Plant growth-promoting traits of yeasts isolated from Spanish vineyards: benefits for seedling development.

It is known that some microorganisms can enhance plant development. However, the use of yeasts as growth-promoting agents has been poorly investigated. The aim of this study was the characterisation of a collection of 69 yeast strains isolated from Spanish vineyards. Phytobeneficial attributes such as solubilisation of nutrients, synthesis of active biomolecules and cell wall-degrading enzyme production were analysed. Strains that revealed multiple growth-promoting characteristics were identified. The in vitro co-culture of Nicotiana benthamiana with yeast isolates showed enhancement of plant growth in 10 strains (up to 5-fold higher shoot dry weight in the case of Hyphopichia pseudoburtonii Hp-54), indicating a beneficial direct yeast-plant interaction. In addition, 18 out of the 69 strains increased dry weight and the number of roots per seedling when tobacco seeds were inoculated. Two of these, Pichia dianae Pd-2 and Meyerozyma guilliermondii Mg-11, also increased the chlorophyll content. The results in tobacco were mostly reproduced in lettuce with these two strains, which demonstrates that the effect of the yeast-plant interaction is not species-specific. In addition, the yeast collection was evaluated in maize seedlings grown in soil in a phytotron. Three isolates (Debaryomyces hansenii Dh-67, Lachancea thermotolerans Lt-69 and Saccharomyces cerevisiae Sc-6) promoted seedling development (increases of 10 % in dry weight and chlorophyll content). In conclusion, our data confirm that several yeast strains can promote plant growth and could be considered for the development of biological fertiliser treatments.