Effects of Temperature and Light on Germination of Urediniospores of the Pearl Millet Rust Pathogen, Puccinia substriata var. indica.

Germination of urediniospores of Puccinia substriata var. indica was evaluated after 2, 4, 6, and 8 h of incubation in petri dishes containing 2% water agar under 10, 16, 20, 25, 30, and 35°C in light (1650 lux, cool white fluorescent), dark, alternate light-dark, and alternate dark-light. Less than 1% germination occurred at 35°C. At 30°C, percent germination did not significantly change after 4 h. At 10°C, percent germination increased with longer incubation. Under all illumination conditions, percent maximum germination after 4 to 8 h occurred at 20-25°C. Response surface analysis indicated that under all four illumination regimes, urediniospore germination greater than 90% occurs between 19 and 22°C after 6-7 h of incubation. Two hours of continuous light appeared to significantly delay germination, but exposure to light during the first hour of incubation was stimulatory when followed by 1 h dark.