Physiology of dwarfism and methods to achieve dwarfisms

1. Welcome

2. Master Seminar
Advances in dwarfism of fruit
plants
Warang Omkar Sunil
M.Sc (Hort.) Fruit Science
Course Instructor
Dr. B. R. Salvi
Chairman & Research guide
Dr. P. M. Haldankar
Department of Horticulture,
College of Agriculture, Dapoli

3. Content
• Introduction
• Principle
• Physiology of dwarfism
• Methods to achieve dwarfism
• Research findings
• Thrust areas
• Conclusion

4. Introduction
• Dwarfing is an alteration in the normal growth
pattern.
• A dwarf plant is that which is smaller than normal
size at full maturity and possess other
characteristics like precocity, canopy architecture
and time of flowering and altered fruit size.

5. Principle
•To make the best use of vertical and
horizontal space per unit time and to harness
maximum possible returns per unit of inputs
and natural resources.

6. Physiology of dwarfism
• Mechanism - involves anatomical, physiological and biochemical
changes.
• Auxins are produced by shoot tips and translocated basipetaly
downwards to the roots through phloem.
• Dwarfing rootstock controls tree Size-by controlling the auxin passing
through the bark of the rootstock.
• large number of vessels and twice as many xylem fibers are produced in
vigorous rootstocks than dwarfing ones (Beakbane et al., 1974).
• A greater number of non-functioning phloem has been found in
rootstock with thick bark (M9) than those with thin bark i.e MM106 or
M7 ( Chu and Simons, 1984).

7. Methods to achieve dwarfism
• Dwarfness can be achieved by various ways such as:-
1. Use of dwarfing root stock/interstock or use of dwarfing scion
2. Use of bioregulators
3. Use of incompatible root stock
4. Induction of viral infection
5. Pruning and training
6. Nutrients
7. Phenols
8. In vitro techniques
9. Genetic engineering
10. Ringing or girdling
11. Others

8. Use of dwarfing root stock/interstock
• Use of vigour controlling root stocks is one method used to promote early
fruit bearing, reduce vigour and increased yield.
• Various studies suggested a correlation between early flowering and
smaller tree size (Costes and Garcia, 2007).
• Apple dwarfing rootstocks induce two most important effects i.e precocity
and reduction in tree size (Lauri et al., 2006).

9. Correlations for predicting dwarfing capacity of
rootstocks
• Percentage of live tissues of root cross section.
• Bark : wood ratio
• Percentage of ray tissues in root cross section
• High stomatal density on leaves
• Bark is the key factor as it reduces translocation of auxins, sugars and
other compounds.
• Genes exert their effect on dwarfness.

10. Physiological processes of root stock inducing
dwarfness
1. Anatomy of Dwarfing rootstock:-
• Smaller xylem vessels and less xylem fibers
• Have a higher percentage of living tissues than lignified cells
• Higher percentage of bark and wood ray tissues
2. Nutrition:-
More carbohydrates are directed to fruiting structure and less to
tree frame by dwarfing rootstock.

11. 3. Hydraulic conductivity:-
• Reduced root hydraulic conductance helps to induce dwarfism
(Nardini et al; 2006).
4. Translocation of water and minerals:-
• Less effective in uptake of nutrients and water
• Partial blockage at graft union affects water and nutrients
translocation e.g. Reduction in translocation of P and Ca (Bukovac et
al., 1958).

12. 5. Phytohormones:-
• Less auxin flow take place through bark of dwarf rootstock
• Lower concentration of IAA and ABA are observed in dwarfing
rootstock while vigorous rootstock showed higher cytokinin
concentration in root pressure exudate and shoot xylem sap.
• Lack of ability to produce soluble sugars result in reduced
growth e.g starch hydrolysis.
• NAA suppress the conversion while IAA promotes it that is why
NAA cause dwarfing.

13. 6. Bark of the rootstock:-
• Thicker the bark lesser the height as auxins get destroyed by several
enzymes.
• e.g.- dwarfed avocado trees had 22.7 % of bark compared to 12.9 % in
tall ones.
• Greater thickness in the bark of dwarf trees is associated with a higher
degradation of auxins by IIA oxidase, peroxidase and phenolic
compounds present in the bark (Lockhard and Schneider, 1981).

