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Journal of Oil Palm &The EnvironmentAn official publication of the Malaysian Palm Oil Council (MPOC)

Journal of Oil Palm &The Environment 2012, 3:93- 97 doi:10.5366/jope.2012.09

The Future of Oil Palm Clones in MalaysiaSoh A. C.

Abstract

High yielding ability ensures the sustainabilityof a crop through improved resource (land,light, water, fertilizers, labour) use efficienciesbesides profitability. Traditionally perennial treecrop improvement is achieved/expeditedthrough clonal (vegetative) propagation. Thisprompted the research and development intothe tissue culture clonal propagation of oil palmwhich has no natural means of vegetativepropagation in the early 1970s. Oil palm clonalpropagation has now become a technologywith commercial output of clonal plantletsconstituting 5-10% of the annual oil palmplanting material requirement in Malaysia.Nevertheless, with the inefficiencies of thetissue culture technique in terms of lowamenability and risk of somaclonal variationextant, strategies in clonal propagation have toremain as adjuncts to hybrid breedingprograms and strategies. With the lowergenetic variability and heritability for oil yieldconfirmed in advanced DxP hybrids, cloning(and recloning) from such populations isinefficient and runs the risk of concurrent newgenerations of improved hybrids closing theyield advantage gap of clones. Cloning ortetsfrom the early/recombinant phases of hybridbreeding programmes would be more efficientwith the broader genetic variability and higherheritability for yield and other desirable traits.Perhaps the biggest advantage of cloningwould be in the early commercial exploitationof new genetic materials from introgressionprogrammes of wide intra or inter-specificcrosses which would also broaden the geneticbase of the commercial plantings to reducerisk of genetic vulnerability to pest, diseaseand environmental stress debilitation, ensuring

sustainability. These considerations would alsoapply to the alternative cloning strategies ofcloning the best parents for clonal hybrid seedproduction and cloning the progeny embryosor seedlings of the best progenies. These

alternative strategies are gaining interestespecially the former.

Clones are unlikely to supersede hybrid seedsas the dominant oil palm planting material untilthe amenability and fidelity deficiencies in thetissue culture have been resolved orcircumvented and their field performanceadvantage over concurrent improved hybridsclearly demonstrated.

Keywords: oil palm, clonal propagation, tissuecultureJOPE 2012,3:93- 97

Email: soh.aikchin@cffresearch.org

Address: Crops for The Future Research Centre/AAR-UNMC Biotechnology Research Centre

Published: 3 December 2012

Received: 13 July 2012

Accepted: 5 November 2012

2012 Soh A. C.This is an Open Access article which permits unrestricteduse, distribution and reproduction in any medium, providedthe original work is properly cited.

Review Open Access

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1. Introduction

High yielding ability ensures the sustainabilityof a crop through improved resource (land,light, water, fertilizers, labour) use efficienciesbesides profitability. The plantation industriesparticularly in Malaysia and Indonesia havehad a long love affair with clonally propagatedcrops to achieve high yields. It started in theearly days with e.g. tea, coffee, pepper, sisalhemp etc. and enjoyed the heydays in rubber

with the dramatic yield improvementsachieved. This approach has spilled over intocacao until it lost its attractiveness as a majorplantation crop, at least in Malaysia. Theunderlying reasons for this are that these areusually open-pollinated highly heterozygousperennial tree crops with long generationcycles requiring large, long and tediousbreeding efforts to obtain commercial hybridseeds of acceptable genetic homogeneity(Simmonds and Smartt, 1999).

The uniformity of the crop for esthetic,commercial and management considerations

and their relative ease of clonal propagation byconventional vegetative means (e.g. grafting,cutting, budding, layering) are the othercompelling reasons. There may be also othertechnical reasons e.g. few or non-viable seedsdue to inbreeding depression, sterility due topolypoidy, genetic incompatibility systems. It isthus not surprising that a means of clonalpropagation of oil palm was sought which ledto the breakthrough in the in vitro or tissueculture clonal propagation of the oil palm in themid 1970s (Jones 1974, Rabechault andMartin 1976).

