tb may condition a semi-dominant effect on tiller number
Plants homozygous for tb (teosinte branched) are generally highly tillered and produce multiple branches that terminate in tassels. These branches occur at nodes that would normally produce ears. These effects on floral morphology are absent in heterozygotes. However, during backcrossing we noted that tb heterozygotes appeared to be more highly tillered than would normally be expected in given genetic backgrounds. To test tb's role as a positive modifier on tiller number in heterozygotes, plants from cross 1 were scored for tiller number and selfed. Progeny tests of 17 of the resulting selfed families established which plants from the cross tb/Tb X Tb/Tb were heterozygous for tb. The ten tb heterozygotes had an average tiller number of 4.1. The seven Tb/Tb plants had an average tiller number of 2.3. These means are significantly different as determined by the t test. Therefore, this limited data set suggests that tb may be a positive modifier of tiller number even when heterozygous.
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