BotanyBotany

Michael Smith

Dept. of Horticulture & L.A.

Oklahoma State University

Some Commonly Used TermsSome Commonly Used Terms• Node – The location of the

buds on the shoot• Internode – The portion of the

shoot between the nodes• Primary bud – The most

dominate bud at a node• Secondary bud – The second

most dominate bud at a node• Tertiary bud – The third bud at

a node.

Pecans have 3 to 4 buds at each node. Branches older than 1 year only have secondary and tertiary buds. All primary buds grow the 1st year.

Primary bud

Secondary bud

Tertiary bud not visiblein this picture

Node

• Mixed bud – both vegetative (shoot & leaf) and reproductive parts (female flower) in the bud– Terminal mixed buds frequently

abort, leaving a lateral primary compound bud as the distal bud (most terminal).

• Compound bud – contains multiple buds. A pecan compound bud contains:– 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

Catkin – The Male FlowerCatkin – The Male Flower

• Many catkins are produced from a single bud.

• Most of the primary buds on a 1-year-old branch produce catkins.

• Pecan pollen is disseminated to the female flowers by wind.

• One medium size pecan tree can produce enough pollen to pollinate every pecan tree in the world. However, because pollen distribution is at random in the wind, a super abundance of pollen is needed to ensure adequate pollination.

Pollen shedding and pistil Pollen shedding and pistil receptivity of selected cultivarsreceptivity of selected cultivars

Burkett

Stuart

Squirrel

Western

Pollen shed

Female receptive

1 30May

Pecans require crosspollination by a compatiblecultivar. They will not effectively self pollinate.Pollen shedding times for suggested cultivars are listedin a Fact Sheet <LINK>.

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

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

Above, early femaleflower differentiation,about mid February

Below, female flowerdifferentiation, about earlyApril, just before budbreak

Below, female flowers justbefore pollination

Fruit Development - Nut• Fruit grow to full size before the

kernel develops. Nuts attain full size in late August.

• As fruit grows the kernel pushes down the inside of the nut while in the water stage (the water is actually an endosperm without cell walls).

• The endosperm forms cell walls in late August, called the gel stage.

• Next carbohydrates (sucrose) are translocated to the fruit during late August through mid to late October, forming the kernel.

• About 70% of the kernel is oil, a very high energy compound. The kernel also has starch, sugars, protein, potassium, vitamin E, and many other compounds. The oil is high in unsaturated fatty acids, and has been shown to reduce LDL (bad cholesterol) when included in the diet.Water stage, the kernel is ≈ ½ expanded

Fruit cluster – Fruit are borne terminally oncurrent season’s growth that arises frombuds on 1-year-old branches.

• April – Budbreak• May – Current season catkins are expanding, and at the

same time catkins have began differentiating in the compound buds for next year.

• June – Female flowers are pollinated, the catkins shed and fruit begin to develop.

• August – Female flower induction for next years crop takes place, although female flowers will not begin to differentiate until mid February. The fruit are nearly full size and the kernel is in the water stage during this time.

• February – Female flowers begin differentiation, catkins continue to develop.

• April – Budbreak and the whole process starts again.

The next slide depicts flower induction, differentiation, The next slide depicts flower induction, differentiation, flowering and fruit development in a time series.flowering and fruit development in a time series.

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

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.