Plant growth promoting characteristics and stress tolerance of yeasts isolated from Algerian agricultural soils

Abstract

Soil is an important microbial reservoir and studies on soil-plant-microorganism interactions have been particularly interested in bacteria and mycorrhizal fungi roles in soil bio-fertilization unlike yeasts, which remain very little studied. In this context, isolations of various yeast strains have been made from the rhizosphere of different legumes. The molecular taxonomy of the nine isolated strains revealed that they belong to the following three genera: Meyerozyma guillieromondii, Debaryomyces hansenii and Rhodotorula mucilaginosa. These strains, alongside a Saccharomyces cerevisiae strain considered as a reference strain in this work, have been the subject of a study for tolerance to the most encountered stresses in the Algerian biotope mainly salinity, temperature and pH. The latter was carried out on two media (rich medium and minimum medium) where the maximum tolerance reached by certain strains of yeast was 2.1M for salinity and 42°C for temperature. Regarding the pH, the isolated strains for the most part showed a preference for the alkaline pH. The second part of this work was devoted to the demonstration of the PGP (Plant Growth Promoting) function of these strains by studying the following characters: IAA, zinc solubilization, production of NH3, catalase, protease and phosphorus solubilization. Indeed, the vast majority of studied yeasts have at least five of the six PGP characters tested. These results allowed us to select five strains for a study of their PGP effects on the legume Phaseolus vulgaris and this with the aim of using them in soil biofertilization.