|Li, S. - UNIVERSITY OF ILLINOIS|
|Kurtzwell, N - UNIV. OF WISC.-MADISON|
|Grau, C - UNIV. OF WISC.-MADISON|
Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 29, 2004
Publication Date: April 11, 2004
Citation: Li, J.S., Kurtzweil, N.C., Grau, C.R., Hartman, G.L. 2004. Occurrence of stem canker (Diaporthe phaseolorum var. meridionalis) on soybean in Wisconsin. Plant Disease. 88:576. Interpretive Summary: Soybean is susceptible to several soybean pathogens that infect their stems. In the 2000 to 2003 growing seasons in Wisconsin, stem canker symptoms were widespread and associated with yield losses of about 1% state-wide, and up to 25% in individual fields. Affected plants expressed dieback of foliage with dark brown lesions observed on the lower portion of stems. Fungi were isolated from symptomatic plants and a few of the fungal isolates were identified as Diaporthe phaseolorum var. meridionalis (DPM), the cause of southern stem canker. This is the first report of DPM on soybean in Wisconsin. The significance of this report relates to the potential spread of DPM beyond its known southern range in the U.S. This information is useful for soybean breeders, pathologist, and consultants that are interested in disease management practices.
Technical Abstract: Soybean (Glycine max) developed symptoms characteristic of stem canker during the 2000 to 2003 growing seasons in Wisconsin. Symptoms were widespread in 2003 and were associated with yield losses of about 1% state-wide, and up to 25% in individual fields. Affected plants expressed dieback of foliage beginning at growth stage R3 and progressed until the R6 growth stage. Stems with lesions were cut into ca. 5-mm pieces, surface-disinfested with 0.5% NaOCl solution for 3 min, rinsed three times in sterile distilled water, and placed on water agar (WA) or potato dextrose agar (PDA) at pH 4.5. Hyphal tips from colonies of interest were excised and placed on acidified PDA at 25*C under continuous light for 25 to 30 days. Besides Diaporthe phaseolorum var. caulivora (DPC), the cause of northern stem canker, four isolates of D. phaseolorum var. meridionalis (DPM), the cause of southern stem canker, were isolated. Isolates of DPM were tested for pathogenicity in a controlled environment using two inoculation methods. For each isolate tested, DPM was reisolated from three symptomatic plants that were randomly picked for each inoculation method. This is the first report of DPM on soybean in Wisconsin. The significance of this report relates to the potential spread of DPM beyond its known southern range in the U.S.