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Title: Seed rot and damping-off of alfalfa in Minnesota caused by Pythium and Fusarium species

item BERG, LAURINE - University Of Minnesota
item Miller, Susan
item Dornbusch, Melinda - Mindy
item Samac, Deborah - Debby

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/23/2017
Publication Date: 10/17/2017
Citation: Berg, L.E., Miller, S.S., Dornbusch, M.R., Samac, D.A. 2017. Seed rot and damping-off of alfalfa in Minnesota caused by Pythium and Fusarium species. Plant Disease. 101:1860-1867.

Interpretive Summary: Rapid and uniform seed germination is critical for obtaining a productive and persistent stand of alfalfa. However, a number of pathogens attack alfalfa seeds and seedlings, severely reducing plant establishment. The objective of this study was to identify the pathogens causing seed rot and seedling damping off of alfalfa in Minnesota alfalfa fields. Six species of water molds in the genus Pythium and three species of fungi in the genus Fusarium were found to be highly aggressive pathogens. Three of the Pythium species also cause seed rot and seedling root rot in soybean and corn. A high level of resistance to the fungicides Apron XL and Stamina, commonly used to protect seeds, was found in the alfalfa pathogens. Alternative fungicides or plant resistance is needed for improving seed germination and root health of alfalfa plants. The pathogens identified in this study can be used for screening germplasm for resistance to seed rot and damping-off of alfalfa and for developing resistant cultivars that would increase yields and profitability of alfalfa stands.

Technical Abstract: Globally, 15 Pythium species have been found to cause damping-off and seed rot of alfalfa, although surveys of species causing disease on alfalfa in the Midwestern U.S. are lacking. Pathogens were isolated by a seedling baiting technique from soil of five alfalfa fields in Minnesota with high levels of damping-off. Of the 149 organisms isolated, 93 (62%) were identified as Pythium spp. and 43 (29%) were identified as Fusarium spp. P. sylvaticum, P. irregulare, and P. ultimum var. ultimum were aggressive pathogens on germinating alfalfa seedlings. Strains of seven Pythium spp. pathogenic on soybean and corn were also pathogenic on alfalfa. The majority of the Fusarium isolates were identified as F. solani and F. oxysporum with a low number of F. redolans and F. incarnatum-equisetum. The F. oxysporum and F. incarnatum-equisetum strains were the most aggressive in causing seed and root rot. Resistance to Apron XL (mefanoxam) applied as a seed treatment was observed for over half the Pythium strains tested and resistance to Stamina (pyroclostrobin) was observed for the majority of strains. Broad host range and fungicide resistance in a high percentage of Pythium isolates suggests that new fungicides treatments and/or resistant cultivars are needed for managing damping-off in alfalfa production systems.