Auxin and Trinexapac-Ethyl Impact on Root Viability and Hormone Metabolism in Creeping Bentgrass Under Water Deficit

Plant growth regulators have been used to improve turfgrass quality and drought tolerance. This study was designed to investigate if foliar application of auxin (indole-3-butyric acid [IBA] at 2 mM) and trinexapac-ethyl (TE, 45 g ha⁻¹), alone or in a combination, improves creeping bentgrass (Agrostis stolonifera L.) root growth and hormone metabolism under water-deficit conditions. The plants were subjected to well-watered or water-deficit stress (40–50% evapotranspiration replacement) conditions for up to 42 d in growth chambers. Water deficit reduced turf quality and net photosynthetic rate (Pn), leaf indole-3-acetic acid (IAA), isopentenyl adenosine (iPA) content, and root viability. Exogenous application of TE or IBA, alone or in a combination, improved turf quality, Pn, and stomatal conductance under water-deficit conditions. Under water deficit, TE, IBA, and TE + IBA treatments also increased leaf IAA, iPA, and abscisic acid content relative to the control. The combination treatment (TE + IBA) increased root biomass relative to the control under water-deficit and well-watered conditions. Under water deficit, TE, IBA, TE + IBA increased root viability by 16.7, 32.2, and 56.2%, respectively, relative to the control. Under well-watered conditions, IBA, with or without TE, also increased leaf IAA and iPA, as well as root viability. Results suggest that foliar application of auxin and TE at proper rates may promote root viability and hormonally mediated adjustments to drought, resulting in improved turf quality under water-deficit conditions.