Caracterização molecular de Chrysodeixis includens em soja no Brasil

Abstract

Soybeans are one of the crops with the highest expression in Brazil, both in area planted as in sales volume. The culture has as main pests defoliating caterpillars. Among these, stands out Chrysodeixis includens, pest that went from of secondary status in the 90s to a major defoliating caterpillar soybeans. Studies on genetic variation among populations and genetic structure of this species have not yet been carried out, and can help to indicate management practices. Molecular markers are tools indicated to genetically characterize insect populations. In order to use molecular tools, first, it is necessary a method for DNA extraction in quantity and quality that enables the practice in the laboratory. The goals of the study were to compare three DNA extraction methods for soybean caterpillars to applicate in PCR techniques, and analyze the molecular variability and the genetic structure of populations of C. includens in soybeans. Caterpillars of C. includens and S. eridania were collected from different sites in center soybean regions of Brazil, in 2011/12. The confirmation of the species was based on morphological characteristics of caterpillars according to identification keys. Samples of C. includes and S. eridania coming from Goiás were used for DNA extraction comparison test. The methods used were based on cell lysis by Sarcosyl, CTAB and SDS. Each method was compared for quantity, quality, economy and performance in PCR. The best DNA extraction method was chosen for extraction of all the caterpillars samples for molecular characterization work. Thirty populations of C. includens from nine Brazilian states were subjected to analysis of molecular variability and genetic structure with ISSR markers. The observed DNA extraction method with the best performance in the variables o was the DNA extraction method by Sarcosyl. ISSR generated 247 loci in 262 specimens analyzed. The estimated genetic diversity (HE) in populations ranged between 0.072 and 0.120, while the average was 0.094. The analysis of molecular variance indicates that 94% of the variability between individuals was expressed in 6% of the population and among populations (FST = 0.056, p = 0.001). The high level of gene flow and low genetic structure are indicatives of genetic information exchange between different sampling locations. The analysis of the genetic structure suggests the presence of two major groups which are not correlated to their sampling locations in Brazil. These results may indicate the recent colonization of C. includens in Brazil or the pattern of migration of moths following the cropping system in Brazil. Furthermore, the presence of two groups of C. includens suggest that the studies of development of resistance need to be further assessed for them both.