SSR Based Genetic Diversity Analysis in Diploid Algaroba (Prosopis spp.) Population

Algaroba (Prosopis palida and Prosopis juliflora species) provides important environmental and economic benefits for semi-arid regions of the world. These are resistant to drought, and its fruits are used in the manufacture of flour and algarobina syrup. In the present study, the chromosome number, the ploidy level, and the genetic diversity based on 40 microsatellite loci of Prosopis spp. were determined in samples of a Brazilian algaroba population. The cytogenetic analysis in the metaphase showed only diploid individuals (2n = 28), with multiple cells featuring two CMA3/DAPI- heterochromatic blocks suggesting diploid level. However, polysomatism was found by the presence of some cells with four CMA3/DAPI- blocks, showing the tetraploid level just in some somatic cells. Among all of the primers tested for cross-amplification in algaroba, 22 were selected to characterize the samples. Thirteen loci revealed allele polymorphisms in the population and are recommended for future population studies and genetic improvement. The mean values of the analyzes showed low genetic diversity (two alleles per locus and HE = 0.181), reflecting the history of the introduction of algaroba in this sampled locality, and suggesting the genetic bottleneck and probable events of founders, as well as the characteristics of the species of this genera. However, amplified loci indicated low inbreeding (allelic fixation index of -0.007), although heterozygosis was higher than expected by the Hardy-Weinberg equilibrium. Therefore, this algaroba population is formed by diploid individuals and adjusts to the tendency of low number of alleles per locus SSR commonly observed in different species of Prosopis.