A step further – optimizing the natural apple tree habit with the Salsa tree training concept

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Acta Hortic. 1130. ISHS 2016. DOI 10.17660/ActaHortic.2016.1130.22
XXIX IHC – Proc. Int. Symposia on the Physiology of Perennial Fruit Crops and
Production Systems and Mechanisation, Precision Horticulture and Robotics
Eds.: D.S. Tustin et al.
151
A step further – optimizing the natural apple tree habit
with the Salsa tree training concept
P.E.Lauri1,B.Hucbourg2,M.Ramonguilhem3andR.Joannin4
1INRA,UMRAGAP,équipeAFEF,CiradLavalette,34398MontpellierCedex5,France;2GRCETAdeBasseDurance
Extension service, Route de Mollégès, 13210 St Rémy de Provence, France; 3Aquifruit, Techniques et
Développement Extension Service, 2200 Ch Principal, « Le lion d’Or » Route de Beaupuy, 47200 Marmande,
France;4Agropommeextensionservice,Saint‐Joseph‐du‐Lac,J0N1M0–QC,Canada.
Abstract
There is no straightforward relationship between tree density and economic
performance. If the general trend towards higher planting densities has led to
successful results, it has also been ascertained that knowledge on the biology of the
tree and on its reactions to pruning and training procedures is still crucial. The search
for the best compromise between tree manipulations to maintain a given canopy
shape and the minimizing of adverse vegetative reactions has now provided rather
satisfactory answers. As a whole, utilizing a specific tree shape has the advantage of
giving simple objectives and clear rules to implement in orchards. However this may
delay entrance into production and does not improve regularity of bearing. This is
typically what happens when the objective is to establish conic- or cylindric-shaped
tree with a single trunk. Our experience on free-standing apple trees over the past 20
years in France has shown that there is a clear interest in using the strong branches
that may naturally develop from the bottom of the tree. These scaffold branches
behave as intermediate structures between the trunk and fruiting branches and
maintain a better distribution of vegetative growth within the canopy along with
better light distribution to the fruiting sites. Based on these observations we have
proposed some simple rules to train the tree. This canopy system, known as Salsa, is
increasingly interesting to growers due to its satisfactory yield quantity and quality
with lower labour inputs, due to less time required for training and pruning to shape
the tree.
Keywords:apple,ideotype,pruning,Salsasystem,treearchitecture,treetraining
INTRODUCTION
Theorchardplantingsystemcombinestheorchardlayout,andatthetreescale
includespruningprocedures,i.e.,theart andscienceofcutting awaya portionofplantfor
horticulturalpurposes,and training,i.e.,the managementoftheoveralltreeshape(Ferree
andSchupp,2003;Robinson,2003).Thesetwoscalesareintimately related, and for
example,thechoiceofplantingdistanceshastointegratethechoiceoftherootstockwhich
hasadirectimpactontreearchitectureand size.Onthe otherhand,therootstock‐cultivar
combinationhasanimpactonhowthetreewillreacttothetrainingandpruningprocedures
(Forsheyetal.,1992).
Trainingsystemscanbecategorizedintooneofthefollowingfourtreecanopyshapes,
i.e.,spherical,conic,flatplanarandV‐shaped(Robinson,2003).Themainobjectiveforeach
istoimproveyieldandfruitqualitywithafastentranceintoproduction.However,thefact
thatdifferenttrainingsystemsareco‐existinginthedifferentappleproductionregionsover
the world shows that the grower’s choice is a compromise among several constraints.
Indeed, the natural environment, soil and climate, and the prevalence of some pests and
diseasesmaypartlyaffectthechoiceoftherootstockwhichwillaffecttreevigorandfruiting
pattern. The socio‐economic context also has a great influence duetotherelativecostof
orchard management, especially for training, pruning and harvesting in a given region,
whichdirectlycontributestotheeconomicsuccessoftheorchardoveritslifetime.
