Streptomyces spiroverticillatus induces poplar canker resistance against Botryosphaeria dothidea

Botryosphaeria dothidea is a destructive pathogen responsible for poplar canker, a disease that severely damages poplar trees by inducing stem lesions, growth inhibition, and eventual tree death, thereby causing substantial economic losses in forestry. Although conventional chemical fungicides are effective, their use poses significant environmental and health concerns, highlighting the need for safer biological control strategies. This study investigated the potential of Streptomyces spiroverticillatus, an antagonistic bacterium, to induce resistance in poplar against B. dothidea. Treatment with the cell-free supernatant (CFS) of S. spiroverticillatus markedly enhanced key defense-related physiological and biochemical responses in poplar leaves. Biochemical assays revealed that treated plants exhibited a 20% increase in total phenolics, a 37% rise in flavonoids, and a 40%-62% elevation in lignin content compared with controls. Furthermore, the activities of phenylalanine ammonia-lyase (PAL) and chitinase-enzymes critical for antimicrobial compound biosynthesis and fungal cell wall degradation-increased by 90% and 28%, respectively. Field trials confirmed the biocontrol efficacy of S. spiroverticillatus, reducing disease incidence by 61.17% (preventive) and 71.29% (curative), with corresponding disease reduction rates of 46.26% and 54.83%, respectively. These results outperformed carbendazim treatments, which showed preventive and curative efficacies of 49.97% and 50.04%, and disease reduction rates of 34.18% and 38.42%, respectively. These findings demonstrate that S. spiroverticillatus activates the innate defense mechanisms of poplar, stimulates the accumulation of antimicrobial metabolites and strengthens resistance against B. dothidea. This study identifies S. spiroverticillatus as a promising and environmentally sustainable biocontrol agent for the effective management of poplar canker.