JASP 3 -- 1985.pdf - International Herbage Seed Group

20 JOURNAL OF APPLIED SEED PRODUCTION, VOL. 3, 1985has been investigated for over 10 years. Recent attentionhas focu,sed on two products, paclobutrazol (PP333) andflurprimidol (EL500), both of which have significantlyincreased ryegrass seed yields by increasing fertile tillerproduction and reducing seed abortion (Hampton andHebblethwaite, 1985a;b Hebblethwaite et al., 1985).Both retardants are root active with some foliar activity,and both are inhibitors of gibberellin biosynthesis whichresults in prolonged stem retardation and internode compression(Shearing and Batch, 1982; Anon., 1983). In thispaper we compare the effects of PP333 and El500 onperennial ryegrass growth and seed yield.MATERIALS AND METHODSExperiments were carried out at the University of Nottinghamexperimental farm, Sutton Bonington, Loughborough,Leics., on soil of the Astley Hall series. Certifiedbasic seed of perennial ryegrass cv. S24 was sown on 18August 1981 and 23 August 1982 at 12 kg ha- 1 with a rowwidth of 15 em and in plots 1.5 x 12 m. Details ofexperimental management have been previously described10Lodging 1982(Hampton and Hebblethwaite, 1985a; Hebblethwaite et al. ,1985).PP333 and EL500 were applied at spikelet initiation (25March 1982; 29 March 1983) at active ingredient rates of1.0 and 2.0 kg ha-l for both products in 1982, and 1.0 kga.i. ha-l for PP333 and 2.0 kg a.i. ha-l for EL500 in 1983.Growth retardant treatments plus an unsprayed control werereplicated four times in a randomized complete blockdesign.Growth analyses were carried out at regular intervals;techniques used for data accumulation have been previouslypublished (Hampton and Hebblethwaite, 1985a). Seed washarvested at 40% seed moisture content in both years bycutting 5.5 m2 per plot in 1982 and 2.8 m2 per plot in 1983with a reciprocating knife mower (Mayfield). The cutmaterial was placed in cloth bags and cool air dried to12-15% straw moisture content before the seed was threshed,cleaned and weighed. Yield results are expressed at 0%moisture content.RESULTSLodging and Stem LengthIn untreated plots, lodging began at ear emergence inboth years, and was severe by anthesis. Growth retardantapplication delayed the onset of lodging until after anthesisin 1982 (Figure 1), with PP333 at 2.0 kg a.i. ha-l preventinglodging completely. In 1982 (Figure 1) and 1983, lodgingin plots which had received EL500 at 2.0 kg a.i. ha-l wasnot significantly different from that for plots which hadreceived PP333 at 1.0 kg a.i. ha-l.PP333 and EL500 reduced stem length in both years. In1982, the stem length of plants treated with PP333 at 2.0 kga.i. ha-l was significantly less than that of plants treatedwith EL500 at the same rate of active ingredient by 56 daysafter application (Table 1). Greater retardation occurred atinternodes three and four (base of stem = one) in PP333treated plants. In 1983, the pattern of internode lengthreduction was similar for PP333 at 1.0 kg a.i. ha-l andEL500 at 2.0 kg a.i. ha-l.Table 1. The effect of growth retardants on stem length,1982.Treatment Days after growth retardant application,1982kg a.i. ha-l 34 56 69 99Stem lengthMAY JUNE JULYFigure 1. The effect of growth retardants on lodging, 1982.( e =nil; Ill = PP333, 1.0 kg a.i. ha-1; j = PP333 2.0 kga.i. ha-1; o = ELSOO 1.0 kg a.i. ha-t; 0 = ELSOO. 2.0 kga.i. ha-t; E = peak ear emergence; A = peak anthesis; I = S.E.diff.16 d.f.-----------------------(em)---------------------------nil 28.5 49.5 53.7 60.2EL500 2.0 11.3 29.8 40.7 51.6PP333 2.0 9.2 21.6 24.6 33.1S.E. diff. 1 1.53 2.61 3.73 3.16LSD .05 3.75 6.39 9.14 7.74