Assessment of Genetic Diversity in Psidium guajava L. using Simple Sequence Repeat Markers

Accurate identification of cultivars and assessment of diversity in guava (Psidium guajava L.), a nutraceutical and medicinal plant, is vital for germplasm management and genetic improvement. In this study, 20 simple sequence repeat (SSR) markers were used to characterize genetic relationships among 39 guava accessions obtained from the Pacific Basin Tropical Plant Germplasm Resource Center, Hilo, HI. Microsatellite alleles were detected using WellRED fluorescent-labeled primers and capillary electrophoresis. Pairwise genetic distance computed using the distance procedure in GenAlEx 6 showed that all accessions could be unambiguously differentiated based on SSR fingerprints. A total of 163 alleles were detected ranging from a minimum of 2 to a maximum of 15. Summary statistics for expected heterozygosity of individual SSR loci computed using PowerMarker version 3.0 showed an average of 0.73. The mean observed heterozygosity was very low indicating a high rate of inbreeding among cultivars. Multivariate analysis showed clustering of accessions into well-defined groups that reflected their geographical origins. These results demonstrate the effectiveness of SSRs in cultivar identification and genetic diversity assessment. Identification and selection of parents for guava improvement programs is possible using these molecular markers.