Potential Effects of Brevibacillus spp. in Control of Brown Spot Disease and Productivity of some Faba Bean Genotypes

Abstract

This study investigated the interaction between Botrytis fabae, faba bean genotypes and a promising Brevibacillus brevis isolate under greenhouse and field conditions in Toshka, Egypt. Several B. fabae isolates obtained from naturally infected foliage were compared in pathogenicity tests; isolate Bf-5 was consistently the most aggressive, causing 45% necrotic leaf area on detached leaves and was
therefore used for all subsequent inoculations. Five bacterial antagonists were screened in vitro, and Brv-M1 showed the strongest activity, reducing radial mycelial growth of B. fabae by about 39% and lowering spore germination by roughly 30–35% compared with the control. Brv-M1 also produced clear halos of chitinase, β-1,3-glucanase and protease in plate assays, indicating a multi-enzymatic
mode of action. GC–MS analysis of the ethyl acetate extract revealed a chemically diverse mixture of non-volatile metabolites. Under greenhouse conditions with artificial inoculation, foliar application of Brv-M1 to 17 faba bean genotypes led to moderate reductions in chocolate spot severity, generally in the range of 6–25% depending on genotype, and was accompanied by increased peroxidase, catalase and total phenolic levels in several responsive lines. In the field at Toshka, natural chocolate spot pressure remained moderate disease severity 31.7–42.5% in untreated plots, and Brv-M1 treatment lowered severity to about 22.8–39.3%, corresponding to 6–28% reduction without substantially altering disease incidence. Agronomic data across two seasons showed that a small subset of genotypes particularly G12 and G15, together with the local check Mariout 2 combined relatively low or intermediate disease levels, clear benefits from Brv-M1 treatment, and superior yield performance e.g. seed yield 51–53.5 g plant⁻¹ under the hot, arid conditions of Toshka. Overall, the results indicate that Brv-M1 acts as a biologically realistic, partial suppressor of chocolate spot, mediated by a
mixture of lytic enzymes and structurally diverse metabolites. The convergence of good agronomic adaptation and favourable disease response in Mariout 2, G12 and G15 highlights these genotypes as promising candidates for use in combination with Brv-M1 within integrated chocolate spot management packages. Some additional work—particularly on formulation, field performance and biosafety is still needed before Brv-M1 can be confidently integrated into faba bean integrated disease management programs.