Wednesday, May 3, 2017

Pecan flowering season underway

    I haven't been able to check our pecan trees at the Experiment Field since last week because the Neosho River is flooding our orchard. But yesterday, while the sun was shining, I visited several trees on my farm and noticed that pecan pollination season has begun. Pecan trees produce two types of flowers on the same tree--male and female.
    Male flowers or catkins are produced on one-year-old wood. A yellow arrow points to pecan catkins in the photo at right. If you look closely  catkins, you will notice that each catkin holds numerous pollen capsules roped along a single stem. As the catkins mature, pollen capsules split open, releasing thousands of yellow pollen grains.
    The female flowers or pistillate flowers are located at the terminals of this year's new growth. The red arrow in the photo above points to a cluster of pistillate flowers hidden among new emerging leaves. The female flowers of this pecan cultivar (Faith) are tipped by red colored stigmas which makes them a little easier to spot in the photo.
    Each pecan cultivar has a distinctive flowering habit. Some pecan cultivars are protogynous, meaning that pistillate flowers become ready to accept pollen before the catkins on that same tree releases pollen. Other tree are protandrous, meaning pollen is released from catkins before pistillate flowers become receptive. Pecan trees have this separation in the timing of of male and female flowering to ensure cross pollination among different trees and to promote hybrid vigor of the resulting progeny. 
    The timing of pecan flowering is also related to a cultivar's date of bud-break. Cultivars that start the spring flush of new growth early will also start flowering early, regardless of flowering habit (protandrous or protogynous). Lets look at some examples of the bud-break effect on flowering.

   Faith and Hark are two protandrous cultivars that have widely deferring dates of bud break.  Faith is one of the earliest cultivars to start growth in the Spring while Hark breaks bud about 10 days later.  In the photo above, note that the Faith catkins are starting to turn a little yellowish indicating that pollen release is just days away. In contrast, Hark catkins are still very green and not nearing maturity. The pistillate flowers of Faith are emerging from the terminal of the new growth while it is still difficult to find Hark flower clusters even though I know the are coming (I dissected some Hark terminals and found pistillate flower primordia with a hand lens). 

    I also photographed a couple of protogynous cultivars--Kanza and Jayhawk (photo above). The bud-break dates for these cultivars are a little closer, with Jayhawk breaking bud before Kanza by just a day of two. The pistillate flowers of protogynous cultivars are small and often concealed among emerging leaves at shoot terminals. However, it looks that the stigmas on the Jayhawk tree were beginning to produce the sticky substance needed to capture pollen from the air. Kanza stigmas were still dry and not fully mature.
    With two different flowering habits and differences bud break, the pecan pollination season can usually last almost 4 weeks. Pollination is an amazing process that ushers in a new season of nut production and a time of year that I look forward to each year.