Screening endophytic actinobacteria with potential antifungal activity against Bipolaris sorokiniana and growth promotion of wheat seedlings

Actinobacteria secrete substances that limit or inhibit the growth of plant pathogenic fungi and may be used in the biocontrol of these microorganisms. The aim of this study was to characterize physiological and enzymatic activity of endophytic actinobacteria, evaluate their antifungal activity against Bipolaris sorokiniana root colonization, and evaluate their efficiency in promoting the growth of wheat seedlings. Antibiosis was analyzed using the double-layer method, the agar well diffusion test, and volatile metabolites. Physiological and enzymatic activity was evaluated through chitinase, glucanase, siderophores, indole-3-acetic acid, nitrogen fixation and phosphate solubilization tests. In vivo assays were evaluated by root colonization, biocontrol test and efficiency to promote the growth of wheat seedlings. From all isolates tested, 69.6% of them presented antifungal activity against at least one B. sorokiriana isolate. Among these, 17% of the isolates produced bioactive metabolites in the supernatant when grown in submerging culture. The highest production of bioactive metabolites was at 30°C, between 72 and 96 h of incubation. Three isolates produced volatile compounds, chitinase, glucanase, siderophores and exhibited nitrogen fixation, produced indole-3-acetic acid, efficiently colonized the root system of seedlings of two wheat cultivars. The best isolate [6(2)] showed, under the greenhouse, the capacity to promote an increased biomass and tillers per wheat plant.