Biocontrol and plant growth promotion by combined Bacillus spp. inoculation affecting pathogen and AMF communities in the wheat rhizosphere at low salt stress conditions

Abstract

Applying plant growth-promoting rhizobacteria (PGPR) improves the efficiency of soil-borne disease control and is considered a sustainable practice. However, the effect of PGPR on the fungal community, especially pathogenic fungi and arbuscular mycorrhizal fungi (AMF), remains unclear. In this study, we examined the effects of a compound microbial agent (consisting of Bacillus subtilis HG-15 and Bacillus velezensis JC-K3) on the incidence and yield of wheat under low salt stress, as well as compared the diversity and community composition of the rhizosphere fungal and AMF communities of wheat in the CK (not inoculated bacterial agent) and BIO (inoculated with a bacterial agent) groups. Chlorophyll relative content (SPAD), net photosynthesis rate (Pn), transpiration rate (Tr), leaf water use efficiency (WUEL), grains per spike and wheat yield in the BIO group increased more than in the CK group. The number of diseased plants and disease incidence was observed to be reduced. The relative efficacy reached 79.80%. We classified 1007 fungal operational taxonomic units (OTU) based on Miseq sequencing data: 11 phyla, 173 families, 319 genera, and 521 species. Fifty-four OTUs were classified from the AMF effective sequences, including 1 phylum, 3 families, 3 genera, and 17 species. The inoculation of bacterial agents reduced the relative abundance of pathogen genera such as Gibberella, Fusarium, Cladosporium, and Alternaria in wheat rhizosphere. It increased the relative abundance of AMF species such as Glomus-group-B-Glomus-lamellosu-VTX00193, Glomus-viscosum-VTX00063, and Glomus-Glo2-VTX00280. In addition, pH, EC, exchangeable K, available N, total N, organic matter, and olsen P were the main driving forces for shaping wheat rhizosphere fungi. The pH value was positively correlated with the relative abundance of fungal communities in soil, especially Gibberella, Cladosporium, Fusarium, and Alternaria. In summary, inoculation with Bacillus subtilis HG-15 and Bacillus velezensis JC-K3 affected wheat yield, incidence, rhizosphere soil chemical properties, rhizosphere fungi, and AMF fungal diversity and community. The findings may provide a theoretical foundation and strain support for constructing efficient PGPR-community and clarifying its mechanism of pathogenic bacteria inhibition.

Arbuscular Mycorrhizal Fungi and Higher Plants

“…The rational use of AMF with other microorganisms maximizes plant tolerance to diseases by competing with harmful pathogens (Devi et al 2022). Studies have also revealed that the combined application of AMF and other beneficial plant microorganisms like plant growth-promoting rhizobacteria (PGPRs) impacts plant root exudation, thereby altering the rhizosphere niche (Ji et al 2022). Furthermore, deciphering the far-reaching changes in plant metabolome, microbiome, and molecular reprogramming under the influence of AMF in diseased and non-diseased conditions will provide better outcomes in AMF-mediated plant disease management.…”

Transcriptome-based analysis of the effects of compound microbial agents on gene expression in wheat roots and leaves under salt stress

“…Photosynthetic electron transport in photosystem I, photosynthesis, dark reactions, and the reductive pentose-phosphate cycle were the main types of biological processes in leaves ( Figure 2D ). This indicated that the BIO treatment mobilized the primary and secondary metabolisms and finally regulated the expression of related genes through signal transduction and ion transport, which clearly induced the salt stress defense responses and had the greatest effects on ion absorption and antioxidant activity of wheat root cells and on the photosynthesis of leaf cells ( Abdelgawad et al., 2022 ; Ji et al., 2022a ).…”

“…Bacillus velezensis JC-K3 and Bacillus subtilis HG-15 are two strains of rhizosphere-beneficial bacteria with both growth-promoting and disease-preventing functions ( Ji et al., 2021 ; Ji et al., 2022b ). The two strains have no antagonistic effects and can stably colonize wheat roots in saline-alkali land.…”

“…Both strains have the characteristics of producing ACCD, indole-3-acetic acid (IAA), siderophore, and proline. They have clear effects in promoting wheat growth and can systematically induce wheat to synthesize more soluble sugars and proteins, thereby reducing salt stress damage and promoting plant root development and nutrient absorption ( Ji et al., 2021 ; Ji et al., 2022a ). In particular, inoculation with JC-K3 increases the abundance of bacterial communities in branches and leaves, reduces the abundance of fungal communities, and reduces the richness and diversity of bacterial and fungal communities in wheat roots.…”

Interactions between halotolerant nitrogen-fixing bacteria and arbuscular mycorrhizal fungi under saline stress

“…Halotolerant PGPRs with 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase activity can reduce plant ethylene accumulation, prevent oxidative stress, promote plant growth, and regulate the rhizosphere microbial community structure. Consequently, halotolerant PGPRs have become a valuable microbial resource for promoting crop growth in saline-alkali soils ( Ji et al, 2022a ; Li et al, 2023 ). Among the beneficial microorganisms in saline soils, ascomycetous fungi (AMF) can form a symbiotic relationship with most crops, improving soil nutrient acquisition, promoting plant growth and water absorption, and initiating defense responses in host plants ( Bennett and Groten, 2022 ).…”