DIVERSIDADE E ESTRUTURA GENÉTICA DE POPULAÇÕES DE Psidium guajava L. (MYRTACEAE) ORIUNDAS DO BRASIL E DO MÉXICO

Abstract

The guava (Psidium guajava L.) is a tropical fruit tree of high economic importance because it is widely marketed. This species also provides food and shelter to many kinds of animals. For its rapid development features, the guava is used for the recovery of deforested forests and maintenance of ecological corridors. Despite this importance, it is not known center of origin and / or diversity of this species, and this information is important for conservation and / or crop breeding programs. To date it has not done detailed studies of population genetics of wild guava encompassing a wide geographical area. In this sense, the objective of this work was to study the genetic diversity and structure of populations of guava collected in Brazil and Mexico between latitudes -27 ° to + 16 °. For molecular analysis were used nine populations of guava (six from Brazil and three from Mexico) of each population were collected around 32 individuals all them evaluated with 12 microsatellite loci. Forty-four alleles were obtained with average of 3.66 alleles per locus. There were found three private allele in populations of Mexico and only one private allele for the population of Brazil. Around 76% of loci showed in Hardy-Weinberg disequilibrium. The Shannon diversity index was low in all populations and also for the species (H'= 0.557). The observed and expected heterozygosity (Ho and He) values were also low (Ho = 0.105 and He = 0.337). The fixation index was high (0.668) and low gene flow (nm = 0.495). The He showed strong correlation (r = -0.90) with the latitude of each population of Brazil. The Mantel test showed no correlation between genetic and geographic distance. The molecular variance among populations was 34%, and 52% among individuals. Twenty-three components explained 89.4% of the genetic variation of all individuals of the nine populations. The populations showed a high level of genetic differentiation (FST = 0.336; DST = 0.346). The clustering of populations based on genetic divergence showed three groups, two of them formed by populations from Brazil and a third group of the population from Mexico. The number of genetic groups was found K=3 and corresponds to the same groups formed by the analysis of genetic divergence. The results indicated that the guava is a species with low genetic diversity probably driven by the predominance of its autogamous nature and its seeds low dispersion; they also produce high genetic structure. The genetic similarity between populations of Mexico with the populations of southern Brazil indicates a probable local adaptation in response to climate-ecological conditions. Alternatively, this similarity can be interpreted as a product of the introduction of guava by man in deforested areas of the Atlantic Forest. The cline of genetic diversity showed by populations of guava, as well as the number of private alleles by population groups indicate that the region of America close to the Equatorial line can be considered as one of the probable centers of diversity of guava and from this region the species dispersal to the south.