Evaluating and Selecting Alfalfa for Reaction to Crown Rot1

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Abstract
Crown rot is a major problem of alfalfa, but cultivars have not been evaluated for resistance. In this study 32 alfalfa (Medicago saliva L.) cultivars in 3‐ and 4‐year‐old broadcast plots at four locations in Minnesota were observed for degree of crown rot. Also, more than 100 cultivars were evaluated for crown rot after 3 years in a spaced‐plant test. Plants with little or no crown rot were selected and intercrossed, and their progenies were evaluated for crown rot severity. All cultivars were injured by crown rot, only small differences were observed among cultivars. In both broadcast and spaced‐plant tests, the winter‐hardy cultivars generally had less crown rot than the moderately hardy cultivars. ‘Teton’, ‘Ramsey’, and ‘Victoria’ (winter‐hardy cultivars), and ‘Pat 30’ and ‘WL 303’ (moderately hardy cultivars), had the least crown rot. The frequency of disease‐free plants was less than 0.2% of the plants evaluated. Intercrossing plants with the least rot produced progenies with significantly lower crown rot scores than the parental cultivars. The pathogenic fungi most commonly isolated from near the necrotic plant tissue were: Phoma medicaginis Malbr. and Roum., Fusarium solani (Mart.) Appel and Wr., and Rhizoctonia solani, Kuehn.

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