupe. Plant Dis. 73:581, 1989.
