Sugarcane molasses as substrate to soil yeasts: Indole-3-acetic acid production and maize initial growth promotion

Abstract

Plant growth promoter microorganisms (PGPM) associate with plants with benefits to plant productivity and protection. Among these microorganisms, yeasts have shown potential results. The aims here were to prospect yeasts with PGPM traits from organic maize soil and to evaluate molasses as substrate to produce indole-3-acetic acid (IAA). The isolates were selected considering IAA production, phosphate solubilization and phytopathogen control, following the phenotypic characterization. Seven strains were selected, identified by sequencing of D1/D2 domain of rDNA 26S gene and evaluated to produce IAA in molasses and potato dextrose broth (PD) with and without tryptophan. Non-filtered medium (NFM) and cell-free filtrate (CFF) of yeasts were used in an in vivo assay of maize seed germination and initial development. Twenty-eight yeasts were isolated, and 82% tested positive for the PGPM traits. The strains were identified as Torulaspora globosa (three strains), Aureobasidium pullulans, Candida pseudointermedia, Trichosporon asahii and Cryptococcus sp. T. globosa and C. pseudointermedia stood out regarding the IAA production. Molasses was more beneficial to cell growth and/or IAA production to five out of seven yeast strains. In general, the in vivo assay with maize demonstrated that the seed treatment with cell-free filtrates of yeasts promoted the initial development of plants (radicle and coleoptile), and the seed treatment with non-filtered medium resulted in higher maize plant development after 12 days of pot cultivation. The results indicate molasses as a medium for a prospective yeast-based biostimulant product for agricultural use and pointed out for the soil yeast species T. globosa and T. asahii as biological agents to contribute to plant growth promotion.