Genetic Diversity and Population Structure of Zoysiagrass (Zoysia spp.)

Zoysiagrass (Zoysia spp.), belonging to the subfamily Chloridoideae, is widely used  turfgrass in the southern United States and in the transition zone.  Taxonomic relationships among the species within the genus Zoysia were mainly based on gross morphological features and have long been controversial. We took RAD tag sequencing approach to evaluate genetic relationships of 41 accessions of zoysiagrass, including commercial varieties, breeding lines, and unimproved germplasm. A total of 389,242 SNP markers were generated from RAD tag sequencing. Cluster analysis suggested limited genetic variation in zoysiagrass, with an average genetic similarity among 41 accessions of 0.9256. Genome-wide heterozygosity was evaluated for each individual of the 41 selected accessions. Interestingly, the average individual genome-wide heterozygosity of 14 commercial varieties was estimated at 0.001935, relatively higher than the one of the 27 non-commercial accessions at 0.001705 (p=0.019), indicating heterosis has played a major role in zoysiagrass selection. STRUCTURE analysis revealed clear population structure over the geographical range extending from the Hokkaido Island of Japan to Southeastern Asia and New Zealand.  Our result suggested three distinct genetic populations were initially formed due to geographic isolations, and three hybrid populations evolved from subsequent natural hybridization between the purebred populations along transition zones. The assessment of genetic diversity among zoysiagrass cultivars provided the necessary information to estimate the potential in genomic selection for zoysiagrass improvement.