Streptomycetes isolated from the rhizosphere of agricultural soils in the Valle del Mezquital, Mexico: in vitro production capacity of growthpromoting metabolites and antagonists against phytopathogenic fungi

The Valle del Mezquital, Mexico, is one of the main cropproducing areas in the country. This valley is irrigated by wastewater, primarily from Mexico City. This characteristic creates unique environmental conditions that can impact microorganisms in agricultural soils. In this study, actinomycetes were isolated from the rhizosphere of agricultural soils to characterize them and determine their potential as plant growth promoters and inhibitors of phytopathogenic fungi. Thirteen strains of the Streptomyces genus were isolated, and in vitro studies revealed that all could produce indoleacetic acid, siderophores, and organic acids. Streptomyces thinghirensis and Streptomyces lateritius solubilized phosphates, while Streptomyces lusitanus produced HCN. Previously unreported strains with antagonistic activity against plant pathogenic fungi were identi!ed, the main ones being Streptomyces pseudogriseolus, Streptomyces atrovirens, Streptomyces lateritius, Streptomyces nigra, and Streptomyces griseoplanus. The results obtained provide new knowledge into Streptomycetes that have not been previously studied and may o"er tools for the biological control of diseases caused by phytopathogenic fungi, as well as strategies for enhancing productivity under conservation tillage conditions.