Botany Michael Smith Dept. of Horticulture & L.A. Oklahoma State University
Some 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. Node Primary bud Secondary bud Tertiary bud not visible in this picture
Terminal mixed bud • 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. Primary compound bud Secondary compound bud
Pecan compound bud Outer bud scale Central bud scales Apex Leaf primordia Inner catkin bud scales
Shoot, leaves, and maybe female flower Catkin
Catkin – 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 receptivity of selected cultivars 1 May 30 Burkett Stuart Squirrel Western Pollen shed Female receptive Pecans require cross pollination by a compatible cultivar. They will not effectively self pollinate. Pollen shedding times for suggested cultivars are listed in a Fact Sheet <LINK>.
Induction – Stimulus causing a bud to change from vegetative to reproductive • Differentiation – Visible evidence (microscopic) of reproductive tissue development Below, female flower differentiation, about early April, just before budbreak Below, female flowers just before pollination Above, early female flower differentiation, about mid February
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. Fruit cluster – Fruit are borne terminally on current season’s growth that arises from buds on 1-year-old branches. Water stage, the kernel is ≈ ½ expanded
The next slide depicts flower induction, differentiation, flowering and fruit development in a time series. • 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.
Budbreak Pollination Catkin differentiation for next year, ≈ 3 weeks after budbreak Water stage Pistillate flower induction Shuck split April May June July Aug Sept Oct Nov Dec Jan Feb Mar Defoliation Type 1 catkins nearly developed, Type 2 catkins incompletely developed Bud swell Pistillate flower differentiation Amling & Amling, 1983 Type 2 catkins resume development, Type 1 begins expansion
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.