A Bacterial Consortium from Pinus tabuliformis Enhances Growth and Induces Systemic Resistance Against Blue-Stain Canker Caused by Leptographium procerum
Leptographium procerum as a symbiotic fungus of Dendroctonus valens contributes significantly to pine decline and wood degradation in Pinus tabuliformis, yet effective and environmentally friendly management options remain limited. To explore biological control alternatives, we isolated endophytic bacteria from surface-sterilized healthy tissues of P. tabuliformis and identified them at the genus level by 16S rRNA gene sequencing. From 155 obtained strains, we screened for antagonistic activity against L. procerum, along with chitinase, siderophore, and IAA production, and selected Bacillus sp. strain Bt18 and Bacillus sp. strain Bm20 as the most promising candidates. When applied as a consortium to seedlings, the two strains significantly promoted growth, increasing root length by 48.2%, fresh weight by 57.9%–74.3%, and dry weight by 63.4%–80.0% relative to controls. Moreover, consortium-treated seedlings remained symptomless after pathogen inoculation, whereas control seedlings developed necrotic lesions averaging 2.41 cm2. Time-dependent increases in catalase, polyphenol oxidase, phenylalanine ammonia-lyase, and superoxide dismutase activities indicated that the consortium induced systemic resistance. These results show that P. tabuliformis harbors diverse beneficial endophytes, and the Bt18–Bm20 consortium offers a promising, green strategy for managing blue-stain disease in pine forests.