Activation of Teliospore Germination in Uromyces appendiculatus var. appendiculatus. II. Light and Host Volatiles

The effects of light and host volatiles on teliospore germination in Uromyces appendiculatus var. appendiculatus were studied. 1. Light intensities ranging 15-26000 lux supported teliospore germination and basidiospore formation. The optimum light intensity was 17000 lux under the described conditions. Light-dark alternation was necessary for teliospore germination: no germination occurred under continuous light or continuous dark conditions. The process of teliospore germination, basidiospore formation, and basidiospore release followed a synchronous, rhythmic pattern of development. Teliospore germination was triggered by the phase change light --> dark (i.e. "light off"). Under long-day conditions basidiospore release exhibited a nocturnal periodicity with peak maxima occurring ~ 7 h after light was turned off. 2. Fifteen days after a 10 d exposure to host volatiles, 70-80 % of the treated spores germinated; minor increases in spore mortality were observed. Inoculations made with seedling-treated teliospores resulted in heavy pycnial infections. 3. The heat and seedling activation methods developed for teliospores of bean rust proved ineffective when applied to dormant teliospores from six other unrelated rust species. ; published