The role of lytic enzymes in biocontrol of sapstain fungi Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/4t64gq29p

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  • The biocontrol potential of Trichoderma harzianum strains B-2A, B-8A, B-4B, B-15B, and B-41 and Serratia plymuthica was evaluated using agar plates and wood wafers of unseasoned ponderosa pine (Pinus ponderosa laws). All five isolates of Trichoderma harzianum and Serratia plymuthica could inhibit stain fungi growth in agar plates and exhibited bioprotectant potential against sapstain fungi on wood wafers. The production of chitinase and protease related to the breakdown of stain fungal cell walls was studied in liquid media and wood wafer cultures for test bioprotectants. Higher chitinase activity was obtained in chitin-containing media. Although the synthesis of chitinase was repressed by simple carbon substrates in liquid media, chitinase activity was still detected on wood wafer cultures when the bioprotectant was pregrown on media containing these same carbon sources. No protease activity was detected in liquid cultures, but protease activities were detected on wood wafer cultures. The relationship between biocontrol performance and lytic enzyme activities was evaluated using mixed cultures of bioprotectants and stain fungi on wood wafers. Generally, fungal stain inhibition increased with increases in chitinase. Increasing chitinase activity above about 0.08 uU/m1 had a minimal effect on fungal stain inhibition. Further statistical analysis indicated that biocontrol efficacy appeared to be related to LOG (chitinase activity) but not to LOG (protease activity). No synergistic effects were found between protease and chitinase in biocontrol of sapstain fungi. The mechanisms for the biocontrol of sapstain fungi were further studied using living bioprotectant cells and its sterilized filtrate. Live cells effectively prevented discoloration of wood wafers , while the filtrates generally failed to inhibit stain fungi growth in wood wafers over a 4- week incubation. Purified chitinase of Streptomyces griseus partially inhibited spore germination of Ulocadium chartarum, but varied with chitinase source. No inhibition of U. chartarum spore germination occurred after treatment with purified protease.
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