Abberton, Michael T.

Marshall, Athole H.

Michaelson-Yeates, Terry P. T.

Rhodes, Ian

Williams, T. Andy

English

Hybrids between the stolonifeous white clover (Trifolium repens L., 2n=4x=32) and rhizomatous Caucasian clover (T. ambiguum M.Bieb, 2n=4x=32) have been produced. A backcross 2 (BC2) generation with white clover as the recurrent parent combines the growth habit of both parent species with the objective of increasing the persistency of large leaved T. repens varieties under grazing. T. ambiguum is more drought tolerant than T. repens. The drought tolerance of the hybrids in comparison with the parental species was compared in deep soil bins over a four week drought cycle. Soil moisture content, leaf relative water content (RWC), and leaf water potential were measured on plants subjected to drought and those watered normally and maintained at field capacity. T. ambiguum and the backcross hybrids were able to maintain a higher leaf RWC and leaf water potential than T. repens at comparable levels of soil moisture. The dry matter production of the hybrids and parental species was also compared in field plots sown with a perennial ryegrass companion. In the first harvest year, under a cutting regime, the yield of T. repens was highest and T. ambiguum lowest with the hybrids intermediate between the parents, with the BC2 approaching the yield of T. repens. These hybrids will be evaluated over further years and under grazing. The implications of these results for T. repens germplasm improvement programmes are discussed