2. Breeding Clonal Propagated Crops

2.1. Vegetative propagated crops

While many clonal crop varieties have beendeveloped directly from vegetative propagationof natural occurring mutants or sports,chimaeras and hybrids, these are usuallyindigenous or relatively unimproved varieties.Breeding methods for more advanced clonallypropagated crops e.g. cassava, rubber, usuallyadopt the following approaches:Hybridization is made between two or moregenetically divergent parents but withcomplementary desirable traits. Selection

begins in the widely segregating F1 or F2 ofthe cross of two open-pollinated parents. Thefinal desirable recombinant genotype isexpected to be present in this widely

segregating population (Simmonds and Smartt1999).The mission is to seek out this winninggenotype through repeated cycles of selection,cloning and replicated field testings ofincreasing rigour until at least the fifth cycle(C5) before the selected clones can beconsidered for release as cultivars or varieties.

2.2. Oil palm

The above approach is possible becausecloning and recloning by conventionalvegetative propagation is efficient and reliableproducing sufficient propagules of good fidelity.This cannot be said as yet for tissue culture orin vitro propagation of the oil palm as not allpalms can be cloned or recloned to givesufficient plant regenerants and of assuredfidelity (Soh et al 2006a, b). As such clonalpropagation in oil palm has to remain as anadjunct to hybrid seed production.Furthermore, as hybrid seed breeding is anestablished if not advanced industry, theadvantage of commercial clonal cultivars must

always be judged against that ofcontemporaneous hybrid seed cultivars. An oilpalm breeding cum adjunct cloning strategymust take this into consideration.

3. Oil Palm Cloning Strategies and ClonePerformance.

3.1. Experiences to date

Attempts at commercial clonal palm production(Bakasawit, Tropiclone) soon began at theUnilever and CIRAD laboratories (Jones 1974,Rabechault and Martin 1976) which pioneeredthe in vitro technique followed by others. The

discovery of the ubiquity of the mantlingsomaclonal variation (abnormality) in theplantlets produced from all the laboratories inthe mid 1980s curtailed its further developmentfor a period. With subsequent resurgence inconfidence in the efficiency and fidelity of thecloning technique in late 1990s more cloneshave since being planted in trial, pilot test andcommercial fields. Although the trials weremainly designed to evaluate cloneperformance, analysis of the results wouldprovide insight to the development ofappropriate strategies in the breeding andselection for clonal propagation.

Soh (1986) investigated the feasibility of theprojected 30% increase in oil yield of clonalpalms over current DxP hybrids (Jones 1974,Hardon et al. 1987), by applying general

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quantitative analyses (Falconer and Mackay1996) on data from three Deli Dura (D) xAVROS Pisifera (P) or Tenera (T) hybridprogeny test trials. The following were theresults and inferences derived:Broad-sense heritability (h

2B) was 0.2

12-15% improvement in oil yield wouldbe achievable by cloning the top 5% ofthe palms

30% improvement might be achieved

by recloning the top clones after clonaltests. But by which time, the nextgeneration of improved DxP would beavailable reducing the advantage ofclones back to 12-15%.

Ortet selection would be more efficienton less advanced DxP hybrids.

Alternative cloning strategies suggested in thelight of the inefficiencies of cloning and ortetselection were:

Cloning the parents of the best crossfor biclonal F1 hybrid seed production

Cloning reproduced seedlings of the

best cross and recloning the bestclones after clonal test.

