Rootstocks
Chapter 4
Davies and Albrigo
Seedling Trees
• Problems
–Protracted Juvenility
• Thorns
• Non-precocious
–Soil related
Advantages of Budlings
• Best scion and best stock
• 20 horticultural characteristics
–Tree vigor
–Rooting depth
–Freeze tolerance
–Soil adaptation to high salinity
More Rootstock Influences
–Resistance to nematodes, foot
rot, citrus blight
–Fruit yield, size, texture,
internal quality
–Maturity date
• Study Table 4.1
Rough Lemon
•
•
•
•
•
•
Citrus jambhiri - NE India
Polyembryony
For deep infertile sand (FL ridge)
Susceptibility to blight
Lack of freeze tolerance
High yields (80 - 100 tons / Ha)
Nucellar Embryony
Apomixis
development of an embryo without the fusion of
male and female gametes.
Polyembryony
occurrence of more than one embryo in a seed.
Nucellar embryony
embryos form from nucellar tissue.
Nucellar embryony in citrus means that most embryos
are vegetative not zygotic.
They are produced from nucellar tissue and are
therefore clones of the mother tree.
Pollination is needed to trigger nucellar development .
Nucellar polyembryony in Citrus
Nucellar Embryony
Nucellar embryos begin development as soon as
pollination occurs while zygotic embryos take four
weeks to develop; thus, nucellar embryos crowd out
the zygotic embryos.
There are various degrees of nucellar embryony.
Some cultivars produce only nucellar embryos, and
some vary in the percentage of nucellar embryos.
Three citrus types produce monoembryonic and
therefore zygotic seed;
‘Temple tangelo’
‘Clementine’ tangerine
Shaddock, Citrus grandis (pomelo)
Implications of nucellar embryony.
Rootstocks such as 'Rough Lemon', 'Sour Orange',
and P. trifoliata can be produced true-to-type from
seed.
Virus can be eliminated from infected clones.
However, because nucellar seedlings are juvenile it
takes a long time to obtain productive clones.
These can then be propagated by budding from the
indexed nucellar mother tree.
Breeding of citrus is made difficult because of the
difficulty obtaining genetically variable populations.
More Rough Lemon
• Root depth 4.6 m (drought
tolerant)
• Wide range of pH.
• Tolerant to
–Tristeza (CTV)
–Citrus exocortis viroid (CEV)
–Citrus xyloporosis viroid
More Rough Lemon
• Highly susceptible to
– foot rot
–burrowing nematodes
–blight (unknown cause)
• Poor quality fruit
–‘Valencia’/ RL = 11.4 %
–‘Valencia’/ SO = 13.2 %
More Rough Lemon
• Fruit characteristics
– Thick Peel
– “Puffy”
–Regreening
–Not good enough for fresh mkt.
–Higher prodn of kg-solids
Kg Solids (Pounds-solids)
• Function of
–Yield
–Juice content
–Total Soluble Solids (TSS)
Sour Orange (C. aurantium)
• Most widely planted stock in the
world.
–Scions of SO - moderate vigor
–Slower than scions of RL but
not dwarfed.
More Sour Orange
• Higher TSS per fruit, but kgsolids are lower than RL, CM,
and CV on sandy soils.
• Produces deep, moderately
branched root system.
• Scion vigor better on fertile soils.
• Used on heavy poorly drained
soils. Does well on high pH soil.
SO Freeze Hardiness
• Cultivars on SO equal to:
–Cleo, trifoliata, and citrumelo
• Superior to lemon types and
citranges.
• Does not regrow as rapidly as
lemon types after freeze.
Sour Orange and Soil Prob.
• No problem with
–Xyloporosis
–Phytophthora foot rot
• Susceptible to
–Burrowing nematodes
–Citrus nematodes
Fruit Quality on SO
• Fruit size smaller than on RL, but
larger than on Cleo.
• TSS and TA are high thus
preferred stock in:
–LRGV, Indian River, and Spain.
• Grapefruit Lower height/
diameter ratio than on Cleo.
