Variations in Kernel Shape and Texture in Corn-Belt Maize.--Typical kernels were selected from 140 different inbred lines of dent corn. These included as many of the standard inbreds such as 38-11, WF-9, etc. as could be obtained, together with some of the newer inbreds and various "second-cycle improvements" on older inbreds. Care was taken to obtain healthy and well-grown ears in spite of the weakness of some of the inbreds. As representative a kernel as possible was selected from each ear and the variation of the entire collection was repeatedly examined and compared with collections of open-pollinated varieties from various parts of the New World.
Much of the variation in this material, more than at first seemed possible, is accounted for by differences in the texture (hard dent, soft dent, etc.) and in the position at which the kernel shows its maximum width. The latter character varies from wedge-shaped kernels like WF-9 to broad-based, pointed ones like K 43. If a small percentage of "buckshot" and poorly developed kernels are excluded and too difficult to classify, the remainder show a clear set of transitional stages between these two extremes. At the one end is the flat, wedge-shaped kernel fairly similar to many of the older open-pollinated varieties. It is widest at its apex, and allowing for the shrinkage when it dents, it is also thicker at that point Consequently it not only tapers to the base, it also slopes to the base (i.e. the narrowing is in two dimensions). The kernels at the other extreme are both wide and high at the base, bulging out broadly below and tapering conewise toward the apex.
Between these two extremes it is possible to select a whole series of intermediates. Those about in the middle are flattish kernels, widest in the middle and also slightly thicker there. It is they and the ones even less pointed which are of most interest in this classification. It does not seem probable that one would have recognized what is apparently a slight degree of pointing, until he had seen all the intermediate types laid out in this way. These different kernel shapes seem to result from various intermediates between two fundamentally different growth patterns, similar to some of those which have been analyzed in Cucurbits by Sinnott.
The kernels were then classified for texture. At the one extreme (grade 1) were a few inbreds which showed no capping of soft starch. In the next class were those which were capped but not perceptibly dented. Next (grade 3) were both capped and dented but without a wrinkled pericarp due to the collapse of the soft starch area. Finally there was a class whose kernels were capped, dented, and with the pericarp distinctly wrinkled at the apex.
When these grades of denting and pointing had been determined, the entire collection was sorted out simultaneously for both characters. A few of the small kernels remained difficult to classify and there may well be other factors such as long kernels vs. wide kernels which need to be considered. However this simple two-way scheme worked surprisingly well and brought similar types together. The distribution was as follows:
POINTING OF KERNEL
Figures show No. of kernels in each class.
It will be seen that there is a fairly strong negative correlation between denting and pointing. The heavily dented kernels are all widest at the apex and the less the degree of denting the higher is the proportion of pointed kernels.
After the kernels had been laid out in this way it was apparent that certain other characters were correlated with pointing or with denting. The association of red pericarp with pointed kernels was particularly conspicuous. Of those widest at the apex only 7 percent were so affected whereas 10 percent of the medium pointed, and 53 percent of those widest at the base. This may be related to the fact that in Mexico, the supposed ancestral home of our dent corns, pointing of the kernels is very closely associated with red pericarp. Red pericarp was found to have no obvious connection with denting but blistering of the pericarp was strongly associated with denting, as well as negatively with pointing. Another feature which (though it varies greatly in its expression) is characteristic of certain inbreds, is a silvery appearance of the pericarp, apparently due to air. This showed no association with denting but was strongly correlated with pointing.
After the above analysis had been made it was interesting to examine various inbred, single-cross, and open-pollinated-varieties. The interaction of various factors in producing different types of dent corn is much clearer after such an examination. The production of a smooth, dimpled dent (such as characterizes OS 420 among the inbreds) is very evidently the combination of a high degree of denting with a fairly high degree of pointing. It is the pointing which shapes up the kernel and gives the ear its neat appearance.
Edgar Anderson (Missouri Botanical Garden)
Ray E. Snyder (Pioneer Hi-bred corn Breeding Company)