Molecular identification, toxigenic potential and effects of Aspergillus associated to bean seeds and grains

Abstract

Brazil is one of the world leaders in bean production, besides being one of the biggest consumers of this grain. The deterioration of bean seeds during storage can be enhanced due to the conditions of the storage environment as well as the action of microorganisms. Fungi of the genus Aspergillus are known for their ability to proliferate under low humidity conditions, which favors their association with stored seeds and grains. In addition, these are the main producers of mycotoxins, being a problem of seed health and food safety. The objective of this work was to study the biological relationships between bean seeds and Aspergillus species under natural and controlled storage conditions, as well as under stress conditions caused by accelerated aging and substrate water restriction. In addition, we aimed to identify, using molecular techniques, the main Aspergillus species associated with bean seeds in Brazil, and to characterize their toxigenic potential by prospecting genes involved in mycotoxin biosynthesis. It was observed that the natural storage caused a greater reduction in the physiological quality of bean seeds, however, the association with A. ochraceus and A. parasiticus affected the seed germination even in the controlled environment. In the seeds subjected to stress conditions, water conditioning caused less damage to the physiological quality of the seeds than accelerated aging, and evidenced the differences between the effects of A. ochraceus and A. parasiticus. In both stress conditions, it was observed that the association with A. parasiticus was more harmful to seed quality than A. ochraceus. The molecular identification of Aspergillus strains isolated from 35 lots of Brazilian bean seeds revealed the presence of seven species: A. flavus (n=39), A. pseudocaelatus (n=1), A. westerdijkiae (n=7), A. ostinaus (n=3), A. wentii (n=2), A. ochraceus (n=1), A. niger (n=24) e A. luchuensis (n=10). Genes involved in aflatoxin synthesis were detected only in A. flavus strains. All A. niger isolates showed the full complement of genes belonging to the fumonisins bissinthetic pathway. In none of the isolates was detected the presence of genes involved in ochratoxin biosynthesis.