Factors affecting induction Factors affecting induction and differentiation of pistillate and differentiation of pistillate

flowers on pecan treesflowers on pecan trees

Michael Smith

Dept. of Horticulture & L.A.

Oklahoma State University

• Mixed bud – both vegetative (shoot & leaf) and reproductive 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

• 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.

Terminal mixed bud

Primary compound bud

Secondary compound bud

Outer budscale

Innercatkinbud scales

Centralbud scales

Leafprimordia

Apex

Pecan compound bud

Catkin Shoot, leaves, andmaybe female flower

• Induction – Stimulus causing a bud to change from vegetative to reproductive

• Differentiation – Visible evidence (microscopic) of reproductive tissue development

AprilMay

JuneJuly

AugSept

OctNov

DecJan

Feb Mar

Budbreak

Pollination

Catkin differentiation for next year, ≈ 3 weeks after budbreak

Defoliation

Type 1 catkins nearly developed,Type 2 catkins incompletely developed

Type 2 catkins resume development,Type 1 begins expansion

Shuck split

Water stage

Pistillate flowerinduction

Pistillate flower differentiation

Amling & Amling, 1983

Bud swell

Effect of bud removal on female flower clusters

Buds removedNumber of female flower

clusters/branch

None 0.8

Most apical primary bud

0.8

3 most apical primary buds

0.8

Upper ½ of primary buds

0.9

Wood and Payne, 1983

All primary buds appear to have equal fruiting potential whengrowth is initiated.

Cultivar Shoot type

Days from maturity to defoliation

Return bloom

(%)

Squirrel Fruiting 33 82

Vegetative 92

Cape Fear Fruiting 16 49

Vegetative 82

Return flowering of previous year’s shoot types

Fruit development reduces return bloom. Early fruit maturationpromotes return bloom.

Extending the postripening period during the “on” year of ‘Cheyenne’ on return bloomExtended by inducing early budbreak with Dormex

Treatment

Shoots with female flowers

(%)Normal leaf retention

(about 4 wks after shuck split)

3

Extended leaf retention

(about 7 weeks after shuck split)

5

Wood, 1995

Early fruit maturation, or extended leaf retention following fruitmaturation promotes return bloom.

Influence of cluster size on return bloom (%) of ‘Pawnee’

All fruit on tree hand thinned at ½ kernel expansion

Fruit per bearing shoot

Fruiting shoots

VegetativeTerminal 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

When trees are overloaded, secondary shoot growth tends to increasereturn bloom, lateral fruiting shoots have less return bloom than terminal shoots.

Effect of defruiting date on return bloom of terminal and lateral shoots

• Terminal shoots returned more bloom than lateral shoots

• Return bloom of lateral shoots declined 2 – 4 weeks earlier than terminal shoots.

Date of defruitingWood, 1995

0

10

20

30

40

50

60

70

80

90

100

Frui

ting

shoo

ts (%

)

June July Aug Sept Oct

Dough stage

Lateral shoots

Terminal shoots

Avoid excessive crops by mechanical fruit thinning

0

1

2

3

4

5

6

Flow

ers/

1-yr

-old

bra

nch

50% kernel size

Defoliation date

Female flowers/150 shoots

None 137 15 August 0 1 September 0 15 September 29 1 October 106 15 October 161

Defoliation date on return bloom of ‘Western’

Early defoliation will eliminate or reduce return bloom.Hinrichs, 1962

Effect of defoliation date on carbohydrate concentration and return bloom

6

8

10

12

14

16

Aug Sept Oct Nov Check

Defoliation date

Tot

al C

HO

(%

)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Nut

s/sh

oot

Nuts/shoot Roots Trunk New shoots

Worley, 1979

Worley’s data confirmed that of Hinrichs, and suggested that carbohydrate storage may be involved.

Relationship of Jan. root starch to same-year yield

050

100150200250300350400450

20 40 60 80 100 120

Root starch (ug/mg dry wt)

Yiel

d (k

g/m

2 tr

unk

area

)

Stuart Schley

• 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.

Wood, 1989

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

1.5

1.7

1.9

2.1

2.3

2.5

2.7

2.9

June July Aug Sept Oct

Lea

f N

(%

)

0102030405060708090

mg

N/f

ruit

Fruiting Vegetative Fruit

Effect of fruit development on leaf N and fruit N

Fruit tends to act as a sink, first increasing leaf N on fruiting shoots, thendepleting leaf N as it is transported to the rapidly developing nut.

4000

5000

6000

7000

8000O

ctN

ov Feb

Apr

May Ju

lO

ctN

ov Feb

Apr

May Ju

lO

ctN

ov Apr

May Ju

lO

ctN

ov Apr

Nitr

ogen

(g/tr

ee)

Whole tree (with leaves & fruit) Perennial parts (no leaves or fruit)

1997 1998 1999 2000 2001

1. Most N absorbed while leaves rapidly expanding2. Some N absorbed while trees are dormant3. Little N absorbed at other times or loss similar to absorption4. Leaves may act as a N storage reserve for reallocation during the

growing season

75 lb/a N applied in March and 50 lb/a applied in Oct

Nitrogen application rate and time on yield of ‘Maramec’

Nitrogen rate (lb/a) Yield (lbs/tree)

Mar Oct 1999 2000 2002

0 0 4.8 15.2 20.9

60 0 5.9 14.5 25.3

80 0 5.9 13.2 32.8

100 0 4.6 8.6 25.7

40 20 5.7 14.3 27.5

40 40 6.4 14.1 39.4

40 60 4.2 10.6 25.5

0 100 5.5 15.2 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 N rate

(lb/a)

Oct N rate

(lb/a)

Fruiting shoots (%)

1996 1998 1999 2000 2002

75 0 33 87 45 73 57

50 34 81 43 58 46

150 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’

Treatment

Yield (lbs/tree)

1999 2000 2002

None 9.9 8.8 22.9

75 lb/a Mar 12.8 11.9 26.6

75 lb/a Mar + 50 lb/a Aug

10.8 16.5 25.7

75 lb/a Mar + 50 lb/a Oct

6.4 9.2 18.7

No benefit from Oct. N, benefit 1 yr for Aug. N

SummarySummary• 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.