14. 7. Reduced root system of dwarfing rootstocks:-
• dwarf rootstocks have small and limited root systems.
• More dwarfing a rootstock the smaller is its root system.
• e.g.- M9 has limited root system compared to seedling rootstock
(Fernandez et al., 1995).
8. Depletion of solutes in xylem sap of scions by dwarfing rootstock:-
• It has been observed that dwarfing root stocks and inter stocks lead to
depletion of xylem sap with respect to N, P, K, Ca and Mg (Jones
1976).

15. 9. Dwarfing root stocks induce restricted canopy development of scion
variety:-
• Induce wider crotch angles to lateral branches and spreading habit in
scions. Horizontal branches show both decreased vegetative growth
and enhanced flowering and fruiting (Crabbe, 1984).
• Reduce the growth of both vertical and horizontal branches and
effects being greater on vertical branches (Webster, 1995).

16. 10. Precocious and heavy fruiting at the expense of vegetative
growth:-
• Trees on dwarfing root stocks show a higher ratio of fruit yield to
vegetative growth than those on vigorous root stocks.
11. Reduced carbohydrates transport from leaves to root:-
• Dwarfing rootstock have been found to block the transport of
carbohydrates from leaves to roots.

17. Some important dwarfing rootstocks of
fruit crops
1. Apple :- M27, M9, EMLA 26.
2. Pear:- Quince C
3. Peach:- Siberian C, St. Julien X, P. besseyi and Rubira.
4. Plum:- St. Julien A, St. Julien K, Pixy.
5. Cherry:- Giesela series, Stockton Morello, Oppenheim, Charger.
6. Mango:- Olour, Vellaikolumban
7. Citrus:- Trifoliate Orange, Flying Dragon
8. Guava:- Pusa Srijan, P. friedrichesthalianum
9. Ber:- Jhar ber

18. Use of bioregulators
• A wide varieties of growth regulators re being used to regulate the
growth rate of the fruit trees.
• Paclobutrazol:-It inhibit the GA synthesis and thereby retards growth,
shorten elongation and reduced internodal length.
• Dwarfing mechanism due to PBZ is based upon:-
i. Shorter internodes due to less GA in tissues
ii. Reduces ABA levels in shoot tips (Kurian et al; 1993).
iii. Reduces the levels of cytokinins (Kurian et al; 1993).
iv. Enhances the total phenolic content of terminal buds (Kurian et al;
1993).

19. • Gibberlins biosynthesis inhibitors –
• Onium compounds- CCC, Mepiquat chloride, Phosphon-D.
• Triazoles- Uniconazole, Tripenthenol, Paclobutrazol.
• Pyrimidines- Inhibit synthesis of gibberlins.
• New molecules-Tetcyclasis, morphactins

20. Bioregulator Concentration Crop Effect Recommended
by -
PBZ 15 mg / liter Plum,
pear,
apricot
Reduced
shoot
length
Grochowska
and Hodun
(1997)
TIBA 3.5 mg / liter Plum,
sour
cherry
Reduced
shoot
length
Grochowska
and Hodun
(1997)
PBZ 2.5 – 5 g/l Mango Reduced
50% of tree
volume
Iyer and Kurian
(1993)
PBZ 500-1000 ppm Satsuma
mandarin
Inhibits
vegetative
growth
Okuda et al.
(1996)

21. Use of incompatible rootstock
• Dawrfness can be imparted by the use of incompatible scion and
rootstock.
Crop name Root stock Scientist
Ber Jhar Verma et al., 2000
Pear Quince Francesscatto et
al.,2007

22. Induction of viral infection
• Inducing viral infection
• It is not commercially adopted.
• Eg. Citrus, Apple.
Symptoms of Citrus Exocortis viriods on Citrus plants

23. Pruning and training
• Slow growing trees responds more to pruning.
• A compact and bushy tree achieved by removal of apical portion.
• Limitation:- grape, apple and some other temperate crops.
• Of the various training systems being followed in apple e.g. spindle bush and single
vertical axis raised on M9, M7 and M4 root stocks has been found promising for
HDP w.r.t size control and higher yield per unit land area (Gyuro, 1978).
Spindle Bush system Vertical axis system

24. Nutrients
• Moderately vigorous trees utilize less nitrogen
• Vigorous one use more nitrogen.

25. Phenols
• Phenols reduce vegetative growth by inhibiting mitosis,
cell division, cell elongation and increase IAA oxidation.
• Some phenols also inhibit translocation of sugar and
auxin or act by regulating polar auxin transport.
• Eg. Coumarin, phloridzin

26. In vitro techniques
• Seeds are subjected to different level of BA (Benzyl
adenine) and TDZ (Thidiazuron).
• The plants produced with TDZ and BA were slower in
growth and dwarf in size than non-treated plants
(Khattak et al., 2004).

