American Breeders Association 6: 233-237 (1909)
LATENT COLORS IN CORN
R. A. EMERSON,
University of Nebraska.

The inheritance of color in corn has been so thoroughly studied by numerous investigators, notably Carrens, Webber, and Lock, that little can be added to the general outline. There are, however, at least four points that have not been satisfactorily cleared up. I refer to (1) the occurrence of varying strengths of bluish purple in F1 from a cross of purple with non-purple, (2) the presence of mottling in F1 from the same cross, (3) striped color pattern of "calico" corn, (4) colors, latent in one or both parents, made visible in crosses of purple with non-purple and yellow with non-yellow. Data concerning the first three of these problems are being accumulated but are not ready for presentation. It is with the fourth, latent colors, that this account will deal. There is much yet to learn about latency of colors in corn, but some things have been made out that seem worthy of the attention of the members of this organization.

LATENT RED.

aThe actual numbers of these four classes of grains found on two ears that were carefully examined were 467, 158, 146, and 55, where 465, 155, 155, and 51 are the nearest approach to the ratio of 9:3:3:1 possible with the 826 individuals.

A cross of Queen's Golden popcorn with pollen of Black Mexican sweet corn resulted in numerous ears, the individual grains of which—something over 17,000 in all—varied from nearly yellow, through yellowish brown, greenish brown, and purplish brown, to nearly black, the color in any particular case being due to the combination of the strong, medium, or weak bluish purple of the aleurone with the dominant yellow of the underlying endosperm. Queen's Golden popcorn, it should be understood, has non-purple aleurone and orange-yellow endosperm, while Black Mexican sweet corn has purple (black) aleurone and white endosperm. In F2, grown from self-fertilized F1 plants, the characters are segregated and recombined in such a way that there result, on the average, out of 16 grains, 9 with colored aleurone and yellow endosperm more or less like the F1 grains, 3 with colored aleurone and white endosperm somewhat like Black Mexican, 3 with non-colored aleurone and yellow endosperm much like Queen's Golden, and 1 with non-colored aleurone and white endosperm like neither parent nor like the first hybrid generation.a

bThe difficulty will be better appreciated when it is recalled that on the same ear there were wrinkled sugary grains with clear hyaline endosperm and smooth starchy ones with endosperm horny in some cases and somewhat floury in others, that some grains had white and others yellow endosperm color, and finally that the red and purple aleurone colors varied greatly in intensity. This will doubtless suggest to anyone undertaking a study of color in corn the desirability of starting with parents differing as little as possible in grain characters other than the particular ones to be studied.

But the point that concerns us now is not that there are, in F2, grains with colored aleurone and other grains without such color nor even that the aleurone color varies in intensity, but that there are different aleurone colors. In case of many F2 ears of Queen's Golden x Black Mexican, some grains have shown a reddish color usually quite distinct from the bluish black or bluish purple color already noted. My records of aleurone colors in P2 of the hybrid under consideration show that 23 plants had some reddish grains. The total number of grains produced by these plants was 6,247. The number of grains with purplish, reddish, and non-colored aleurone, respectively, were 3,606, 1,092, 1,549, while they should have been 3,514, 1,171, 1,562 to have equaled exactly the dihybrid ratio 9: 3: 4. The differences between the actual and the theoretical numbers were + 92 for purple, — 79 for red, and — 13 for non-colored aleurone. The count for non-colored aleurone is very close to expectation. The greater differences in case of purple and red are possibly without significance other than as an indication of the difficulty of distinguishing between purple and red in certain cases.b Had the deficiency in red grains been compensated by an excess of grains with non-colored aleurone instead of by purple ones the differences might not be without significance.

The white grains appearing in F2 from a cross of yellow with black are not to be taken as the appearance of a character latent in either of the parents. White is neither visible nor latent in the yellow parent. The black parent has white (colorless) endosperm beneath the purple aleurone layer, but white cannot be said to be latent, though hidden by the outer purple, any more than yellow color of peas can be called latent simply because it cannot be seen through the green pod. We are dealing with a dihybrid in which the two characters—color of aleurone and color of endosperm—are just as Independent of each other as are seed and pod colors in peas.

No red grains have been observed in F1 of the hybrid under consideration when the parent stocks were of known purity and the cross-pollinations made by hand under guarded conditions. This is also true of various other crosses of black with non-black that I have grown. I have examined 1,090 F1 grains of yellow-black and 2,940 of white-black hybrids or a total of 4,030 grains all with purplish aleurone, none with red. In addition to these I have records from 32 ears of Queen's Golden from detasseled plants standing close to Black Mexican plants and at a considerable distance from any other corn. From these ears approximately 16,000 grains were examined and all of them had purplish aleurone, except 35, which were distinctly red. So far as these reds were tested they behaved just like the red grains occurring in F2. This indicates to me merely that at least one of the Black Mexican plants from which the pollen came may have been a hybrid. This notion is strengthened by the fact that a few of the F2 ears grown from this cross showed no wrinkled grains though all of them had about the ordinary percentage of grains with colored aleurone.

