1. White-capped red pericarp - E. G. Anderson reported (Genetics 9:442-453. 1924) an allelic series of maize pericarp and cob colors with their genes at the locus of P. These included self red pericarp with red cob R-R (Anderson's symbols are used here, the first letter representing pericarp and the second cob color), colorless pericarp with red cob W-R, colorless pericarp with white cob W-W, variegated pericarp and cob V-V, mosaic pericarp and cob M-M, white-capped red pericarp with red cob C-R, and white-capped red pericarp with white cob C-W. That these combinations of pericarp and cob colors constitute an allelic series has not been questioned heretofore, so far as I am aware, and is not now questioned except for C-R and C-W. In fact, all the data with which I am familiar tend to substantiate Anderson's conclusions except for white-capped red pericarp. Heretofore I have regarded C-R and C-W as belonging to the P series of alleles and long ago (Nebr. Agr. Exp. Sta. Rpt. 74: 57-90. 1911) published records for C-W - involving exceedingly few individuals - in support of this idea. Anderson's records involved adequate numbers. For the backcross (C-W × W-R) × W-W, the two parental types only were obtained, 1684 C-W and 1751 W-R. But he reported that: "This cross is not wholly satisfactory, since heterozygous C-W is light colored, making immature ears difficult to separate from white." He found no red-cobbed ears with white-capped red pericarp, while the white-cobbed ones all exhibited this pericarp color. But in his description of W-R, he said: "Pericarp white (colorless) in some varieties, pale orange in others."

If these statements seem to imply that both Anderson and I were wrong in our early interpretations respecting C-W, I must admit that I have no evidence to support such an implication. But for C-R I shall here present evidence which indicates that the white-capped red pericarp of Bloody Butcher is conditioned by multiple genes. The C-W combination studied earlier by Anderson and by me is that seen in Northwestern Dent. The color patterns of the pericarp of these two varieties are identical in appearance and the intensity of pigment of both is reduced noticeably when made heterozygous by crossing with colorless pericarp types. In this respect both differ from self-red, variegated red, and mosaic red. It seems strange, therefore, that white-capped red of Northwestern Dent, C-W, should differ in inheritance from the apparently identical pericarp color of Bloody Butcher, C-R. Both Anderson (1924) and I (1911) reported crosses of C-W × W-R and of most of the other possible combinations of pericarp and cob color patterns, but neither one of us reported results of C-R × W-W.

All the crosses to be reported here involve a single one of Dr. Wiggans' inbred strains of Bloody Butcher (C-R), his inbred #4. This was crossed with three others of his inbreds; namely, Cornell 11 inbred #3 (W-R), Luce's Favorite inbred #1 (W-W) and Onondaga White inbred #2 (W-W). Generations F₂ and F₃ and repeated backcrosses to W-W have been studied. Since in one of the crosses, C-R × W-R, white cob color is not involved, both parents having red cobs, I shall present first the evidence involving pericarp color alone from all the crosses. In the presentation to follow the intensity of pericarp color is indicated in six grades. Grade 0 indicates pericarp in which no tinge of color can be seen, grade 6 the color intensity of the Bloody Butcher parent, grade 5 that of most F₁ ears, grade 1 a barely discernible tinge of color and 2, 3, 4 intermediate grades, in ascending order of color intensity. The mean grade of color intensity is presented both for all ears and for ears with some color in the pericarp. In table 1 are given the records of nine different F₂ cultures of the three crosses and of nine backcrosses of F₁ to colorless pericarp.

Table 1

The ratio of plants with colored to those with colorless pericarp is 4.8 : 1 for F₂ and 1.4 : 1 for backcrosses instead of 3 : 1 and 1 : 1, respectively. The frequency distribution of individuals of grades 1 to 6 are those typical of multiple gene inheritance. The mode and the mean grade are somewhat lower in the backcross than in F₂, just as F₁'s of lower grade than the colored parent.

Progenies of selfed F₂ and of selfed backcross plants with diverse grades of pericarp color are recorded in table 2.

Table 2

Individuals of various pericarp color grades of the first backcross generation were backcrossed a second or third time. The progenies of these backcrosses are reported in table 3.

Table 3

Tables 2 and 3 not only exhibit frequency distributions characteristic of multiple-gene inheritance, but also demonstrate that selection is effective in isolating diverse types, as in most instances of quantitative inheritance.

In many of the crosses reported above, cob color, as well as pericarp color, was involved. In table 4 the data for F₂ and the first backcross generations are presented for red-cob and white-cob ears separately.

Table 4

The segregation of cob colors was sharp without appreciable intergrades between red and white. The ratios of red-cob to white-cob ears, 341 : 118 and 212 : 202 in the F₂ and backcross generations, respectively, are approximately the 3 : 1 and 1 : 1 ratios expected where a single gene pair is concerned. The mean grades for pericarp color were somewhat higher in the red-cob than in the white-cob lots. This is the more pronounced when mean grade is calculated from all ears, because a higher percentage of the white-cob ears have colorless pericarp than is true of red-cob ears.

From the cross C-R × W-W, there have been obtained the four combinations; namely, C-R, W-R, C-W, W-W, expected on the basis of independent inheritance of pericarp and cob colors. The numerical relations, however, do not fit those of independent inheritance - 9-3-3-1 and 1-1-1-1 - as indicated in table 5.

Table 5

If we were dealing with dihybrid inheritance, these data would indicate linkage of pericarp and cob colors with 26% or 31% of crossing over for F₂ or backcross progenies, respectively. It is conceivable that there is one primary gene for whitecapped red pericarp which is modified in its expression by other genes.

Records of F₃, and of F₂ after one or more backcrosses, are summarized in table 6.

Table 6

Individuals of various pericarp-color grades among backcross and F₂ progenies were backcrossed to W-W, with the results shown in table 7.

Table 7

Tables 6 and 7 show at least that low grade pericarp color is closely linked with red cob color. That even this very low grade pericarp color cannot be allelic to cob color is shown by the occurrence of cultures in which the red-cob ears, as well as the white-cob ones, exhibit no discernible trace of pericarp color.

In addition to the cultures that segregated for cob color there occurred, in F₃ and backcross generations of the cross C-R × W-W, progenies that bred true for red or for white cob color, as shown in table 8.

Table 8

It will be noted from table 8 that six cultures produced nothing but W-W ears like one parent of the original cross; that three cultures produced only C-R ears like the other parent but with considerable variation in intensity of pericarp color; that one culture had only C-W ears like Northwestern Dent but with some variation in pericarp color intensity; that, while no true breeding W-R lots have been obtained, two cultures (table 7) contained only W-R and W-W ears, from which homozygous W-R stocks can presumably be obtained.

From all this it seems obvious that white-capped red pericarp of Bloody Butcher is not a member of the P allelic series but is conditioned by multiple genes one or more of which are linked with red cob and therefore with P. So far as the P allelic series is concerned, Bloody Butcher is apparently W-R to which has been added other genes for pericarp color not of that series.

Since white-capped red pericarp of Northwestern Dent is identical with that of Bloody Butcher in appearance and in having its intensity reduced in the heterozygous condition, it will be interesting to discover whether Anderson and I were wrong in, our earlier interpretation and, if then right, what relation exists-between C-W of Northwestern Dent and the C-W that has come from the cross of C-R × W-W. The study is underway.

R. A. Emerson