An unexpected guest: plant growth promoting yeasts from Patagonia.

M. C. MESTRE

La Falda

Workshop; II Workshop Latinoamericano sobre PGPR; 2014

Bacteria, filamentous fungi and yeasts are found in soils worldwide; although yeast had received less attention than the others groups. Soil yeasts are found in the bulk soil, the rhizosphere, the mycorrhizosphere and inside roots. The relevance of yeasts to soil function is not yet fully understood, although it is known that they influence soil aggregation, contribute to nutrient cycles and interact with plants. Soil yeasts were traditionally associated to soil organic matter decomposition process. More recently it was also described their ability to act as plant growth promoters by producing compounds such as auxins, siderophores and polyamines; or to inhibit the growth of plant roots pathogens (as bio-control agent). In the last 10-15 years, the yeast diversity in the Andean Patagonia region has been surveyed in many natural habitats which had render a high number of new yeast species and somepotentialbiotechnological tools (photo-protective compounds or psicro-tolerant enzymes). The native forests in the region, with its low anthropogenic impact and minimal atmospheric pollution, represent an opportunity to study both the natural eco-functional role of soil yeast as well as to survey for new biotechnological tools. Forestry is one of the main economic activities in Nor-Patagonia region, and there is an increasing interest in promoting this activity for improving the socio-economic development of the region. In countries where forestry industry had a high development, microorganisms are sometimes used for seedling production in nursery; but in Argentina this is not a common practice. After diversity studies conducted in the Norwestern-Patagonia natural forests (which render a collection of nearly 600 isolates distributed in 40 species), we decided to study the potential use of soil yeast as plants growth promoters for forestall production. Four main characteristics were test in-vitro: auxine-likes and siderophores compound production, phosphate solubilization and growth inhibition of pathogens (Pythium, Fussarium and Verticillium). One of the challenges was to select a group of procedures suitable for yeast, as these microorganisms had some special growth requirement. We initiated the surveys with classical bacterial media and then, modified them when needed. As initial screening we used 2 well characterized isolates of each species in the collection.For some species a great intra specific variation was observed, while in others the variations were only on the level of production. Plant growth promoting characteristics seems to be more widely distributed among species from Ascomycota Phyllum. We were able to identify one ascomycetous and one basidiomycetous species able to produce high amount of auxine like compounds, which will be candidates to explore auxins-like metabolic pathway in yeast. Some yeast showed a high siderophores production (up to 550% yield), and this feature seems to be species specific. Only weak PO4 solubilization was observed, that seems to be associated to fermenting Ascomycetous species. Four yeasts were test as biocontrol agents, resulting in up to 30% of growth inhibition of Pythium and Verticillium.