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Title: IDENTIFICATION OF PHOMA SCLEROTIOIDES, THE CAUSAL AGENT OF BROWN ROOT ROT, IN WISCONSIN AND MINNESOTA

Author
item Samac, Deborah - Debby
item HOLLINGSWORTH, C - UNIVERSITY OF MINNESOTA

Submitted to: North American Alfalfa Improvement Conference
Publication Type: Abstract Only
Publication Acceptance Date: 7/21/2004
Publication Date: 7/21/2004
Citation: Samac, D.A., Hollingsworth, C.R. 2004. Identification of Phoma sclerotioides, the causal agent of brown root rot, in Wisconsin and Minnesota [abstract]. North American Alfalfa Improvement Conference, July 19-21, 2004, Ste. Foy, Quebec, Canada. Abstract No. 51.

Interpretive Summary:

Technical Abstract: Brown root rot (BRR) is a fungal disease, caused by Phoma sclerotioides, which is associated with stand decline and reduced yield of forage legumes such as alfalfa, red clover, bird's-foot trefoil, alsike clover, and sweet clover. To determine the distribution of the fungus in Midwestern States, a survey for the pathogen was initiated in the fall of 2003 and continued in spring 2004. During 2003, samples were assayed from Iowa, Illinois, Minnesota, and Wisconsin. In 2004, samples from three additional counties in Wisconsin and two counties in Minnesota have been assayed to date. The survey confirmed the presence of the fungus in Shawano County, WI, although from only 1 of 19 locations tested. In addition, plants from Columbia, Oconto, Pierce, and St. Croix Counties tested positive for the fungus. The survey found the fungus in seven Minnesota counties for the first time. In northwestern Minnesota, plants from Marshall, Pennington, and Red Lake Counties were positive by the PCR assay. A majority of the plants tested positive for the fungus from the Pennington and Red Lake County locations. In addition, the fungus was isolated from plants from these counties and from plants obtained from Otter Tail County. PCR positive plants were also obtained from southern locations including Sherburne, Wabasha, Washington, and Winona Counties. No positive plants were found in samples submitted from Iowa or Illinois. Plants positive for the fungus originated from both younger (2-year-old) and older (3- to 11-year-old) stands. From plants assayed in fall 2003, the presence of a lesion on the root was not strongly associated with a positive PCR result. Roots with and without lesions were PCR positive. This research indicates that plants lacking symptoms can harbor the fungus. The fungus was identified from plants with rotted roots in spring 2004 as well as from plants with healthy roots. In some, but not all cases, the presence of the fungus was associated with serious winter injury to the alfalfa stand.