c-m816667 is one of three confirmed c unstable mutants and one stable mutant from the 1980 c sh wx isolation plot. This plot contained Uq and its receptor a-ruq (Peterson and Friedemann, Maydica 26:213-249), and produced 1.85 x 10⁶ kernels. c-m816667 displays spots on a colorless background. This c allele material was shown to contain one Uq when crossed with a-ruq, as follows:

c-m Sh Wx a Uq x a-ruqC
c     sh wx  A +     a-ruq C

The Uq relationship was established by backcrossing a-ruq spotted and colorless kernels to the c sh wx tester (Table 1, A and B, respectively). If c-m816667 is controlled by Uq only the cross of spotted by C sh wx will express c mutability. This is confirmed In Table 1A. The colorless a-ruq selections indicate that Uq was absent. The confirmation test would then be expected to produce only the colorless c phenotype. This Is largely confirmed, but there were the exceptions (Table 1B). These selections had been made from an ear which exhibited variable Uq potting frequencies. The possibility exists that these two were a-ruq Uq with low frequency spotting rather than a-ruq, no Uq colorless. This was tested by backcrossing to a-ruq. The cross was as follows:

c-m Sh Wx a-ruq (+/-)Uq x a-ruqC
c     sh wx    A       +           a-ruq C

This cross exhibited a-ruq Uq spotting. It can be concluded that these two selections were misclassified. These should have been grouped with the selections in Table 1A.

In each of the ears of Table 1A which shows c mutability, it has been confirmed that Uq is segregating independently of the c locus. The spotting of c-m816667 is due to the interaction of c-ruq and Uq.

Table 1.

Elizabeth Oberthur and Peter A. Peterson

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