White clover (Trifolium repens L.) lines were selected from within large and small-leaved cultivars of Grasslands Kopu and Grasslands Tahora, respectively, for long or short internodes, and for high or low branching frequency from plants grown in sun and shade (50% full sunlight). Lines were compared for drought tolerance in a perennial ryegrass (Lolium perenne L.) sward in boxes. Prior to imposing drought branching frequency selections did not differ in branching frequency, although the low branching frequency selection had a higher percentage of rooted nodes. After an imposed drought treatment sun-selected lines grew better than shade-selected lines relative to their non-stressed controls suggesting that white clover selected under full-sun may be more drought-tolerant than lines selected in shade. Selections for different stolon morphologies did not differ in stolon and root growth at the end of the drought

Caradus, J R

Karsten, H D

Woodfield, D R

English

University of Kentucky

University of Kentucky UKnowledge IGC Proceedings (1997-2023) XVIII IGC (1997) Manitoba & Saskatchewan Response to Drought of White Clover Lines Selected for Different Stolon Morphologies H D. Karsten Cornell University J R. Caradus AgResearch Grasslands, NZ D R. Woodfield AgResearch Grasslands, NZ Follow this and additional works at: https://uknowledge.uky.edu/igc  Part of the Agricultural Science Commons, Agronomy and Crop Sciences Commons, Plant Biology Commons, Plant Pathology Commons, Soil Science Commons, and the Weed Science Commons This document is available at https://uknowledge.uky.edu/igc/1997/session7/7 <>Grasslands 2000</> 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 IGC Proceedings (1997-2023) by an authorized administrator of UKnowledge. For more information, please contact UKnowledge@lsv.uky.edu. Session 7 - Plant Physiology and Growth 7-15ABSTRACTWhite clover (Trifolium repens L.) lines were selected from withinlarge and small-leaved cultivars of Grasslands Kopu and GrasslandsTahora, respectively, for long or short internodes, and for high orlow branching frequency from plants grown in sun and shade (50%full sunlight).  Lines were compared for drought tolerance in aperennial ryegrass (Lolium perenne L.) sward in boxes.  Prior toimposing drought branching frequency selections did not differ inbranching frequency, although the low branching frequency selectionhad a higher percentage of rooted nodes.  After an imposed droughttreatment sun-selected lines grew better than shade-selected linesrelative to their non-stressed controls suggesting that white cloverselected under full-sun may be more drought-tolerant than linesselected in shade.  Selections for different stolon morphologies didnot differ in stolon and root growth at the end of the drought.KEYWORDSBreeding, drought, morphology, selection, stolon, white clover(Trifolium repens L.)INTRODUCTIONWhite clover (Trifolium repens L.) persistence may be improved byselection for high stolon growth rate and/or high node branchingfrequency (Beinhart et al., 1963).  Recent selections for divergentstolon morphology in large-leaved (Grasslands Kopu) and small-leaved white clover cultivars (Grasslands Tahora) offer the potentialto evaluate the effect of stolon morphology on moisture stresstolerance.  Caradus and Chapman (1991) described selections forextremes of internode length (long and short) and stolon branchingfrequencies (high and low).  Lines were selected either under fullsun or shade (50% sun), to provide 16 different lines.  The lightselection regime is of interest since light influences both stolon andbranch development rate.  Stolon elongation rate increase andbranching frequency decreased when stolons were shaded and/orexposed to a low red to far-red light ratio (Moulia et al., 1989).Utilising these different stolon morphological selections the aim wasto determine :a) whether differences in stolon morphology of plants selected inmonoculture are also apparent when the plants are grown in aperennial ryegrass sward, andb) whether stolon morphology can influence drought tolerance ofwhite clover.METHODSSix genotypes per line, chosen to represent each of the 16 stolonmorphology selections, were vegetatively propagated using rootedstolon tips.  