More Fruit Quality - SO
• High TA may delay maturity.
• If TSS limiting (like in ‘Hamlin’)
then SO advances maturity.
• TSS may by 1.5% higher than RL.
• High TSS + phytophthora resist.
makes SO popular in tropics.
Splitting AO
• Scions on SO have smooth, thin
peel.
• Thus excessive splitting can
occur more frequently than on
Cleo.
• Problem on sw oranges and
mandarins - not on GF, Temple.
Sour Orange Selections
• ‘Bittersweet’
–More tolerant to phytophthora
• C. taiwanica tolerant to CTV ??
• ‘Bittersweet’ higher yields than
C. taiwanica.
‘Cleopatra’ Mandarin
• C. reticulata - minor importance
in world.
• Large and mod. vigorous trees
• Deep, densely branched root sys
• Yield sw oranges intermediate
between RL and SO.
• Comparable yields of SO.
More Cleo
• Less precocity - takes 10 - 15 yr
• As freeze hardy as most and
better than the lemons or
‘Carrizo’ Citrange.
• Adapted to wide variety of soils.
Resistant to high salinity, high
pH, and calcareous soils.
Cleo’s BIG Advantage
• Tolerant of CTV, CEV, and
Xyloporosis.
• But it is susceptible to:
–Burrowing and Citrus
Nematodes.
• Reaches 12 - 15 yrs before
blight kills it.
Cleo Fruit Quality
• Fruit size smaller.
• Fruit quality between SO and RL.
• Peel smooth and thin - more
splitting in oranges but not
important in grapefruit.
• Excellent stock for: ‘Temple’ and
mandarin hybrids.
Citrus macrophylla
• Very similar to lemons and limes.
• Lemons and limes do very well
on this stock.
• Big problem - freeze sensitive.
• Sw oranges and GF very large
but thick peel.
• Adapted to cool, dry climates.
Trifoliate Orange
• Widely used for satsumas and
oranges in Japan, China,
Argentina, and Australia.
• Dwarfing has been due to CEV.
• CEV inoculations induces dwarf
Freeze Hardiness of
Trifoliate Orange
• Stock very hardy.
• But scions become quiescent
later than on SO and RL.
• Scions not affected by CTV or
CEV, but taken out by blight.
• Better on heavy poorly drained
soil.
Fruit Quality on Trifoliate
• Usually small fruit prob because
large crops and smaller root sys.
• Excellent quality, similar to those
on SO and RL.
• Fruit peel smooth and thin.
Citranges
• Sw. orange x trifoliate hybrids.
• Several tested:
–‘Rusk’, ‘Morton’, ‘Savage’,
‘Benton’, C-35, ‘Carrizo’, and
‘Troyer’
–‘Troyer’ in CA & ‘Carrizo’ in FL
• Scion over grows stocks.
‘Swingle’ Citrumelos
• ‘Swingle’ citrumelo is most
widely grown stock in FL.
• Released in 1974 - now world .
• Not affected by CTV, CEV, or
xyloporosis.
• More freeze hardy than RL or
‘Carrizo’. Same as SO.
Unpublished results of
TAMUK Citrus Center 2003/2004
C-22
C-146
C-57
Af. Shad.
Sour
Troyer
Gou Tou
2002 2003
(lb/tree)
505.5 605.5
412.0 558.0
385.0 576.0
321.0 568.0
362.5 423.3
255.0 489.0
164.0 418.5
% Sol. Solids % Acid
8.65
8.85
8.65
8.85
9.30
8.40
8.00
0.92
0.92
0.89
0.95
0.91
0.81
0.81
Copyright 2004- TAMUK
Sizes
• C-22
Extra-fancy 56- 3.15%
48- 13.64%
40- 21.03%
36- 20.62%
Total Weight: 8051 Lb
• Sour
Extra-fancy 56- 1.46%
48- 5.92%
40- 13.50%
36- 15.53%
Total Weight: 4186 Lb
Copyright 2004- TAMUK
THE END