James S. Cole

Effects of light, temperature and humidity on sporulation of Erysiphe cichoracearum on Tobacco.

The formation and release of conidia were studied in two ways; by the direct observation of conidiophores and by trapping the spores at the downwind end of an environment tunnel containing infected tobacco plants. About 5–6 conidia were produced and detached per conidiophore per day at constant temperature in continuous light, or in alternating periods of 13 h light and 11 h darkness. Conidia were produced more slowly in the dark periods of the alternating light and dark regime and faster in the following light period than at corresponding times in continuous light. There were no marked changes in the rate of production in continuous light where periods of different temperature (18 and 24 ° C) alternated. Conidia were caught at a constant rate in the tunnel in continuous light and continuous dark, at constant temperature and humidity. In alternating 12 h periods of 23 and 16 ° in continuous light or continuous dark, fewer conidia were caught in the cooler period. The catch increased soon after the change to 23 ° and then gradually diminished. In alternating 12 h periods of 1 and 8 mb saturation deficit in continuous light the catch remained almost constant. In alternating light and dark, the catch was small in darkness, followed a normal distribution with a peak 8 h after the beginning of the photoperiod and was unaffected by changes in temperature and humidity.