Summary: Bacillus subtilis GLB191 (hereafter GLB191) is an efficient biological control agent against the biotrophic oomycete Plasmopara viticola , the causal agent of grapevine downy mildew. In this study, we show that GLB191 supernatant is also highly active against downy mildew and that the activity results from both direct effect against the pathogen and stimulation of the plant defences (induction of defence gene expression and callose production). High‐performance thin‐layer chromatography analysis revealed the presence of the cyclic lipopeptides fengycin and surfactin in the supernatant. Mutants affected in the production of fengycin and/or surfactin were thus obtained and allowed us to show that both surfactin and fengycin contribute to the double activity of GLB191 supernatant against downy mildew. Altogether, this study suggests that GLB191 supernatant could be used as a new biocontrol product against grapevine downy mildew.

Beneficial rhizobacteria promote plant growth and protect plants against phytopathogens. Effective colonization on plant roots is critical for the rhizobacteria to exert beneficial activities. How bacteria migrate swiftly in the soil of semisolid or solid nature remains unclear. Here we report that sucrose, a disaccharide ubiquitously deployed by photosynthetic plants for fixed carbon transport and storage, and abundantly secreted from plant roots, promotes solid surface motility (SSM) and root colonization by Bacillus subtilis through a previously uncharacterized mechanism. Sucrose induces robust SSM by triggering a signaling cascade, first through extracellular synthesis of polymeric levan, which in turn stimulates strong production of surfactin and hyper-flagellation of the cells. B. subtilis poorly colonizes the roots of Arabidopsis thaliana mutants deficient in root-exudation of sucrose, while exogenously added sucrose selectively shapes the rhizomicrobiome associated with the tomato plant roots, promoting specifically bacilli and pseudomonad. We propose that sucrose activates a signaling cascade to trigger SSM and promote rhizosphere colonization by B. subtilis. Our findings also suggest a practicable approach to boost prevalence of beneficial Bacillus species in plant protection.

Summary: The rhizosphere microbiome plays an important role in the growth and health of many plants, particularly for plant growth‐promoting rhizobacteria (PGPR). Although the use of PGPR could improve plant production, real‐world applications are still held back by low‐efficiency methods of finding and using PGPR. In this study, the structure of bacterial and fungal rhizosphere communities of Jinxiang garlic under different growth periods (resume growth, bolting and maturation), soil types (loam, sandy loam and sandy soil) and agricultural practices (with and without microbial products) were explored by using amplicon sequencing. High‐efficiency top‐down approaches based on high‐throughput technology and synthetic community (SynCom) approaches were used to find PGPR in garlic rhizosphere and improve plant production. Our findings indicated that Pseudomonas was a key PGPR in the rhizosphere of garlic. Furthermore, SynCom with six Pseudomonas strains isolated from the garlic rhizosphere were constructed, which showed that they have the ability to promote plant growth.

The ability of a rhizosphere-derived microbial product (composed of a consortium of a strain of Bacillus subtilis and a strain of Trichoderma harzianum) to suppress common scab disease in potato caused by Streptomyces spp. was examined over a two-year period. Relative to the condition in which 0 kg·ha^-1 of the designated microbial product was applied (control), the disease index decreased by 30.6%-46.1%, and yield increased by 23.0%-32.2% in treatments in which 225 or 300 kg·ha^-1 of the microbial product was administered, respectively. The bacterial communities present in the rhizosphere were assessed at an early stage of tuber formation, a time at which tubers are susceptible to common scab. Potato plants in which soils were treated with 225 or 300 kg·ha^-1 of the microbial product harbored rhizospheric microbiota with lower α-diversity and an increased relative abundance of taxa representing the beneficial bacteria. In summary, a select microbial product composed of a consortium of Bacillus subtilis and Trichoderma harzianum effectively suppressed common scab disease and increased tuber yield by establishing a high relative abundance of beneficial bacteria in the rhizosphere.