Biocontrol of Fusarium oxysporum f.sp. phaseoli and Phytophthora capsici with autochthonous endophytes in common bean and pepper in Castilla y León (Spain)

Abstract

Fusarium oxysporum f.sp. phaseoli and Phytophthora capsici are soil pathogens which cause diseases to common bean (Phaseolus vulgaris) and pepper (Capsicum annuum), respectively. Some microorganisms associated with plants show different biocontrol mechanisms against pathogens. The agricultural use of these mechanisms is a chief strategy as an alternative to chemicals. In a previous work, we isolated and taxonomically identified 68 endophytic bacteria from common bean and 54 from pepper. The isolations were carried out in farms located in regions protected by a PGI: “Alubia de La Bañeza-León” in the case of common bean, and “Pimiento de Fresno-Benavente” in the case of pepper. The aim of the present work was the evaluation of such bacteria and AM fungus, as potential biocontrollers of F. oxysporum f.sp. phaseoli and P. capsici. In total 18 out of the 122 isolates controlled in vitro the growth either of F. oxysporum or P. capsici, or both pathogens. Such controller bacteria were tested in the plants in which they were isolated (common bean or pepper), which were grown in hydroponic conditions and inoculated with F. oxysporum f.sp. phaseoli and P. capsici, respectively. Two isolates belonging to the species Pseudomonas brassicacearum and Bacillus siamensis, respectively, were the best controllers of Fusarium root rot in common bean. Moreover, two isolates belonging to Bacillus pumilus were the best controllers of P. capsici in pepper plants. In trials carried out in microcosm conditions, common bean plants inoculated with the pathogen F. oxysporum, plus an autochthonous Rhizobium leguminosarum strain and the B. siamensis isolate, showed a very weak pathogen attack. Regarding the pepper microcosm assay, the co-inoculation with one of the B. pumilus isolates plus an autochthonous mycorrhiza controlled P. capsici in the plants inoculated with the pathogen, even at the same level than the chemical fungicide. This opens the door for the development of biocontrollers, alternative to chemicals, in these two crops.