Screening for indole-3-acetic acid synthesis and 1-aminocyclopropane-carboxylate deaminase activity in soil yeasts from Chile uncovers Solicoccozyma terrea as an effective plant growth promoter

Abstract Background and aims Plant growth-promoting microorganisms (PGPMs) stimulate plant growth by a series of mechanisms, including atmospheric nitrogen fixation, phosphorus solubilization and the synthesis of plant hormones. Within the group of PGPMs, several species of bacteria and fungi have been extensively studied. However, little information is available with regard to soil yeasts. The present study was conducted to identify yeast strains isolated from different soils in Chile that present plant growth promotion activity. Methods Twenty-three strains were evaluated either for their capacity to synthesize indole-3-acetic acid or show aminocyclopropane-1-carboxylate deaminase activity. The effect on tomato seedling growth was evaluated in vitro , and two strains were selected for in vivo evaluation of plant growth and root ethylene synthesis. Results All the strains analyzed presented IAA synthesis within the range between 0.8 and 3.3 μg IAA mL −1 . Solicoccozyma terrea (YCPUC75 and YCPUC79 strains) was the only yeast with ACC deaminase activity. In vitro inoculation of tomato seeds with eight of the evaluated strains resulted in an increase in the root volume and the number of lateral roots. In the second experiment, a 40% reduction in root ethylene synthesis was achieved by adding S. terrea (YCPUC79) to the root zone, which resulted in a 26% increase in plant growth. Conclusions Solicoccozyma terrea YCPUC79 is an effective plant growth promoter stimulating root growth and reducing root ethylene synthesis.