Yeasts are an interesting group of microorganisms, which occur naturally in soil and on plant surfaces. Few studies have analysed their potential as plant growth promoters. Thus, the aim of this study was to evaluate the indole acetic acid (IAA) production and phosphate solubilization by the yeasts Torulaspora globosa (CCA5S51 and CCA5S55), Meyerozyma guilliermondii (CCA3C98), and Rhodotorula mucilaginosa (CCA2F32), and the influence of T. globosa (CCA5S55) in the development of tomato seedlings. The results showed that T. globosa strains present both plant growth promotion traits (IAA production and phosphate solubilization). The strains of T. globosa (5S51 and 5S55) showed high IAA production (641 and 669 µg.ml-1, respectively) after 48 h of incubation, while Rh. mucilaginosa produced 406 µg.ml-1 of IAA after 120 h. The strains CCA5S55 and CCA5S51 could also solubilize 47 and 35% of tricalcium phosphate in the medium, respectively, after 12 days of incubation; whereas M. guilliermondii (CCA3C98) solubilized only 10% of the tricalcium phosphate after 12 days. The inoculation of tomato seedlings with T. globosa stimulates the plant growth; root height was statistically superior when the higher cell concentration was inoculated. The root dry weight was enhanced with addition of glucose and tryptophan. The conclusion is the yeast species T. globosa is able to produce IAA in the presence of tryptophan and also solubilize phosphate in vitro. The inoculation of tomato seedlings promoted its development. The cell concentration and the addition of glucose and tryptophan must be evaluated in details to attain optimized yields.
Key words: indole acetic acid (IAA) production, phosphate solubilisation, yeast as plant growth promoter.
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