Paclobutrazol protects black spruce seedlings against predisposition to gray mold induced by high temperature and drought

Effects of paclobutrazol on the ability of high temperature and drought to predispose black spruce (Piceamariana (Mill.) B.S.R) seedlings to infection and sporulation of Botrytiscinerea Pers.:Fr. were examined. Paclobutrazol was applied as a soil drench at doses of 0, 20, and 40 mg/seedling pair on the first and third days of 2- and 4-week periods before the seedlings were subjected to darkness at 35 and 45 °C, or to drought, for various periods and inoculated with the pathogen. The paclobutrazol treatments markedly reduced sporulation incidence and the number of spores produced by the pathogen on needles of seedlings subjected to the environmental stresses for periods that marginally or moderately exceeded those needed for predisposition to B. cinerea. Sporulation in needles of paclobutrazol-treated seedlings increased substantially only when the stress treatments were relatively prolonged. The activity of paclobutrazol in suppressing effects of environmental predisposition of the seedlings to infection ...