Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/26/1998
Publication Date: N/A
Citation: Interpretive Summary: A serious disease of alfalfa in the South is Sclerotinia. This is a cool season disease which destroys new alfalfa seedlings and dense mature stands. Recently new alfalfas have been released with increased levels of resistance to the disease, but this particular disease organism is variable. It attacks many different plants and continues to evolve all of the time. Thus, current research evaluated resistance to Sclerotinia collected throughout the U.S. The more resistant alfalfa plants developed in Mississippi were found to have greater resistance to Sclerotinia collected from across the country.
Technical Abstract: Development of resistance to Sclerotinia trifoliorum in alfalfa (Medicago sativa L.) requires resistance to populations of isolates and an appreciation for variability in measurements of resistance to each isolate. Stem necrosis caused by five pathogen isolates were measured with multiple inoculations of 50 alfalfa plants. Statistical analysis showed no interaction of pathogen isolate and alfalfa plant for stem disease. Differences among plants and among pathogen isolates were significant (P=0.05). For the plants, resistance to isolates were correlated (r=0.48 to 0.60) and selection for resistance to one isolate should improve resistance to other isolates. Statistical analysis on the variation in disease with five separate inoculations of an isolate showed the variability in responses to inoculation was more affected by genotype of the plant than by genotype of pathogen and variation in measurements was not proportional to the mean length of the necrotic region. Some variation in disease responses observed in earlier studies that was attributed to variation in technique and micro climates, and to the unknown was under some genetic control.