--Michael G. Muszynski and Peter A. Peterson
The original phenotype of the c2-m881058P allele (MNL 64:9) was
medium spotted (2-6 aa-b, Reddy and Peterson MGG 194:124, 1984), but upon
outcrossing three mutable phenotypes segregated: high (6-8 aa-d), medium
(2-6 aa-b) and low (1-3 aa-a) in approximately equal ratios. Kernels (c2-m/c2)
were selected from each class and crossed by and on c2/c2. Each
class segregated as follows:
| Phenotype | Segregation on Outcross Ear | |||
| Planted | High | Medium | Low | cl |
| High | 1/4 | - | 1/4 | 1/2 |
| Medium | 1/8 | 1/8 | 1/8 | 5/8 |
| Low | - | - | 1/2 | 1/2 |
| colorless | - | - | 1/4 | 3/4 |
The only class which bred true was the low spotted class and also segregated 50% on an outcross, thus the c2-m allele contains a regulatory element which conditions low mutability. Two factors which modify this low spotting are independently segregating in this mutant. One factor (Stimulator) stimulates the c2-m low spotting to high spotting and segregates upon outcrossing plants from high spotted kernels. Another factor (Restrainer), which restrains the high spotting to medium and the low spotting to colorless, is also segregating. Both factors are unlinked to the c2-m allele and to each other.
F1 kernels (C2/c2-m A1/a1-o Wx/wx + Stim.) were backcrossed
to c2/c2 and a1-m(r)/a1-m(r) tester lines to test for En(Spm)
relation. The results, on a per plant basis, are summarized as follows:
| Cross to c2 Indicates | Cross to a1-m(r) Indicates |
| 1. c2-m | 1 En-low |
| 2. c2-m + 1 Stim. | 1 En-low and 1 En-std |
| 3. c2-m + 2 Stim. | 1 En-low and 2 En-std |
| 4. C2 + 1 Stim. | 1 En-std |
These data indicate that the element at c2-m881058P is a weak
or low En. The Stimulator is a standard En, which
can compensate for the En-low and boost the mutability to a high
spotting pattern. The Restrainer is probably a suppressor of mutability
similar to the I element of a1-m(r)102 (Cuypers et al., EMBO
J. 7:2953, 1988), which restrains the high mutability to a medium pattern
and the low c2-m::En-low spotting to colorless. System tests to
other element systems were negative.
Return to the MNL 65 On-Line Index
Return to the Maize Newsletter Index
Return to the MaizeGDB Homepage