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First Report of Stachybotrys chartarum Causing Soybean Root Rot

Stachybotrys chartarum (Ehrenb. ex Link) S.J. Hughes was isolated from surface-disinfested soybean (Glycine max (L.) Merr.) root lesions. The fungus was cultured on potato dextrose agar, and its morphology was examined by light and environmental scanning electron microscopy. Conidiophores were determinate, macronematous, solitary or in groups, and simple or irregularly branched. Phialides occurred in whorls and were obovate or ellipsoidal. Conidia were unicellular, round to ellipsoidal, 5 to 13 × 4 to 7 μm, initially hyaline, smooth-walled, and dark brown to black and rough-walled when mature. A pure culture obtained from infected soybean roots was used to test pathogenicity under greenhouse and growth-chamber conditions. S. chartarum was grown on sterilized sorghum grain for 2 weeks and placed in soil 2 to 3 cm below sown soybean seeds. Noninfested sorghum grain was used as a control. All soybean plants inoculated with S. chartarum had root lesions ranging from 7 to 25 mm 21 days after sowing, while control plants did not have any measurable root rot. The DNA sequence of the internal transcribed spacer (ITS) region was 100% identical to S. chartarum strain ATCC 9182 (1) but differed from all published sequences of other Stachybotrys and Memnoniella spp. in GenBank (1). Polymerase chain reaction with S. chartarum-specific primer StacR3 and IT51 (1) amplified a 198-bp DNA fragment from the total genomic DNA. The molecular evidence further supports the identification of S. chartarum isolated from soybean. This is the first report of S. chartarum causing soybean root rot.

Reference: (1) R. A. Haugland and J. L. Heckman. Mol. Cell. Probes 12:387, 1998.