The gl1-c cgl line used in our experiments was provided to the Maize Genetics Stock Center by Dr. Sprague in 1989. Initial crosses of this line by gl2, gl3, and gl6 testers made in 1999 gave 0 to 3 kernels per ear when gl1-c cgl was used as a female, but full sets when used as a male. The few kernels produced on female outcross ears gave rise to nonglossy seedlings. The male outcross progeny were also nonglossy. The disparity in ear sets suggested the involvement of a gametophytic factor. If the gl1-c cgl line carried a Ga1-S allele, then pollination by our glossy tester lines carrying ga1 would give poor sets since ga1 pollen shows poor pollen tube growth on Ga1-S silks. However, pollination of this line by a Ga1-S line would give a full kernel set. We tested this hypothesis by crossing the gl1-c cgl line by a Ga1-S tester the following winter. Female outcrosses of gl1-c cgl produced full sets, confirming that this line carries a Ga1-S allele.
In order to get better sets on gl1-c cgl females in our experiments, we converted gl2, gl3, and gl6 tester stocks to a Ga1-S background. We completed these conversions in 2000. During the summer of 2001, we reciprocally crossed Sprague’s gl1-c cgl line with our gl2, gl3, and gl6 Ga1-S lines. Full seed sets were observed in both directions, and all progeny produced nonglossy seedlings. Thus, we failed to reproduce Dr. Sprague’s results and we conclude that the cytoplasmic glossy phenomenon is not real.
The question remains as to how Dr. Sprague obtained the results that
he reported. Since his gl1-c cgl line is homozygous Ga1-S
and most genetic stocks are ga1, few seeds would set when gl1-c
cgl is used as a female in crosses with most glossy testers. However,
gl1-c cgl Ga1-S pollen from self-contamination would be fully functional
and capable of out-competing ga1 tester pollen on gl1-c cgl Ga1-S
silks, and would result in the production of glossy (homozygous gl1-c)
progeny. Sprague’s observation that the glossy progeny from such crosses
are always homozygous for gl1-c and never carry the glossy tester
allele used in the cross provides support for a self-contamination hypothesis.
The fact that female crosses involving gl8 and gl17 produced
nonglossy progeny could indicate that either these particular tester lines
carry Ga1-S, or that the crosses were made with no self-contamination
by the gl1-c cgl parent.
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