Impact of seaweed extract-based cytokinins and zeatin riboside on creeping bentgrass heat tolerance

Heat stress is the primary factor limiting summer performance of creeping bentgrass (Agrostis stolonifera, L.) in many temperate to subtropical regions. Seaweed extract (SWE)-based cytokinins have been used to improve stress tolerance, but their specific effects on creeping bentgrass under supraoptimal temperatures are lacking. This study was designed to determine whether SWE-based cytokinins affect creeping bentgrass heat tolerance,, and to compare effects of SWE-based cytokinins to those of a trans-zeatin riboside (t-ZR)-standard. Concentrations of t-ZR in two SWE sources (referred to as Oce and Aca) were determined. Treatments were applied twice to creeping bentgrass at an equivalent t-ZR concentration of 10 mu M. One week after the initial treatment, heat stress was imposed (35/25 degrees C [day/night]) for 42 d. The Oce SWE, Aca SWE, and t-ZR treatments resulted in leaf t-ZR concentrations that were, 39, 32, and 28% higher, respectively, relative to the control at 14 d of heat stress, The Oce SWE, Aca SWE, and t-ZR treatments also increased superoxide dismutase, activity and alleviated the decline of turfgrass quality, photochemical efficiency, and root viability. Ashed SWE provided results similar to the water control. Beneficial effects of SWE on heat tolerance appear to be associated with their organic, especially cytokinin, components and not the mineral (ashed) fraction. Proper application of SWE-based cytokinins may be an effective approach to improve summer performance of creeping bentgrass.