1. White-capped red pericarp. In News Letters 16 and 17 (1942 and 1943), I presented data indicating that white-cap red pericarp of such varieties of maize as Bloody Butcher is not a member of of the multiple allelic series at locus P as has been supposed and suggested that this color is conditioned by multiple genes as in quantitative inheritance, one or more of which are closely linked with P. In Bloody Butcher white-cap red pericarp is associated with red cob (C-R), while in Northwestern Dent an apparently identical pericarp color is associated with white cob (C-W). Northwestern Dent alone was involved in the earlier work which had lead [sic] to the idea that white-cap red was allelic to P, and Bloody Butcher alone was involved in the results reported in recent News Letters. It became important, therefore, to repeat the study with Northwestern Dent in order to determine whether the apparently identical pericarp color of the two varieties is inherited in the same way. Results to date indicate that intensity of color of white-cap red of Northwestern Dent also is conditioned by multiple genes, one or more of which are linked with P. But certain complications have arisen which give the whole problem added interest -- not to say added perplexity.
For comparison with more recent data, there are here presented records from News Letter 16 (1942), including F2 and backcrosses of Bloody Butcher, C-R, with colorless inbreds, W-W. Pericarp-color grade "O" is colorless and "6" is about the intensity of Bloody Butcher.
Cob color here shows approximately normal mono-genic segregation, but the ratios of colored to colorless are not those typical of mono-hybrids. The mean grade of pericarp color of red-cob segregates is materially higher than that of white-cob ones. The four possible combinations of cob color and pericarp color appear with frequencies indicating linkage.
The same type of cross was repeated with F4C-R and W-W segregates from the original Bloody Butcher cross. The results are:
Here again segregation of cob color is normal and the mean pericarp-color grade is higher for red-cob than for white-cob segregates. But one color-class, W-R, did not occur and the ratios of colored to colorless pericarp are far from those typical of mono-hybrids.
White-cap red pericarp of Northwestern Dent, associated with white cob, C-W, also has now been studied. Crosses of this variety with a red-cob colorless-pericarp inbred, W-R, selfed and crossed with W-W are recorded below.
Northwestern Dent was also crossed with an F4W-R segregate from the original cross of Bloody Butcher with W-W, and F1 was outcrossed with an F4W-W segregate of the same original cross. The data obtained are given below.
The two crosses behaved essentially alike. There was some departure from 3:1 and 1:1 ratios for cob color. The striking features of these records are (1) the absence of the W-W color class in F2 and the near absence of it in the out-cross to W-W, (2) the relatively few ears and low grade of the C-R class in the out-cross, and (3) the red-cob ears in both F2 and the out-cross. Thus, in the Northwestern Dent crosses pericarp color, particularly of the higher color grades, tends to be associated with white cob rather than with red cob the reverse of that in the Bloody Butcher crosses. In short, the tendency is to maintain the parental associations of cob and pericarp colors.
Crosses of C-W with W-R, not involving Northwestern Dent but rather C-W and W-R segregates from the original crosses of Bloody Butcher, C-R, with W-W inbreds, have given results wholly unlike those in which Northwestern Dent as used as the C-W parent. The available data are given below.
Here again cob color segregated normally. The striking features of these data are (1) the relatively high frequency of the W-W class -- all but absent in the Northwestern Dent crosses -- (2) the high frequency of the C-R class in the out-cross, and (3) the higher color grade of red-cob ears. In short the behavior of these crosses of C-W/W-R, in both F2 and the out-cross generations, was much less like the behavior of crosses of the same color types when C-W came from Northwestern Dent than like the cross of C-R/W-W when C-R came from Bloody Butcher.
Eight F3 cultures have been grown from the three color classes, C-R, C-W, and W-R, obtained in F2 from the cross of Northwestern Dent, C-W, with an inbred W-R. The results are given below.
As in F2, the pericarp-color grade is higher when associated with white than with red-cob; and as in F2, the W-W class did not occur. In one case the F2 recombination class C-R apparently bred true in F3 for the presence of both cob and pericarp color. It is evident that diverse intensities of pericarp color can be isolated by inbreeding and selection when Northwestern Dent is involved in crosses with colorless pericarp just as is true of Bloody Butcher crosses as reported in News Letter 17 (1943).
From this report and earlier ones, it can be said that the intensity of white-cap red pericarp of such maize varieties as Bloody Butcher and Northwestern Dent and of their crosses with colorless pericarp strains, is influenced by genes whose action is like that of genes conditioning other quantitative characters. It can also be said that some of these genes are linked with the gene for red or white cob.
To assume that some of the effective genes of Bloody Butcher are represented by ineffective alleles in Northwestern Dent and that the reverse is true of other such genes, and further to suppose that some of them are more closely linked with the cob-color alleles, is of little help without the added assumption of interaction of some intensity genes with red cob and of others with white cob. On such assumptions it might be expected that an F4 C-W individual from a cross involving Bloody Butcher would have at least some of the genes of Bloody Butcher with the same linkages and interaction with red cob as in Bloody Butcher. Such C-W plants might then be expected to behave differently in crosses with W-R from that of the C41 plants of Northwestern Dent. It is not worth while at the present stage of the study to go into further detail about this complex and somewhat hazy hypothesis. The principal thing to be said in its favor is that it seems amenable to experimental genetic test.