Bacillus strains from a fire affected oyamel-fir forest soil as biocontrol and plant-growth-promoting bacteria

The exploration of microbial strains for the biocontrol against Fusarium diseases in maize, from extreme environments within native ecosystems, holds significant importance. For these reasons, this study aimed to obtain bacterial strains from the soil of a Mexican oyamel-fir forest impacted by fire, with the goal of inhibiting the growth of strains of the species complexes of F. oxysporum , F. sambucinum , F. incarnatum-equiseti and F. fujikuroi , which are responsible for maize rot diseases in the country. Bacterial strains were isolated and in vitro characterized for their production of indoleacetic acid, siderophore, and hydrolytic enzymes. Additionally, they were evaluated for their ability to solubilize phosphate, and inhibit the growth of Fusarium spp. Furthermore, the strains were identified through a 16S rRNA phylogenetic analysis and in vivo evaluated for promoting maize seedling growth and inhibition of seedborne Fusarium spp. Bacillus sp. B4 and B28 inhibited the growth of the strains of the four Fusarium species complexes up to 76 -98 % in dual cultures; additionally, they prevented systemic infection and reduced mycelial growth on maize seed coat by up to 50 %, caused by seedborne Fusarium strains within the F. fujikuroi species complex. Moreover, both strains were non -plant pathogenic, and demonstrated cellulases, pectinase, and siderophore production. Furthermore, B4 and B28 exhibited the ability to enhance maize seedlings length and water holding capacity. Bacillus sp. B4 and B28 are valuable native genetic resources, that could offer a sustainable alternative to replace or reduce chemical fertilizers and pesticides used in Mexican maize producing areas.