One clone of each of the six white clover genotypesfrom each line was planted in separate boxes containing 8-week oldendophyte-free 'Nui' perennial ryegrass (Lolium perenne L.) swardslocated in a glasshouse.  Each box (0.3 m by 0.2 m by 0.2 m) waslined with polythene film.  Boxes were filled with a freely-drainingTerrace Medifibrsit, a Pongakawa peaty loam of volcanic origin.  Thesoil was weighed and packed in the boxes to a bulk density of 0.75Mg/cm3 and the equivalent of 60 kg/ha P, 30 kg/ha K, 150 kg/ha S,was added to each box.  Time Domain Reflectometer (TDR) rodswere inserted into the boxes to monitor the volumetric soil moisturecontent.  After trimming the sward and allowing the plants to establishfor one month, water was added to bring the boxes to 59% moisturecontent using the TDR measurements.  In each box the youngestnode on one stolon of three plants was marked with an oil-basedpaint.  Boxes were watered every 2 to 3 days and maintained asclose as possible to the same moisture content, and herbage wasI.D. NO. 415RESPONSE TO DROUGHT OF WHITE CLOVER LINES SELECTED FORDIFFERENT STOLON MORPHOLOGIESH.D. Karsten1, J.R. Caradus2, and D.R. Woodfield21Department of Soil, Crop and Atmospheric Sciences, Cornell University, Ithaca, NY, USA2AgResearch Grasslands, Private Bag 11008, Palmerston North, New Zealandharvested every 2 to 3 weeks.  Marked stolons were harvested after39 days and the stolon length, number of branches, number of nodes,number of rooted nodes, and clover dry weights were measured.From these measurements, internode length, stolon elongation rate,and percentage of nodes with branches or a root were calculated.Since the selections across different cultivars differed in size andbecause we were interested in comparing the growth of droughtedplants relative to their paired, non-stressed controls, the absolute plantmeasures were not compared.  Rather, an index of each droughtedplant relative to its paired, watered plant was calculated.  Some ofthe watered control plants did not form branches during the droughtperiod, and many of the treatment plants also did not have branches.Because the data were not normally distributed, the mean populationof nodes branching on the droughted plants is not reported.  Pre-planned contrasts of selection groups were analysed using GLM ofSAS.  The pre-planned comparisons were: (a) Kopu vs. Tahora, (b)long internode vs. short internode selection, (c) high branchingfrequency vs. low branching frequency, and (d) sun-selected vs.shade-selected lines.  Contrasts (b) through (d) were also made withinKopu and Tahora.RESULTS AND DISCUSSIONPre-drought:  Prior to imposing the drought treatment, the totalherbage (grass and clover) from the eight harvests did not differ forany of the cultivars or pre-planned comparisons.  When clover weightwas determined separately for harvests 2, 4, and 8, only the Kopu vsTahora contrast was significant (p< = 0.05), with Kopu producing56% more herbage than Tahora.  Before the drought, Kopu hadsignificantly (p< = 0.05) shorter internode length (37 vs. 42 mm),slower stolon elongation rate (5.4 vs. 7.3 mm/day), and a lowerpercentage of rooted nodes (41 vs. 47%) than Tahora. Internode length(55 vs. 29 mm) and stolon elongation rate (9.1 vs. 4.7 mm day-1)were significantly higher in the long than the short internode selectionwhen compared across cultivars.  The percentage of branching nodesand the number of branches did not differ between selections eitheracross or within either of the cultivars.  