Post on 31-Mar-2015
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.