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Use of Hypodermic Inoculations of Alfalfa for Identifying Host Reactions and Races of Colletotrichum trifolii¹

A hypodermic inoculation technique was used to nondestructively determine the differing resistance to race 1 and race 2 of alfalfa plants in breeding and genetic studies. Stem inoculations were made with hypodermic syringes fitted with 23-27 gauge needles. Conidial concentrations ranged from 1 to 9 million conidia/ml. Symptoms could be classified in 10 to 14 days. Susceptible stems formed large lesions at the inoculation site and wilted and collapsed. Resistant stems continued to grow normally with no lesion development. Hypodermic inoculations resulted in disease resistance reactions similar to those obtained with conventional spray inoculation techniques. We have isolated clones with the following combinations of resistant ( + ) and susceptible (–) reactions to race 1 and race 2, respectively: + +, + –, and – –.

Key Words: Medicago sativa • Disease resistance

² Research plant pathologist and research agronomist, respectively, Field Crops Laboratory, Plant Genetics and Germplasm Institute, ARSEA, USDA, Beltsville Agric. Research Center, Beltsville, MD 20705.

Received for publication May 26, 1981.