Effects of Growth Regulation By Trinexapac-Ethyl Treatment On the Content of Phytohormones Involved in the Abiotic and Biotic Stress Responses.

Trinexapac ethyl (TE) is widely used as a growth regulator to control turfgrass growth. The objective of this study is to understand the response of the phytohormones jasmonic acid (JA), indole acetic acid (IAA), salicylic acid (SA), abscisic acid (ABA) and zeatin riboside (ZR) following TE treatment and during drought stress responses in Kentucky bluegrass (Poa pratensis). Recent evidence suggests that significant cross-talk exists between giberellic acid (GA) and systemic and induced resistance (SARS and IRS) pathways, which involve JA and SA and lead to stress resistance. In order to evaluate the effects of inhibition of GA synthesis by TE on SARS and IRS, two cultivars, ‘Kenblue’ and ‘A06-46’, were treated with three foliar application of TE [1.95 ml l^-1 (v: v); a.i. TE = 0.113%] at one week interval and then subjected to drought or water treatments for 15 days in growth chamber. Determination of phytohomones content in leaf tissues was done using liquid chromatography mass spectrometry (LC-MS).   Both TE treated cultivars exhibited significantly higher relative water content (RWC), turf quality (TQ), photochemical efficiency (F_v/ F_m), photosynthetic yield (quantum yield), photosynthetic rate (P_n) and chlorophyll content and lower electrolyte leakage (EL) compared to non-treated plants under drought suggesting that TE helped in mitigating drought stress in KBG.  TE treated plants showed significantly higher RWC, TQ, F_v/F_m, transpiration rate (T_r) and chlorophyll content under irrigated condition compared to untreated plants. Significant difference in phytohormones content was observed in TE treated plants under both drought and irrigated conditions compared to untreated plants. The results suggested that TE significantly alters phytohormones other than GA while improving the drought stress response in KBG.