27. Genetic engineering
• DNA coding of sorbitol- 6 –phosphate dehydrogense (S6PDH) which is
the key enzyme in sorbitol biosynthesis introduced into Japanese
persimmon induced dwarfism. The physiological mechanism behind this
dwarfing effect has been attributed to accumulation of sorbitol which
might have caused an osmotic imbalance between cytosol and vacuole
(Deguchi et al., 2004).
• Various genes have been identified in fruit crops that can induce
dwarfism eg. Ipt (isopentenyl transferase), OSHI, rolA etc.
• In apple reduction in stem length and node number was achieved
through over expression of gaai gene isolated from Arabidopsis (Zhu et
al., 2008).

28. Ringing or Girdling
• With the removal of bark the flow of carbohydrates down to the roots
restricted and, therefore carbohydrates accumulate above the girdle
producing differential effect on root development. This in turn, leads to
differential effect on shoot growth.
• Cutting and Lyne (1993), supported the hypothesis that less cytokinins
and gibberellins above the girdle are likely to reduce meristematic
activity and cell elongation, leading to reduction in vegetative growth.

29. Others
• Proteins, tengu- su inducer (TENGU) excreted by bacterial phytoplasm
inhibits auxin related pathways there by affecting plant development
(Hoshia et al., 2009).
• Down regulation of GA synthesizing genes.
• Dwarfing through mutations:-
Gamma irradiation applied twice induced dwarfism in Irwin cv. of
mango seedlings and the survival percentage was 65% (Yitzu and
Loonshung, 2000).

30. Research Findings

31. Table no. 1. Tree growth of four apple cultivars on several rootstocks at
12 year old
Cultivar Rootstock Tree girth Tree Crown
Height Spread
Jonathan M7 40. 5 4.4 4. 8
M9 23.2 2. 6 2. 8
M26 34. 4 3. 6 3. 8
MM106 46. 7 4. 6 5. 6
M. prunifolia 53. 0 4. 9 6. 5
Starking
Delicious
M7 40. 5 4. 4 5. 0
M9 25. 2 3.5 3. 6
M26 44.5 4. 9 5. 4
MM106 48. 3 5. 4 6. 5
M. prunifolia 58. 8 4. 7 7. 0
Golden
Delicious
M7 47.3 5.0 5. 8
M9 29. 3 3. 4 3. 4
M26 43. 0 4. 6 4. 8
MM106 54. 3 4. 9 6. l
M. prunifolia 59. 3 4. 8 6. 6
Fuji M9 26.7 2. 8 3. 2
M26 53. 0 4.7 6.0
MM106 59.0 4. 6 6.0
M. prunifolia 64. 8 5. 0 7.2
Shichiro Tsuchiya (1979) Morioka, JapanDwarfing Rootstocks of Apple

32. treatments Pooled
mean of
height (m)
Plant volume (m3) Pooled over
the years
mean(m3)
% reduction in
volume
2003 2004 2005 2006
Ratna/
vellaikolumban
3.6 289.0 293.3 270.6 320.7 285.9 24.9
Ratna/
Mixed rootstock
3.7 360.8 334.5 329.5 498.0 380.8
Alphonso/
Vellaikolumban
3.8 306.1 303.1 270.7 414.2 323.5 39.1
Alphonso/
Mixed rootstock
4.7 582.6 465.4 483.3 593.9 531.3
Kesar/
Vellaikolumban
4.6 512.4 397.2 406.1 599.5 478.8 26.4
Kesar/
Mixed rootstock
4.6 679.5 569.0 576.0 781.4 651.5
SE± 0.17 57.3 48.2 50.0 76.5 27.9
C.D (p=0.05) 0.5 169.0 142.2 147.4 225.7 78.4
Table:2-comparative performance of mango varieties grafted on
vellaikolumban and mixed rootstock (11 year old trees)
Gawankar et al. (2010), Dapoli

