Monday, August 22, 2016

Kernel filling: 22 August 2016

    August is the month when pecan kernels start to fill. This morning I collected some nut samples from several cultivars and cut them in half to reveal the stage of kernel fill. Warren 346 is one of the earliest ripening cultivars we have in our collections and, as you can see in the photo above, this nut is rapidly approaching full kernel fill. The Peruque nut has laid down a layer of kernel tissue all along the inside surface of the seed coat. The Kanza nut still contained ample water but I could see evidence that kernel deposition has started as the seed coat wall appears to be thickening. For a close up look at the kernel filling process, check out this post: Pecan kernel filling.     

    When I cut open nuts from several mid-season ripening pecan cultivars, I found all three cultivars still in the water stage (photo above). However, you can still see differences in the development of the kernel. As the seed coat becomes filled with water, the water accumulates under pressure and presses outwards to expand the region where pecan kernel will form. Note now the kernel space inside the Lakota nut is much larger than the Waccamaw and Greenriver nuts. Lakota has advanced further towards kernel filling than the other two cultivars.

   I've mentioned a clone we've labeled SWB617 in previous posts. We think this tree originated as a  Giles seedling so I thought it would be interesting to compare SWB617 with Giles in terms of nut development (photo above).  The Giles nut was still in the water stage while SWB617 had started to deposit kernel inside the nut. However, I spotted a potential kernel filling problem inside the SWB617 nut. Notice how thick the layer of kernel has formed on the dorsal side of each kernel half. Compare that to the thin layer that has developed next to the inner wall partition (blue arrow).  
   Uneven kernel deposition is a sign that the tree is under stress and is having difficulty pumping enough energy into the seed. Two common stresses that cause poor kernel fill are lack of available soil moisture and excessive crop load. Water seems to be the culprit in this case. However, all is not lost. A good soaking rain this weekend could relieve the water stress and this nut would still go ahead and fully fill out its kernel.