Transcript Factors affecting induction and differentiation of pistillate flowers on

Factors affecting induction
and differentiation of pistillate
flowers on pecan trees
Michael Smith
Dept. of Horticulture & L.A.
Oklahoma State University
• Mixed bud – both vegetative
(shoot & leaf) and reproductive
Terminal mixed bud
parts (female flower)
– Terminal mixed buds frequently
abort, leaving a lateral primary
compound bud as the distal bud.
• Compound bud – contains
multiple buds.
– 2 catkin buds
– Central mixed bud with 2 catkin
groups, shoot, leaves and female
flowers
Primary compound bud
• Typically 1 to 3 distal primary buds
develop shoots and catkins. The
other primary buds initiate growth
but the shoot aborts and the
catkins continue to develop.
• Secondary buds remain dormant
unless the primary bud is killed.
Secondary compound bud
Outer bud
scale
Pecan compound bud
Central
bud scales
Apex
Leaf
primordia
Inner
catkin
bud scales
Catkin
Shoot, leaves, and
maybe female flower
• Induction – Stimulus causing a bud to
change from vegetative to reproductive
• Differentiation – Visible evidence
(microscopic) of reproductive tissue
development
Budbreak
Pollination
Catkin
differentiation
for next year,
≈ 3 weeks
after
budbreak
Water stage
Pistillate flower
induction
Shuck split
Defoliation
Type 1 catkins nearly developed,
Type 2 catkins incompletely developed
Pistillate flower differentiation
Amling & Amling, 1983
Type 2 catkins resume development,
Type 1 begins expansion
Bud swell
Effect of bud removal on female flower clusters
Buds removed
None
Most apical primary
bud
3 most apical primary
buds
Upper ½ of primary
buds
Number of female flower
clusters/branch
0.8
0.8
0.8
0.9
All primary buds appear to have equal fruiting potential when
growth is initiated.
Wood and Payne, 1983
Return flowering of previous
year’s shoot types
Cultivar
Shoot type
Squirrel
Fruiting
Days from
maturity to
defoliation
Return
bloom
(%)
33
82
Vegetative
Cape Fear
Fruiting
92
16
Vegetative
Fruit development reduces return bloom. Early fruit maturation
promotes return bloom.
49
82
Extending the postripening period during the
“on” year of ‘Cheyenne’ on return bloom
Extended by inducing early budbreak with Dormex
Treatment
Normal leaf retention
(about 4 wks after shuck
split)
Extended leaf retention
(about 7 weeks after shuck
split)
Shoots with female
flowers
(%)
3
5
Early fruit maturation, or extended leaf retention following fruit
maturation promotes return bloom.
Wood, 1995
Influence of cluster size on
return bloom (%) of ‘Pawnee’
All fruit on tree hand thinned at ½ kernel expansion
Fruiting shoots
Vegetative
Terminal w/o
secondary
growth
Terminal with
secondary
growth
Lateral
without
secondary
growth
Unthinned
70
46
65
31
One
88
98
90
96
Two
85
95
94
90
Three
96
79
94
81
Fruit per
bearing
shoot
When trees are overloaded, secondary shoot growth tends to increase
return bloom, lateral fruiting shoots have less return bloom than terminal shoots.
Effect of defruiting date on return
bloom of terminal and lateral shoots
100
Terminal shoots
Fruiting shoots (%)
90
80
70
60
Lateral shoots
50
Dough stage
40
30
20
10
0
June July
Aug
Sept
Date of defruiting
Wood, 1995
Oct
• Terminal shoots
returned more bloom
than lateral shoots
• Return bloom of
lateral shoots
declined 2 – 4 weeks
earlier than terminal
shoots.
Avoid excessive crops by
mechanical fruit thinning
Flowers/1-yr-old
branch
6
50%
kernel size
5
4
3
2
1
0
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50
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Defoliation date on return
bloom of ‘Western’
Defoliation
date
None
15 August
1 September
15 September
1 October
15 October
Female flowers/150
shoots
137
0
0
29
106
161
Early defoliation will eliminate or reduce return bloom.
Hinrichs, 1962
Effect of defoliation date on carbohydrate
concentration and return bloom
Nuts/shoot
Roots
Trunk
New shoots
3.5
3.0
14
2.5
2.0
1.5
1.0
12
10
8
0.5
0.0
6
Aug
Sept
Oct
Nov
Check
Defoliation date
Worley’s data confirmed that of Hinrichs, and suggested that
carbohydrate storage may be involved.
