SSR Allelic Diversity of Bermudagrass (CYNODON SPP.) Cultivars Released from 1936 to 2016.

The process of selection during crop improvement has a potential for decreasing genetic diversity. A decline in genetic diversity can hinder the ability for continued improvement and increase genetic vulnerability. The objective of this study was to analyze levels of allelic diversity at gene and population levels in 85 bermudagrass (Cynodon spp. L. C. Rich) cultivars released for turf use between 1950 and 2016. Thirty-seven SSR primer pairs were used to determine whether allelic diversity has changed over this time period. Cultivars were grouped according to decade of release, program type, propagation method, and species. Allele numbers were maintained since the pre-1980s at 30 out of 48 loci. A decline in diversity was observed in cultivars released in the 1980s, but was followed by a significant increase in each subsequent decade with the exception of the 2010s. STRUCTURE results identified three subpopulations among bermudagrass cultivars and indicated that all subpopulations were maintained over the past seven decades of breeding. We found vegetatively propagated cultivars tended to be more diverse than seeded ones, most likely because many are interspecific hybrids with parents of different origins. Our study demonstrated that modern plant breeding has not resulted in a decline in bermudagrass genetic diversity, and that the history of interspecific hybridization and germplasm collection in the genus has helped increase diversity over time.