GLIOCLADIUM ROSEUM REDUCES PHYSIOLOGICAL-CHANGES ASSOCIATED WITH INFECTION OF BLACK SPRUCE SEEDLINGS BY BOTRYTIS-CINEREA

Black spruce (Picea mariana) seedlings were treated with Gliocladium r oseum (5 x 10(7) conidia/mL) or with water, kept in high relative humi dity (RH) for 24 h, challenge-inoculated with Botrytis cinerea (5 x 10 (5) conidia/mL) or with water, and returned to high RH for 24 h, entir ely at 20-21 degrees C. The seedlings were subsequently kept in a grow th chamber and were evaluated at 2-4 day intervals for sporulation pot ential of B. cinerea, electrolyte leakage, chlorophyll content, and ph otosynthetic rate. After 6-15 days, B. cinerea sporulated in 56-63% of needles and produced 29.3-40.5 x 10(3) conidia/needle in plants treat ed with water and challenged with the pathogen, whereas in plants trea ted with G. roseum prior to inoculation with B. cinerea sporulation in cidence 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 seed lings treated with G. roseum and water. Electrolyte leakage, chlorophy ll 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% (r elative to leakage after the tissues were heat killed), 9.3 to 10.6 mg chlorophyll/g dried shoot, and 8.6 to 15.8 mu mol CO2 . m(-2). s(-1). In seedlings treated with water and B. cinerea, electrolyte leakage i ncreased to 47-51% after 9 days, chlorophyll declined from 9.5 to 5.1 mg/g dried shoot during 2 to 15 days, and photosynthetic rate fell fro m 9.0 to 0.4 mu mol . m(-2). s(-1) at 2 to 15 days after inoculation. We conclude that G. roseum effectively suppressed B. cinerea in seedli ngs and prevented significant changes in electrolyte leakage, chloroph yll level, and photosynthetic rate associated with gray mold, but it d id not affect these Variables when the pathogen was not present.