Inthispaper,wepresenttheworksthathavebeendeveloped overthepast20years

152
onthefruitingbrancharchitecturewiththeappliedobjectivetooptimizetreetrainingand
pruning.Inasecondpartwewillreportontheevolutionoftraining over thepast10years
whichaimsto combinefruitqualityand regularyieldwitha fastentranceintoproduction
andareductionofthe managementcosts.TheSalsatrainingsystemisbasedoni)abetter
useofthenaturaltreearchitectural framework,especiallyduringthe veryfirstyearsafter
plantation,andii)abetterdistributionofthefruitingshoot,i.e.,thebourseand itsbourse‐
shoot(s),withinthecanopy.
KNOWLEDGE OF INTRINSIC TREE ARCHITECTURE TO OPTIMISE TREE TRAINING
Theinterestinbetteruseoftheintrinsictreegrowthandfruitingpatternsinsteadof
developing training and pruning methods that constrain the treehasbeenadvocatedby
manyhorticulturistsoverthepastdecades(Lespinasse,1977,1980; Forsheyetal.,1992).
Thisconceptwasbasedonstudiesattheoveralltreescale.Forexample,spur‐typecultivars,
i.e.,withastrongtrunkandbranchframeworkbearingshortlateralshoots,haveanatural
tendencytoalternate(LooneyandLane,1984;HirstandFerree,1995)whereascultivars
with fruiting in terminal position on long shoots, i.e. Type IVaccordingtoLespinasse’s
typology, have a more regular fruiting pattern (Lespinasse, 1992; Lespinasse and Delort,
1986;Laurietal., 1995). Thisgeneralrelationshipbetweenthe overalltreeshape andthe
fruitingpatternhasbeenrelatedatthebranchscaletotherelationship between shoot
lengthandreturn‐bloom(LauriandLespinasse, 1993; Lauri andTrottier, 2004).However,
thereareknownexceptions,suchasthecultivar‘Fuji’whichbelongstoTypeIVaccordingto
Lespinasse’stypologyandischaracterizedbyanalternate‐bearing pattern (Lauri et al.,
1997b). Therefore, all relations between the whole‐tree typology and the fruiting pattern
shouldbeconsideredwithcaution.
Inthefollowingwepresentthetwomainconceptsonwhichthebasicprinciplesofthe
Salsatrainingsystemwereestablished(Hucbourgetal.,2006),
‐ the establishment of a multi‐trunk tree when the cultivar intrinsically has this
potential,withouttheneedofregularheadingcut,
‐ thedisplayoffruitingshootswithinthetreecanopywithouttheneedforfruiting
branches.
From the single- to the multi-trunk tree
Maintainingauniquetrunkisoftenartificialbecausethetree intrinsically develops
sylleptic shoots concurrent to the trunk in the year of plantation (Figure 1a). This is
especiallytrueonsemi‐vigorousorvigorousrootstocks,andtoalesserextentontrees
grafted on dwarfing rootstocks such as M.9. It also varies depending on the cultivar. This
phenomenon is usuallynotobservedbythegrowerplantingone‐ortwo‐year‐old grafted
treesbecausetheselateralbranchesareremovedinthenurserytoinvigoratetheinitial
trunk and to encourage proleptic branching higher on the trunk inthefollowingyear.
However,keepingtheselateralsunprunedwouldhavetwoadvantages.First,itallocatesthe
vigouronamulti‐trunkframeworkcomposedofseveralreiterativetrunks,whichvigouris
intermediatebetweentheoneofthetrunkofacentralaxissystemandtheoneofafruiting
branch.Thisentailsafasterbalancebetweenvegetativegrowthandfruiting,especiallyin
thefirstyearsafterplantation.Second,itincreasesconsistentlythefirstyields,comparedto
thesingle‐trunktrainingsystems.

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
Figure1. Unpruned3‐year‐old‘GrannySmith’treegraftedonM7(a),andsilhouetteofa5‐
year‐oldSalsa‐trainedtreeinacommercialorchard(b)(Credit,Pierre‐EricLauri,
INRA,Montpellier).Thenumberofreiterativetrunksdependson
rootstock/cultivarcombinationandgrowingconditions.
From the fruiting branch to the fruiting shoot
Inpastdecades,thefruitingbranchconcept,i.e.,abranchinsertedalongthevertical
trunkandbearingthefruitingshoots,hasbeenproposedasaway to balance vegetative
growthandfruiting.ThefruitingbranchconceptwasoriginallydevelopedintheSolenand
thenintheSolaxesystemsandpromotedaninterestinbranchbending(Lespinasse,1996).