33. Table no. 3- Effect of rootstocks on growth and vigour of new
apple varieties
Variety Plant girth (cm) Plant height (cm) Plant spread (cm)
M-9 MM-106 M-9 MM-106 M-9 MM-106
Lal Ambri 17.99 17.44 194.14 216.30 178.97 172.18
Sunheri 16.99 17.08 195.91 212.92 171.62 168.05
Shireen 14.90 15.91 196.32 208.09 172.15 166.07
Fidrous 15.01 13.75 193.04 204.68 168.90 163.34
Akbar 15.90 14.82 192.24 209.33 170.77 168.81
CD @ 5% Rootstock 0.48 0.51 0.29
Variety 0.76 0.81 0.47
Rootstock x Variety 1.08 1.14 0.66
Rift et al., 2008, Kashmir

34. Rootstock Origin CA (m2) Growth rate(cm2
TCA/month)
Vellaikulumban Sri Lanka 4.16 4.91
Chandrakaran Cochin, India 4.54 4.76
Saigon unknown 4.62 5.42
Pico Philippines 5.52 5.34
Elephant tusk Thailand 6.38 6.70
Phoenix Australia 6.67 7.51
Neil Australia 6.83 5.63
kurukan India/Sri Lanka 7.52 7.42
caraboa Philippines 6.54 6.45
Orange Indonesia 7.12 10.33
LSD 0.05 0.19 0.51
Table no. 4: Field evaluation of different rootstocks for growth of
‘Kensington Pride’ mango (4 year old trees)
Canopy Area (CA),
trunk cross sectional area (TCA)
Smith et al., 2008, Australia

35. Table no. 5. Effect of different rootstocks on growth parameters of the
Ber (cv. Seb) plants during 1993-94 (5 year old plants)
Rootstocks Plant height
(m)
Spread of plant (m) Trunk diameter (cm)
E W N S Below union Above union
Z.nummularia 1.85 2.0 2.40 3.7 5.2
Z. spinachristi 2.05 2.6 2.75 6.1 6.5
Z. mauritiana 2.20 2.9 3.05 7.0 7.3
Z. rotundifolia 2.34 3.4 3.50 7.4 7.8
CD at 5% 0.46 0.31 0.23 2.01 1.32
Prasad & Bankar (2006), Jodhpur, Rajasthan

36. Table no. 6:- Effects of interstock type, interstock length and grafting point height on
vegetative growth of apple ‘‘Annurca Rossa del Sud’’ cultivar.
Treatments Circumference of
rootstock (cm)
Circumference of
scion (cm)
Plant height (cm) Canopy Volume
(m³)
Graft combinations
CV/M27/SR 21.9 19.9 280.2 8.9
CV/M9/SR 29.4 26.2 356.1 21.7
CV/SR 55.4 45.9 483.5 45.8
Interstock length
10 cm 28.9 25.1 342.7 19.3
20 cm 22.4 21.0 293.6 11.2
Grafting point height
10 cm 33.5 28.2 351.5 21.1
20 cm 29.7 21.7 351.0 21.7
Di Vaio et al. (2008), South Italy

37. Table no. 7- Rootstock/ interstock effects on number of different axillary
annual shoot types grown by Royal Gala apple trees in their second year
of development (8 year 0ld trees)
Treatment Vegetative extension
shoots
Vegetative spurs
MM.106 21.7±1.0 a 18.2± a
MM. 106/MM.106 18.3±1.5 ab 16.4± ab
MM. 106/M.9 13.5± 1.9 b 16.4±ab
M. 9/MM.106 6.2± 1.3 c 10.6± b
M. 9 5.8± o.7 c 11.7± b
M. 9/M.9 6.6± 1.o c 9.9± 2.2 b
Seleznyova et al., 2008, New Zealand

38. Table no. 8- Irrigation water uptake in fully grown Golden Delicious apple trees on semi
dwarfing MM 106, local Hashabi and dwarfing M9 rootstocks
Rootstock Month Monthly total (mm) Sap
flow
Hashabi June 189
July 208
August 208
Total 606
M9 June 155
July 163
August 158
Total 476
MM106 June 225
July 227
August 231
Total 682
Cohen & Naor., 2002, Israel

39. Table no. 9:- Total soluble sugars concentration (% dry mass) in the
scion, graft union, rootstock and rootstock shank of ‘Rainier’ sweet
cherry trees on ‘Gi 5’ and ‘Colt’ rootstocks
Rainier X Gi5 Rainier X Colt
Scion 2.71 1.58
Graft union 1.92 2.23
Rootstock 1.44 2.39
Rootstock shank 1.66 2.35
‘Gi 5’ (Prunus cerasus L. X Prunus canescens L., dwarfing)
‘Colt’ (Prunus avium X Prunus pseudocerasus L., vigorous)
M.A. Olmstead et al. (2010), East Lansing, Mich.

