A Streptomyces Agent for Biocontrol of Phytophthora Blight and Its Modulation of Rhizosphere Microbiomes in Passion Fruit

Passion fruit and its seedlings hold significant economic value for both domestic and export markets in Taiwan. Among the diseases affecting passion fruit, Phytophthora blight, caused by <i>Phytophthora nicotianae</i>, severely impacts seedling survival and fruit production. This study aimed to develop a microbial agent to control Phytophthora blight by evaluating the potential of <i>Streptomyces cavourensis</i> strain PES4, isolated from rhizosphere soils in Taiwan. Additionally, the impact of strain PES4 application on microbial communities in the field was investigated. Our results demonstrated that <i>S</i>. <i>cavourensis</i> PES4 exhibited strong antagonistic activity against several bacterial, fungal, and oomycete pathogens, including <i>P</i>. <i>nicotianae</i>. Applying a 100-fold diluted culture broth of strain PES4 significantly reduced the severity of Phytophthora blight on passion fruit leaves and fruits. Weekly applications of strain PES4 throughout the growing season enhanced plant growth, yield, and fruit quality compared with the water control. Next-generation sequencing was used to analyze the influence of strain PES4 application on the rhizosphere microbiome. The application of strain PES4 did not affect microbial richness or diversity but did alter the composition of bacterial and fungal communities. Specifically, strain PES4 application reduced the relative abundances of Proteobacteria and Actinobacteria while increasing Acidobacteria, Verrucomicrobia, and Gemmatimonadetes at the phylum level. At the genus level, <i>Rhodanobacter</i> and <i>Streptomyces</i> populations increased. Regarding fungal communities, strain PES4 application promoted the populations of <i>Trichoderma</i> and <i>Mortierella</i>, while <i>Penicillium</i> and <i>Colletotrichum</i> populations declined. In conclusion, <i>S</i>. <i>cavourensis</i> PES4 is a promising plant probiotic with both growth-promoting and biocontrol activities against Phytophthora blight in passion fruit. Its application can modulate the rhizosphere microbiome by enhancing beneficial bacterial and fungal populations and suppressing plant pathogenic ones, suggesting its potential as a sustainable biocontrol agent.[Formula: see text] Copyright © 2026 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.