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Aberystwyth UniversityDrought tolerance of interspecific hybrids between T. repens and T. ambiguumMarshall, Athole H.; Abberton, Michael T.; Michaelson-Yeates, Terry P. T.; Rhodes, Ian; Williams, T. AndyPublication date:2001Citation for published version (APA):Marshall, A. H., Abberton, M. T., Michaelson-Yeates, T. P. T., Rhodes, I., & Williams, T. A. (2001). Droughttolerance of interspecific hybrids between T. repens and T. ambiguum. 10-21. http://hdl.handle.net/2160/3419General rightsCopyright and moral rights for the publications made accessible in the Aberystwyth Research Portal (the Institutional Repository) areretained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by thelegal requirements associated with these rights.            • Users may download and print one copy of any publication from the Aberystwyth Research Portal for the purpose of private study orresearch.            • You may not further distribute the material or use it for any profit-making activity or commercial gain            • You may freely distribute the URL identifying the publication in the Aberystwyth Research PortalTake down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediatelyand investigate your claim.tel: +44 1970 62 2400email: is@aber.ac.ukDownload date: 09. Jul. 2020  ID # 13-06DROUGHT TOLERANCE OF INTERSPECIFIC HYBRIDS BETWEEN Trifoliumrepens AND Trifolium ambiguumA.H.Marshall, M.T.Abberton, T.P.T.Michaelson-Yeates, I.Rhodes and A.WilliamsInstitute of Grassland and Environmental Research, Plas Gogerddan, Aberystwyth,Ceredigion, UK, SY23 3EB.AbstractHybrids between the stolonifeous white clover (Trifolium repens L., 2n=4x=32) andrhizomatous Caucasian clover (T. ambiguum M.Bieb, 2n=4x=32) have been produced. Abackcross 2 (BC2) generation with white clover as the recurrent parent combines the growthhabit of both parent species with the objective of increasing the persistency of large leaved T.repens varieties under grazing. T. ambiguum is more drought tolerant than T. repens. Thedrought tolerance of the hybrids in comparison with the parental species was compared indeep soil bins over a four week drought cycle. Soil moisture content, leaf relative watercontent (RWC), and leaf water potential were measured on plants subjected to drought andthose watered normally and maintained at field capacity. T. ambiguum and the backcrosshybrids were able to maintain a higher leaf RWC and leaf water potential than T. repens atcomparable levels of soil moisture. The dry matter production of the hybrids and parentalspecies was also compared in field plots sown with a perennial ryegrass companion. In thefirst harvest year, under a cutting regime, the yield of T. repens was highest and T. ambiguumlowest with the hybrids intermediate between the parents, with the BC2 approaching the yieldof T. repens. These hybrids will be evaluated over further years and under grazing.  The  implications of these results for T. repens germplasm improvement programmes arediscussed.Keywords: T. repens, Caucasian clover, interspecific hybrids, drought tolerance, yieldIntroductionWhite clover (Trifolium repens L.) is the most important forage legume component ofpastures in temperate northern Europe. It produces forage of high quality and in associationwith Rhizobium trifolii fixes atmospheric nitrogen, reducing the level of fertiliser nitrogenneeded in mixed swards (Rhodes et al., 1999). Breeding programmes seek to improve traitssuch as seasonal and annual dry matter production, persistency and stress tolerance and whileprogress has been made in these areas, improvements are still necessary. T. ambiguum(Caucasian clover) is a rhizomatous but slow to establish perennial forage legume. Hybridsbetween the stoloniferous white clover (T. repens L) and rhizomatous T. ambiguum have beendeveloped that combine the growth habits of both species (Abberton et al., 1998), with theobjective of improving the persistency of large leaved white clover varieties under grazing. Abackcross 2 generation has been produced that contains up to 7 % of its dry matter asrhizomes. T.ambiguum is also reported to be more drought tolerant than white clover.Improved drought tolerance of white clover is desirable to increase the locations over which itmight be grown. This paper reports experiments designed to assess the drought tolerance ofthe hybrids in comparison with white clover and the growth of the hybrids in field plots undercutting.Material and methodsThe plant material was a T. ambiguum population (Ah1254) collected in Turkey in1971 and T. repens variety Menna. Fertile F1 plants were used as the basis for two  generations of backcrossing to T. repens as the recurrent parent (Meredith et al., 1995). Fourbackcross 1 and backcross 2 genotypes were chosen on the basis of possessing both stolonsand rhizomes with the latter accounting for between 5-10% of the plants dry weight. Thiscompares with nearly 60% in T. ambiguum (Abberton et al., 1998). These were cloned andused in the experiments described below.Deep soil bins: Each bin of 1m x 1m x 1.4m was lined with a polyethylene bag with drainageholes in the bottom. The bins contained a 60cm layer of hardcore, 30cm coarse grit and anupper layer of 30cm JI potting compost. Each bin contained 4 clonal cuttings of each of the 4genotypes. The bins were well watered and maintained at field capacity until the treatmentperiod. A drought cycle was imposed over a 4  week period during which the bins were keptunwatered.  