APS Abstracts of Presentations

Molecular identification of pathogens from soybean stem canker epiphytotics in South Dakota. D. ZHANG and T. E. Chase. Plant Science Department, South Dakota State University, Brookings, SD. Phytopathology 93:S94. Publication no. P-2003-0690-AMA.

A collection of 267 isolates was established from soybean plants with characteristic stem canker lesions and symptoms in South Dakota during 1999-2001. RFLP analysis of the ITS region of nuclear ribosomal DNA, was carried out to aid in identification of individual isolates. PCR amplified DNA fragments defined by the ITS4 and ITS5 primers were digested with restriction enzymes Alu I, Hha I and Rsa I. Analysis of resultant RFLPs enabled classification of isolates among different groups within the Diaporthe/Phomopsis complex. Two hundred-six isolates (77%) were identified as D. phaseolorum var. caulivora (DPC), the causal pathogen of northern stem canker, and included both known subgroups: 163 DPC A (79%) and 43 DPC B (21%); 40 isolates (15%) belonged to Phomopsis longicolla, causal pathogen of Phomopsis seed decay; a third group of 21 isolates (8%) could not be identified with certainty to a previously characterized group but most closely resembled D. phaseolorum var. meridionalis (DPM), the causal pathogen of southern stem canker. RAPD and vegetative compatibility studies were also conducted and indicate variability among isolates within sub groups.