The higher productivity of modern fruit tree cultivars, compared with wild trees, is mostly related to their higher partitioning of dry matter into fruit [i.e., higher harvest index (HI)] (Patrick, 1988), rather than to differences in photosynthetic abilities (Loomis, 1983). In cultivated species, HI often reaches 75% (Cannell, 1985), whereas it is much lower in wild species. The increase in HI is obtained both by a shorter initial unproductive period (i.e., early bearing) and by maintaining higher partitioning into fruit in the mature tree (more abundant yield, relative to tree size) to the detriment of vegetative growth (Archbold et al., 1987; Forshey and McKee, 1970). In fact, reproductive and vegetative growth are in competition for the available resources and one inhibits the other (Grossman and DeJong, 1995a, 1995b; Kramer and Kozlowski, 1979; Spurr and Barnes, 1980).
Because of this competition, it has long been assumed that reducing vegetative growth is essential to bring about early and abundant fruiting (Browning, 1985). Containing plant vigor, e.g., by controlled water stress (Mitchell et al., 1989); containing root volume with drip irrigation (Mitchell and Chalmers, 1983) or by root pruning (Geisler and Ferree, 1984); dwarfing rootstocks (Avery, 1970; Preston, 1958); and shoot removal, chemical control of vegetative growth, or both (Mulas et al., 2011; Rugini and Pannelli, 1992; Williams et al., 1986), all result in enhanced yield.
However, the opposite is also true: once reproduction starts, the crop will compete with, and reduce, vegetative growth and, therefore, vigor, as shown also by modeling (Grossman and DeJong, 1994; Smith and Samach, 2013). This is the case for mature trees of many species (Berman and DeJong, 2003; Costes et al., 2000; Lauri and Térouanne, 1999; Salazar-García et al., 1998; Stevenson and Shackel, 1998), including olive (Castillo-Llanque and Rapoport, 2011; Connor and Fereres, 2005; Dag et al., 2010; Lavee, 2007; Monselise and Goldschmidt, 1982; Obeso, 2002; Rallo and Suárez, 1989). In young trees, the removal of all blossoms or fruits results in dramatic increases in growth relative to the fruiting trees (Chandler and Heinicke, 1926; Embree et al., 2007; Forshey and Elfving, 1989; Mochizuki, 1962; Verheij, 1972). Similarly, earlier and more abundant fruiting (i.e., higher partitioning into fruit) is at least one of the mechanisms involved in the effect of dwarfing rootstocks (Avery, 1970; Preston, 1958) and in some cases, the only mechanism (Lliso et al., 2004), although in other cases, it is probably not the only one. In fact, defruiting apple trees on dwarfing rootstocks allows tree vigor to increase dramatically, but still less than in trees with more vigorous rootstocks (Avery, 1969; Barlow, 1964). It could be argued, therefore, that early and abundant fruiting is not just a consequence of lower vigor, but once induced, it becomes a cause of the reduction in vigor.
Whether different partitioning into fruit (i.e., difference earliness and abundance of fruiting) could be the cause of differences in vigor among different cultivars has not been studied.
In olive, as for other fruit trees, vigor reduction and early and abundant production are also desirable traits (Rallo et al., 2007; Tous et al., 1999), but few cultivars possessing these traits have been identified, despite much research on reduced vigor or even dwarf cultivars (Barranco, 1997; León Moreno, 2007; Sonnoli, 2001). Nor has it been possible to successfully induce these traits in traditional olive cultivars by grafting, despite much research on olive rootstocks (Baldoni and Fontanazza, 1990; Barranco, 1997; Pannelli et al., 1992, 2002; Troncoso et al., 1990). Recently, the so-called SHD orchards have been developed, using the few cultivars found to have sufficiently low vigor and early yield. SHD olive orchards, if indeed technically and economically viable, are important for the olive industry because they allow continuous (i.e., straddle harvester) mechanical harvesting (Rallo et al., 2007; Tous et al., 1999), thus greatly reducing costs and hand labor requirements. However, the straddle harvester requires small-canopy trees (Camposeo et al., 2008; Tous et al., 2006) and traditional cultivars tend to “escape” from the small volume allowed, thus requiring intense pruning, which stimulates vegetative growth and reduces fruiting (Jerie et al., 1988). SHD orchards also require early and abundant fruiting if they are to be economically viable (De Benedetto et al., 2003). It is important, therefore, to understand the mechanisms implicated in early and high production and reduced canopy size.
So far, the cultivars that proved most suitable for SHD olive orchards are Arbequina, Arbosana, and Koroneiki (Tous et al., 2006), three cultivars characterized by low vigor compared with most traditional cultivars (Rosati et al., 2013; Tous et al., 2006). However, they are also characterized by early and abundant bearing, as well as low alternate bearing (Caruso et al., 2012; Díez et al., 2016; Farinelli and Tombesi, 2015; Godini et al., 2011; Moutier, 2006; Moutier et al., 2008). Trees of these cultivars produce large crops, relative to their size, already in the second and third year after transplanting.