Worley, 1979
Nuts/shoot
Total CHO (%)
16
Relationship of Jan. root starch
to same-year yield
Yield (kg/m2 trunk area)
Stuart
Schley
450
400
350
300
250
200
150
100
50
0
20
40
60
80
Root starch (ug/mg dry wt)
Wood, 1989
100
120
• High Jan. root
starch may reduce
reversion of
induced buds to a
vegetative state, or
abortion of flowers
during
differentiation.
• Jan. starch conc.
would have little
impact on female
flower induction.
Foliage management for
annual production
• Maintain healthy foliage
– Pests
• Aphids, mites, walnut datana, other foliage feeders
• Disease, particularly pecan scab
– Balanced nutrition program
• Deficient or excess N
• Deficient K
• Deficient Zn
– Avoid either excess or deficient water
• Excess water in spring is particularly detrimental
– Reduces photosynthesis while flooded, plus recovery takes
twice as long as flood duration.
– Reduces leaf expansion – thus photosynthetic potential is
reduced for the entire growing season.
• Nut filling is the most critical time for drought
Effect of fruit development on
leaf N and fruit N
Vegetative
Fruit
2.9
90
80
70
60
50
40
30
20
10
0
Leaf N (%)
2.7
2.5
2.3
2.1
1.9
1.7
1.5
June
July
Aug
Sept
mg N/fruit
Fruiting
Oct
Fruit tends to act as a sink, first increasing leaf N on fruiting shoots, then
depleting leaf N as it is transported to the rapidly developing nut.
75 lb/a N applied in March and 50 lb/a applied in Oct
Whole tree (with leaves & fruit)
Perennial parts (no leaves or fruit)
7000
1.
2.
3.
4.
Most N absorbed while leaves rapidly expanding
Some N absorbed while trees are dormant
Little N absorbed at other times or loss similar to absorption
Leaves may act as a N storage reserve for reallocation during the
growing season
6000
5000
4000
Oct
Nov
Feb
Apr
May
Jul
Oct
Nov
Feb
Apr
May
Jul
Oct
Nov
Apr
May
Jul
Oct
Nov
Apr
Nitrogen (g/tree)
8000
1997
1998
1999
2000
2001
Nitrogen application rate and
time on yield of ‘Maramec’
Nitrogen rate (lb/a)
Mar
0
60
Oct
0
0
1999
4.8
5.9
80
100
40
40
0
0
20
40
5.9
4.6
5.7
6.4
40
0
60
100
4.2
5.5
Yield (lbs/tree)
2000
15.2
14.5
13.2
8.6
14.3
14.1
10.6
15.2
2002
20.9
25.3
32.8
25.7
27.5
39.4
25.5
24.0
No benefit from October applied N, all N treatments produced similar yield until 2002
N rate and application time on
fruiting shoots of ‘Mohawk’
Spring Oct N
N rate rate
(lb/a)
(lb/a)
75
150
Fruiting shoots (%)
1996
1998
1999
2000
2002
0
33
87
45
73
57
50
34
81
43
58
46
0
29
77
58
70
58
50
29
84
43
52
58
No benefit from Oct. application. No yield difference between N rates.
Nitrogen rate and application
time on yield of ‘Mohawk’
Yield (lbs/tree)
Treatment
1999
2000
2002
None
9.9
8.8
22.9
75 lb/a Mar
12.8
11.9
26.6
10.8
16.5
25.7
6.4
9.2
18.7
75 lb/a Mar + 50
lb/a Aug
75 lb/a Mar + 50
lb/a Oct
No benefit from Oct. N, benefit 1 yr for Aug. N
Summary
• Induction of catkins is within 3 weeks of budbreak,
and female flowers in late July to early Aug.
– The stimulus and hormonal/growth regulator changes associated
with flower induction are unknown.
– Winter stored carbohydrates are positively correlated with
retention and development of female flowers.
• Differentiation of catkins begins about 3 – 4 weeks
after budbreak, and female flowers about bud swell.
• Fruit development reduces return bloom.
– Early fruit maturation promotes return bloom.
– Fruit thinning and/or hedging to control crop load.
• Premature defoliation or reduced leaf function
reduces return bloom.
–
–
–
–
Follow a recommended pest management program.
Maintain a balanced nutrition program.
Avoid flooded or water saturated soils during leaf expansion.
Avoid late season drought stress.