Genetic diversity and population structure of local avocado (Persea americana Mill.) from northern Tanzania assessed using SSR markers

Avocado is one of the economically and nutritionally essential fruits in Tanzania. Most avocados in Tanzania are seed-propagated and have adapted to diverse landscapes and agroclimatic conditions. However, the genetic diversity and structure of the local avocado germplasm from northern Tanzania have yet to be studied. In this study, the genetic diversity of 270 local avocado trees sampled from six districts (populations) in the Tanga, Kilimanjaro, and Arusha regions was evaluated using 11 microsatellite markers. The results revealed a substantial genetic diversity within these northern Tanzanian avocado populations, with a total of 197 alleles detected across all loci, with an average of 17.91 ± 4.81 alleles per locus. The average observed and expected heterozygosity were 0.58 ± 0.06 and 0.72 ± 0.08, respectively. All loci showed significant deviation from the Hardy–Weinberg equilibrium. The Lushoto and Korogwe populations were more diverse than the Rombo populations, which showed the lowest diversity. The analysis of molecular variance (AMOVA) showed that most genetic differentiation occurred within individual trees, with 6.63%, 5.49%, and 0.85% of the variation detected in hierarchical partitions among populations (districts), regions, and altitudinal ranges, respectively. Genetic differentiation and gene flow between populations confirmed the high genetic similarity among the studied avocado populations. Hierarchical cluster analyses showed a genetic admixture among trees, suggesting the presence of gene flow among populations within the same regions. The STRUCTURE and DAPC analysis suggested three genetic groups among the sampled avocado trees. When compared to a worldwide avocado collection, most sampled avocados from northern Tanzania did not group with commercial avocado accessions, thereby suggesting the presence of valuable genetic diversity that could be beneficial for future breeding programs. This study indicated that avocados cultivated in the studied districts of northern Tanzania exhibit high genetic similarity, with low but significant genetic differentiation among the populations mainly attributed to human-mediated gene flow. Further research on the nutritional profiles of these local avocados is recommended.