Given the competition between crop and vegetative growth, we hypothesize that early bearing is implicated in the difference in vigor between such cultivars and more traditional ones that do not fruit until much older. In a previous study (Rosati et al., 2017), we found that tree growth, in terms of both tree diameter and canopy volume increments, was inversely related to tree yield across 12 cultivars in young olive trees. Similarly, Di Vaio et al., (2013) found that across 20 cultivars, the least vigorous tended to have greater early yields. However, correlation does not prove causality and only by defruiting the trees it would be possible to test whether fruiting is indeed a cause, rather than a mere consequence, of reduced vigor in early-bearing low-vigor cultivars.
In this article, we test the hypothesis that earlier and more abundant bearing is the cause, or one of the causes, of reduced vigor. To test this hypothesis, we compared the initial growth of deflowered, partially deflowered (i.e., in alternate years), and control fruiting trees in Arbequina, the cultivar most used in SHD orchards, and in Frantoio, a traditional cultivar much more vigorous than Arbequina (Rosati et al., 2013; Vivaldi et al., 2015).
AcebedoM.M.CañeteM.L.CuevasJ.2000Processes affecting fruit distribution and its quality in the canopy of olive treesAdv. Hort. Sci.14169175
ArchboldD.D.BrownG.R.CorneliusP.L.1987Rootstock and in-row spacing effects on growth and yield of spur-type ‘Delicious’ and ‘Golden Delicious’ appleJ. Amer. Soc. Hort. Sci.112219222
AveryD.J.1969Comparisons of fruiting and deblossomed maiden apple trees, and of non-fruiting trees on a dwarfing and an invigorating rootstockNew Phytol.68323336
BarlowH.W.B.1964An interim report on a long-term experiment to assess the effect of cropping on apple tree growthAnnu. Rpt. E. Malling Res. Sta.19638493
BarrancoD.1997Variedades y patrones p. 59–79. In: D. Barranco R. Fernández-Escobar and L. Rallo (eds.). El cultivo del olivo. Mundi Prensa Madrid Spain
BermanM.E.DeJongT.M.2003Seasonal patterns of vegetative growth and competition with reproductive sink in peachJ. Hort. Sci. Biotechnol.78303309
BrowningG.1985Reproductive behaviour of fruit tree crops and its implications for the manipulation of fruit set p. 409–425. In: M.G.R. Cannell and J.E. Jackson (eds.). Attributes of trees as crop plants. Inst. Terrestrial Ecology Midlothian Great Britain
CamposeoS.FerraraG.PalascianoM.GodiniA.2008Varietal behaviour according to the super high density olive culture training systemActa Hort.791271274
CannellM.G.R.1985Dry matter partitioning in tree crops p. 160–193. In: M.G.R. Cannell and J.E. Jackson (eds.). Attributes of trees as crop plants. Inst. Terrestrial Ecology Midlothian Great Britain
CarusoT.CampisiG.MarraF.P.CamposeoS.VivaldiG.A.ProiettiP.NasiniL.2012Growth and yields of the cultivar Arbequina in high density planting systems in three different olive growing areas in ItalyActa Hort.1057341348
Castillo-LlanqueF.RapoportH.F.2011Relationship between reproductive behavior and new shoot development in 5-year-old branches of olive trees (Olea europaea L.)Trees (Berl.)25823832
CostesE.FournierD.SallesJ.C.2000Changes in primary and secondary growth as influenced by crop load in ‘Fantasme’ apricot treesJ. Hort. Sci. Biotechnol.75510519
DagA.BustanA.AvniA.TziporiI.LaveeS.RiovJ.2010Timing of fruit removal affects concurrent vegetative growth and subsequent return bloom and yield in olive (Olea europaea L.)Scientia Hort.123469472
De BenedettoA.JacoboniA.VenziL.PannelliG.2003Valutazione economica di un moderno impianto olivicolo nell’Italia centraleOlivae951017
DíezC.M.MoralJ.CabelloD.MorelloP.RalloL.BarrancoD.2016Cultivar and tree density as key factors in the long-term performance of super high-density olive orchardsFront. Plant Sci.71226
Di VaioC.NocerinoS.PaduanoA.SacchiR.2013Characterization and evaluation of olive germplasm in southern ItalyJ. Sci. Food Agr.9324582462
EmbreeC.G.MyraM.T.NicholsD.S.WrightA.H.2007Effect of blossom density and crop load on growth, fruit quality, and return bloom in ‘Honeycrisp’ appleHortScience4216221625
FarinelliD.TombesiS.2015Performance and oil quality of ‘Arbequina’ and four Italian olive cultivars under super high density hedgerow planting system cultivated in central ItalyScientia Hort.19297107
ForsheyC.G.ElfvingD.C.StebbinsR.L.1992Training and pruning apple and pear trees. Amer. Soc. Hort. Sci. Alexandria VA
