Control effects and mechanisms of metabolites from Streptomyces ahygroscopicus var. gongzhulingensis strain 769 on sclerotinia rot in sunflowers

Abstract

Introduction‌: Sunflower sclerotinia rot caused by Sclerotinia sclerotiorum poses a significant threat to global agriculture. This study investigates Streptomyces ahygroscopicus var. gongzhulingensis 769 (S769) as a novel biocontrol agent against this devastating disease. Methods‌‌: Antagonism assays evaluated S769's efficacy in vitro, while detached leaf, pot, and field trials assessed disease suppression through soil mixing (S769-Ms) and root drenching (S769-i). Mechanistic analyses included enzyme activity assays, microbiome profiling, qPCR quantification of pathogen load, and root transcriptomics. Results‌‌: S769 exhibited 65.79% mycelial growth inhibition in vitro. Field trials demonstrated significant disease control (S769-Ms: 7.36%, S769-i: 5.92% vs. 14.69% control), with 15.85% increase in root fresh weight and 34.26% reduction in shriveled seeds. qPCR confirmed 4.85-fold pathogen reduction in leaves and 2.68-fold in roots. Transcriptomics revealed 6,622 upregulated genes, including MAPK signaling and phenylpropanoid biosynthesis pathways. Discussion‌‌: S769 demonstrates dual action through direct antifungal effects and host defense activation. The enrichment of beneficial rhizobacteria (Sphingomonas, Chitinophagaceae) without altering microbial diversity highlights its potential as a sustainable agricultural solution for sclerotinia rot management.