Mechanisms of Biocontrol on Poplar Anthracnose and Growth Promotion by Trichoderma asperelloides Tas369 and Tri-Trichoderma Composite Strain

To address the need for effective biocontrol of poplar anthracnose caused by Colletotrichum gloeosporioides, in this study, 20 Trichoderma strains were isolated from the rhizosphere of seven tree species on Tianzhu Mountain to screen for potent growth-promoting and antifungal agents. The inhibitory effects of the strains on C. gloeosporioides (Cgl) were evaluated through mycelial growth assays, volatile organic compound tests, and fermentation filtrate analysis, while their growth-promoting capabilities and induction of systemic resistance were assessed in poplar seedlings via biomass measurement, stomatal analysis, and gene expression profiling. The results demonstrated that T. asperelloides Tas369 significantly inhibited pathogen growth and improved seedling growth, increasing stomatal density by 134% and inducing phenylalanine ammonia-lyase (PAL) and peroxidase (POD) enzyme activities. Notably, Trichoderma composite (Tcom) outperformed single-strain treatments, achieving 89.8% control efficacy, reducing the malondialdehyde content by 1.1 mmol/g, and significantly upregulating the key defense genes NPR1 (14.32-fold) and PR1-1 (219.79-fold) through increased activity of the salicylic and jasmonic acid signalling pathways. In conclusion, while Tas369 exhibits strong individual potential, the Tcom consortium provides superior biocontrol through multiple mechanistic interactions, offering an effective and sustainable approach for managing poplar anthracnose in forestry applications.