Laboratory Selection of Alfalfa for Resistance to Anthracnose, Colletotrichum trifolii¹

Abstract

This paper describes a highly efficient procedure for screening alfalfa populations for resistance to anthracnose, Colletotrichum trifolii . Seedlings 2, 4, and 6 weeks old were inoculated with C. trifolii by spraying plants in a moist chamber with a suspension of conidia and comminuted mycelia. Plants differed for types of lesions and degree of resistance. Less than 556 of seedlings selected as resistant were found to be escapes when retested as mature plants. Alfalfa varieties developed by field recurrent selection in southern areas where anthracnose is endemic were significantly more resistant than northern varieties. All varieties tested had at least a few plants with some degree of anthracnose resistance. In an experimental synthetic, one cycle of selection increased the frequency of highly resistant plants from 18 to 7556. Development of an anthracnose‐resistant alfalfa is expected to prolong stand longevity and increase alfalfa productivity in the Middle Atlantic and Southeastern United States.