Tuesday, September 24, 2013

Nut development: 24 Sept. 2013

    Each week I've been documenting the development of three pecan cultivars; early-ripening Osage, mid-season Kanza ripening  , and late-maturing Maramec. This week I found that Osage had quickly moved to develop shell color and create separation between shuck and shell (photo at right).
    This morning I pulled three Osage nuts from a tree and found some variation in the shuck dehiscence process. None of the nuts had split shucks but the nut on the left had fully developed shell color and was completely separated from the shuck. The nut in the center had fully separated from the shuck but was still developing normal shell color. The nut on the right was 3/4 separated from the shuck.
    Why such variation in nut ripening all from the same tree?  For anyone that has every searched for ripe fruit on a peach or apple tree, the answer is simple: location, location, location. The nut on the left was taken from the upper portion of the tree's canopy. The nut in the center was collected from a lower limb while the nut on the right was pulled from an interior limb. Just like fruit trees, sunlight exposure effects the speed of ripening of pecans. Nuts in the upper portions of the canopy will split shuck first followed by nuts on lower limbs. Nuts developing on interior branches will be the last to ripen.

    When I checked Kanza this morning, I found that the kernel was completely packed with kernel (photo at left). Although you can't see it, the kernel filling process continues all the way up to shuck dehiscence. At this point in kernel development, the tree is filling the firm kernel with the long-chain fatty acids (nut oils) that make pecans taste so good at harvest.
   Kanza had not started shuck dehiscence. I used my knife to cut into the shuck near the apex of the nut and found the shuck still firmly attached to the shell (photo above). Shuck dehiscence always starts at the tip of the nut and proceeds towards the base.

       I moved to Maramec next. This time I collected three nuts but with varying degrees of nut scab. In the photo at right I arranged the nuts by the degree of scab infection--from most (left) to least (right). Below each whole nut is a photo of the very same nut cut in cross section.
   Over all, you can see that Maramec is still trying to fill but doing a pretty poor job of packing the inside of the shell with kernel. You can also see the influence pecan scab has on nut size and kernel fill. The heavily scab infected nut is the smallest of the three and has the poorest filled kernel.