Selection for oil to bunch (OB) was moreefficient than for fresh fruit bunch (FFB) yield.Subsequent more elaborate quantitativegenetic analyses (Falconer and Mackay19960, Hallauer and Miranda 1981) usingbetween and within family, between and withinclone variance components, and differencebetween pooled within clone and pooled withinfamily variances from the combined results oftrials of crossed families where the cloneswere derived and the clonal trials (Soh et al2003b) supported Sohs earlier results andinferences. Broad-sense heritability for palmsfrom families of less out-bred parents was 0.07and 0.26 for more out-bred parents. Likewisein the first clonal test trial of clones derivedfrom Deli x AVROS at HRU/AAR, the averageoil yield of clones was about 13% with the bestclone yielding at 21% more than the DxP(AVROS) Control, mainly via better OB thanvia better FFB. In a more recent set of resultsfrom trials of clones derived from crosses withmore out-bred P parentage, the average oilyield of the clones exceeded the DxP controlby 18%, with the top clones by more than 30%(Soh et al 2006a,b). Recloning the betterclones from these has begun but final field testresults of are as yet unavailable. Not all the topyielding clones were selected for recloningbecause of their other less desirable attributes.On average about 20% of the clones were

selected. Again the better yielding clones wereusually those with better OB. From their latesttrial results combining 42 clone-ortet sets andtheir 17 parent crosses of CIRADs secondreciprocal recurrent cycle (RRS), Potier et al(2006) found that in OY the mean of the cloneswas 7% higher than that of the DxP Control(representative of the previous generationscommercial DxP) but was 8.6% below themean of the crosses from which the cloneswere derived. The best clones were only onpar with the best crosses. Incidentally, h2B,from ortet-clone correlation obtained was 0.15.AAR (Wong C.K. pers.comm.) observed asimilar pattern of results. Thus even if the bestclones are recloned they would have tocontend with the next generation of improvedhybrids from the further selected selfedparents which would be also be readily andeasily available by then. If so, the advantageand relevance of oil palm clones ascommercial planting materials would be put toquestion.

4. Breeding and Cloning Strategies

Revisited

As cloning and recloning efficiencies in termsof amenability and fidelity have yet to besubstantially improved, the adoption of theconventional breeding strategy/method forvegetatively propagated crops remainsuntenable and the existing strategy of usingthe cloning option as an adjunct to hybrid seedbreeding advisable. However, as many oilpalm breeding programmes are ratheradvanced producing near true F1 hybridseeds, ortet selection within such geneticmaterials will not be efficient as confirmed by

experiences to date.Ortet selection would be more efficient in theearlier stages of a new breeding programme orthe recombinant phase of a matureprogramme where genetic variabilities arewider and heritabilities higher. Ortets areusually sought (but not limited) from the DxT/Phybrid progeny test trials in these programmes.Ortets can also be sought from therecombinant (TxT/P) parent crosses, whichusually manifest wider genetic variability forthe desirable traits. However, astransegregants for high yield are less frequent,perhaps due to reduced heterosis or the

selected palms are also the important parentsused for further breeding, few ortets have beenselected from such materials.

Cloning from less advanced population wouldalso be advantageous in terms of early

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commercial exploitation of new geneticmaterials and broadening the genetic base ofcommercial field plantings to reduce the risk ofgenetic vulnerability to pest and diseaseepiphytotics and environmental stressesbecause of mono-genotype culture. This wouldbe particularly true with wide crosses andintrogression programmes e.g. newgermplasm x BPRO (breeding parents ofrestricted origin), O(Oleifera) x G (Guineensis)programmes (Escobar and Alvarado 2003),where superior segregants in the intercross orbackcross populations may be expeditiouslyexploited as commercial materials.Presumably the superiority of thesesegregants arose from linkage disequilibriumor chance recombination or epistasis whichmay be difficult to recapture by theconventional breeding approach.

The above deliberations would also apply tohybrid seed production from clonal (anddihaploid) parents, which is an alternativecloning strategy, unless it is used to expandthe seed parent base on limited seed

production due to inbreeding effects in theselfed parents. Production of semiclonal (oneclonal parent) and biclonal (both parentsclonal) seeds is becoming an establishedtechnology.

