Genome-Wide Association Study of Heat Tolerance in Diverse Population of Perennial Ryegrass.

Perennial ryegrass (Lolium perenne L.) is an important cool-season grass species widely cultivated in the temperate regions with high quality for forage and turf. Susceptibility to high temperature in summer limits its broad use around the world. The objective of this study was to identify the significant associations between single nucleotide polymorphisms (SNPs) and heat tolerance traits in diverse perennial ryegrass accessions. Two hundred and seventy-one worldwide accessions were subjected to 35ºC/30ºC (day/night) for 14 days. Significant differences in plant height, tiller number, chlorophyll index (Chl), chlorophyll fluorescence (Fv/Fm), leaf fresh weight, leaf dry weight, and leaf water content (LWC) were found among accessions under control and heat stress. A total of 24,995 SNPs were obtained by genotype-by-sequencing from 271 accessions. After controlling population structure and relative kinship under CMLM model, 12 significant associations (P < 2.0 × 10^-6) were identified including 8 markers with Fv/Fm, 1 with Chl and 3 with LWC. Gene annotation search on perennial ryegrass genome sequence identified 5 candidate genes in the region of significant associations. Gene functional verification is being conducted. The results will reveal genetic and molecular mechanisms of heat tolerance and facilitate genetic enhancement of perennial ryegrass germplasm aimed at improved heat tolerance.