Diversidade e estrutura genética de populações naturais de Gossypium mustelinum Miers ex Watt

Abstract

n Brazil three cotton species occur: G. barbadense, G. hirsutum and G. mustelinum, being the last wild and native of Brazil, found only in the semi-arid regions of Rio Grande do Norte and Bahia. The studied populations distribute themselves preferably near watercourses, like predominant vegetation of ciliary forest. The degradation of the environment by grazing of goats and anthropic activities, caused the reduction of these populations and consequently the variability. However, in spite of the low variability in these populations, this whole gene pool may in the future be useful in breeding programs. Therefore, the detailed knowledge of the structure of the existing variability is essential for a better use of this species as a resource of allelic variability. As commercial varieties have a narrow genetic base, due to the strong selection practiced for breeding and deriving mostly from only one species, G. hirsutum var. Latifolium, the use of new alleles is fundamental to increase allelic combinations, so that germplasm of wild species of the genus Gossypium, such as G. mustelinum, becomes an alternative for such an extension. In order to determine the variability and genetic structure of 16 natural populations of G. mustelinum, DNA extractions, PCR reactions with SSR markers were performed and the amplified alleles were used to estimate the allelic frequencies, the expected and observed heterosomy Genetic diversity analysis and Nei G statistics, as well as clustering analyzes, using the Nei and Neighbor-Joining distance. The distance between the genotypes was calculated based on the proportion of alleles using the MICROSAT program and the genotypes grouped from the UPGMA method in MEGA 4. To determine if the diversity of each of the populations was presented in an organized spatial structure, the matrix Genetic distance was compared to the physical distance matrix using the Mantel test. The results showed that the greatest diversity is found among populations, with a high level of intrapopulation inbreeding, probably due to the effects of genetic drift, evidenced by the high number of exclusive alleles.