40. Table no. 10:- TCA, hydraulic conductance of roots and entire tree of
Crimson Lady peach trees on Nemagaurd and KP-146-144 rootstocks
Rootstock Trunk cross
sectional area
(cm2)
Hydraulic
conductance of
roots
Hydraulic
conductance of
entire tree
Nemagaurd 4.05 6.56 X 10-5 AL 5.23 X 10-5 AL
KP-146-144 0.90 2.49 X 10-5 AL 2.29 X 10-5 AL
Basile et al. (2003), USA
Nemagaurd:- vigorous rootstock
KP-146-144:- Dwarf rootstock

41. Table no. 11:- Mean comparisons of canopy size, height and yield per canopy volume
of Commune clementine grafted on Pomeroy trifoliate orange infected with a single
viroid
Treatment Canopy volume
(m3)
Height (m) Annual yield
(kg/m3)Viroid Isolate
Control 20.68 3.40 3.91
CEVd CEVd-117 15.55 3.09 2.72
CEVd-129 15.21 3.20 3.06
CBL Vd CVd-Ia-117 18.64 3.26 3.60
CVd-Ib 18.83 3.29 4.12
HSVd CVd-IIa-117 20.30 3.31 4.51
CVd-IIb 19.45 3.33 3.48
CVd-IIc 17.35 3.21 3.49
CVd-III CVd-IIIa 15.29 3.05 3.29
CVd-IIIb 14.51 3.02 4.74
CVd-IIIc 12.69 2.88 4.93
CVd-IIId 12.62 2.77 3.61
CVd-IV CVd-IV-Ca 22.85 3.35 3.71
Vernière et al.(2004), France

42. Cultivars Plant
height
(cm)
Leaf no. Stem girth
(cm)
Phenols
(mg/g.)
ABA
(mg/g.)
IAA
(mg/g.)
Bappakai 39.6 17.6 3.30 9.46 10.60 8.46
Muvandan 42.4 24.2 3.20 22.46 13.68 15.48
Olour 31.0 24.0 3.04 31.92 22.40 8.98
Mylepelian 33.6 17.2 2.80 14.78 20.81 8.98
Chandrakiran 23.0 9.4 2.20 39.60 26.94 11.09
Kurukan 25.1 13.2 1.80 50.24 28.97 7.90
Vellaikolamban 17.0 7.4 1.80 59.10 43.19 11.42
CD 5% 3.51 4.75 0.11 4.96 5.69 3.41
SEM 1.31 2.26 0.05 2.41 3.04 1.63
Table no. 12:- Endogenous Hormones and Phenols in Rootstock Seedlings of Mango
Cultivars and their Relationship with Seedling Vigour
Murti and upreti (2003), Banglore

43. Name of the
cultivar
BA conc.
(µM)
Shoot length
(cm)
No. of roots Root length
(cm)
Survival (%)
Golden
Delicious
0 8.1 7.3 1.8 100
20 4.8 4.6 3.6 60
40 3.9 2.6 2.6 30
60 2.7 2.0 1.5 3
USDA 4-20 0 7.9 7.5 1.9 100
20 4.5 3.6 3.0 50
40 3.0 2.7 2.7 20
60 1.0 1.0 1.3 2
LIberty 0 8.0 7.8 1.8 100
20 3.5 3.0 2.8 50
40 2.1 1.6 1.8 25
60 0 0 0 0
Table no. 13:- Growth and survival percentage of Ex-in vitro apple
cultivars plantlets in green house (6 weeks studies)
Khattak et al. (2007), Peshawar, Pakistan

44. Table no. 14:- Mean trunk cross-sectional area (TCA) and tree canopy volume for cv.
Jonagold/M.9 apple trees in different training systems (5 years)
Training system TCA (cm2) Canopy volume
(m3)
Slender Spindle 9.41 1.7
Verticle Axis 11.96 3.0
Hytec 14.85 4.13
Low-Super Spindle 8.74 2.50
High-Super spindle 7.17 1.45
SS – (4,761 trees/ha)
VA – (2,857 trees/ha)
HT – (1,904 trees/ha)
L-Super S – (5,000 trees/ha)
H-Super S – (10,000/trees/ha) Ozkan et al. (2012), Turkey

