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Title: FIRST REPORT OF BROWN ROOT ROT OF ALFALFA CAUSED BY PHOMA SCLEROTIOIDES IN WISCONSIN

Author
item Larsen, Richard
item GRAU, R - UNIV OF WISCONSIN
item Vandemark, George
item Hughes, Teresa
item HUDELSON, B - UNIV OF WISCONSIN

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/14/2002
Publication Date: 6/1/2004
Citation: Larsen, R.C., Grau, R.C., Vandemark, G.J., Hughes, T.J., Hudelson, B.D. 2004. First report of brown root rot of alfalfa caused by phoma sclerotioides in wisconsin. Plant Disease. 88:769.

Interpretive Summary: A relatively new soilborne disease was reported in alfalfa in the continental United States during 1997. The disease, called brown root rot (BRR) of alfalfa, is caused by the fungus Phoma sclerotioides. BRR has been associated with severe decline and winterkill of alfalfa (Medicago sativa L.) in the temperate regions of North America where winters are severe. Although suspected, BRR has not been associated with winterkill of alfalfa in the Upper Midwestern US. Symptoms were observed in Wisconsin during 2003 that included stunting and decline in 1-3 year old plants that were slow to break dormancy in the early spring. Roots frequently exhibited dark brown lesions, or were entirely decayed. Using a rapid method for detection utilizing molecular markers called SCARs that were developed previously by Larsen et al, we evaluated symptomatic alfalfa roots and soil samples collected from three counties in Wisconsin. PCR assays produced DNA fragments of an expected size that were highly specific for P. sclerotioides from alfalfa roots sampled from Marathon (4/4), Marinette (4/5) and Pierce (4/4) counties but not in roots from healthy controls. PCR products were also produced from all field soil samples in Marathon and Marinette counties. Detection of brown root rot has been limited in the United States to Wyoming but has been thought to occur in other states with severe winters. This is the first report of P. sclerotiodes in Wisconsin associated with winter kill of alfalfa and suggests the pathogen may also be present in other neighboring states with similar climates.

Technical Abstract: Brown Root Rot (BRR) has been associated with winterkill of alfalfa (Medicago sativa L.) in the temperate regions of North America where winters are severe. Although suspected, BRR has not been associated with winterkill of alfalfa in the Upper Midwestern US. Alfalfa plants exhibiting symptoms resembling those induced by the causal agent Phoma sclerotioides G. Preuss ex Sacc. were collected from fields in Marinette, Pierce, and Marathon counties in Wisconsin during spring and early summer of 2003. Symptoms included stunting and decline in 1-3 year old plants that were slow to break dormancy in the early spring. Roots frequently exhibited dark brown lesions, or were entirely decayed. Total DNA was extracted from root samples. In addition, total DNA was also extracted from soil samples collected in the root rhizoshphere of symptomatic plants from four fields in two counties. DNA extractions were evaluated for the presence of P. sclerotioides using PCR-based SCAR markers according to the method described previously by Larsen et al. The resulting PCR amplicons of the expected size (499 bp) were detected from alfalfa roots sampled from Marathon (4/4), Marinette (4/5) and Pierce (4/4) counties but not in roots from healthy controls. PCR amplicons were also produced from all field soil samples in Marathon and Marinette counties. Detection of brown root rot has been limited in the United States to Wyoming but has been thought to occur in other states with severe winters. This is the first report of P. sclerotioides in Wisconsin.