Dual Action of Bacillus and Lactobacillus spp.: Promoting Bean Cultivar Development and Suppressing Xanthomonas axonopodis pv. phaseoli

Common bacterial blight (CBB) is a significant disease caused by the seed-borne pathogen Xanthomonas axonopodis pv. phaseoli (Xap), which devastates global bean production. This study evaluated the effects of Bacillus subtilis (Bst26), Lactobacillus plantarum (Lpkb10), their combination (Bst26 + Lpkb10), copper hydroxide (CH), and an untreated control on controlling CBB in three bean cultivars (Göynük, Saltan, and Tezgeldi). Disease incidence (CI), disease severity index (DSI), severity score (SC), area under disease progress curve (AUDPC), and disease control (DC), along with agronomic traits such as plant height, number of primary branches, root length, and fresh root weight, were recorded to assess both infection rates and plant health under each treatment. The findings revealed significant differences in DI, DSI, SC, AUDPC, and DC (p ≤ 0.01) among the bean cultivars for CBB. Among the cultivars, the Bst26 treatment and the combination of Bst26 and Lpkb10 showed the highest control effectiveness, with DI values of 33.11% and 33.46% in Saltan, 35.65% and 44.16% in Göynük, and 37.71% and 42.43% in Tezgeldi, respectively, at 21 days after inoculation (DAI). Bst26 alone and in combination with Lpkb10 effectively controlled CBB, with disease reduction of 56.80% and 46.49% in Göynük, 57.08% and 56.62% in Saltan, and 52.18% and 46.19% in Tezgeldi, respectively. Disease progression was highest in the untreated control, with DI ranging from 77.15% to 82.54% across Göynük, Saltan, and Tezgeldi cultivars. Significant differences (p ≤ 0.01) in plant height, root length, and root weight were observed among treatments and cultivars. Disease parameters were negatively correlated with plant growth traits, and multi-treatment analysis demonstrated that combining bacterial strains effectively reduced disease severity in susceptible cultivars, highlighting their potential for improved CBB management.