Physiological Traits Associated with Drought and Heat Tolerance for a Perennial Grass Species.

Drought and heat are two major abiotic stresses inhibiting growth of cool-season plants in warm and dry climatic regions. Knowledge of physiological traits associated with drought and heat tolerance is essential for selecting germplasm with improved drought and heat tolerance for survival in hot and dry environments. The objective of the study was to determine major physiological traits differentially or commonly linked to drought and heat tolerance in creeping bentgrass (Agrostis Stolinefera), a widely-used cool-season turfgrass species. Plants of eight cultivars  differing in drought or heat tolerance were subjected to drought by withholding irrigation or exposed to heat stress at 35 C. Turf quality as overall drought or heat tolerance indicator, and several physiological measurements, encompassing water status (relative water content, RWC), photochemical activities (Fv/Fm and chlorophyll content), and membrane stability (electrolyte leakage - EL and membrane lipid peroxidation), were evaluated for plants exposed to drought or heat stress. Physiological analysis demonstrated that each physiological parameter was more sensitive to drought stress than heat stress, suggesting that drought stress was more detrimental than heat stress for creeping bentgrass. Physiological measurements were then tested for correlation with each other and overall drought or heat tolerance expressed as turf quality. Correlation analysis showed RWC and EL were the most predictive of overall drought tolerance while EL and chlorophyll content were better predictors for overall heat tolerance.  These results indicated that maintaining cellular hydration was critical for creeping bentgrass tolerance to drought stress, whereas delaying leaf senescence or stay-green trait was highly associated with heat tolerance; cell membrane stability was associated with creeping bentgrass tolerance to both drought and heat stress.