Epicormic shoots and growth plasticity of fruit trees in response to horticultural manipulations

Transcription

1 Epicormic shoots and growth plasticity of fruit trees in response to horticultural manipulations Evelyne Costes 1 Ted DeJong INRA, UMR AGAP, Equipe Architecture et Fonctionnement des Espèces Fruitières Montpellier, France 2 Plant Sciences Department UC Davis, Davis CA, USA

2 Definition Shoots emerging from dormant, latent buds, formed prior to the previous growing season Usually from axillary (preventitious) meristems in Rosaceae fruit trees Trace of epicormic shoot outgrowth Preventitious meristem Track of vascular tissue Photo: T. Dejong

3 Epicormic shoots are commonly observed and used in horticulture Stimulate outgrowth by (or after) bending Natural reaction after diseases From Smith and Wareing (1964) Olive tree infected by Pseudomonas savastnoi (source Wikipedia) Manipulate tree structure by pruning Example of the UFO (Upright Fruiting Offshoot) training system in cherries depends on epicormic shoots.

4 Epicormic shoots contribute to the natural shape and tree ageing: Example of the apricot tree From Costes, 1993

5 Epicormic shoots allow reiterations after traumatic events Global and partial reiterations Drawings from F. Hallé

6 Controversies and drawbacks of excessive reactions with epicormic shoots Epicormics are widely used in horticultural tree manipulations but their role remains controversial: They may represent drawbacks due to - the risk of congestion of the top of the trees or at the center of the trees - Reduced light

7 Excessive, poor pruning can lead to excessive production of epicormics.

8 Tying down branches horizontally can stimulate excessive epicormic shoot growth (Japanese plum)

9 Trellises that are too flat can stimulate excessive epicormic shoots and are pruned out every year (Asian pear)

10 Mechanical topping causes repeat epicormic growth

11 Studies for controlling the number and length of epicormic shoots with chemicals Plant growth regulators (PGR) such as Prohexadione-Calcium or Paclobuttrazol inhibit gibberellin biosynthesis and have been proposed to control epicormics From Miller, 2008 From Jacyna and Dodds, 1995

12 Origin and structure of epicormics Can develop from the bottom to the top of the tree From preventitious buds Almost entirely neoformed Their structure depend on their position within the tree and tree age: Vigourous sprouts in young trees Agony branches in old trees

13 Origin of epicormic shoots: pools of latent buds Depend on shoot organization in each species: Cherry tree Peach tree Drawing from B. Wenden, INRA Bordeaux Apple tree Pool of latent buds remain alive after proleptic shoot development at - the leaf and scar axils - the growth units end/start - Along stems mixed with laterals From Costes et al., 2014

14 Epicormic shoots after pruning in young apple trees Long proleptic (P) New growth after pruning Reiterations after pruning (R) Partial removal of the main stem One-year old apple tree & summer pruning (_S) Short proleptic (P) Sylleptic (S) Two-years old apple tree & winter pruning (_W) Heading cut (HC) of the main stem (M) Very local reaction: a maximum of 5 latent meristems were activated More buds were activated after winter than summer heading cut From Fumey et al., 2011

15 Length of epicormic shoots after a heading cut From Fumey et al., 2011 Reiterations (R) after heading cuts were always longer and with more metamers than control axes (C) Vigourous sprouting, rebalance of the shoot/root ratio?

16 Comparison between proleptic and epicormic shoot structures in adult almond trees Proleptic: 76 total nb of metamers 7 states Sylleptic laterals Associated and central flowers Epicormics: total nb of metamers 4 states Few flowers From Negron et al. (2014)

17 Conditions for epicormic shoots development in peach tree: Effect of light, temperature and date of topping From Gordon et al. (2006) The number of epicormic shoots and their growth depend on light intensity and date of topping (without interaction between the two factors)

18 Effect of crop load on epicormic shoot growth in peach tree Crop load affected the glucose and starch content in roots and bark and reduced the number of epicormic shoots per tree From Gordon and Dejong (2007)

19 No effect on short shoots Epicormic shoots are sensitive to crop load in both their nb of nodes and dry weight Thinned trees produced 1/3 more epicormics than defruited trees but strong reduction in full crop Shoot specific weight (SSW) decreased with crop load From Gordon and DeJong (2007) N: no sprout removal; R: Sprout removal T: Thinned; D: defruited; F: full crop E: Epicormic shoots; L: Long shoots; S: short shoots

20 Comparison of origins of proleptic shoots on a previous year shoot after a period of dormancy vs sylleptic shoots borne on a rapidly growing epicormic shoot that was stimulated by a dormant pruning cut.

21 Epicormic capacity to flower and set fruit Mean (± SE) of flower bud density (# flower buds/total # buds) and % of flowers that bloomed was compared across peach cultivars on proleptic shoots and sylleptic shoots on epicormics. Shoot type Cultivar Lorrie May Flavorcrest Elegant Lady O Henry Proleptic Flower bud density 69.7%±0.02 a 51.9%±0.02 b 44.2% ±0.02 bc 39.3%±0.02 c % bloom 89.8%±0.02 a 91.7%±0.02 a 94.9%±0.02 a 91.0%±0.02 a Sylleptic Flower bud density 51.9%±0.02 a 40.2%±0.02 ab 40.2%±0.02 b 29.9%±0.02 c % bloom 80.2%±0.02 b 80.7%±0.02 b 94.9%±0.02 a 85.6%±0.02 b Proleptic/Sylleptic % bloom p =0.001 a/b p=0.003 a/b p=0.97 a/a p=0.171 a/a Prats et al. EJHS in press Sylleptic on epicormic shoots have a lower percentage of flowers that bloomed in two cvs among four.

22 Final fruit set on proleptic shoots compared with sylleptic shoots on epicormics on four peach cultivars Prats et al. EJHS in press Relationship between initial number of flowers and fruit set differ between sylleptic and proleptic shoots but also depending on the cultivar

23 Summary and conclusions: Epicormic shoots are part of tree architecture As reiterated axes, their structure depend on their within-tree position They are widely used in horticultural tree manipulations but their role remain controversial A risk enhanced in super-high-density orchards, especially with mechanical pruning Epicormics compete for carbohydrates: carbohydrates in excess benefit more to epicormic than proleptic shoots in pruned trees Epicormics have fewer flowers than proleptic shoots, but could have a production potential through sylleptic branching Few quantitative studies on pruning reactions have been performed so far Better understanding tree architecture and epicormic shoot behavior remains a necessity for fruit tree management and training systems

24 Future works? Bud level Bud maintenance survival versus outgrowth: maintenance costs, outgrowth determisms Epicormic behavior Growth speed structure dependence on tree development and age Contribution to tree life and physiology Photosynthesis, allocation to other parts of the tree Production potential

25 Acknowledgements AGAP unit J.L. Regnard (SupAgro) P.E. Lauri (INRA) J.J. Kelner (SupAgro) D. Fumey (doc) Y. Guédon (CIRAD) UC Davis G. Lopez, post-doc C. Negron (doc.) D. Gordon (doc.) Other contributors: A. Rosati, ISO, Italy C. Damiano, ISF, Italy M.T. Prats-Llinàs, IRTA, Spain