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ACG Conference 2008
Winter Yellows -A closer look at this physiological disorder and other issues
Sandra Hardy, NSW DPI Pat Barkley, ACG
ACG Conference 2008
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OutlineWinter Yellows:
Typical symptomsWhat we knowPrevious instances
Reasons why?Weather patternsCarbohydrates
- leaves- roots
Summary Other issues
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Typical symptoms
Yellowing of leavesleaves stay yellow throughout winter
Autumn
Usually latest flush affected
Younger trees (2-5yrs)little/no crop
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Other symptoms include….
Sometimes:whole tree affectedleaf fallout-of-season flowering
Spring recovery
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Previous workAfter 1952After 1952--1954 outbreaks1954 outbreaks……
Affected leaves: Affected leaves: •• low in calcium low in calcium (1(1--2% , 3.52% , 3.5--4.5% in healthy leaves)4.5% in healthy leaves)
•• high in starch high in starch
•• RootsRoots -- starch depleted starch depleted →→ death smallest roots 1stdeath smallest roots 1st
•• Applying N aggravated symptomsApplying N aggravated symptoms
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Previous recorded occurrences - MIA
Plant disease surveys 1952-1986
1953 – widespread (+ coast & lower Murray)1955 – young trees1956 & 1963 – scattered trees, mild symptoms1973 – severe (+ Narromine) 1977- young blocks2005 – widespread
2008 - widespread
ACG Conference 2008
1952 weatherGriffith Weather Data 1952
0
5
10
15
20
25
30
35
40
45
501-
Jan-
52
15-J
an-5
2
29-J
an-5
2
12-F
eb-5
2
26-F
eb-5
2
11-M
ar-5
2
25-M
ar-5
2
8-A
pr-5
2
22-A
pr-5
2
6-M
ay-5
2
20-M
ay-5
2
Date
Tem
pera
ture
(oC)
0
5
10
15
20
25
30
Rai
nfal
l (m
m)
Series2 Series1 Series3
ACG Conference 2008
1953 weather - WYGriffith Weather Data 1953
0
5
10
15
20
25
30
35
40
45
1-Ja
n-53
15-J
an-5
3
29-J
an-5
3
12-F
eb-5
3
26-F
eb-5
3
12-M
ar-5
3
26-M
ar-5
3
9-A
pr-5
3
23-A
pr-5
3
7-M
ay-5
3
21-M
ay-5
3
Date
Tem
pera
ture
(oC)
0
5
10
15
20
25
30
Rai
nfal
l (m
m)
Max Min Rainfall
ACG Conference 2008
2007 weatherGriffith Weather Data 2007
0
5
10
15
20
25
30
35
40
45
1-Ja
n-07
15-J
an-0
7
29-J
an-0
7
12-F
eb-0
7
26-F
eb-0
7
12-M
ar-0
7
26-M
ar-0
7
9-A
pr-0
7
23-A
pr-0
7
7-M
ay-0
7
21-M
ay-0
7
Date
Tem
pera
ture
(oC)
0
5
10
15
20
25
Rai
nfal
l (m
m)
Temp Max Temp Min Rainfall
ACG Conference 2008
2008 weather - WYGriffith Weather Data2008
0
5
10
15
20
25
30
35
40
451-
Jan-
08
15-J
an-0
8
29-J
an-0
8
12-F
eb-0
8
26-F
eb-0
8
11-M
ar-0
8
25-M
ar-0
8
8-A
pr-0
8
22-A
pr-0
8
6-M
ay-0
8
20-M
ay-0
8
Date
Tem
pera
ture
(oC)
0
5
10
15
20
25
30
Rai
nfal
l (m
m)
Max Min Rainfall
ACG Conference 2008
Climatic triggers?