The centrifugal training system was a further step, with the integration of the light well
alongthetrunkandatthebottomofbranchestoimprovelightpenetrationinthetree,and
artificial extinction (also called extinction pruning) to improvethefunctioningofthe
individualfruitingshoots(Lauri,2009).Severalstudieshavebeendevelopedinthepast20
yearsto gainadeeper knowledgeofthe vegetativeand floweringandfruitingstrategiesat
thefruitingbranchscale(LauriandLespinasse,1998,2001;Lauri et al., 2004; Lauri and
Laurens,2005;Lauri,2008).Amainresultwasthatregularbearing at the level of the
fruiting shoot (bourse‐over‐bourse) consistently improved if branching density decreased
whichwasusuallyrelatedtoanincreaseofthelengthofthefruitingshoot(Laurietal.,1995,
1997a,2004;Tustinetal.,2011,2012)and/orofthevolumeofthebourse(Lespinasseand
Delort,1993).Thisconceptofautonomyofthe fruitingshootwithregard toreturnbloom
andfruitqualityisinpartrelatedtoalocaltrophicandlikelyhormonalcontext(Lauriand
Lespinasse,1993;Laurietal.,2004).Aconsequenceofthesefindingsis that although the
fruitingbranchremainsaconvenientconcepttopartitionthevigoronsecondarybranches
whenthereisasingleverticaltrunk,afurthersteptooptimizetreetrainingistoprioritize
allproceduresthatwouldincreasetheautonomyofthefruitingshoot.Asshowninprevious
works,artificialextinctionislikelyoneoftheappropriatepruningprocedurestoachievethis
objective(Laurietal.,1997a,2004;Tustinetal.,2011,2012).
SETTING THE PRACTICAL ASPECTS
ThecurrenttrainingparadigmimplementedinSalsatrained treesistopromotethe
functioningofthefruitingshoottoimprovefruitqualityyearafteryear,andreturnbloomon
thesamefruitingshoot.Thestructuralframeworkonwhichthisfruitingshootisbranched
has a lesser importance. The objective is not to build a tree with a rigid and often time‐
demandingstructureandthatusuallydelaystheentranceintoproduction,buttosearchfor
the best positioning of the fruiting shoots in the tree canopy andtotrainthestructural
frameworkthatoptimizesfruiting.Inthissenseconstrainingthetreetoagivennumberof
axes(e.g.,typicallyasingletrunkintheconic‐shapedtree)withouttakingintoconsideration
theplantmaterialandtheenvironmentisnotrelevant.TheSalsaconceptis basedontwo

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mainproposalsthathavebeenprogressivelyelaboratedinseveralgrowers’orchardsmainly
intheSouthofFrance(Figure1b).Theknowledgeofthebranchingandfruitingpatternsof
therootstock/cultivarcombinationthatisgrownareofhighimportance to adapt these
proposalstoeachsituation(Laurietal.,2011).
‐ At the whole‐tree scale, all branches at the bottom of the tree, usually 2 to 5,
dependingontherootstock‐cultivar combination and the environment, are kept.
Dependingonthegrower,theplantmaterialfromthenurseryor the region (e.g.,
branchesinsertedtoolowonthetrunkmaybedamagedbyheavywinterfrost)only
branchesfrom50cmupwardarekept.Thesebranchesareattached with cordsto
horizontalwiresinaflexiblewayalongtherowoneachsideof the row. The
objective is to develop upright or slanted reiterative trunks on which the fruiting
shootswillbedistributed.Competitionamongthesereiterativetrunksandwiththe
initialtrunkaswellastheirnumberarenotanissue,andtheobjectiveistousethis
structuralframeworktofillthevolume intherowasfastas possible.Althoughthe
round‐shaped tree has repeatedly been shown to be the best crown geometry for
light interception (Smith et al., 2014) but also for the balance between vegetative
growthandfruiting(Lespinasse,1992),thisshapeisdependentonplantingdensity.
