Submitted to: Phytopathology
Publication Type: Abstract Only
Publication Acceptance Date: 3/15/2005
Publication Date: 6/1/2005
Citation: Larsen, R.C., Vandemark, G.J., Hughes, T.J. 2005. The relationship between pathogen dna content and disease severity in alfalfa cultivars infected with verticillium albo-atrum. Phytopathology. 95:S56.
Technical Abstract: Verticillium albo-atrum is a serious soilborne pathogen of alfalfa (Medicago sativa L.) in North America. Standardized tests to evaluate alfalfa for resistance require up to four months for completion and utilize an integer scale to assess disease severity. A quantitative method for evaluating disease severity would enable a more accurate assessment of resistance. The objective of this study was to examine the relationship between pathogen DNA content in infected plants and disease severity ratings. V. albo-atrum DNA extracted from a set of the standard alfalfa check cultivars Oneida VR (HR), Vertus (R), and Saranac (S), and commercial alfalfa varieties Samauri, Vernema, and Wrangler was quantified using a real-time PCR assay. Significantly more pathogen DNA was detected in the susceptible check Saranac than in the other two check cultivars, and significantly more pathogen DNA was detected in Vertus than in Oneida VR. The correlation between pathogen DNA content in foliar tissue and DSI ratings was positive (0.53) and highly significant (P < 0.0001). Resultant DSI ratings of the commercial varieties were 2.72, 2.70, and 2.70 for Vernema, Samauri, and Wrangler, respectively, indicating a level of moderate resistance.