# Pepper root exudate attenuates snap bean root rot by mediating microbial community remodeling

## TL;DR

Pepper root exudates reduce snap bean root rot by changing the soil microbial community and boosting plant defenses.

## Contribution

The study reveals how pepper root exudates reshape microbial communities and induce plant defenses to combat root rot in snap beans.

## Key findings

- Pepper root exudates reduced Fusarium solani abundance and root rot symptoms in snap beans.
- Exudates enriched beneficial microbes like Streptomyces and enhanced microbial network stability.
- Flavone compounds like Chrysin were linked to reduced Fusarium and increased beneficial microbes.

## Abstract

Intercropping, as a sustainable agricultural practice, has shown potential to reduce soil-borne diseases through rhizosphere microbial community remodeling. However, whether pepper (Capsicum annuum L.) confers this benefit to snap bean (Phaseolus vulgaris L.) remains unclear. This study investigated the disease-suppressive effects of exogenously applied pepper root exudates using pot experiments. In vitro assays were used to validate the biocontrol efficacy of antagonistic bacteria and a key flavonoid metabolite (Chrysin). High-throughput sequencing and untargeted metabolomics were combined to analyze changes in the snap bean rhizosphere microbial community and root exudate profiles under pathogen stress. Compared to the treatment inoculated only with Fusarium solani (F. solani) (CKI), the treatment applying root exudates plus F. solani (REI) exhibited a substantial reduction in F. solani abundance, enhanced plant antioxidant enzyme activities, as well as markedly alleviated snap bean root rot symptoms. Furthermore, the REI treatment significantly altered rhizosphere microbial community composition by selectively enriching beneficial microbes (e.g., Actinobacteria, Ascomycota, Streptomyces, Saccharothrix), enhanced the complexity and stability of the bacterial-fungal cross-domain network, and formed a pathogen antagonism network centered on Streptomyces. Moreover, the REI treatment induced the secretion of flavone compounds (e.g., Chrysin) from snap bean roots, whose relative abundance demonstrated an essential positive correlation with Streptomyces and a significant negative correlation with Fusarium. The findings indicate that exogenous application of pepper root exudates mitigates the incidence of snap bean root rot by restructuring the rhizosphere microbial community and promoting the synthesis of endogenous flavone metabolites in the host plant. This study provides a basis for environmentally friendly vegetable disease management and supports the advancement of sustainable agricultural practices.

Root rot induced by Fusarium solani poses a serious threat to snap bean production and the sustainable development of agriculture. Long-term continuous cropping intensifies the incidence of soilborne diseases. Conventional chemical control methods are frequently less effective against these diseases and may result in issues, such as the development of pathogen resistance, a decline in soil microbial diversity, and environmental contamination. Despite the fact that intercropping snap beans with peppers can reduce the incidence of snap bean root rot, the precise mechanisms through which pepper root exudates confer this protective effect remain inadequately understood. This study demonstrates that pepper root exudates can effectively reduce the occurrence of snap bean root rot by reshaping the microbial community and inducing the secretion of plant defense metabolites. The significance of this research lies in elucidating the key mechanisms and application potential of pepper root exudates in enhancing snap bean resistance to root rot, thereby providing essential theoretical foundations and practical guidance for the development of novel biological agents and the advancement of green agriculture.