Screening, Identification, and Production Application of Endophytic <i>Streptomyces</i> W71 from Tobacco Plants in Sanmenxia

Tobacco black shank, induced by <i>Phytophthora nicotianae</i>, ranks among the most destructive diseases threatening global tobacco production. Biological control constitutes a crucial method for the environmentally friendly management of this disease, with the discovery of biocontrol agents serving as the initial step in this endeavor. The present research seeks to uncover new biocontrol agents and plant growth promoters effective against <i>P</i>. <i>nicotianae</i>. A strain of endophytic actinomycete isolated from tobacco, designated W71, was identified as <i>Streptomyces rochei</i>. This strain exhibited strong indole-3-acetic acid production capacity and inhibitory activity against <i>P</i>. <i>nicotianae</i>. In greenhouse trials, <i>S</i>. <i>rochei</i> W71 demonstrated significant plant growth promotion effects, markedly improving agronomic traits, root activity, root morphology indices, and antioxidant enzyme activities of tobacco plants. Field trials conducted at the rosette and prosperously growing stages revealed significant enhancements in several key crop parameters following the application of W71 treatment. These improvements encompassed increased maximum leaf length, maximum leaf width, stem girth, and plant height. Additionally, at harvest, W71 was found to facilitate a remarkable 98.91% boost in yield. In vitro inhibition tests demonstrated potent antagonism: live cells of <i>S</i>. <i>rochei</i> W71 suppressed <i>P</i>. <i>nicotianae</i> growth by 96.84%, outperforming the 70.89% inhibition rate of its cell-free culture filtrate. Greenhouse pot trials yielded an 87.53% disease control efficacy against tobacco black shank, and field trials resulted in a 72.68% control efficacy, indicating satisfactory performance. The study results demonstrate that <i>S</i>. <i>rochei</i> W71 possesses both plant growth-promoting properties and biocontrol capabilities against tobacco black shank, making it a promising candidate for use as a plant growth promoter and biological control agent.