Trinexapac‐ethyl and Paclobutrazol Affect Kentucky Bluegrass Single‐Leaf Carbon Exchange Rates and Plant Growth

Abstract

Trinexapac‐ethyl (TE) [4‐(cyclopropyl‐α‐hydroxy‐methylene)‐3,5‐dioxocyclohexanecarboxylic acid ethyl ester] and paclobutrazol (PAC) [(2RS,3RS)‐1‐(4‐chlorophenyl)‐4,4‐dimethyl‐2‐(1H‐1,2,4‐triazol‐1‐yl)pentan‐3‐ol] are routinely used to suppress clipping production. Single‐leaf turfgrass C exchange rates (CERs) in response to plant growth regulator (PGR) treatment have not been characterized. Individual Kentucky bluegrass (KBG, Poa pratensis L.) plants received label rates of TE or PAC and were placed in growth chambers at 23/18 or 30/25°C. Photosynthetic efficiency and CER measurements were recorded every 4 d for 44 d. Total root length (TRL), root surface area (SA), and average root diameter were measured at the end of the study. Reductions in CERs of TE‐ or PAC‐treated plants were short lived with CERs suppressed 17 to 29% of control (POC) at 4 and 12 days after treatment (DAT), respectively. Plants treated at 23/18°C with PGRs typically had short‐lived increases in CERs following CER suppression. A similar pattern of CER response to PGR treatment was observed at the 30/25°C temperature regime. Quantum efficiency was unaffected, but plants treated with PGRs had reduced root growth. PAC caused the greatest reduction in TRL and SA while increasing root diameter. A decline in TRL and SA in conjunction with increased tillering indicates that PGR reduced TRL and SA on a tiller basis. Changes in single‐leaf CERs do not fully explain PGR‐induced changes in plant growth.

Influence of Sequential Trinexapac‐Ethyl Applications on Cytokinin Content in Creeping Bentgrass, Kentucky Bluegrass, and Hybrid Bermudagrass

“…Inhibition of GA 1 due to TE action restricts leaf cell elongation and increases cell density, resulting in more chlorophyll per unit area and darker green leaves (Ervin and Koski, 2001; Heckman et al, 2005; McCullough et al, 2006). One would assume that increased chlorophyll concentration would be associated with increased efficiency of light capture in PSII, but Beasley and Branham (2007) reported no change in Kentucky bluegrass single‐leaf PE due to a single application of TE. However, results of repeated TE applications to field‐maintained creeping bentgrass (Zhang and Schmidt, 2000) and the species in the study herein indicate that PE (when measured on a canopy, rather than a single‐leaf basis) was consistently higher relative to the untreated species.…”

“…Inhibition of cell elongation has been shown to increase mesophyll cell density and chlorophyll concentration, resulting in dwarfed shoots that are darker green (Ervin and Koski, 2001; Heckman et al, 2005; McCullough et al, 2006). Net photosynthesis may be increased by TE as photosynthetic rates are reportedly unchanged due to TE on cool‐season (Stier et al, 1997; Beasley and Branham, 2007) and warm‐season (Qian et al, 1998) turfgrasses, while maintenance respiration may be decreased (Heckman et al, 2001). Photosynthate not used for leaf elongation must be stored or transported to other organs for growth and maintenance.…”

Greenhouse Investigation of Strobilurin Fungicide Applications on Creeping Bentgrass Root Characteristics under Two Irrigation Regimes

“…Operational procedures were similar to those outlined in Beasley and Branham (2007) except that roots were stored at 4°C and placed in water during the analysis rather than a ethanol and deionized water solution, the exclusion fi lter in this study was set to 0.15 mm rather 0.25 mm, and the scanner was confi gured to 600 dpi rather than 500 dpi. Three techniques were used to quantify creeping bentgrass root development in this research: visual assessments of root length, measurements of root architecture with the WinRhizo Pro system (Regent Instruments Inc., Quebec City, QC), and ashing.…”

Growing Degree Day Models for Plant Growth Regulator Applications on Ultradwarf Hybrid Bermudagrass Putting Greens

“…Temperature has been reported to affect TE efficacy on hybrid bermudagrass and Kentucky bluegrass ( Poa pratensis L.) (Lickfeldt et al, 2001; Fagerness et al, 2002; Beasley and Branham, 2007; Beasley et al, 2007). Fagerness et al (2002) showed that TE provided greater growth suppression duration and magnitude of ‘Tifway’ bermudagrass at 20/10°C day/night air temperatures as opposed to 35/25°C.…”