Two myxobacterial strains against Rhizoctonia solani: comparative genomics of antagonistic potential and phenotypic evaluation of growth-promoting and disease-control effects

Abstract

Although sugar beet ( Beta vulgaris s sp. vulgaris ) is a major sugar crop in China, continuous cropping obstacles frequently constrain its productivity and quality. The application of antagonistic microorganisms or plant growth-promoting rhizobacteria (PGPR) offers a promising biological method for alleviating these constraints. This study evaluated two previously isolated myxobacterial strains with documented antagonistic activity against Rhizoctonia solani : Cystobacter ferrugineus W14 and Cystobacter fuscus W11. Their effects on sugar beet seedling growth under continuous cropping were assessed in a pot experiment, and whole-genome sequencing enabled the comparative profiling of disease resistance-related genes and functional pathways. Inoculation with either strain significantly increased seedling growth parameters, including stem diameter, plant height, and leaf fresh weight, compared with the control (CK). Specifically, strains W14 and W11 significantly increased plant height by 38.40 and 33.62%, respectively, and stem diameter by 44.54 and 31.93%, respectively. Moreover, disease incidence was markedly reduced. W14 and W11 yielded disease index values of 16.11 and 19.46, respectively, corresponding to significant reductions of 70.49 and 64.35%, respectively, compared with the CK. Whole-genome sequencing revealed that strain W14 contained more GH19 family chitinase genes, GH5 family glucanase genes, and secondary metabolite biosynthetic gene clusters than strain W11. Functional annotation assigned more strain W14 genes to three major antagonism-related categories: cell wall degradation, antibiotic synthesis, and signal transduction. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses consistently identified more genes involved in metabolic processes and secondary metabolite biosynthesis pathways in strain W14 than in strain W11. Both myxobacterial strains promoted sugar beet seedling growth and protected against diseases associated with continuous cropping, whereas strain W14 showed a greater genomic capacity for antagonistic traits. These findings provide a theoretical basis for the development of novel biocontrol agents. These genomic differences represent candidate correlates of antagonistic potential and require further functional validation.