Plant Growth-Promoting Yeasts (PGPYs) as a sustainable solution to mitigate salt-induced stress on zucchini plant growth

Among the long-term sustainable solutions to mitigate saline stress on plants, the use of plant growth promoting microorganisms (PGP) is considered very promising. While most of the efforts have been devoted to the selection and use of bacterial PGPs, little has been proposed with yeast PGP (PGPYs). In this study, three PGPY strains belonging to Naganishia uzbekistanensis, Papiliotrema terrestris and Solicoccozyma phenolica were employed singularly and in a consortium to mitigate salt stress of zucchini (Cucurbita pepo). The results demonstrated that these yeasts, when applied to salt-amended soil, mitigated the growth inhibition caused by NaCl. Among the three species, N. uzbekistanensis and P. terrestris showed the most significant improvements in plant performance, with N. uzbekistanensis exhibiting hormetic effects under salt stress by improving root length and dry plant biomass. In general, the root system was the most affected part of the plants due to the presence of the yeasts. The entire rhizosphere bacterial microbiota was significantly influenced by the addition of PGPYs, while the mycobiota was dominated by the introduced yeasts. Metabolomic fingerprinting using FTIR revealed modifications in hemicellulose and silica content, indicating that PGPY inoculation impacts not only the plant but also the soil and rhizosphere microorganisms.