GeislerD.FerreeD.C.1984The influence of root pruning on water relations, net photosynthesis, and growth of young ‘Golden Delicious’ apple treesJ. Amer. Soc. Hort. Sci.109827831
GrossmanY.L.DeJongT.M.1995aMaximum fruit growth potential and seasonal patterns of resource dynamics during peach growthAnn. Bot.75553560
GrossmanY.L.DeJongT.M.1995bMaximum vegetative growth potential and seasonal patterns of resource dynamics during peach growthAnn. Bot.76473482
HasegawaS.TakedaH.2001Functional specialization of current shoots as a reproductive strategy in Japanese alder (Alnus hirsuta var. sibirica)Can. J. Bot.793848
KramerP.J.KozlowskiT.T.1979The physiology of woody plants. Academic Press New York NY
LauriP.É.2007Differentiation and growth traits associated with acrotony in the apple tree (Malus ×domestica Rosaceae)Amer. J. Bot.9412731281
LauriP.É.TérouanneÉ.1999Effects of inflorescence removal on the fruit set of the remaining inflorescences and development of the laterals on one year old apple (Malus domestica Borkh.) branchesJ. Hort. Sci. Biotechnol.74110117
LlisoI.FornerJ.B.TalónM.2004The dwarfing mechanism of citrus rootstocks F&A 418 and #23 is related to competition between vegetative and reproductive growthTree Physiol.24225232
LoomisR.S.1983Productivity of agricultural systems p. 151–172. In: O.L. Lange P.S. Nobel C.B. Osmond and H. Ziegler (eds.). Encyclopedia of plant physiology new series Vol. 12D. Springer-Verlag Berlin Heidelberg New York NY
MitchellP.D.ChalmersD.J.1983A comparaison of microjet and point emitter (trickle) irrigation in the establishment of a high-density peach orchardHortScience18472474
MitchellP.D.van de EndeB.JerieP.H.ChalmersD.J.1989Responses of ‘Bartlett’ pear to withholding irrigation, regulated deficit irrigation, and tree spacingJ. Amer. Soc. Hort. Sci.1141519
MochizukiT.1962Studies on the elucidation of factors affecting the decline in tree vigor as induced by fruit loadBul. Fac. Agr. Hirosaki Univ.840124
MulasM.CaddeoC.BandinoG.SeddaP.2011Shoot pruning and treatment with hexaconazole or urea to increase fruit-set in oliveActa Hort.924233240
PannelliG.FamianiF.RuginiE.1992Effects of the change on ploidy levels on anatomical cytological reproductive, growth performance changes and polyamine content, in mutants of gamma irradiated olive plantsActa Hort.317209218
PannelliG.RosatiS.RuginiE.2002The effect of clonal rootstocks on frost tolerance and on some aspects of plant behaviour in Moraiolo and S. Felice olive cultivarsActa Hort.586247250
ProiettiP.TombesiA.1996Translocation of assimilates and source-sink influences on productive characteristics of the olive treeAdv. Hort. Sci.101114
RosatiA.PaolettiA.Al HaririR.FamianiF.2018Fruit production and branching density affect shoot and whole-tree wood to leaf biomass ratio in oliveTree Physiol.doi:10.1093/treephys/tpy009
RosatiA.PaolettiA.PannelliG.FamianiF.2017Growth is inversely correlated with yield efficiency across cultivars in young olive (Olea europaea L.) treesHortScience5215251529
Salazar-GarcíaS.LordE.M.LovattC.J.1998Inflorescence and flower development of the ‘Hass’ avocado (Persea Americana Mill.) during “on” and “off” crop yearsJ. Amer. Soc. Hort. Sci.123537544
SmithH.M.SamachA.2013Constraints to obtaining consistent annual yields in perennial tree crops. I: Heavy fruit load dominates over vegetative growthPlant Sci.207158167
SpurrS.H.BarnesB.V.1980Forest ecology. 3rd ed. Wiley New York NY
StevensonM.T.ShackelK.A.1998Alternate bearing in pistachio as a masting phenomenon: Construction cost of reproduction versus vegetative growth and storageJ. Amer. Soc. Hort. Sci.12310691075
TousJ.RomeroA.HermosoJ.F.2006High density planting systems mechanisation and crop management in olive p. 423–430. In: T. Caruso A. Motisi and L. Sebastiani (eds.). Recent advances in olive industry. Second Intl. Semin. “Olivebiotech 2006” 5–10 November Mazara del Vallo (TP) Italy
TroncosoA.LiñánJ.PrietoJ.CantosM.1990Influence of different olive rootstocks on growth and production of “Gordal Sevillana”Acta Hort.286133136
VivaldiG.A.StrippoliG.PascuzziS.StellacciA.M.CamposeoS.2015Olive genotypes cultivated in an adult high-density orchard respond differently to canopy restraining by mechanical and manual pruningSci. Hort.192391399
WilliamsM.W.CurryE.A.GreeneG.M.1986Chemical control of vegetative growth of pome and stone fruit trees with GA biosynthesis inhibitorsActa Hort.179453458