Charcoal rot of soybean (Glycine max (L.) Merr.), incited by Macrophomina phaseolina (Tassi) Goidanich, is commonly found in much of the southern soybean production region of the United States, where it can be a major contributor to yield loss in warm, dry seasons (4). The disease has also been reported in northern states including Michigan, Minnesota, North Dakota, and Wisconsin (1,2,3). In early July of the warmer and drier than normal 2012 growing season, wilted soybean plants were observed and collected for diagnosis from a field in Cayuga County, NY. The diseased plants showed brown discoloration of the stem and roots but the diagnostic microsclerotia of M. phaseolina had not yet developed in the epidermis. Cut pieces of roots and crowns were surface-sterilized in 20% sodium hypochlorite, rinsed in sterile distilled water, and incubated on potato dextrose agar at room temperature with a 12-h photoperiod for 7 days. The pathogen was observed growing out of many of the crown and root pieces, and produced abundant microsclerotia as described by Smith and Wyllie (4). Pathogenicity of isolate Mp001NY12 was confirmed using a cut stem inoculation method. Five soybean plants were grown to the unifoliate stage and inoculated by cutting the stem above the unifoliate leaves and applying a fully colonized agar plug to the wound. Within 2 weeks, infection was obvious with microsclerotia formed in the epidermis of all infected plants, and M. phaseolina was reisolated from all infected plants. DNA of isolate Mp001NY12 was extracted from colonies grown on PDA with PrepMan Ultra DNA extraction kit (Applied Biosystems, Foster City, CA), and the DNA was submitted for ITS sequencing with the ITS1 and ITS4 primers used for PCR amplification. The ITS sequence (GenBank Accession No. KC800709) of Mp001NY12 was compared to those in the NCBI GenBank database using a BLAST search, and had 99% nucleotide sequence identity with M. phaseolina (accessions JX945170, FJ415067, and EU250575). To the best of our knowledge, charcoal rot has not been reported previously on soybean or other plant hosts in New York or in other states in the northeastern United States.
References: (1) Baird et al. Mycopathologia 170:169, 2010. (2) C. A. Bradley and L. E. del Rio. Plant Dis. 87:601, 2003. (3) M. E. ElAraby et al. Plant Dis. 87:202, 2003. (4) G. S. Smith and T. D. Wyllie. Charcoal rot. Page 29 in: Compendium of Soybean Diseases, 4th ed. G. L. Hartman et al., eds. APS Press, St. Paul, MN, 1999.