cIt should be noted here that great care is always used to keep undesired pollen away from the silks. The ears are covered with heavy paper bags usually two or three days before the silks appear. The pollen to be used is caught in a bag tied over the tassel before the pollen begins to shed. As a rule the early part of the day, when pollen is abundant in the air, is employed in covering ears to be pollinated some days later and later in the day when there is less pollen drifting about the silks are uncovered for pollination. Before uncovering an ear any exposed tassel near enough to especially endanger the silks in hand Is removed. The silks are left exposed only so long as is absolutely necessary. Care is taken to keep the pollen dusted off from the clothes. The hands and fore-arms are washed in alcohol after each pollination, a jar of alcohol being kept constantly at hand for this purpose.

Red grains whenever they arise appear always to lack some factor necessary to the development of purple color in the aleurone. Such reds have produced, with few exceptions, reds only or reds and grains with non-colored aleurone. Ten plants produced 1,723 F3 red grains, 3 bluish purple ones, and none without aleurone color. Sixteen plants yielded, in F2 and F3 from red seeds, 3,012 red, 3 purplish, and 989 non-colored grains. The 10 plants were evidently homozygous toward the presence both of pigment and of red coloration, while the 16 were homozygous with respect to a reddening factor but heterozygous to the presence of pigment. The ratio of colored to non-colored aleurone in these last was very close to 3:1. The 6 purplish grains found with the 4,735 red ones are to be regarded merely as graphic illustrations of the difficulty of guarding against foreign pollen.c

I have grown a few F4 ears of this red corn, all true red indicating that the loss of purple is permanent. The Voorhees Red sweet corn introduced a few years ago by Halsted of the New Jersey Agricultural Experiment Station is a race of red corn originated in much the same way as the red corn here discussed. It came from a cross of Black Mexican with Egyptian, the latter a white sweet corn.

While F2 reds never produce purples but always reds or reds and non-colored, F2 purples often split into purples and reds or purples, reds, and whites. Four F3 ears from purple F2 seeds contained 1,344 purple grains, 377 red ones, and none non-colored. Five F3 ears from purple seeds produced 603 purple, 231 red, and 299 non-colored grains. Both these lots together show 1,947 purples to 608 reds, not far from the expected 3: 1 ratio. Some F2 purples breed true. Three F3 ears from purple seeds gave 220 purple grains with no reds and no non-colored ones. Five F3 ears from purple seeds yielded 664 purple, 194 non-colored, and no red grains.

The question of what type of latency we are here dealing with is wrapped tip in this question: In which parent is the red color latent? It may be latent by hypostasis in Black Mexican or perhaps latent by separation in Queen's Golden. Red should always become visible in F2 if latent in either one or both of the parents, provided purple is not also latent in Queen's Golden. In the latter case, purple being present in both parents, visible in one and latent in the other, and being epistatic to red, would make it impossible for red to appear in the hybrid even though it were latent in both parents. I do not have the data necessary for a decision as to which parent has red color latent, but it should not be difficult to determine the matter by making the right crosses.

LATENT PURPLE.

It was noted above that red should always appear in F2 if latent in either parent unless purple were also latent in the non-purple parent. In case of some F2 plants of Queen's Golden crossed by Black Mexican the ears had no red grains. Twenty-four plants of this lot produced 3,435 purple grains with the usual admixture of non-colored grains, but no red ones. This means either that red was latent in neither parent or that black was latent in Queen's Golden. It is possible that red might be latent in certain plants of either one or both parents and not latent in other plants of the same race. The same is true with respect to purple as a latent character in Queen's Golden. Numerous reciprocal crosses of White Rice popcorn with Black Mexican sweet corn have been examined but in none of them have red grains appeared.

I have two crosses that afford direct evidence of the latency of purple in non-colored races. A race of corn with red aleurone was established from a red grain occurring in F2 of the cross of Queens Golden by Black Mexican. In both F3 and F4 this bred true to the red color when self-pollinated. Two ears of this red race were pollinated from White Rice popcorn and one ear of Evergreen sweet corn was pollinated from the red race. In these three cases every grain (325 in all) was brownish to greenish purple, none showing red. The purple color must have been latent in the non-colored parents, for if it were present in the colored parent that race would have been purple,since purple is epistatic to red.

LATENT YELLOW.

From the cross of Queen's Golden with Black Mexican there resulted in F2, as noted above, many grains without aleurone color, most of these were orange-yellow like Queen's Golden and some were white. In addition to these two types which were seen on all F2 ears, certain ears had grains of a strong yellow (not orange) and others of a very pale yellow, difficult to distinguish in some cases from white. My records of the numbers of such grains in F2 are not sufficiently complete to be of value. It is worth noting, however, that some of these grains bred true in F3 to the light color while others produced light yellow and white in approximately the ratio of 3:1. Whether yellow is latent by separation in the parent with non-colored endosperm or by hypostasis in the orange-colored parent has not been determined.

Black Mexican Sweet Corn