ASHS 2025 Conference

The irrigation of grasses dominates domestic water use across the globe, and a better understanding of water use and drought resistance in grasses is of undeniable importance for water conservation. Drought resistance is a complex trait composed of three distinct, but complementary, strategies: escape, avoidance, and tolerance. In grasses, drought escape is commonly displayed via summer dormancy, and drought avoidance and tolerance are displayed by grasses experiencing dehydration. Breeding programs have released cultivars with improved drought resistance, but the underlying mechanisms remain unknown. In this study, we used a number of plant physiology methods to characterize the mechanisms driving drought resistance in four zoysiagrass cultivars reported to exhibit contrasting levels of drought resistance. They were Lobo, Zeon, Empire, and Meyer. A dry-down was performed through deficit irrigation until 70% decline in evapotranspiration. No drought escape mechanism was identified in this project. Drought avoidance was characterized by the rate of dehydration over time, and drought tolerance was characterized by the decline in functional traits with increasing dehydration. Through this approach, we were able to separate avoidance from tolerance and demonstrate that drought tolerance governs drought resistance in commercial cultivars of zoysiagrass. Interestingly, we also demonstrated that canopy mortality during drought can only be reliably assessed using image analyses shortly after rehydration. This is because severe leaf rolling occurs during drought, confounding leaf rolling with actual leaf mortality. This study advances our understanding of i) drought resistance across commercial cultivars of zoysiagrass and ii) potential methods to select drought-resistant cultivars in turfgrass breeding programs.