Análise de desquilíbrio de ligação e diversidade genética em soja utilizando marcadores moleculares

Abstract

The success of plant breeding depends mainly on the choice of parents genetically divergent and selection of genotypes with desirable agronomic characteristics over generations. The marker-assisted selection (MAS) is a biotechnology technique that aims to help the breeder in the selection of genotypes based on plant DNA. The efficiency of MAS is directly influenced by the accuracy of genetic mapping. Among the methodologies for mapping, association map stands out for its high accuracy. This methodology is based on the linkage disequilibrium between the marker and the gene that controls the trait. The study of blocks of linkage disequilibrium in culture can provide important information to perform an association mapping. This study aimed to analyze the genetic diversity and linkage disequilibrium in 153 Brazilian soybean cultivars using a set of 4938 SNP markers and 20 microsatellite markers. The percentage of heterozygosity of the cultivars had an average of 8 %, ranging from 3 to 41 %. Genetic distances ranged from 0.0052 to 0.4216, with a mean of 0.32, indicating low genetic diversity present in the Brazilian germplasm. Cluster analysis by UPGMA formed 14 groups, which cultivars adapted to the same growing region were in the same group. It was also observed that some cultivars from different breeding programs had more than 95 % of similarity. . In the analysis of linkage disequilibrium were observed 567 blocks of disequilibrium, where the average blocks per chromosome was 28.35, ranging from 20 to 41. The number of SNPs per block ranged from 2 to 15, with an average of 2.69. Approximately 65% of identified blocks contained only two markers and less than 2 % containing seven or more markers. The average size of the blocks was 410.68 kb, ranging from1.173 kb to 13692.9 kb. Over 70 % of the disequilibrium bocks had less than 200 kb. About of 20 % of the cultivars genome had blocks in linkage disequilibrium. This work demonstrates the great genetic similarity in Brazilian soybean cultivars and the need for the introduction of cultivars from other germplasm for maintaining the diversity of Brazilian germplasm. The analysis of linkage disequilibrium in tropical soybean may provide important information for association mapping of important agronomic traits, increasing the efficiency and utilization of MAS by the Brazilian breeding programs.