Cytokinin-containing seaweed and humic acid extracts associated with creeping bentgrass leaf cytokinins and drought resistance

Drought continues to be a major limiting factor for creeping bentgrass (Agrostis palustris Huds. A.) quality and persistence on golf course fairways, greens, and tees. Little breeding specifically aimed at improving bentgrass drought resistance has been completed. However, a number of reports indicate that treatment with natural products such as seaweed extracts and humic acids improve cool-season grass drought resistance possibly by hormonal up-regulation of plant defense systems against oxidative stress. This study was conducted to determine the response of exogenous natural product treatment of three creeping bentgrass cultivars subjected to drought. 'Penn G-2', IL-93', and 'Penncross' creeping bentgrass were treated with seaweed extract (SWE) at 0.5 kg ha(-1), humic acid (HA; 80% a.i.) at 1.5 kg ha(-1), alone or in combination, and maintained in a greenhouse at approximately field capacity (-0.01 MPa) or allowed to dry until near the permanent wilting point (-1.5 MPa). Unashed samples of SWE and HA contained 66 mug g(-1) and 57 mug g(-1) zeatin riboside (ZR), respectively, while ashed samples contained no detectable cytokinins as determined by enzyme-linked immunosorbent assay (ELISA). There were no significant differences between cultivars in response to drought, except for ZR concentration, which was higher in Penn G-2 than in L-93 or Penncross foliage. Turf quality and photochemical efficiency began to decline 14 d into the dry-down for the control and at 21 d in the natural product-treated bentgrass. The combination of HA + SWE enhanced root mass (21-68%), and foliar alpha-tocopherol (110%) and ZR (38%) contents. This is the first known report indicating that these natural products contain cytokinins and that their application resulted in increased endogenous cytokinin levels, possibly leading to improved creeping bentgrass drought resistance.