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Evaluation of Selected Alfalfa Cultivars and Related Medicago Species for Resistance to Race 1 and Race 2 Anthracnose¹

Only one cultivar (‘Saranac AR’) with high resistance to both race 1 and race 2 of Colletotrichum trifolii Bain has been identified in alfalfa (Medicago sativa L.) since race 2 was first described in 1979. To identify additional alfalfa cultivars with resistance to both races and to assess the resistance potential in related Medicago species, 45 U.S. alfalfa cultivars and experimental lines, most characterized as anthracnose (race 1) resistant, and 36 annual and perennial Medicago species were evaluated for resistance to race 1 and race 2 of C. trifolii.

Eighteen of the 45 cultivars had resistance to race 1 exceeding 20%; 6 exceeded 50%. Of the 18 cultlvars with resistance to race 1 exceeding 20%, 5 had resistance to race 2 exceeding 20%, but only Saranac AR (53%) and ‘Aquarius’ (72%), both tracing to the same germplasm source, had resistance exceeding 30%. No cultivars were resistant to race 2 without being resistant to race 1.

Of 24 annual and 12 perennial Medicago species evaluated, 10 annuals and 2 perennials had resistance to race 1 exceeding 40%. Eight of the 10 annuals also had resistance to race 2 exceeding 40%. Four annuals with low resistance to race 1 had resistance to race 2 exceeding 45%. Medicago littoralis, M. murex, M. rigidula, M. tenoreana, and M. truncatula had greater than 90% resistance to both races. Medicago arborea and M. romanica, both perennials, which had resistance to race 1 exceeding 40%, also had resistance to race 2 exceeding 40%. Medicago suffruticosa was susceptible to race 1 but had high resistance to race 2.

Results of these studies revealed that among the presently available anthracnose (race 1) resistant cultivars, high resistance to race 2 was limited to two cultivars tracing to one germplasm source. High resistance to both races is potentially available in other Medicago species.

Key Words: Colletotrichum trifolii Bain • Medicago sativa L. • Medicago sp. • Disease

² Research agronomist and research plant pathologist, USDA, Field Crops Laboratory, Plant Genetics and Germplasm Institute, Beltsville Agricultural Research Center (BARC), Beltsville, MD 20705.

Received for publication January 12, 1981.

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