Effect of light and temperature on number and length of Helminthosporium gramineum conidia produced in culture

Abstract

Helminthosporium gramineum sporulated in culture when grown at 26 °C on barley leaf pieces on 1.5% water agar and then exposed to fluorescent light at intensities of 0.0045, 0.0076, and 0.0338 cal cm−1 s−2 (1 cal = 4.184 J) followed by incubation at 6, 12, 18, or 24 °C. The number of conidia produced increased with time of irradiation and time at low temperature. Length of conidia at maturity was increased by prolonged exposure to low temperature and the greatest mean length of conidia occurred after 16 h at 12 °C. A lapse of time between irradiation and exposure to reduced temperature resulted in sterile conidiophores. Sporulation occurred in continuous light and constant temperatures from 12 to 18 °C, but a reduction in temperature after irradiation at 24 °C or above was necessary for formation of conidia. Conidium formation was inhibited by constant temperatures above 21 °C but not by light at any temperature.