ISSR Analysis Reveals High Genetic Variation in Strawberry Three-Way Hybrids Developed for Tropical Regions

The cultivated strawberry (Fragaria x ananassa Duch.) is a species of temperate origin, and the extension of this crop into tropical regions is dependent on genetic breeding. Breeders in the UNICENTRO's Strawberry Breeding Program (USBP) selected, from among 2,000 hybrids, 40 hybrids that were adapted to photoperiod and temperature conditions of tropical regions. In this study, we used inter-simple sequence repeat to characterize 40 three-way hybrids developed by USBP and evaluated the genetic relationship of these hybrids with commercial cultivars, heirloom cultivars, and single hybrids. We used nine inter-simple sequence repeat primers to genotype 14 commercial cultivars, five heirloom cultivars, five single hybrids (SH), 20 three-way hybrids with short-day behavior (SDH), and 20 three-way hybrids with photoperiod-insensitive behavior (PIH). The percentage of polymorphism (100%) and both, the Nei genetic diversity (h = 0.34) and the Shannon index (I = 0.51), showed high variability and diversity, respectively, in the evaluated strawberry genotypes. Commercial cultivars showed the highest diversity indices (h = 0.30, I = 0.46), followed by PIH hybrids (h = 0.27, I = 0.41). In the dendrogram, the genotypes were distributed into three groups (commercial cultivars, heirloom cultivars, and single hybrids; SDH and PIH). This clustering was confirmed by principal coordinate analysis and Bayesian inference analysis. The overall analysis of the data revealed the efficacy of USBP in three-way hybrid development with different genetic characteristics compared with those of available commercially cultivars. These hybrids have substantial potential in becoming new strawberry cultivars.