Disruption of the ech42 (endochitinase-encoding) gene affects biocontrol activity in Trichoderma harzianum P1

The biocontrol strain P1 of Trichoderma harzianum was genetically modified by targeted disruption of the single-copy ech42 gene encoding for the secreted 42-kDa endochitinase (CHIT42). Stable mutants in which ech42 was interrupted, and unable to produce CHIT42, were obtained and characterized. These mutants lacked the ech42 transcript, the protein, and endochitinase activity in culture filtrates, and they were unable to clear a medium containing colloidal chitin, Other chitinolytic and glucanolytic enzymes expressed during mycoparasitism were not affected by the disruption of ech42, The disrupted mutant D11 grew and sporulated similarly to the wild type. In vitro antifungal activity of the ech42 disruptant culture filtrates against Botrytis cinerea and Rhizoctonia solani was reduced about 40%, compared with wild type; antifungal activity was fully restored by adding an equivalent amount of CHIT42 as secreted by P1, The mutant exhibited the same biocontrol effect against Pythium ultimum as strain P1, but the antagonism against B. cinerea on bean leaves by the mutant was significantly reduced (33% less biocontrol), compared with strain P1, Conversely, the endochitinase-deficient mutant performed better than the wild type (16% improvement of survival) in biocontrol experiments in soil infested with the soilborne fungus R. solani, These results indicate that the antagonistic interaction between the T. harzianum strain and various fungal hosts is based on different mechanisms.