Good summer rainfall
Sudden cold snaps in early-mid autumn
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Carbohydrates (CHO)• Solar energy stored as chemical energy
in form of CHO & other compounds
• Leaves manufacture CHO
• Accumulated: leaves (1st), branches, trunks, roots (last)
• Tree CHO levels variable: seasonal demands of competing developing vegetative & reproductive sinks
• Starch main CHO
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CHO - sinks & storage
• Actively growing organs – strong/priority SINKS
• Storage: roots (highest) > leaves/branches> trunk (lowest)
• Allocation to storage – lower priority thanneeds of actively organs
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CHO – sinks & storage• Reserves affect flowering, fruit set and yield
following year
Large crop loads (e.g. “on” year ):• depletes CHO → severe tree collapses/dies e.g. Murcott• reduces summer/autumn flush
CHO accumulation:• most rapid between 5 – 15°C• affects photosynthesis/CHO transport
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LeavesLong lived: 2+yrs if N adequate
Photosynthesis rates relatively low
Photosynthesis optimum 25-30°C, → reduced - at high temps >35 °C & low temps
Up to 45% dry matter – mostly cell walls complex CHO
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Leaves & CHO
Age affects CHO storage & export
No CHO export until FULLY expanded(1-2mths)
Significant importer prior to export
New flush – strong sink
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Leaves & CHO
Older/shaded leaves export greater portion of CHO& more rapidly
Shaded leaves– significant contributorto autumn & winter CHO reserves
Starch not readily mobilised for export
No sinks → chloroplasts packed with starch →cell membrane damage
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Movement of carbohydrates
Fruit source CHO principally from leaves of same growth cycle(Source: Goldschmidt & Koch, adapted from Powell & Krezdorn 1977)
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Root growth
3 factors:- shoot growth*- soil temperature- soil water
• Growth alternates with shoot growth- greatest when shoots not growing
* Major factor controlling intensity of root growth
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Root growthValencia on Rough lemon Valencia on Carrizo citrange
Source: Bevington & Castle 1985.
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Root growth –temperature & water
Soil temperature:• most intense at > 27°C• limited < 22°C• none below 14°C
Soil water:• Little growth < - 50 kPA (-0.05MPa)
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Roots & CHO reserves
• Highest CHO reserves usually in root
• Starch accumulation in roots mostly autumn & winter - dependent fruit/vegetativeflush demands
• Build up greatest in absence of veg/fruit sinks (e.g. off year)
→ C depletion high under a heavy crop load
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Summary - why leaves turn yellow
• Latest leaf flush – able to produce CHO – but can’t export (leaves too young)+ also a sink for CHO
• If no/little fruit – no sink competition for CHO → flush
• CHO movement to roots restricted
• Sudden low temperatures → photosynthesis slows + CHO accumulates
So …..
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Summary - why leaves turn yellow
• Youngest leaf flush → loaded with starch→ normally re-greens following springSevere - permanent damage to leaf structure
• Roots starved of CHO → die
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Reducing impact of winter yellowson young trees
Avoid promotingvigorous autumnflush
Leave somefruit on
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Other reasons for leaf yellowing
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→ root curling
Don’t plant root-bound treesCheck young tree roots before planting
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Other reasons for leaf yellowing…
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… root death
Choose soil type carefullyManage irrigation to avoid over watering
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Other contributors to tree collapse
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→ collar rot
Remove/check tree guards
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ReferencesBevington,K.B. and Castle,W.S. Annual root growth patterns of young citrus trees in relation to shoot growth,
soil temperature and soil water content. 1985. J.Amer.Soc. Hort. Sci. 110 (6): 840-845.Cameron, S.H. Starch in young orange tree. American Soc. for Horticultural Science. Pp 110-114.Castle,W. S. 1978. Citrus root systems: their structure, function, growth and relationship to tree performance.
Proc.Int.Soc.Citriculture. 62-69.Fraser, L.R. and Barkley,P. Virus and related diseases of citrus in New South Wales. Dept. of
Agriculture,NSW.Goldschmidt,E.E. and Koch,K.E. 1996. Citrus in Photoassimilate distribution in Plants and Crops Source-sink
relationships. Ed. E.Zamski and A.A.Schaffer.pp 797-823 Goldschmidt, E.E. 1999. Carbohydrate supply as a critical factor for citrus fruit development and Productivity.
HortScience, Vol34(6) October. pp. 10201024Lenz,F. 1978. Photosynthesis and respiration of citrus as dependent upon fruit load. Proc.Int.Soc.Citriculture.
pp 70-71Purvis,A.C. and Yelenosky,G. 1983. Translocation of carbohydrates and proline in young grapefruit trees at
low temperatures. Plant Physiol 73, pp877-880.Schaffer,A.A; Liu,K.; Goldschmidt,E.E.; Boyer,C.D. and Goren,R. 1986. Citrus leaf chlorosis induced by sink
removal: startch,nitrogen and chloroplast ultrastructure. Plant.Physiol. 124: 111-121.Syvertsen,J.P. and Lloyd,J.J. 1994. Citrus in Handbook of environmental physiology of fruit crops. Vol 2
Subtropical and tropical crops. Ed. B.Schaffer and P.C.Anderson. Pp65-99.Vu,J.C. Photosynthetic responses of citrus to environmental change. In Handbook of Plant and Crop Stress.
Ed M. Pessarakli. Pp 947-961Yelonosky,G. and Guy,C.L. 1977. Carbohydrate accumulation in leaves and stems of Valencia orange at
progressively colder temperature. Botanical Gazette 138 (1): 13-17