25th Annual Report of
the New Jersey State Agricultural Experiment Station
for the year ending October 31, 1904. 456-460
Experiments in Crossing Sweet Corn
Byron D Halsted, Sc.D.
Earle J Owen, B.S., and J. K. Shaw, B.S., Assistants
Crossing Corn—New Series.
In 1903 Plot I, Series III, was planted with alternate rows of "Black Mexican" and "Country Gentleman." The first named variety as previously described is black-grained, medium in size of plant and in time for maturity and with eight rows of large grains upon the slender cob. It is of remarkably high quality but with the serious objection of being nearly black and, therefore, not largely grown for the table. The "County Gentleman" upon the other hand is a white-grained sort somewhat larger in plant than the "Mexican" and ten days, or so, later in coming into season for the picking of the ears which have the long, pointed grains irregularly set upon the cob. It is seen that the two varieties, named above, are very unlike, in fact, it would be difficult to select two sorts of first-class sweet corn with fewer points in common.
It was strikingly noticeable last season that the "Country Gentleman" was abundantly fertilized by the "Mexican" while the reciprocal cross was apparently the rare exception. It was almost impossible to find an ear of the white sort without few or many dark grains while among all the "Mexican" ears only sufficient white grains could be found to plant but a few hills the present year. Hand pollination was successful with the "Gentleman" and ears were thus obtained that showed the cross in every grain. The color of these crossed grains was a shade of lead color and in this respect is quite different from the cross that developed into the "Voorhees Red."
PLATE I. First year after cross between “Black Mexican" and "Country Gentleman" Corn. Upon the left is an ear and two sections of the "Mexican" parent and the "Gentleman" is similarly shown upon the right. The crosses are shown between them.
Forty hills were planted this season with grains from the same hand-pollinated ear of "Mexican" upon "Gentleman." The ear from which the grains were taken is shown near the middle of plate II of the report for 1903. This block of hills standing by itself at one corner of the Experiment Area has shown a vigor of plant and evenness of growth that has been remarkable and being bred within themselves it is evident that each ear is very closely related to all the others. All came originally from the same two stalks that were bred together followed by a further breeding within the family of brothers and sisters, so to say. On the other hand the hills representing the scattered white grains upon several "Mexican" ears crossed naturally and widely showed a great range of vigor and in fact presented an unevenness of growth that contrasted strongly with the companion set of hills above described.
Plate I shows a set of six ears embracing the first generation of the "Mexican-Gentleman" crosses. The ear to the left is a typical specimen of the "Black Mexican" variety, it being slender eight-rowed and the grains of a uniform very dark color. At the opposite end—to the right, is an ear of the "Country Gentleman", is comparatively short, with the long white grains arranged without regard to definite rows. The contrast between the two parents is easily made by a study of these two ears.
The two ears nearest to the "Mexican" ear, and left of the middle of the plate are the result of the "Mexican" as a pollinizer upon the "Gentleman," that is, the grains from which these ears were produced came from an ear of "Gentleman" corn that had been artificially pollinated with the "Mexican and the grains as before stated showed the immediate influence by being lead-colored instead of white as in the normal "Gentleman." The ear nearest to the "Mexican" is twelve-rowed from base to tip and represents those that are perhaps more nearly like the "Mexican" than the "Gentleman." The number of white (colorless) grains is 121 disposed in the twelve rows as follows: 10, 6. 11, 15, 7, 9, 15, 9, 10, 5, 12, 12. Twenty-five grains are tinged more or less with the dark and these also are quite evenly distributed over the whole car, there being from one to five in each row. The black grains number 311 and were arranged among the white ones, as shown in the plate, with the rows as follows: 31, 28, 28, 27, 30, 24, 15, 24, 20, 29, 25, 30. There are nearly three colored grains to one of the white or colorless kernels. The next ear to the right approaches more the type of the "Gentleman" in general shape and in having the grains irregularly disposed in the upper half. Below the middle the rows are quite distinctly twelve in number. Here the mixture of white, tinged and black grains is practically the same as in the ear to its left. This type of ear is very desirable in its size and shape and it remains to be determined what will be the result from planting the three colors of grains separately and developing a breed, if possible, from each by selection for a term of years.
A practical test of the corn as it became ready for the table this season demonstrated that the combination has produced a sweet corn of very high quality as might be expected from the reputation of the two parents used in the experiment.
