Effects of Wheat Crown Rot Occurrence on Rhizosphere Soil Microbial Community Structure and Metabolite Composition

This study aimed to elucidate the relationship between rhizosphere soil microbial community structure, key metabolites, and the occurrence of wheat crown rot by examining the differences in rhizosphere soil microbial community composition and soil metabolites between healthy and diseased wheat plants, interpret the causes of wheat crown rot from a microbial ecological perspective, and to provide new insights and theoretical bases for disease management.

Rhizosphere soils from healthy and crown rot-affected wheat plants were collected as research subjects. Metagenomic sequencing and metabolomic profiling were employed to investigate variations in microbial community structure and differential metabolites between diseased and healthy plants. Redundancy analysis (RDA) was performed to determine the correlations between soil microbial communities and soil nutrient properties, and the relationships between microbial community structure and key differential metabolites were further explored.

The occurrence of wheat crown rot significantly reduced plant fresh weight and plant height. Although the contents of available phosphorus, available potassium, and nitrate nitrogen in the rhizosphere soil of diseased plants were lower than those of healthy plants, the differences were not statistically significant. High-throughput sequencing analysis revealed that the richness and diversity of both bacterial and fungal communities in the rhizosphere soil of diseased plants were decreased. At the genus level, differential abundance analysis showed that, among bacteria, the relative abundances of Nocardioides, Arthrobacter, Sphingomicrobium, and Lysobacter were significantly increased in the diseased rhizosphere soil, with increases of 73.51%, 21.53%, 23.48%, and 60.69%, respectively, whereas the relative abundances of Streptomyces and Bradyrhizobium were significantly decreased by 23.50% and 16.66%, respectively. Among fungi, the relative abundance of Trichoderma was significantly increased by 130% in the diseased rhizosphere soil, while those of Tulasnella and Dentiscutata were significantly decreased by 45.79% and 81.36%, respectively. Redundancy analysis (RDA) of microbial community composition and soil nutrients indicated a significant correlation between soil microbial communities and soil nutrient variables. Beneficial genera such as Nocardioides, Arthrobacter, and Bradyrhizobium were positively correlated with available potassium, organic matter, and nitrate nitrogen, whereas pathogenic genera including Aspergillus and Penicillium were positively correlated with organic matter and ammonium nitrogen, respectively. Furthermore, a total of 160 differential metabolites were detected between the rhizosphere soils of healthy and diseased plants. Combined analysis of soil microbial communities and metabolites revealed that Streptomyces and Bradyrhizobium were significantly positively correlated with three organic acids (9-oxo-octadecadienoic acid, dodecanoic acid, and 13-hydroxyoctadecadienoic acid) which are involved in plant defense and immune responses, while Lysobacter, Nocardioides, Sphingomicrobium, and Trichoderma showed significant negative correlations with these compounds.

The decreased diversity and altered community structure of rhizosphere soil microorganisms in diseased plants may be a key factor contributing to the occurrence of wheat crown rot. Moreover, microbial community structure was significantly correlated with soil nutrient properties. Additionally, soil metabolite profiles were markedly altered in diseased plants and showed significant correlations with soil microbial community structure.