Optimal Conditions for In Vitro Growth, Asexual Spore Release, and Germination ofThyronectria austro-americana

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Abstract
Growth of the honeylocust [Gleditsia triacanthos] pathogen T. austro-americana, on C and N sources, and on other nutrients. Spore release from excised naturally formed pycnidia was practically instantaneous when water was added at temperatures between -15 and 40.degree. C after storage at 25.degree. C and 35-45% RH [relative humidity] for 12 mo. Spore germination occurred at 15-40.degree. C with optimal germination at 25-35.degree. C. Germination was delayed at 96-75% RH over that found at 100% RH and completely inhibited at 62%. C and organic N compounds promoted, but were not necessary for, germination. Water extracts of honeylocust wood stimulated germination. The fungus apparently is well adapted for growth and dissemination in the varied climates where the host is planted.