Estudo da variabilidade de Aspergillus flavus link associado a amêndoas da castanheira do brasil (Bertholletia excelsa bonpl.) da região Amazônica

Abstract

Brazil nuts are an important commercial product of northern Brazil, however this product has been rejected by the international market due to high levels of aflatoxin contamination. The fungus considered more important in the production of these mycotoxins is Aspergillus flavus. In order to provide data for the development of an efficient strategy for the detection of aflatoxigenic A. flavus, which will contribute greatly to the quality control of the Brazil nuts, this main scope of this work was to study the genetic diversity of the fungi A. flavus isolated from almonds produced by different regions of Amazon. For this we have used microsatellite markers (SSR) which have proven to be effective for the study of genetic diversity between individuals and populations. We have selected 100 isolates of Aspergillus sp., and species identification was performed by sequencing the rDNA ITS region. It was identified 32 Aspergillus nomius, 49 Aspergillus flavus, 16 Aspergillus tamarii and 1 Aspergillus fumigatus. In the study of genetic diversity was used 12 SSR markers developed specifically for the species A. flavus and selected from the literature. Two groups of isolates of A. flavus were formed according to the origin of Brazil nuts (Humaitá / AM and Acre), and a third group isolated from nuts previously acquired in trade fairs in Belém / PA were also included in the study, totaling 86 individuals. Ten of the twelve markers used were efficient in PCR amplification. According to the result all the 10 loci studied were polymorphic, and from the 86 individuals analyzed 118 alleles were identified ranging from 110-390 base pairs. The number of alleles per locus ranged from 8-16 with a mean of 11.7. The statistical mean value for genetic differentiation (Gst) was 0.099, which represents a low genetic variation between the groups. However, the genetic diversity within groups accounted for 85.9% of the total genetic diversity, indicating a greater variability within groups. The coefficient of similarity wasused to estimate the genetic distance between the 86 A. flavus, it ranged from 0.7 to 1.0 with an average of 0.96. The genetic distance was also calculated between populations and ranged from 0.562 to 0.7287. Thus it is concluded that the isolates showed high polymorphism among them, however a greater variability was found within the groups (85.5%), while diversity among the groups was only 14.5%. And according to the groups formed by genetic diversity analysis of A. flavus using SSRs markers, there was no correlation with the origin of the isolates