Caracterização molecular de acessos de mamoeiro com uso de marcadores microssatélites

Abstract

The papaya tree is found in almost every country of tropical America and Brazil is ranked as the world's leading producer, contributing with 25% of the market. The objective of this study was to evaluate 96 papaya accessions from the Papaya Active Germplasm Bank (Papaya-AGB) of Embrapa Cassava and Tropical Fruits (CNPMF) by molecular characterization using microsatellites markers. For genomic DNA extraction the Doyle & Doyle method with some modifications was used. Fifteen polymorphic primer pairs were selected. DNA fragments generated with each microsatellite primer pair were separated in 1000-3% agarose gels stained with ethidium bromide and in 6% polyacrylamide denaturating gels stained with silver nitrate. The size of the polymorphic loci was determined by comparison with the 50-bp mass ruler. The accessions were evaluated for allele frequencies, heterozygosity, polymorphism information content (PIC), inbreeding index and structure of genetic diversity. The 15 primer pairs amplified 68 alleles. The mean number of alleles per locus (NA) was 4.5. The PIC values ranged from 0.189 to 0.691 with the highest value found for primer CP16. The observed heterozygosity (Ho) was lower than the expected heterozygosity (HE), for all selected microsatellites loci. The high estimate of inbreeding index (0.672) and excess of homozygotes detected, indicate the presence of inbreeding among the accessions analyzed. The genetic structure inferred from the dendrogram generated with the genetic distance matrix showed 23 groups, what confirms the genetic divergence of the genotypes and the potential to increase genetic variability by developing new varieties.