Donovan, M. O.

Gilliland, Trevor J.

Hurley, G.

English

University of Kentucky

University of Kentucky UKnowledge International Grassland Congress Proceedings XXI International Grassland Congress / VIII International Rangeland Congress Prediction of Reproductive Initiation from Relative Ear Emergence Timing in Lolium perenne L. Varieties G. Hurley Teagasc, Ireland M. O. Donovan Teagasc, Ireland Trevor J. Gilliland Queens University Belfast, UK Follow this and additional works at: https://uknowledge.uky.edu/igc  Part of the Plant Sciences Commons, and the Soil Science Commons This document is available at https://uknowledge.uky.edu/igc/21/14-1/17 The XXI International Grassland Congress / VIII International Rangeland Congress took place in Hohhot, China from June 29 through July 5, 2008. Proceedings edited by Organizing Committee of 2008 IGC/IRC Conference Published by Guangdong People's Publishing House This Event is brought to you for free and open access by the Plant and Soil Sciences at UKnowledge. It has been accepted for inclusion in International Grassland Congress Proceedings by an authorized administrator of UKnowledge. For more information, please contact UKnowledge@lsv.uky.edu. 　 Multifunctional Grasslands in a Changing World 　 Volume Ⅱ 　 瞯 ]565　 瞯Grasslands/Rangelands Production Systems——— Seed Science and TechnologyPrediction of reproductive initiation from relative ear emergence timing in Lolium perenne L .varietiesG . H urley 12 M . O�Donovan1 and T . J . Gilliland231 Dairy Production Research Centre , Teagasc Moorepark , Fermoy , Co . Cork , I reland , 2 School o f Biological Sciences ,Queens University Bel f ast , Northern I reland , 3 A gri‐Food & Biosciences Institute , Crossnacreev y , Northern I reland ,trevor .gilliland＠ af bini .gov .ukKey words : ryegrass ,reproduction ,initiation ,headingIntroduction During May to June perennial ryegrass varieties predominately comprise of reproductively developing tillers inwhich the digestibility of the stem falls much faster than the leaf , with associated water‐soluble carbohydrate and protein losses( Terry and Tilley , １９６４) . Even when at similar digestibilities , leaf has a ２０％ higher voluntary DM intake than stem , ( Laredoand Minson １９７５ ) and so stemmy compositions limit animal intake . Spring defoliation timing is known to interact with thedegree of reproductive development to affect stem content in a sward ( Holmes & Hoogendoorn , １９８３ ) . Using defoliationtiming to control stem content has not , however , been wholly effective in practice , partly because the degree of reproductivedevelopment can�t be easily assessed prior to visible stem elongation . This study examined the relationship between the timingof reproductive initiation and ear emergence in eight perennial ryegrass varieties and determined the effect of latitude andmeteorological conditions on the timing of these grow th stages .Materials & methods The timing of reproductive initiation and ear emergence were measured on ４０ vernalised spaced plants foreach of eight perennial ryegrass varieties in Ireland at ５４°３２′N in ２００５ and on the same plants on a similar loam soil at ５２°０９′Nin ２００６ . The mean ear initiation ( EI) date of each variety was determined by examining the apex of one tiller from each plant onalternative days from mid‐March , for the presence of the diagnostic double ridge of reproductive initiation . The critical daylength ( minimum length of daylight for reproductive initiation) was calculated in hours for each plant by interpolation of thestandard day length x latitude relationship . Ear emergence ( EE) was recorded as the date and day length when three seed headshad visibly emerged on a plant . The １０‐year ( １９９７‐２００６ ) �mean date of ear emergence�( MDEE) , that is used to classifyvarieties in the UK and EU Common Catalogue was compiled at the northern site for the eight test varieties . Temperature ( ℃ )and photosynthetically active radiation ( PAR) , (４００‐７００nm , MJ m‐２ day‐１ ) were accumulated from １ January to EI and betweenEI and EE in both ２００５ and ２００６ at both sites .Results & discussion There was a significant effect of site and variety on both EI and EE . When the day length differencebetween the two latitudes ( maximum of ６０ minutes on １６ June) was removed , EI responded to a fixed photoperiod in eachvariety at both sites/ years , with only a minor climatic response associated with the grow th time for a visible apical change tooccur . Timing of ear emergence was dependent on growing conditions not photoperiod and so differed significantly ( p ＜ ０ .００１)between sites / years , though variety rank order was largely retained . The timing of ear emergence was also strongly correlatedwith the EI date at each site ( northern r２ ＝ ０ ．９５ ，southern r２ ＝ ０ ．９２ sites) and also when combined with the official MDEEfor the eight varieties ( r２ ＝ ０畅９４） ．As a consequence EI correlated very strongly with MDEE ( r２ ＝ ０畅９４ ） y ＝ ０ .０９９７x‐３８９７畅８ .Conclusions The discovered relationship between EI and MDEE was sufficiently robust to provide a calibration to estimate thecritical initiation date of any variety on the EU common catalogue for which MDEE dates are available on the UK , though somecaution may be necessary if applying to variety maturities and latitudes beyond those studied .ReferencesHolmes CW . Hoogendoorn CJ . １９８３ . Some effects of grazing management in early lactation and topping on the grow th andquality of pasture . In : Dairy f arming A nnual , Massey University , Palmerston North , New Zealand , pp . ３６‐４３ .Laredo MA Minson DJ . １９７５ . The voluntary intake and digestibility by sheep of leaf and stem fractions of Lolium perenne .Journal o f British G rassland Society ３０ , ７３‐７７ .Terry and Tilley ,１９６４ ) . The digestibility of the leaves and stems of perennial ryegrass , cocksfoot , timothy , tall fescue ,lucerne and sainfoin , as measured by an in vitro procedure . Journal o f British G rassland Society １９ , ３６３‐３７２ .

Prediction of Reproductive Initiation from Relative Ear Emergence Timing in \u3ci\u3eLolium perenne\u3c/i\u3e L. Varieties

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Prediction of Reproductive Initiation from Relative Ear Emergence Timing in \u3ci\u3eLolium perenne\u3c/i\u3e L. Varieties

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