Four bins comprising the four lines (T. repens, T. ambiguum, BC1 and BC2) werekept unwatered and four bins were watered once a week back to field capacity.Field: Plots (2.7m x 1.5m) were sown on 1 September 98 with the intermediate perennialryegrass variety Fennema at a rate of 25kg/ha. On 1 September 1998 each plot was plantedwith 8 clonal plants of each of 4 genotypes of either parent or the BC1 or BC2 generations.There were 4 replicate plots. Prior to sowing all plots received 100 kg/ha P2O5 and 200 kg/haK2O and 4 t/ha of lime. In spring 1999 plots received an additional 100 kg/ha P2O5 and 200kg/ha K2O and 40kg/ha N (34.5%N). Plots were lightly cut in 1998 and in 1999 were sampledfive times at five-week intervals with a reciprocating blade mower (width of 0.23m) at aheight of 3 cm.  Herbage was weighed and a 100g sub-sample of herbage was taken fromeach plot for botanical analysis. This was separated into grass and legume component, driedin an oven at 80°C overnight, weighed and milled using a 1mm sieve.  ResultsOver the 4 week drying cycle, the soil moisture content of the unwatered bins declineduntil they reached their lowest levels at weeks 3 and 4 (Figure 1).  The leaf relative watercontent (RWC) of T. repens decreased (Figure 1) as the soil moisture content declined, andreached approximately 50% RWC by the end of the 4 week cycle. The leaf RWC of T.ambiguum plants was constant at more than 80% despite the soil moisture content decreasingto a similar level to T. repens. Leaf RWC of the BC1 and BC2 hybrids showed a responsebetween those of T. repens and T. ambiguum. Leaf water potential of the plants in the wateredbins remained greater than 10bar throughout the cycle. The leaf water potential in theunwatered bins decreased over time. Leaf water potential, after four weeks, was lowest in T.repens (-40bar), greatest in T. ambiguum (-8bar) and intermediate in the backcrosses (-20bar).In the field experiment the DM yield of T. repens was greatest and T. ambiguumlowest with the hybrids intermediate (Table 1). The yield of the BC2 was greater than theBC1 but was still significantly lower than T repens. These differences were reflected in thetotal DM yield and in the %legume content. The plots with T repens had the highest clovercontent and the greatest DM yield, with T. ambiguum the lowest. Total DM yield and %clover content of the hybrids were intermediate with the BC2 greater than the BC1.DiscussionMoisture stress is one of the most important constraints on the growth and persistenceof T. repens (Barbour et al., 1995). T. ambiguum is a drought tolerant rhizomatous foragelegume. This preliminary study has confirmed differences in the drought tolerance of the twospecies. It has shown that as the soil dried, the leaf RWC of T. repens decreased but in T.ambiguum, the leaf RWC remained higher and constant at comparable levels of soil moisture.  In the BC1 and BC2 hybrids the soil dried at the same rate as T. repens, but the leaf RWCdecreased much more slowly and their responses were intermediate between the two parentalspecies. They were also able to maintain a greater leaf water potential than T. repens atcomparable soil moisture contents. This may be attributed to the fact that T. repens has ashallow root system whilst T. ambiguum has rhizomes, which improve the plants droughttolerance. The BC1 and BC2 hybrids contain both rhizome and stolon that may contribute tothe greater drought tolerance of the hybrids. The yield of the BC2 hybrids, although greaterthan T. ambiguum and the BC1 was still less than T. repens. The yield in later years still needsto be quantified. The hybrids appear to combine the drought tolerance of T. ambiguum with aforage yield closer to T. repens. Further work is needed to improve the yield of the hybridswhilst retaining the benefits conferred by the rhizomatous growth. Research on furtherbackcross generations is being carried out to elucidate the physiological basis of droughttolerance in these hybrids and to use molecular marker techniques to ensure the efficientintrogression of the rhizomatous trait.ReferencesAbberton, M.T., Michaelson-Yeates T.P.T., Marshall A.H., Holdbrook-Smith K. andRhodes I. (1998). Morphological characteristics of hybrids between white clover, Trifoliumrepens L. and Caucasian clover, Trifolium ambiguum M.Bieb. Plant Breeding 117: 494-496.Barbour M., Caradus J.R., Woodfield D.R. and Silvester W.B. (1995). Water stress andwater use efficiency of ten white clover cultivars. In: White clover New Zealandscompetitive edge. Lincoln University, New Zealand No6. Editor:D.R.Woodfield, 159-162.Coolbear, P., Hill M.J. and Efendi F. (1994). Relationships between vegetative andreproductive growth in a four year old stand of caucasian clover (Trifolium ambiguumM.Bieb) cv.Monaro. Proc. Agron. Sci. NZ 24: 77-82.  Meredith, M.R., Michaelson-Yeates T.P.T., Ougham H.J. and Thomas H. (1995).Trifolium ambiguum as a source of variation in the breeding of white clover. Euphytica 82:185-191.Rhodes, I., Collins R.P., Williams T.A., Michaelson-yeates T.P.T. and Marshall A.(1999). Breeding white clover for cool, wet regions. In: Crop development for cool wetregions of Europe (ed. M Sanchez-Diaz) OOPEC Luxembourg pp 64-75.Table 1- Dry matter yield of T.repens, T.ambiguum and their hybrids in plots.____________________________________________________________________Species Legume (kg/ha) Grass (kg/ha) Total DM (kg/ha) %legume____________________________________________________________________T.repens 5.92 3.46 9.39 64T.ambiguum 0.031 2.90 2.93 1BC1 2.39 3.46 5.90 41BC2 4.26 3.07 7.33 58s.e.d. 0.233*** ns 0.398(***)____________________________________________________________________  0510152025301 2 3 4Time (weeks)Soil water content (%)0102030405060708090100Leaf water content (%)Figure 1 - Soil moisture content (%) (    ) and relative leaf water content (----) of clovermonocultures in bins during a four-week period without watering.T. repens ( !), T. ambiguum ( ♦ ), BC1 ( ▲ ) and BC2 (  − ).

Drought tolerance of interspecific hybrids between T. repens and T. ambiguum

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Drought tolerance of interspecific hybrids between T. repens and T. ambiguum

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