Interaction of Trichoderma asperellum with Phytophthora ramorum inoculum soil populations and enzyme secretionAuthor(s): Supriya Sharma; Wolfgang Schweigkofler; Karen Suslow; Timothy L. Widmer
Source: Proceedings of the sudden oak death sixth science symposium. Gen. Tech. Rep. GTR-PSW-255. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station: 99.
Publication Series: General Technical Report (GTR)
Station: Pacific Southwest Research Station
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There is a continuing desire to investigate the potential of biological control to manage the spread of Phytophthora ramorum. A specific isolate of Trichoderma asperellum has been demonstrated to be effective in reducing P. ramorum soil populations to non-detectable levels. This study was conducted to investigate the interaction of different T. asperellum application rates with different initial soil populations of P. ramorum in a mock nursery setting and to investigate the impact of these interactions on important enzyme levels. Field trials were set up in the fall and spring where soil in a nursery bed was infested with P. ramorum chlamydospores at three different levels (< 2, 5-10, and > 15 cfu/cm3 soil). A commercially formulated wettable powder of a T. asperellum isolate was applied at two different levels (106 and 107 cfu/cm3 soil) by drenching the soil and raking into the top 3 cm of soil. Soil samples were collected every 4 weeks and baited with rhododendron leaf disks to determine the presence of P. ramorum. Overall results were inconsistent and difficult to make definitive conclusions. In the spring trial, only the high application rate of T. asperellum eliminated P. ramorum at all three initial soil populations.
The primary mechanism involved in the biological control of P. ramorum with the tested T. asperellum isolate appears to be direct parasitism. The enzyme laminarinase, which catalyses the hydrolysis of β-1-3 linkages in polysaccharides of D-glucose residues connected by β-1-3 linkages or mixture of β-1-3 linkages and β-1-6 linkages, is believed to be an important enzyme in cell wall degradation of Phytophthora spp. Studies were conducted to determine if enzyme activity was induced in the presence of P. ramorum. Secreted laminarinase activity was measured in liquid medium in the presence of various levels of P. ramorum mycelium. As a comparison, enzyme activity was also measured in the presence of P. tentactulata and in medium alone. After 24 and 120 h, laminarinase activity was significantly higher in the presence of P. ramorum mycelium compared to controls in the medium alone. Enzyme activities increased as P. ramorum mycelium was increased. Enzyme levels did not increase in the presence of P. tentaculata, regardless of the amount of mycelium present in the medium.
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CitationSharma, Supriya; Schweigkofler, Wolfgang; Suslow, Karen; Widmer, Timothy L. 2017. Interaction of Trichoderma asperellum with Phytophthora ramorum inoculum soil populations and enzyme secretion. In: Frankel, Susan J.; Harrell, Katharine M., tech. coords. Proceedings of the sudden oak death sixth science symposium. Gen. Tech. Rep. GTR-PSW-255. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station: 99.
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