RESUMO Alternaria sp. é um fungo que causa podridão em diferentes culturas agrícolas, causando danos a cadeia de produção. Agentes de controle biológico são uma alternativa para reduzir o uso de agrotóxicos nas lavouras, uma demanda social para a agricultura moderna. O objetivo deste trabalho é demonstrar o efeito antagônico da levedura Trichosporon asahii (3S44) no desenvolvimento micelial de Alternaria sp. e alguns dos mecanismos de ação in vitro. Trichosporon asahii apresenta atividade antagônica frente Alternaria sp., com inibição micelial (57,47%). Os ensaios indicaram a produção de compostos orgânicos voláteis (COVs), competição por nutrientes, formação de biofilme, produção de toxina killer e β-1,3-glucanase como mecanismos de ação de T. asahii. Coletivamente, os resultados demonstraram o potencial de T. asahii no controle do desenvolvimento micelial de Alternaria sp. e mecanismos de ação da levedura, para futuros estudos biotecnológicos.

ABSTRACT Alternaria sp. is a fungus that causes rot in several crops, causing damage to the agricultural production chain. Biological control agents constitute an alternative to reduce the use of pesticides in the crops, a social demand for modern agriculture. The aim of the present study is to demonstrate the antagonistic effect of the yeast Trichosporon asahii (3S44) on the mycelial development of Alternaria sp. and some in vitro mechanisms of action. Trichosporon asahii showed antagonistic activity towards Alternaria sp., presenting mycelial inhibition (57.47%). The assays indicated production of volatile organic compounds (VOCs), competition for nutrients, biofilm formation, production of killer toxins and β-1,3-glucanase as mechanisms of action of T. asahii. Collectively, our results showed the potential of T. asahii to control the mycelial development of Alternaria sp. and some mechanisms of action of this yeast for future biotechnological studies.

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.

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.