Tuesday, August 27, 2013

Nut development: 26 August 2013

   This summer, I've been following kernel development of three pecan cultivars; Osage, Kanza and Maramec (photo above). I choose these three cultivars because they represent early, mid season, and late ripening pecan cultivars. Previously, I had cut open nuts longitudinally to reveal the progress of kernel expansion from from the small heart stage to full water stage. However, with the kernel development process starting to switch over from the expansion phase to the kernel filling phase, its time to look at nut development from a new angle. At this stage, a cross sectional cut through the nut gives a clearer picture of the kernel filling process. Lets take a closer look at nuts from each of these cultivars.

    Osage is the earliest ripening of the three cultivars and at this point in the 2013 growing season, kernel deposition has begun. In the photo at right, you can see that a translucent band of kernel tissue has formed just under the seed coat. As time progresses, this kernel tissue will continue to thicken growing inward and eventually filling the entire kernel cavity.
    After comparing the photo of Osage to the photos of Kanza and Maramec (photos below) I discovered something new about kernel expansion I hadn't seen before. Once the kernel becomes fully extended in length, the kernel continues to expand but in an outward direction. This outward expansion compacts internal packing material up against the inside of the shell. By comparing the close-up photos of Osage, Kanza, and Maramec you can easily see this process in action.

    Taking a closer look at the cross-section of a Kanza nut reveals that kernel deposition has not yet started. And since the packing material surrounding the kernel was only partially compressed, this Kanza kernel was still expanding radially.

     Late-ripening, Maramec had no kernel deposition and no compaction of the packing material. I'm now wondering if Maramec will even ripen for first fall freeze.
   Hopefully the return of hot summer temperatures this week will help stimulate pecan crop development. Its nearly September and most cultivars are still weeks behind in terms of the normal kernel filling period. Lets hope for a long warm Fall.