A series of Dotted phenotypes have been recovered from advanced generations of virus exposed cultures. One, Dt6, is on chromosome 4. No linkage has been established for the remainder and they are being carried under temporary designations, Dt(a), Dt(b) etc. Each is inherited as a simple dominant and each is of separate origin as judged by line of descent.

Unexpected behavior was noted in the F2's of a series of dt:dt crosses. Each dt stock was derived from a Dt:dt segregation and the dt parent had been selfed for at least one additional generation to ensure the correctness of the classification. Among the crosses all F1 seed were colorless and non-dotted. The F2 behavior is illustrated in the table. Three different patterns were observed. In the first group no dotted segregants were observed in F2. Most of the crosses involving a-m1(Spm) and a-m4(Ac) were in this group.

In the second group the F2 segregations approximated a 1:1 segregation with an excess of the non-dotted class, possibly through failure to recognize kernels with only one or two small dots.

In the third group the dotted class approximates a 1:3 ratio with, in most cases, a deficiency of the dotted class.

F3 progeny tests of the dotted class have been obtained for a number of the crosses tested. Among a large number of F3 progenies none bred true for the dotted phenotype. The range in breeding behavior roughly paralleled that exhibited by the F2's. In a few cases the more extreme dotted F2 kernels gave segregations approximating 3 Dt:dt. It is too early to speculate on the origin of Dt from the dtxdt crosses but some types of interaction between receptor or regulatory loci must be involved. Tests to establish the identity of some of the recovered Dt phenotypes are underway.

The breeding behavior just described contrasts sharply with Ac or Spm behavior as illustrated by the following results. The cross of a-m1/a1 dt2 wx exhibiting dotting in F1 indicates the presence of Spm in the dt2 parent. F2 and backcross data were as follows:
  Dt Wx Dt wx dt Wx dt wx Recombination
F2 552 53 217 170 24
BC 1107 286 480 1106  26

This appears to be a new location for Dt and the symbol Dt7 is suggested.


G.F Sprague

Please Note: Notes submitted to the Maize Genetics Cooperation Newsletter may be cited only with consent of the authors.

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