45. Table no.15:- Effect of the training system on trunk cross-sectional area,
the canopy volume and crop load in the apple cultivar ‘Braeburn’
grafted on M9 rootstock (5 years)
Training System TCA (cm2) Canopy volume
(m3)
Crop load
(Number of fruit
of cm²/TCA)
Slender Spindle 30.2 2.33 2.39
Solen 24.6 1.80 2.24
Verticle Axis 31.6 3.81 3.07
Gandev et al. (2016), Bulgeria

46. Table no. 16:- Comparison of trunk cross-sectional area, crown volume and yield
efficiency per TCSA among training systems of ‘Topaz’ apple trees after 5 years.
Treatment TCSA (cm2) Crown volume
(m3)
Yield efficiency
per TCSA
(kg.cm−2)
SS-WP 26.70 3.161 2.813
SS-WP+SP 29.26 3.590 2.661
MS-WP 29.23 2.924 2.461
MS-WP+SP 29.25 2.908 2.423
TCSA = trunk cross sectional area
CV = crown volume
SS = slender spindle
WP = winter pruning
SP = summer pruning
MS = modified slender spindle
Sus et al. (2017), Czech Republic

47. Table no. 17:- Influence of training system on tree height, trunk cross sectional area,
canopy volume and yield efficiency of Ziraat sweet cherry (4 years).
Training
system
Tree height
(cm)
TCSA (cm2) Canopy
volume (m3)
Yield
efficiency
(kg cm¯²)
SB 243.4 44.65 2.59 0.32
SL 254.6 49.80 3.18 0.28
VCL 257.2 38.76 3.06 0.39
S.B: Spanish bush
S.L.: Steep leader
V.C.L.: Vogel central leader
Aglar et al. (2016), Turkey.

48. Table no. 18:- Effects of HDP and two training methods on ‘Jonica’ dwarf apple trees
grown in Sub Carpathian region (8 years old tree)
Rootstock Training system Trees/ha Trunk cross
sectional
area(cm2)
M. 9 Slender spindle 2700 34.94 a
2050 30.21 a
Vertical axis 3834 20.29 b
2700 24.94 b
P 22 Slender spindle 2700 14.68 c
2052 15.87 c
Vertical axis 3834 10.81 c
2700 13.38 c
Adam and Augustyn, 2003, Poland

49. Table:19- Effects of methods and rates of paclobutrazol on tree height, volume, and
shoot length of 'Tommy Atkins' mango 3 months after treatment application.
Treatments Height of trees (m) Tree volume (m3) Length of new
shoots (cm)
Soil drench
0 (control) 5.64 a 98.55 a 26.50 a
2.75 g a.i/ tree 5.24 b 90.06 b 23.09 b
5.50 g a.i/ tree 5.31 ab 90.07 b 23.24 b
8.25 g a.i/ tree 5.22 b 86.53 bc 22.99 b
Foliar application
0 (control) 5.62 a 95.99 a 26.02 a
2.75 g a.i/ tree 5.30 ab 89.96 b 23.16 b
5.50 g a.i/ tree 5.30 ab 87.85 bc 23.13 b
8.25 g a.i/ tree 5.19 b 85.78 c 22.96 b
SED 0.05 1,65 0.64
Teferi et al., 2004, New Zealand

50. Thrust Areas
• Understanding the physiology of dwarfing rootstocks and their effect on scion
vigour.
• Commercializing the use of incompatible rootstocks and use of viral infections
for dwarfing
• Need to develop dwarf rootstocks for evergreen subtropical fruit crops for
HDP.
• Need to develop dwarf rootstocks which does not affect the fruit quality of
scion cultivar.
• Opportunities will also exist to modify the root growth of crops for which no
dwarfing rootstocks exist presently.
• Screening of dwarf cultivars for dwarfing genes in fruit plants eg. S6PDH,
GID1c from brachytic dwarf peach.

51. Conclusion
• Dwarfing in fruit crops can be achieved through various approaches like use of dwarfing
rootstock, root pruning, training, use of growth retardants, control of nutrient elements
etc.
• Paclobutrazol are most effective and widely used growth retardant.
• Dwarfing rootstock plays important role in controlling tree size and induce precocious
bearing in fruit plants.
• Pruning practices like tip pruning, pinching, removal of apical buds, heading back, etc.
control the tree size.
• Ringing and girdling control the tree size by restricting the flow of carbohydrates and
auxins to the roots.
• Recently genetic engineering has widen the gene pool which can be manipulated to
induce dwarfism and harvest maximum benefits in horticultural crops.

52. Thank You