Towards Association Mapping of Drought and Heat Tolerance in Perennial Ryegrass.

Association mapping provides a powerful tool for dissecting genetic complex traits. The long-term goal of the objective is to conduct candidate gene-association mapping of drought and heat tolerance in perennial ryegrass (Lolium perenne L.). A total of 180 perennial ryegrass accessions were evaluated for drought and heat tolerance in three locations varying in climate and soil texture. Large variations in leaf wilting, canopy temperature, chlorophyll fluorescence, leaf water content, and activities of antioxidant enzymes were found among these accessions. Five genetic population structures (Q) were identified using 109 simple sequence repeat markers. No obvious relative kinship (K) was found in the population. The Q model (based on population structure) resulted in the smallest Bayesian Information Criterion (BIC) values for fitting different traits, compared to other models (i.e., simple linear, Q, K, and mixed QK). It was the best model in explaining phenotypic trait variation related to whole-plant tolerance under simultaneous drought and heat stress. The gene of GPX encoding glutathione peroxidase showed high linkage disequilibrium (LD) level (average R² = 0.44). A LD decay of GPX (R² = 0.2) extended more than 500 bp. The results provide important information for future candidate gene-association mapping for drought and heat tolerance of perennial ryegrass.