Effects of Variation in Water Potential on the Viability and Behaviour of Conidia of Peronospora Tabacina Adam

Abstract

Ab8tractA method is described for the collection of dry conidia of P. tabacina. Conidia were shown to lose or gain water according to the ambient humidity. When stored at 91'4% R.H., 50% of conidia were swollen, while all were shrunken at 88% RH. and all swollen at 94% RH. Average weight per conidium increased from 1· 04 ng at 0% R.H. to 2· 65 ng at 99% R.H.Immersion of conidia in sucrose solutions caused shrinkage and prevented germination. When transferred to water, germination occurred, indicating that reduction of germination in sucrose solutions was due to reduced water potential and not to loss of viability.Conidial viability was affected by temperature (5-25°C) and relative humidity, viability decreasing most rapidly at the higher temperatures and humidities. When conidia were allowed to start germination and then dried, they remained capable of completing germination, but their viability gradually fell to zero, the rate of fall being most rapid at high temperatures and humidities.At low relative humidities conidia were considerably more resistant to inactivation by ultraviolet irradiation than were conidia in water. Low humidities also decreased the effect of high temperatures on conidial viability.The rate of sedimentation of conidia in still air was lower at low relative humidities (0'742 em/sec at 34% RH.) than at high humidities (0'953 em/sec at 79%R.H.).The epidemiological significance of these findings is discussed.

A regional analysis of the meteorological aspects of the spread and development of blue mold on tobacco

“…Asexual spores, called sporangiospores, are generally viable for only a few hours; however, with temperatures near 20 "C, attached or detached spores of P. tabacina have been found to survive for as long as 1 to 2 weeks (KrC)ber, 1965;Hill, 1969a, b). Viability of spores decreases with increasing ultraviolet radiation loads (Shepherd, 1962;Shepherd et al, 1971). Sporangiospores lose much of their ability to germinate when sprayed on leaves and allowed to dry immediately (Cohen and Rotem, 1971;Cohen et al, 1974).…”