Ortet selection from commercial fields hasbeen shown to be not a worthwhile exercisebut would be the only option for laboratorieswithout breeding trials besides outsourcingfrom those who have.

Owing to the inefficiency of cloning, theavailability of sufficient good ortets frombreeding trials has always been a limitation in

expanding production in most tissue culturelaboratories. Use of embryos, seedlings or fieldplantings of reproduced best crosses orcrosses from the best combining parents toserve as ortet gardens have been suggestedto circumvent this (Soh et al, 2003c). However,as with recloning, the resultant clones wouldbe one generation behind the concurrent newhybrid in terms of genetic advancement.Hence this approach has not taken-off. Amodified version of this approach which aimsto ensure that cloning improvement runsahead of breeding improvement has beensuggested and being investigated. (Wong

Choo Kien, Durand du Gasselin personalcommunication). The approach involvescloning a sample of the seedembryos/seedlings of all DxP crossesundergoing progeny-testing. The seedlingderived clones and the corresponding DxP

families are field-tested at the same time. Onlythe best clones which supersede the bestfamily in the clone cum progeny test arerecloned to produce commercial clones whichare better than the best reproducedcommercial hybrid seeds. This approach maybe used for both the advanced and lessadvanced hybrid populations.

The issues of commercial field plantings ofclones in terms of their composition, planting

configuration and the agro-managementpractices to fully exploit the advantage ofclones and the field trials needed have beenhighlighted earlier (Soh et al, 2003a, 2006a,b).If these issues are not being addressed, theadvantage of clones vis a vis hybrid seedswould be further undermined.

5. Concluding Remarks

Owing to the inefficiencies in the tissue cultureprocess in terms of clonal amenability andfidelity still extant, clonal propagation strategyin oil palm remains as an adjunct in the hybridseed breeding programme. Cloning (and

recloning) ortets from advanced DxP hybridpopulations is inefficient due to the low geneticvariability and heritability for yield resulting inlittle yield improvement over new improvedhybrids which are concurrently available. Thiswould question the advantage and relevanceof commercial clonal plantings with their highercost and attendant risks of somaclonalvariation and pest, disease and environmentalstress vulnerability. Cloning in the earlier orrecombinant phases would be more efficientwith wider genetic variabilities and higherheritabilities for yield and other desirable traits.This would also apply to the alternative clonal

seeds and cloning embryos/seedlingsapproaches, especially the former which hasnow become a technology.

Perhaps the biggest advantage of clones is theearly commercial exploitation of new geneticmaterials from introgression breedingprogenies derived from wide (intra andinterspecific) crosses, and thus broaden thegenetic base of the commercial crop to reduceits genetic vulnerability risk to biotic and abioticstresses and ensuring i ts sustainability.

Lastly adaptability trials are an integral part ofcultivar development and such trials on clonal

plantings should be carried out to ensureexploitation of the full potential of clones.

Clones can only capture a major share of theoil palm planting material market when theissues low culture amenability and

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unpredictability of fidelity can be resolved orcircumvented (presumably through molecularmarker technologies) and their fieldperformance advantage over concurrentimproved hybrids clearly demonstrated.

References

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compact clones and seeds. In: Proc.PIPOC 2003. Malaysian Palm Oil Board,Kuala Lumpur, pp. 75-90.

2. Falconer, D.S. and Mackay, T.F.C. 1996Introduction to quantitative genetics.Longman,Harlow, Essex.

3. Hallauer H.R. and Miranda J.B. 1981.Quantitative genetics in maize breeding.Iowa State Press Ames, USA

4. Hardon, J.J., Corley, R.H.V. and Lee, C. H.(1987) Breeding and selecting the oil palm.In:A.J. Abbot and R.K. Atkin (Eds.),Improving vegetatively propagated crops.Academic Press, London, pp. 63-8

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