Effects of wetness duration, temperature, and light on infection of black spruce seedlings by Botrytis cinerea

Postinoculation wetness duration, temperature, and light conditions were investigated in relation to infection of container-grown seedlings of black spruce (Picea mariana (Mill.) B.S.P.) by Botrytis cinerea Pers.:Fr. Seedlings were predisposed to the pathogen by treatment at 35 +/- 1 degrees C in darkness for 4 days immediately before inoculation, and infection was assessed indirectly by estimating sporulation incidence of the pathogen on 6-mm segments of the needles. Sporulation incidence was zero when the temperature during 32 h of the postinoculation wetness was 1, 4, and 36 degrees C, about 7-10% at 12 degrees C, 40-47% at 28 degrees C, and maximal (44-56%) at 20 degrees C. Sporulation incidence was zero at all tested temperatures when wetness duration was 8-12 h, but increased progressively when the wetness period was increased from 12 to 32 h. Light and darkness during the wetness period did not significantly affect sporulation incidence. Logistic regression models were developed that adequately described sporulation incidence, and by inference, infection incidence, as functions of the postinoculation wetness period and temperature, and were validated using sets of independent data