Molecular Characterization and Genetic Structure in Avocado (Persea americana Mill.) Using Simple Sequence Repeat (SSR) Markers

Avocado (Persea americana Mill.) is an economically important tropical fruit native to Mesoamerica.  It belongs to the Lauraceae family and is subdivided in three horticultural races (Guatemalan, Mexican, and West Indian) based primarily on ecological adaptation, botanical and physiological traits.  The objectives of this study are:  a) to characterize the population structure, genetic diversity, and horticultural race of 344 total plants in the SHRS, Fairchild Farm, and P. schideana collections using a set of 20 SSR markers and b) to evaluate the mislabeling errors present in the collection.  Preliminary fingerprinting analysis using a set of 20 SSR markers amplified a total of 331 alleles with a mean number of alleles per locus of 16.55 and average polymorphism information content (PIC) value of 0.75 indicating a high variability in the allele frequency for the collection.  Bayesian  analysis clustered the individuals into five groups representing the Guatemalan, Mexican, West Indian races of P. americana , admixed interracial hybrids and a  P. schideana  species group.  In addition, Principal Component Analysis (PCA) and genetic distance analysis were calculated among all possible individual combinations within the SSR diversity data with results agreeing well with the Bayesian analysis.  Although the 20 SSRs do not provide complete resolution of all individuals, we were able to estimate mislabeling errors at approximately 9 %.