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ARS Home » Midwest Area » St. Paul, Minnesota » Plant Science Research » Research » Publications at this Location » Publication #328359

Title: Pythium and Fusarium species causing seed rot and damping-off of alfalfa

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

Submitted to: North American Alfalfa Improvement Conference
Publication Type: Abstract Only
Publication Acceptance Date: 5/16/2016
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Seed rot and damping-off is an important disease of alfalfa, severely affecting stand establishment when conditions favor the disease. This disease may have been overlooked as a cause of poor stand establishment and reduced vigor of adult plants. 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. A survey for soil-borne seedling pathogens identified soils from commercial production fields in Minnesota with high levels of damping-off. Pathogens were isolated by a seedling baiting technique from soil of five alfalfa fields. Of the 149 organisms isolated, 93 (62%) were identified as Pythium species and 43 (29%) were identified as Fusarium species by a combination of morphological characteristics and DNA sequences. Pythium species were identified using the ITS and mitochondrial cytochrome oxidase c subunit I gene sequences and Fusarium species were identified using the ITS and elongation factor 1-''gene. Three species, P. sylvaticum, P. irregulare, and P. ultimum var. ultimum, were pathogenic on germinating alfalfa seedlings at 21°C using a standard agar plate test. Assays with soil infested with individual strains confirmed that these strains cause pre- and post-emergence damping off. Strains of seven species isolated from infected soybean, P. irregulare, P. intermedium, P. sylvaticum, P. recalcitrans, P. conidiophorum, P. ultimum var. sporangiferum, and P. ultimum var. ultimum, were also pathogenic on alfalfa in the plate test. 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. All species caused seed rot, damping-off, and root rot when tested in the agar plate assay. Strains of F. oxysporum and F. incarnatum-equisetum were the more aggressive in causing seed rot. Assays with Apron XL (mefanoxam) treated seed showed that sensitivity varied between and within Pythium species with approximately 56% of strains insensitive to the fungicide. In Apron XL amended medium, hyphal density was reduced at all concentrations but all strains had a similar growth rate as on non-amended medium. Insensitivity to Stamina seed treatments (pyraclostrobin) occurred in 94% of Pythium strains tested. The presence of broad host range species and fungicide resistance of a high percentage of Pythium isolates suggests that crop rotation and these widely used seed treatments are not effective tools for managing this disease. These results indicate that resistant cultivars are needed for managing damping-off in alfalfa production systems.