Dependingonthegrower,theobjectiveistoobtainaparallelepiped‐shapedtreeof
about3mhighand0.8‐1mwidth,withplantingdistancesof3.5×1.2‐1.5 m
corresponding to ca. 2000‐2400 trees ha‐1orca.6000reiterativetrunksha
‐1. In
otherorchardswithmoredominanttrunks,treeshaveamorecylindricalshapewith
similarheightasabovebutwithalowerplantingdensity,i.e., 4.2‐4.5×1.5‐1.8 m
correspondingto1200‐1600treesha‐1.
TheSalsa‐trainedtreemay beobtaineddirectlyinthegrower’sorchardbyplanting
bench‐graftedtrees.Onemayalsotakeadvantageofthetwo‐branchtreesystemthat
ispatentedbysome nurseries (e.g., VivaiMazzoniNurseries,Italy) andsoldunder
thetrademarkednameBibaum(“twotrees”inGerman).Ithastobenoticedthatthe
Salsasystemdoesnotbelongtothepalmettesystem,thislatter one being mainly
basedonheadingcutsoftheleadereachconsecutiveyear,andonattachingtheside
brancheshorizontallyoroblically.
‐ThefruitingbranchconceptisabandonedintheSalsasystem. As a consequence,
branchbending,whichisatime‐consumingoperation,is consistently reducedand
evencancelledespeciallywhenthereismorethantworeiterativetrunks.Fruiting
shoots are directly attached along the reiterative trunks and are distributed
homogeneouslywithinthetreecanopyvolume.Toimprovetheautonomy of the
fruiting shoots the porosity of the canopy is obtained through both artificial
extinctioninspringtoremoveexcessfloweringspursandyoungshoots,andwinter
thinningcutscarriedouton2‐yearoldandolderbranchesinovercrowded and
shadedsitesinthecanopy. Oncethefruiting shootispositioned withinthecanopy,
theobjectiveistomaintainagoodlightinterceptionandtoavoidcompetitionwith
otherfruitingshoots.
Our experience with the Salsa system in growers orchards over the last 10 years
generated some valid points. From the economic point of view, theSalsasystemreduces
investment at planting and during the orchard life‐span leadingtoafasterreturnon
investmentincomparaisontothereferencetrainingsystemsinFrance.Itiswellcompatible
withacultivarrotationthroughtop‐workingafter10‐15years.Itisgenerallyshownthatthe
Salsasystemleadsto,
oabetterbalancebetweenvegetativegrowthandfruiting,especially in conditions
withhighgrowthpotential,
oadecreaseinfruitsunburn,
oanimprovedaccesstothetreeandaneasieruseofplatformsfor treetrainingand
fruitpicking.
Anoutstandingaspectisthatfruit‐setisreducedcomparedtotheCentrifugaltraining
systemwherebendingtendstoincreasefruit‐set.Althoughthephysiologicalinterpretation
isnotelucidated,thishasaclearadvantageinreducingtheneedsforchemicalfruitthinning

155
especiallyinorganichorticulture.
DISCUSSION AND CONCLUSION
The apple tree ideotype is discussed in several papers especiallyinrelationtotree
architectureandfruiting,aswellastoresistanceortolerancetothemainpestsanddiseases
(Lespinasse,1992;Dickmanetal.,1994;Laurietal.,1995;LauriandCostes,2005;Parisiet
al., 2014). However, a tree ideotype is only one element of thepuzzlethatleadstothe
economic success of the orchard. The symbiosis between the genetically‐determined tree
ideotypeandtheculturalideotype,thislatteroneincludingthe pruning and training
procedures,iscrucial.Improvingtrainingandpruningsystemsisanever‐endingstory,andit
islikelythatboththeprogressinourknowledgeintreearchitectureandphysiology,andthe
releaseofnewplantmaterialbybreederswillentailnewproposalstobetterfitwiththese
newconditions.Atalargerscale,theimprovementoftreetrainingsystemswillhavetobe
adaptedtothemorefrequentextremetemperatureanddroughtepisodesforecastedforthe
21stcentury(IPCC,2013).Itislikelythattheexperiencedevelopedinregionsoftheworld
with mild winter and/or hot and sunny summer brings valuable information on how to
improve the pruning and training to maintain high and regularly fruiting in adverse
environments.
ACKNOWLEDGEMENTS
WewarmlythankKarenMaguyloforhersuggestionsonthewording.
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