Gliocladium roseum reduces physiological changes associated with infection of black spruce seedlings by Botrytis cinerea

Black spruce (Picea mariana) seedlings were treated with Gliocladium roseum (5 X 10(7) conidia/mL) or with water, kept in high relative humidity (RH) for 24 h, challenge-inoculated with Botrytis cinerea (5 X 10(5) conidia/mL) or with water, end returned to high RH for 24 h, entirely at 20-21 degrees C. The seedlings were subsequently kept in a growth chamber and were evaluated at 2-4 day intervals for sporulation potential of B. cinerea, electrolyte leakage, chlorophyll content, and photosynthetic rate. After 6-15 days, B. cinerea sporulated in 56-63% of needles and produced 29.3-0.5 X 10(3) conidia/needle in plants treated with water and challenged with the pathogen, whereas in plants treated with G. roseum prior to inoculation with B. cinerea sporulation incidence was only 1-8% and spore production was 0.5-6.6 X 10(3) conidia/needle. The pathogen did not sporulate in the water checks or in seedlings treated with G. roseum and water. Electrolyte leakage, chlorophyll content, and photosynthetic rate did not differ significantly among seedlings treated with water only, with G. roseum and water, or with G. roseum and B. cinerea, and ranged respectively from 5.6 to 13.3% (relative to leakage after the tissues were heat killed), 9.3 to 10.6 mg chlorophyll/g dried shoot, and 8.6 to 15.8 micromole CO2.m-2.s-1. In seedlings treated with water and B. cinerea, electrolyte leakage increased to 47-51% after 9 days, chlorophyll declined from 9.6 to 5.1 mg/g dried shoot during 2 to 15 days, and photosynthetic rate fell from 9.0 to 0.4 micromole.m-2.s-1 at 2 to 15 days after inoculation. We conclude that G. roseum effectively suppressed B. cinerea in seedlings and prevented significant changes in electrolyte leakage, chlorophyll level, and photosynthetic rate associated with gray mold, but it did not affect these variables when the pathogen was not present.