Anthracnose Resistance Increases Alfalfa Yields1

Development of high levels of anthracnose (Colletotrichura trifoliiBain) resistance in alfalfa (Medicago sativaL.) in the early 1970's stimulated interest in obtaining estimates of the increased productivity associated with resistance. This paper reports the results of forage yield trials established at 24 locations in the eastern, midwestern, and western United States. Each trial included four pairs of anthracnose‐susceptible and anthracnose‐resistant bioindicator strains: 1) Glacier and Beltsville 1‐An4, 2) Saranac and Beltsville 2‐An4, 3) Vernal and Beltsville 3‐An4, and 4) Team and Arc. Forge yields were recorded for 3 years at 18 locations and for 2 years at six locations. Average annual forage yields were significantly higher for the resistant strains than for the susceptible strains at 15 of the 24 locations, averaging 1.1 mt/ha/year (10%) greater for the resistant than for the susceptible strains. A 0.8 mt/ha/year (7%) yield advantage of resistant strains over susceptible strains was obtained over all 24 locations. These results clearly indicate the value of anthracnose‐resistant alfalfa cultivars to U,S. agriculture.