In the 1984 Newsletter (MGNL 58:101), Johnson reported data indicating that Rf4, which restores fertility to cms-C cytoplasm, was on 8L linked to the wx T8-9(6673) breakpoint. Crosses were made by Johnson and V. E. Gracen at Cornell to determine whether Rf4 is linked to v16 or j, two markers on 8L. F2 progeny were scored at Raleigh, North Carolina, but no linkage of Rf4 with either marker was apparent (see data below). Note, however, that the weak linkage between v16 and j (28 m.u.) was not detected by this F2 analysis. It is possible that Rf4 is on 8L but proximal to v16, since the reported breakpoint of wx T8-9(6673) is 8L.35, while TB8-La at 8L.70 uncovers v16. Alternatively, the Rf4 locus may not be on Chromosome 8, because remnant seed of the wx T8-9(6673) cross grown out at Raleigh produced very weak plants that could have been male-sterile for many reasons. Laughnan and Gabay-Laughnan (Ann. Rev. Genet. 17:27, 1983) said that data from their studies indicated at least two cms-C restorers, one of which was on chromosome 2. The data presented here are consistent with Kheyr-Pour et al.'s findings (Genetics 98:379, 1981) that the inbred A619 has a single major restorer gene for cms-C restoration. This gene was designated Rf4 by Kheyr-Pour.
A v16 j source from the Maize Genetics Cooperation (Coop 78-630-8 self) was crossed as male to A619 cms-C (Rf4/Rf4) and to NyD410 cms-C (rf4/rf4). The NyD410 control was male-sterile in the F1, showing that the v16 j source did not carry restorer genes for cms-C. The F1 of the A619 cross was selfed, and the F2 progeny were scored.
P. H. Sisco
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