Maize treatment with yeast cells induces resistance against Fusarium rot.

Maize is one of the most cultivated species and requires agrochOPemicals for nutrition and pathogen control. Fusarium verticillioides is responsible for damaging plants and stored grains. Plants naturally exposed to stresses have defense mechanisms that are triggered by chemical or biological agents, known as induced systemic resistance. In this study, the yeast Torulaspora globosa (strain CCA6S01) was evaluated as an immune response promoter in maize against F. verticillioides. The treatments started 4 days after maize emergence and consisted of control (saline solution), acetylsalicylic acid (ASA, 100 mg/L), yeast cells (1 × 105 cells/mL), or yeast metabolites (cell-free filtrates). After running the treatments, the plants were inoculated with 1 mL of a F. verticillioides suspension at a concentration of 1 × 106 spores/mL. The application of yeast cells provided similar results to ASA treatment, a known inducer of plant resistance. Yeast cells provided maize plants with fewer rot symptoms and higher activities of enzymes related to plant resistance. Thus, we concluded that T. globosa (strain CCA6S01) might be used in agriculture practice as a plant protection agent. It can help to decrease the application of fungicides in the field and maintain plant productivity under stress.

Phosphate solubilization and indole acetic acid production by rhizosphere yeast Torulaspora globosa: improvement of culture conditions for better performance in vitro.

The rhizosphere yeast Torulaspora globosa is known to produce indole acetic acid (IAA) and to solubilize minerals. Due to the prospective use of this yeast as a biostimulant for agricultural applications, this work aimed to optimize the cultural conditions for both IAA production and phosphate solubilization. For phosphate solubilization, the temperature (20, 25 and 30 °C), initial medium pH (3.0, 5.0, and 7.0), and shaker speed (without mixing, 100 rpm, 150 rpm, and 200 rpm) were considered using the one-factor-at-a-time (OFAT) design. Temperature of 25 °C, initial medium pH 7.0, and static cultures were the conditions of greatest phosphate solubilization, with 40% of the total phosphorus content solubilized from calcium phosphate (419.86 mg L-1) after 48 h. By using the response surface methodology, the maximum IAA production (217.73 µg mL-1) was obtained with the highest initial pH 7.0, the lowest nitrogen, and glucose concentrations (5 g L-1 and 10 g L-1, respectively) and the lowest agitator speed (100 rpm). Further tests indicated that nitrogen affected significantly IAA production and the absence of nitrogen in the medium promoted higher IAA production (457 µg mL-1). The results obtained here may contribute to the scaling up for industrial and agricultural applications of a yeast-based product with T. globosa.

Release of potassium from rock powder by the yeast Torulaspora globosa

The alteration of minerals in rocks and the availability of elements for plant nutrition require long periods of time, and microorganisms are thought to induce the release of potassium and phosphate from rocks. In this context, this work evaluates the role of the yeast Torulaspora globosa, isolated from the sugar cane rhizosphere, in the solubilization of potassium from alkaline ultramafic rock powder. The experiments were performed in liquid medium, with or without agitation, at 30°C with the following treatments: culture medium + alkaline ultramafic; culture medium + yeast suspension; and culture medium + yeast suspension + alkaline ultramafic. The results showed that as much as 38% of the total potassium in the rock was released in the medium with the yeast during a 15-day period of incubation. Acid production may be the mechanism by which the yeast solubilizes potassium because the total acidity increased during the sampling period. Agitation (which increased oxygen availability) resulted in approximately 20% more biosolubilization of the alkaline ultramafic rock than with the static culture. These data indicate the potential for this yeast in biosolubilization processes and biofertilizer production.

Bioprospection of yeasts as biocontrol agents against phytopathogenic molds

Yeasts isolated from sugar cane and maize rhizosphere, leaves and stalks were screened against the phytopathogenic molds Colletotrichum sublineolum and Colletotrichum graminicola, both causal agents of the anthracnose disease in sorghum and maize, respectively. Strains identified as Torulaspora globosa and Candida intermedia were able to inhibit the mold growth, with the first species also exhibiting killer activity. No previous report on the application and potentiality of these yeasts as biocontrol agents were found neither the killer phenotype in Torulaspora globosa.