Submitted to: Plant Disease
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/5/2006
Publication Date: 5/1/2007
Citation: Larsen, J.E., Hollingsworth, C.R., Flor, J., Dornbusch, M.R., Simpson, N.L., Samac, D.A. 2007. Distribution of Phoma sclerotioides on alfalfa and winter wheat crops in the North Central U.S. Plant Disease. 91:551-558. Interpretive Summary: Brown root rot of alfalfa, a fungal disease that causes root rot and winterkill, was first detected in Minnesota and Wisconsin in 2003. The disease has likely been overlooked previously because the pathogen is very slow growing in culture, making diagnosis difficult. The development of a PCR-based assay has allowed rapid testing of root samples to detect the pathogen. A survey was conducted to determine the distribution of the fungus causing brown root rot in Minnesota and Wisconsin. The pathogen was found to be widespread in both States and was detected in roots of alfalfa plants from 17 counties in Minnesota and 14 counties in Wisconsin. The fungus was isolated from roots of alfalfa, winter wheat, and perennial ryegrass plants. DNA sequencing diagnostic genes showed the fungus to be the same as that causing disease on alfalfa in Wyoming and similar to the fungus causing disease on alfalfa in Canada. A new PCR assay was developed with increased sensitivity for detecting the fungus in plant tissues and soil. The fungus was shown to cause disease on winter wheat plants. Although the fungus was previously found associated with roots of diseased cereal and turf plants, this is the first demonstration of pathogenicity on wheat. Locations in which a high incidence of brown root rot was discovered should be managed to reduce populations of the fungus by rotating to annual crops.
Technical Abstract: Brown root rot of alfalfa, caused by Phoma sclerotioides, has been reported in several States in the northern U.S. and in western Canada. A survey was conducted to determine the distribution of the fungus in Minnesota and Wisconsin. Isolates of the pathogen were recovered from roots of alfalfa, winter wheat, and perennial ryegrass plants. The internal transcribed spacer (ITS) 1, 5.8S, and ITS2 of the rDNA of the isolates from alfalfa and wheat were identical and matched the sequences of a P. sclerotioides isolate from Wyoming. The fungus was found to be widespread in both States and was detected in roots of alfalfa plants from 17 counties in Minnesota and 14 counties in Wisconsin using a PCR-based assay. A real-time PCR assay was developed that increased sensitivity of detecting the pathogen from plant tissues and soil. The isolates from alfalfa caused disease on inoculated winter wheat plants. Although the fungus was previously found associated with roots of diseased cereal and turf plants, this is the first demonstration of pathogenicity of P. sclerotioides on wheat.