Biocontrol potential of endophytic Bacillus spp. Against early blight disease in potato (Solanum tuberosum)

• Endophytic Bacillus strains isolated from healthy potato plants. • Isolates showed strong antifungal activity against Alternaria solani . • Volatiles and metabolites suppressed pathogen growth effectively. • Field trials confirmed reduced early blight and improved yield. • B. velezensis FM-1 proved the most effective biocontrol strain. Early blight, caused by Alternaria solani , is a major disease of potato crops worldwide, leading to considerable yield losses. Although chemical fungicides are commonly used for disease management, concerns over their environmental impact have driven the search for sustainable alternatives. This study evaluates the potential of endophytic bacteria as biocontrol agents for managing early blight in potatoes.Three endophytic bacterial strains— Bacillus velezensis FM-1, B. velezensis FM-10, and Bacillus subtilis FM-15—were isolated from healthy potato plants in Beni Suef Governorate, Egypt. Field trials were conducted over two consecutive growing seasons (2022–2023) to assess their effectiveness in controlling early blight. Evaluations included disease incidence and severity, plant growth parameters, and tuber yield. Antifungal activity was assessed via mycelial growth inhibition assays and analysis of volatile organic compound (VOC) production. All three isolates (FM-1, FM-10, and FM-15) showed strong antagonistic activity against A. solani , with up to 47.44 % inhibition of mycelial growth. VOCs produced by FM-1 completely suppressed fungal growth, while FM-10 produced 26 secondary metabolites contributing to disease inhibition. Field application of the bacterial treatments significantly reduced both disease incidence and severity. B. velezensis FM-1 exhibited the highest efficacy among the bacterial treatments. Although the fungicide Topas 100 EC provided the greatest overall control, the bacterial treatments enhanced plant growth, leading to increased plant height, branching, tuber weight, and total yield compared to untreated controls. Additionally, FM-1 and FM-15 significantly increased total phenolic content (11 and 10 mg/g dry weight, respectively) and proline levels (∼9 mg/g), while reducing malondialdehyde (MDA) accumulation (∼6 mg/g) relative to the control (7 mg/g). This study demonstrates the promising biocontrol potential of Bacillus spp., particularly B. velezensis FM-1, in managing early blight in potatoes. Beyond disease suppression, these endophytic strains enhance plant physiological responses and productivity, offering a viable and eco-friendly alternative to synthetic fungicides for sustainable agriculture.