Yesterday, I spent some time out in my pecan grove inspecting emerging leaves and catkins. Its much too early to see the kind of nut crop we are going to have in 2019, but by looking carefully at catkins I can determine a pecan tree's flowering habit.
Pecan cultivars that shed pollen before their pistillate blooms are receptive are said to have a
protandrous flowering habit. Cultivars that produce receptive female flowers before shedding their pollen have a
protogynous flowering habit. Nature has designed pecan trees with two flowering habits to ensure that every nut produced by a tree has the hybrid vigor that results from cross pollination.
In the photo above, Oswego is an example of a protogynous cultivar while Yates 68 is protandrous. Now look at the emerging catkins. The Yates 68 catkins are already quite large, seemingly developing faster that the new leaves. In contrast, the catkins on Oswego are just emerging while several new leaves are expanding on the new shoot.
This distinctive difference in catkin appearance can been seen as spring growth continues.. The photo at left shows the protandrous Faith cultivar in comparison to protogynous Kanza. As a general rule the catkins of protandrous cultivars are short and fat while catkins of protogynous cultivars are long and thin.
While inspecting my trees, I collected shoots from three protandrous cultivar and three protogynous cultivars. Since the time of bud break differs among cultivars, these photographs offer a glimpse at early shoot development.
The first set of shoots were collected from protandrous cultivars (photo at right). Starting with Hark, note that the catkins of protandrous cultivars emerge before the leaves start to unfurl. As bud break continues, catkins continue developing at a fast rate becoming quite large early in the season.
The photo of protogynous cultivars (at left) illustrates that shoot growth starts of quickly while catkin development is delayed. Remember that pistillate flowers are produced on the terminals of new shoots. So, early shoot growth is just a precursor of early female flower receptivity. Catkin emergence on protogynous cultivars seems much slower than new shoot growth.
