A number of apparently different controlling element systems have been found in populations derived from my earlier AR studies. Some years ago, a number of these were supplied to P. A. Peterson and he and Friedemann (MNL 54:2, 56:6) have reported on one they designated Uq. Under my terminology this stock is designated a-mt-1.
In the original stock, this phenotype exhibited a coarse but fairly uniform mottling and gave rise to both self-colored and colorless seeds in high frequency, about 5% colored and 2% colorless. Changes were both somatic and germinal and true breeding types were easily established. A third type of change to a fine mottling or dotting was also observed but in much lower frequency. Subsequent tests indicate that the two mutant types are due to mutations at different loci. The self-colored type is due to mutation of the a-mt-1 allele to A. This new A, when homozygous, retains the brown cob color typical of standard a. The colorless mutation Is at a second locus (Sta sta) which controls the mutability of a.
Results from a series of crosses involving the colored and colorless mutant types with standards are presented in the following table.
a-mt-1 behaves as a stable a allele. In the presence of Sta a-mt-1 is mutable, giving rise to typically mottled seeds. The behavior of the A mutant type remains somewhat anomalous. When crossed to standard A C R stocks, the F2 results are as indicated in the last line of the table.
G. F. Sprague
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