The low branching frequencyselection had a significantly (p< = 0.05) higher percentage of rootednodes than the high branching frequency selection (45 vs. 35%).Although a difference in branching frequency was not evident duringthis 5 weeks of stolon growth, it may become evident under differentenvironmental conditions, since branching differences are sensitiveto light quantity and quality (Moulia et al., 1989).Drought: The sun-selected lines, when compared across cultivars,had higher drought indexes for internode length, stolon elongationrate, and total clover dry weight than the shade selected lines (Table1). The swards in droughted boxes wilted and collapsed, whichconceivably allowed more light or a different red/ for red ratio oflight to reach the stolons than in the watered, more upright swards.The longer internodes and higher elongation rates of lines selectedin the sun may be due to these plants being more responsive to lightthan those selected in the shade.  The selection for stolonmorphologies under different light regimes may produce lines whichrespond differently to a range of light/shade environments.  However,the drought indices of the stolon morphology selection groups didnot differ for any of the plant characters measured across or withincultivars (Table 1).ACKNOWLEDGMENTSThis work was funded by the Foundation for Research Science andTechnology (New Zealand) and the senior author was supported bya New Zealand and United States of America Fulbright Scholarship.Session 7 - Plant Physiology and Growth 7-16REFERENCESBeinhart, G., P.B. Gibson, J.E. Halpin and E.A. Hollowell. 1963.Selection and evaluation of white clover clones.  III. Clonaldifferences in branching in relation to leaf area production andpersistence. Crop Science. 3: 89-92.Caradus, J.R. and D.F. Chapman. 1991. Variability of stoloncharacteristics and response to shading in two cultivars of whiteclover (Trifolium repens L.).  New Zealand Journal of AgriculturalResearch. 34: 239-247.Moulia, B., C. Varlet-Grancher and R. Jacques. 1989.Phytochrome control of white clover morphogenesis:description andecological signification. Plant Physl (Life Sci. Adv.) 8: 108-11.Table 2The mean recovery index for plant characters across all cultivars selections for each selectio, with the significance of pre-plannedcontrasts.Selection Internode length Stolon elongation Percent of Number of Percentage of Clover dryindex rate index branching nodes branches index nodes rooted index weight indexCultivarKopu 1.1 1.2 0.25 1.3 1.0 1.9Tahora 1.0 1.0 0.36 2.1 0.90 1.3Internode lengthLong 1.1 1.0 0.27 1.4 1.0 1.6Short 1.1 1.0 0.34 2.0 0.99 2.6Percentage of nodes branchingHigh 0.87 0.94 0.37 2.2 1.0 0.93Low 1.0 1.0 0.23 1.3 1.0 1.3LightSun 1.1 1.0 0.35 2.0 1.0 1.0Shade 0.96 0.99 0.27 1.5 0.97 1.4ContrastKopu vs. Tahora NS NS NS NS NS NSLong vs. Short internode NS NS ** ** NS NSlengthHigh vs Low % of NS NS NS NS NS NSnodes branchingSun vs. Shade NS NS NS NS NS NSNS = not significant, * p < or = 0.05,  ** p < or = 0.01Table 1The mean drought index of stolon and root characters, and white clover dry weight between cultivars and across cultivars for eachselection group, with the significance of pre-planned contrasts.  The drought index is the performance of each droughted plant dividedby the performance of its paired, watered plant at the end of the drought.Selection Internode length Stolon elongation Percent of Number of Percentage of Total clover dryindex rate index branching nodes branches nodes rooted index weight indexCultivarKopu 0.96 0.65 0.01 0.05 0.51 0.70Tahora 0.70 0.46 0.01 0.04 0.74 0.40Internode lengthLong 0.75 0.48 1.3 0.06 0.60 0.81Short 1.0 0.55 2.6 0.08 0.57 0.92Percentage of nodes branchingHigh 0.72 0.47 0.0 0.0 0.52 0.24Low 0.82 0.71 3.0 0.03 0.80 0.33LightSun 0.96 0.96 2.0 0.07 0.68 0.67Shade 0.71 0.71 0.4 0.03 0.56 0.43ContrastKopu vs. Tahora NS NS NS NSLong vs. Short internode NS NS NS NSlengthHigh vs Low % of NS NS NS NSnodes branchingSun vs. Shade * * NS *NS = not significant, * p < or = 0.05,  ** p < or = 0.01

Response to Drought of White Clover Lines Selected for Different Stolon Morphologies

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Response to Drought of White Clover Lines Selected for Different Stolon Morphologies

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