Don't judge a pecan by its cover

     Over the past several days, I've been in a hydraulic lift collecting pecans from our pecan breeding plot (photo at right). Moving from tree to tree, it is amazing to witness the genetic diversity of pecan. Fortunately, we used early maturing parents for this project and now, 15 years later, most of the trees in this planting have ripened their nuts by the first week of October (not all though).
    As you might expect, I have found nuts of all sizes and shapes. Some have thin shells. Some will need a sledge hammer to crack them open. In addition, there are huge differences in reaction to leaf and nut diseases. After looking at so many seedling pecan trees with such diverse sets of cultivar traits, I now have a greater appreciation of how rare it is to find a truly exception new pecan.

    Today, I collected nuts from five different trees just to give you an idea of the type of variation I am seeing in our breeding plot (photo at left). All of these nuts had achieved shuck split with nut "E" probably splitting the earliest. I choose these five pecans because they were roughly the same size in the shuck. When pulling these nuts from the tree, these five nuts appeared to be fairly large. But looks can be deceiving.

   In the photo at right, you can see the same five nuts pulled out of their shucks.  The differences in size and shape are obvious. A big shuck doesn't always produce a big nut (nut C) and surprisingly large nuts can fall from not-so-impressive shucks (nut E).

   The shuck is only the first cover that needs to be peeled back to reveal a pecan's true character. The second cover is the shell. In the photo at left, I've arranged the same five nuts in the same order, but this time, each nut is cut in cross section. Note the differences in shell thickness.  Nut "A" has the thinnest shell, while nuts "D" and "C' have heavy shells. Now look at the packing material as it dips down into the dorsal groves of each kernel half. Long narrow dorsal groves means that the packing material might get stuck in the kernel during the cracking process. Nuts "C" and "E" might have a problem in this regard.
    Overall nut quality for 2013 looks great. You can look forward to seeing all the nuts we collect this year from the pecan breeding plot on display at the nut exhibits held in conjunction with the KS, MO and IL nut growers annual meetings early next year.

Time for Fall fertilization

 

    With an 85% chance of rain tonight, today was a good day to spread some fertilizer in our pecan orchards (photo above).  An early October application of nitrogen  along with the regular springtime fertilizer application has been our standard practice for over 15 years now and has led  to increased yields and a reduction in alternate bearing. Today we spread 100 lbs. of urea fertilizer/acre. That works out to 46 lbs of actual nitrogen per acre.  The costs associated with this fertilizer application were $411/ton for the urea and $8/ton for the rent of the spreader. Doing the math, we invested $20.95/acre today in building the productive capacity of our pecan trees.
     Next March, we'll be back with the fertilizer buggy to make a springtime application of both nitrogen and potassium. 

A story about resistance to pecan scab

USDA 75-8-5

    I was out looking at the pecans in our cultivar trials and came across something I thought was pretty interesting. We have two USDA clones under trial that originate from the same cross; Osage x Creek. The clones are numbered 75-8-5 and 75-8-9. The 75 represents the year (1975) the cross was made, the 8 represent the parents (in this case, Osage x Creek), and the final number is the number given to the seedling tree within all seedlings of that cross.

USDA 75-8-9

       USDA 75-8-5 is pictured above while USDA 75-8-9 is pictured at left. Wow, the difference in scab susceptibility hit me like a brick. Seeing this obvious difference between siblings in the amount of scab found on the nuts made me starting thinking about the inheritance of scab resistance. This took me on a quest to look up the ancestry of these two USDA clones.

       Above is a flow chart of the ancestry of USDA 75-8-5 and USDA 75-8-9. The parents of these clones were the same: Scab resistant, Osage and scab susceptible, Creek. Going back another generation I found that the scab resistance of Osage originated from its Major parent. Looking at the ancestry of Creek, I found scab susceptibility in all cultivars that make up the Creek side of the family tree.
    I don't think that scab resistance is a single gene inheritable trait because we see such a wide range of reactions to the scab fungus. However, a quick look at the family tree would lead me to expect that only a portion of Osage x Creek crosses would demonstrate some level of resistance to scab.
    Even though 75-8-5 looked scab free in our trials in 2013, this USDA clone has demonstrated only mediocre scab resistance under conditions of  high humidity in southern Georgia; a location of much higher scab pressure than SE Kansas (my location).

Nut development: 1 Oct 2013

Osage

   Again this week I looked at the development of three pecan cultivars: Osage, an early-ripening cultivar; Kanza, a mid-season pecan; and Maramec, a late-ripening cultivar. As noted in yesterday's post on cultivars ripening since last week, Osage has completed the nut development process for the year by splitting open its shuck (photo at right).

Kanza

    Kanza has filled it kernel and I found the very first indications that the shuck of this cultivar was starting to separate from the shell. In the photo at left, the red arrow points to the area where the shuck has started to separate from the shell. At this point, all you can see is a hairline crack between shuck and shell. Remember, that during shuck dehiscence, the process always begins at the nut's apex and works downward towards the base. The green arrow points to another indication that shuck separation has begun. The light tan spots near the tip of the nut are the very beginnings of black streaks normally found on the outside of the shell at harvest.

Maramec

     I think that Maramec has largely completed kernel fill and you can see that this year's nut quality will be fair to poor (photo at right). The kernel has failed to press all the internal packing material up firmly against the inside of the shell and there are still air spaces near the kernel. You might also note that this Maramec nut is much smaller than normal which can be largely attributed to scab infection. At this point in time, Maramec is not showing any signs of shuck dehiscence. Will we harvest Maramec this fall? It will probably depend on when we get our first hard freeze this fall and if the scab infection will prevent shuck split.