Pepper root exduate attenuates snap bean root rot by mediating microbial community remodeling

Pepper-snap bean intercropping is a potential ecologically intensive cropping pattern that boosts plant disease resistance via root exudate-mediated inter-root microbial regulation. Yet, it's unclear if exogenous application of pepper root exudates can mitigate root rot in snap bean. In this study, potting and in vitro validation tests were used to explore the inhibitory mechanism of exogenously applied pepper root exudate on snap bean root rot. Results showed that the REI treatment significantly cut the root rot incidence of snap bean and the disease index, suppressed the relative abundance of pathogenic fungi, and increased the antioxidant enzyme activities and dry biomass of snap bean plants. Compared to the CKI treatment, the REI treatment reshaped the microbial community structure, significantly enriching Actinobacteria and Ascomycetes, while inhibiting Fusarium solanis spp. Also, the REI treatment enhanced the complexity and stability of the bacteria-fungi cross-domain networks, forming an antagonistic flora with Streptomyces spp. as the core. It induced the accumulation of flavones (like Chrysin) in the snap bean root system, which synergistically inhibited pathogenic fungi by regulating the colonization of antagonistic microbes such as Streptomyces spp. In vitro tests showed that exogenous application of Streptomyces spp.or Chrysin significantly reduced the root rot index and incidence respectively. Overall, exogenous application of pepper root exudates enhanced snap bean's disease resistance by attracting beneficial microorganisms to create a biological barrier and activating plant endogenous flavones metabolism to form chemical defense. This study uncovered the disease resistance mechanism of exogenously applied pepper root exudates, contributing to green prevention and control technologies and promoting agricultural sustainability.