Solubilização de fosfato natural para a cana-de-açúcar pela levedura rizosférica Torulaspora globosa

Abstract

Many Brazilian soils have a widespread low availability of phosphorus (P) to plants, a condition that leads to the need of frequent phosphate fertilization to ensure economically viable agricultural production. However, the continuous application of large amounts of soluble P for long periods has led to a high retention and accumulation of this nutrient in the soil, with low utilization by plants over time. Despite having low water solubility, natural phosphates (FNs) have had their use increased in recent years, considering that have a lower cost and equivalent potential of industrialized phosphates. This potential does not only depend on their characteristics, but also on the attributes of the soil-microorganism-plant system where they are applied. There are several groups of microorganisms in the rhizosphere that show competence to extract and/or solubilize fractions of soil P and inorganic FNs with low solubility, including fungi and yeasts - these are called phosphate solubilizing microorganisms. The objective of this study was to evaluate the yeast capacity to solubilize P and make it available for the nutrition of sugarcane plants. Experiments were carried out and the yeast was cultivated in vitro (in a laboratory) and ex vitro (in a greenhouse). During in vitro assays in liquid culture medium NBRIP treatments with addition of yeast and different sources of phosphate were tested in incubation for five days at 25ºC and 160 rpm. The concentration of soluble P (molybdenum blue method) and the pH of the culture medium were measured on the day of assembly of the assays and after five days of incubation. In the ex vitro tests, sugarcane plants were cultivated in pots with soil fertilized with FN and inoculated with Torulaspora globosa. Pots with soil without addition of P and with addition of Monocalcium Phosphate (FM) were used as control. After plant cultivation, root and shoot dry biomass, leaf length, number of leaves of each plant, observation of spores in the soil, evaluation of mycorrhizal colonization and analysis of P and Ca concentration in the root and in the aerial part of the plant were measured. During the in vitro assays there was an increase in the acidification of the culture medium in the presence of FN and yeast. Furthermore, the yeast T. globosa was responsible for a significant increase in the concentration of soluble P in the NBRIP culture medium in treatments with yeast and rock phosphate. In ex vitro assays, no significant interaction was found between phosphate and yeast factors in the analyzes performed. After the cultivation of sugarcane plants, the treatment with FM showed higher values ​​of aerial parts growth, dry biomass and concentration of P in the aerial part. The potential of FNs solubilization by the yeast T. globosa should continue to be evaluated, mainly in tests carried out ex vitro.