Effects of trinexapac-ethyl foliar application on creeping bentgrass responses to combined drought and heat stress

Simultaneous drought and heat stress is detrimental to turfgrass growth, Growth regulators may influence plant responses to stresses. The objective of this study was to determine effects of pretreatment with trinexapac-ethyl (TE) on creeping bentgrass (Agrostis stolonifera L.) responses to subsequent exposure to combined heat and drought stress. Plants were treated with TE (1.95 mL L-1 [v/v], Primo Maxx) every 14 d for 42 d and then exposed to combined drought and heat (35 degrees C) in growth chambers. Application of TE increased turf quality and relative water content and chlorophyll content during 21 d of stress. Trinexapac-ethyl-treated plants had increased growth rate and maintained constant canopy photosynthetic rate (Pn) and photochemical efficiency (Fv/Fm) during the stress period, while these parameters declined for the untreated control. Trinexapac-ethyl-treated plants maintained lower evapotranspiration rate (ET) under nonstressed control conditions, but higher ET at 21 d of stress. Trinexapac-ethyl-treated plants showed no differences from untreated plants in osmotic adjustment, and had lower levels of total nonstructural carbohydrates during the stress period. The study suggests that TE application enhanced turf performance under stress, as demonstrated by maintenance of higher turf quality and growth rate during a prolonged period of com bined stress. The beneficial effects of TE on bentgrass stress responses could be related to the maintenance of photosynthetic activities and greater level of cellular hydration. These and other published data indicate that use of TE on creeping bentgrass that seasonally experiences heat and drought stresses could benefit its performance.