SOIL SALINITY SHIFTS CULTIVABLE MICROBIAL COMMUNITIES OF WHEAT (Triticum turgidum subsp. durum) RHIZOSPHERE IN THE YAQUI VALLEY, MEXICO

Abstract

Saline soils are a common issue in commercial fields using intensive and irrigated agricultural practices under arid or semi-arid climates, such as the Yaqui Valley in Mexico, one of the most important wheat-producing regions worldwide. This study aimed to assess the cultivable microbial diversity (having plant growth-promoting attributes) associated with wheat rhizosphere in commercial fields, under a saline soil gradient in the Yaqui Valley. Thus, seven wheat commercial zones were studied according to their electrical conductivity (0.9 to 6.4 dS cm^-1). The isolation of microorganisms was carried out by dependent culture techniques, sequencing of the  16S (bacteria) and 5.8S (fungi) rRNA genes , and plant growth-promoting attributes were evaluated: phosphate solubilization (Pikovskaya medium), siderophore production (Chrome Azurol S medium), indole production (Salkowsky reagent), and hemolytic activity (Petri dishes 5 % Sheep Blood). Wheat commercial zones with 1.6 dS m^-1 showed the highest fungal (2.59 x 10⁶ CFU g^-1 dry soil) and bacterial (2.88 x 10⁷ CFU g^-1 dry soil) populations, being Rhizopus and Bacillus the most abundant and well-distributed microbial genera, respectively. The impact of saline soils on the microbial metabolic background was not species- or genus-specific; it was at a strain-specific level. In addition, 52 % of fungal and 83 % of bacterial strains showed the ability to produce γ-hemolysis, suggesting it is not harmful to humans and animals. This work provides a microbial culture collection where their members have shown several beneficial traits that potentially increase the yield and quality of wheat growing under saline soil conditions.