Trinexapac-Ethyl and Auxin Impact on Root Growth and Quality of Creeping Bentgrass Under Deficit Irrigation.

Creeping bentgrass quality declines during summer months.  Trinexpac-ethyl (TE) is commonly used to suppress shoot growth but its impact on root growth and drought tolerance has not been conclusively studied. This study was designed to investigate effects of TE (4.5 mg m^-2) alone or in combination with auxin (indole-3-butyric acid, IBA, 2 µM) on root growth and quality of creeping bentgrass under two soil moisture regimes – well-watered and mild drought stress. Treatments (TE, IBA, and TE+IBA) were applied to the foliage biweekly. Two weeks after initial treatment, the grass was subjected to either well-watered or deficit irrigation (compensate for 70% to 30% loss via evapotranspiration) for 42 days. The TE, IBA, and TE+IBA increased root viability, and TE + IBA also increased root biomass relative to the control under deficit irrigation. The TE and TE + IBA improved turf quality, net photosynthetic rate, and transpiration rate under deficit irrigation. The TE, IBA, and TE + IBA increased leaf indole-3-acetic acid, and abscisic acid content under deficit irrigation. TE and TE + IBA also increased leaf cytokinin isopentenyl adenosine content under deficit irrigation. The results suggest foliar application of TE plus auxin may improve creeping bentgrass quality, root function, and physiological fitness under deficit irrigation conditions.