STUDIES ON METHODS AND MATERIALS FOR TESTING ALFALFA FOR RESISTANCE TO BACTERIAL WILT

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Abstract
Several methods for inoculation of alfalfa with the bacterial wilt organism were compared in the greenhouse and field. The root-ball soak method, not previously described, proved particularly rapid and effective for greenhouse tests. All methods of root and crown inoculation tested gave good results, but spraying and other methods of stem inoculation were not dependable. In the field, the best results were obtained with bare-root soak inoculation before transplanting, and with hypodermic injection of the roots in the fall.Cultures of the bacterium of tested virulence and infected plant materials proved equally effective as inoculum, but the latter were more easily handled and stored. The organism remained highly viable in dried plant material stored for three years at room temperature, 5 °C, and −20 °C. The pulverized plant inoculum gave best results when soaked in water for 4 to 12 hours before use. It was gradually inactivated with longer periods of soak.Infection increased progressively with age in seedlings and rooted cuttings of Grimm alfalfa inoculated in the greenhouse at ages ranging from 3 to 10 weeks. Maximum susceptibility at 7 to 10 weeks of age was associated with the extensive formation of secondary tissues in the root and crown. The disease generally developed more rapidly in seedlings than in clonal material.

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