Drought responses of Kentucky bluegrass and creeping bentgrass as affected by abscisic acid and trinexapac-ethyl

Abstract

The plant growth regulators abscisic acid (ABA) and trinexapac-ethyl (TE) may affect turfgrass responses to drought stress through regulating shoot growth and water relations. The objectives of this study were to investigate the effects of foliar application of TE and ABA on turf growth of two cool-season turfgrass species, Kentucky bluegrass (Poa pratensis L.) and creeping bentgrass (Agrostis stolonifera L.) exposed to drought stress, and to examine water relations associated with changes in drought tolerance due to TE or ABA treatment. 'L-93' creeping bentgrass and 'Brilliant' Kentucky bluegrass plants were foliar sprayed with 0.904 mL·ha-1 a.i. TE five times before exposure to drought or with 6.75 mL/week of ABA at 100 μm before and after exposure to drought in growth chambers. Drought stress was imposed by withholding irrigation until plants were permanently wilted. Foliar application of TE or ABA maintained higher soil volumetric water content, leaf relative water content, and turf quality for a longer period of time during 28 days of stress exposure for Kentucky bluegrass and creeping bentgrass compared with the untreated control. Leaves of TE-treated and ABA-treated plants in both species also had lower ψS at 28 days of drought stress than the untreated control. Creeping bentgrass treated with TE or ABA and Kentucky bluegrass treated with TE exhibited significantly lower shoot vertical growth rates at the initiation of drought stress, but maintained higher growth rates during prolonged drought compared with the untreated control. Turf treated with TE or ABA also showed higher levels of photochemical efficiency than the untreated control for both species. Our results suggest that TE or ABA application could prolong the survival of turfgrass under conditions of drought stress by suppressing shoot vertical growth and lowering water use during the early phase of drought and by sustaining growth and photosynthetic activity during prolonged periods of drought stress through osmotic adjustment for retaining cellular hydration.