Dynamics of phyllosphere microbiome and screening of antagonistic microbes for managing needle cast disease of Pinus tabuliformis

Pinus tabuliformis, a keystone conifer species in North China, faces escalating threats from needle cast disease caused by Lophodermium pinastri, which triggers premature defoliation and forest degradation. In this study, we employed 16S rRNA and ITS metabarcoding to characterize the phyllosphere microbial communities associated with diseased, healthy, and withered needles of P. tabuliformis, followed by isolation and screening of potential microbial antagonists for biological control. L. pinastri was confirmed as the pathogen of P. tabuliformis needle cast supported by evidences of integrated morphological and molecular identification and its infection induced significant shifts in both fungal and bacterial community structures. L. pinastri served as the definitive indicator fungus in withered needles, while Cladosporium was the most abundant fungal genus across all needle samples, and Epicoccum served as an indicator in diseased needles. Notably, Both Cladosporium and Epicoccum exhibited resistance activity against L. pinastri despite being reported common plant pathogens. Sphingomonas, the most abundant and indicative bacterium, showed no antagonistic activity despite its known plant-growth-promoting role. Culture-based screening identified several antagonistic strains including Erwinia phyllosphaerae, Bacillus cereus, B. subtilis, and Penicillium oxalicum as potential antagonists, inhibiting L. pinastri significantly with inhibition rates exceeding 80 %. These findings elucidate the microbial response of P. tabuliformis to pathogen invasion and highlight promising candidate biocontrol agents, providing a scientific foundation for developing sustainable, eco-friendly strategies to manage pine needle cast disease.