Effects of plant growth regulators on the mechanical traits of perennial ryegrass (Lolium perenne L.)

Abstract

Plant growth regulators (PGRs) are widely used on sport turfgrass to reduce mowing frequency and inhibit seedhead formation. However, PGRs may also affect turf colour, density and wear tolerance. The objective of this study was to examine the effects of plant growth regulators on the mechanical properties of leaves of perennial ryegrass (Lolium perenne L.). A pot trial was conducted in three seasons in 2016-2018. Three cultivars were tested, ‘Barlicum’, ‘Vulcanus’, and ‘Info’. Six different PGRs, trinexapac-ethyl, paclobutrazol, flurprimidol, mefluidide, ethephon and gibberellic acid, were applied at five different rates. An untreated control turfgrass was also tested for each cultivar. The turfgrass height was measured using a falling plate metre. The biomechanical parameters, i.e., strain-at-break, stress-at-break, modulus of elasticity and work-to-break, were determined using a tensile testing machine.All tested PGRs significantly changed plant growth dynamics. Trinexapac-ethyl, paclobutrazol, flurprimidol, mefluidide and ethephon application reduced plant growth. Gibberellic acid resulted in higher plant growth. This effect was usually observed at 7, 14 and 21 days after PGR application. Perennial ryegrass leaves under tensile stress exhibited a characteristic behaviour with a nearly linear initial period followed by a decrease in the stress rate under a constant strain rate. All PGRs resulted in reduced mechanical strength parameters, namely, stress-at-break and modulus of elasticity. Gibberellic acid also resulted in lower strain-at-break. The work-to-break parameter was affected by all PGRs except ethephon. The PGRs application rate significantly affected certain mechanical parameters only when paclobutrazol, flurprimidol and gibberellic acid were used.