Diversidade genética em populações naturais de Hancornia speciosa Gomes no Estado do Rio Grande do Norte: implicações para conservação

Abstract

The Hancornia speciosa Gomes is a native of Brazil with wide distribution in the country. Its fruit is well appreciated by local people and is used for the manufacture of sweets, ice creams and pulps. Urban growth and agricultural expansion led to fragmentation forest areas where the species occurs, with a consequent reduction in population size, which can cause serious implications for the maintenance of long-term species. The objective of this study was to evaluate the remaining genetic diversity in seven populations of H. speciosa at Rio Grande do Norte state. In DNA's quality evaluation, the genetic material obtained from stems showed similar purity to the extracted sheet, obtaining values for the ratio between the absorbance (A260/A280) of 1.46 for the stem and 1.42 for the sheet, both were slightly below the value considered optimal which is between 1.5 and 2.5. The stem tissue showed DNA quality for molecular analyzes of the species. For the selection, 19 ISSR primers were tested, six of them were selected (UBC 808, UBC 810, UBC 826, UBC 827, UBC 841, UBC 842), for presenting clear locus, unambiguous and in great numbers, totaling 63 locus, and 30 (47.62%) showed polymorphism. The PIC value (polymorphic content information) for the selected primers averaged 0.37, ranging from 0.26 to 0.44, indicating that they are useful to evaluate the genetic diversity of the species. For the total population, the number of polymorphic locus was 57 (81.43%), with the total number of effective alleles (Ne) 1.493. The genetic diversity of Nei (He) was 0.287 and the Shannon index (I) was 0.429. Among populations the number of polymorphic locus was considered low, ranging from 29 (41.43%) in Cotovelo's population, to 33 (47.14%) in Macaíba. The diversity indices He and I for each population ranged respectively 0.161 and 0.237 in Parque das Dunas's population to 0.206 and 0.294 in Macaíba's population. According to the Bayesian analysis, the genotypes were divided into five groups (K = 5). The patterns observed in allelic diversity indicate the occurrence of bottleneck in all populations, according to the model of mutation steps. The infinite alleles model revealed imbalance between mutation and genetic drift only in the Parque das Dunas's population. The gene flow rates (Nm) revealed an exchange of alleles between all populations. The results suggest that genetic diversity is distributed among different populations, it is essential to conservation of areas of its occurrence to maintain the genetic diversity of the species.