<i>Streptomyces</i>-Based Bioformulation to Control Wilt of <i>Morchella sextelata</i> Caused by <i>Pestalotiopsis trachicarpicola</i>

In recent years, there has been extensive documentation of pathogenic fungi infecting <i>Morchella sextelata</i>. However, investigations of microorganisms with antagonistic properties against these pathogens are limited. This study successfully isolated two isolates of the genus <i>Streptomyces</i> (F16 and F19) from the rhizosphere soil of <i>M. sextelata</i> fruiting bodies, both of which exhibit potent antagonistic activity against <i>Pestalotiopsis trachicarpicola</i>, the causative agent of <i>M. sextelata</i> wilt disease. Comprehensive characterization, including physiological–biochemical tests and 16S rDNA sequence analysis, led to the identification of these isolates as <i>Streptomyces</i> sp. F16 and <i>Streptomyces</i> sp. F19. Both isolates significantly inhibited <i>P. trachicarpicola</i> through multiple mechanisms. The volatile compounds produced by these isolates effectively suppressed the conidial germination of <i>P. trachicarpicola</i> in vitro. Furthermore, fermentation filtrates at various dilutions exhibited pronounced antifungal activity against conidial germination, with <i>Streptomyces</i> sp. F16 showing 66.93% inhibition at a 50× dilution and <i>Streptomyces</i> sp. F19 achieving 49.22% inhibition under identical conditions. Field experiments have demonstrated the practical applicability of these antagonists. The topical application of fermentation filtrates (diluted 50×) from both isolates significantly reduced the incidence and severity of disease in <i>M. sextelata</i> cultivation. Notably, the yield improvements were substantial: fields treated with <i>Streptomyces</i> sp. F16 produced 299.6 g/m², whereas those treated with <i>Streptomyces</i> sp. F19 yielded 277.65 g/m². These yields significantly surpassed those of both the untreated control group (231 g/m²) and the <i>P. trachicarpicola</i>-inoculated group (134.93 g/m²). These findings indicate that the two isolates not only effectively control <i>P. trachicarpicola</i> but also increase the yield of <i>M. sextelata</i>.