Beneficial effect of Bacillus sp. P12 on soil biological activities and pathogen control in common bean

Soil is the foundation for agriculture and the medium where almost all food-producing plants are grown. Extensive use of fertilizers and pesticides has affected soil quality, with dangerous ecological effects; therefore, environmentally friendly biological alternatives have been widely recommended. This study explored the potential of Bacillus sp. P12 strain for improving soil quality and consequently favoring growth of common bean (Phaseolus vulgaris L.) and, on the other hand, for controlling infection with the plant pathogen Macrophomina phaseolina, which induces charcoal rot. P12 inhibited in vitro the development of six native M. phaseolina strains isolated from Salta region, with fungal inhibition ranging between 55 and 70%. This bacilli synthesized different isoforms of the lipopeptides kurstakin, surfactin, iturin, polimyxin and fengycin in the presence of the plant pathogen, as determined by MALDI-TOF. Under greenhouse conditions, incidence of M. phaseolina was 100% in white common bean cv. Alubia in the control treatment, whereas seeds inoculated with P12 showed a 40% reduction of the pathogen effect at the end of the trial. Activities of the soil enzymes FDA, DHA and AP were increased (22, 31 and 6.2%, respectively) in the rhizosphere where P12-treated seeds were grown. P12 treatment decreased metabolic quotient, suggesting greater metabolic efficiency. P12 also enhanced the glomalin-related soil protein in the rhizosphere soil. Moreover, populations of the potential native biocontrol agents Trichoderma spp. and Gliocladium spp. increased in the rhizosphere where P12 treatment was applied. Here, Bacillus sp. P12 was found to not only is a potential biocontrol agent, but also improves soil quality, which would enhance properties required for maintaining a healthy soil, rich in nutrients and beneficial microorganisms, thereby improving agricultural production.