Turning now to the reciprocal cross, namely, the "Country Gentleman" as the pollinator and the "Black Mexican" as the mother plant, quite different results are obtained in the first generation. It will be recalled that the white grains were very few upon the "Mexican" ears in last season's efforts to effect a cross. These white grains from several ears were planted by themselves and types of the results for this year are shown in the two ears to the right of the middle of the plate and left of the type of the male parent, the "Country Gentleman." The ear nearest the middle has its fourteen rows well defined, but otherwise there is not much resemblance to the mother parent ("Mexican") for the grains are long and narrow and white (colorless) with only ten exceptions. It is practically a "Gentleman" ear in its shape, it even having the bend common to its male parent that suggests the general outline of a fair-sized banana. The exposed ends of the grains are more regular in outline than upon the "Gentleman," a fact doubtless due to their being in well formed rows. There is a shade of amber in them all that might also serve to distinguish them from the "Gentleman" grains. The ear figured next to the left of the "Gentleman" is very much like the one already described and differs from it in being somewhat larger in diameter and having the fourteen rows, quite distinct at the base but much less so above the middle, and in this it is a further approach to the male parent. There are six grains that show the darkness that suggests the "Mexican" parentage.
The differences between the reciprocals in this cross are very striking. The mother plant in each case has given in the first generation an ear that resembles more the male than the female parent. In other words the two crossed ears upon the left of the middle of the plate are from a "Country Gentleman" ear fertilized by the "Black Mexican" and they would be classed with the latter rather than the former; in other words, they go with the male parent and three-fourths of the grains are of the same dark color and to be distinguished from the "Mexican" chiefly by their much greater length. In the same way the ears that have come from white grains in "Mexican" ears of last season have given ears this year that in their size and shape and the color of the grain, closely resemble the "Gentleman." In short, the male parent in both crosses has controlled to a large extent the character of the ear. Perhaps the most subject to remark is the almost entire removal of the dark color from "Black Mexican" grains in the first season after the cross, while in the reciprocal it is retained in nearly three-fourths of the kernels.
A glance at the sections of the cobs in the lower portion of the plate shows something of the differences in the size and shape of the cob and of grain between the parents and the two crosses. The pair to the left is of the "Mexican". the outer most showing the upper end of the section and the embryo (chit) of the grains while the obverse is seen to its right. The broad grains with their large embryo are quite in contrast with the corresponding pair from the "Gentleman" ear shown at the extreme right of the plate, with the long narrow irregular grains. In the "Mexican” the embryo is upon the upper side of the grain, that is, occupies a large part of the side toward the tip of the ear. The "Gentleman" grains observe this general rule only in part, as many of the kernels have their embryo in the opposite direction. The two sections shown in the plate are broken from the same ear and the chits are seen upon the end, the right one showing the section toward the stem (butt) end of the ear. The two crosses as seen in section indicate that cob and grains have the blended form and size of the two parents.
CybeRose note: It is interesting that the author supposed that the pollen should control the color of the grain in both directions. In fact, xenia (so-called) is a matter of dominance. That is, if one parent has black kernels while the other has white, the cross-pollinated kernels should be black regardless of which parent provides the pollen.
'Black Mexican' is known to carry a transposon (jumping gene). When this transposon is silenced, apparently a nearby "gene" involved in the regulation of pigment synthesis is also silenced. This results in the black kernels, but "the silks are white or light green, the stamens light green, and the glumes light green, commonly, but occasionally with a few reddish, longitudinal stripes." Webber, 1906. But when the transposon is not silenced, which can occur following self-pollination or hybridization, the pigments revert to their (presumed) original condition: white seeds and colored silks, stamen and glumes. The dots of pigment often found on these white kernels result from the transposon (and the adjacent gene) being silenced again.
It is also interesting that the progeny of Black Mexican x Country Gentleman (white kernels only) were much more variable than those of the reciprocal cross (black kernels only). It would be interesting to repeat the cross in both directions, and to raise four groups of offspring: BM x CG (black kernels), BM x CG (white kernels), CG x BM (black kernels) and CG x BM (white kernels) to learn whether the increased variability is associated with the un-silencing of the transposon. I have several other examples of crosses involving white flowered or white fruited "mutants" giving more variable progeny than normally colored forms of the species.