The homozygous recessive bd bd is tightly linked to the homozygous dominant Pn Pn near the end of the long arm of chromosome 7. In a typical background of present-day maize, the bd phenotype is highly branched like the ramosa genes but also female sterile by delayed style growth. Because of this female sterility, previously it has been impossible to propagate the double homozygous condition. The interaction of modifying genes on the bd bd phenotype is under study. The addition of the tassel seed-2 gene (ts2) on chromosome 1 not only leaves the ear female sterile but worsens the situation by also making the tassel male sterile and monstrously branched, but not hopelessly monstrous. The further addition of the silkless gene (sk) on chromosome 2 restores a sort of balance with a new previously unknown phenotype. Thus, the complex of the following four genes, Pn Pn, bd bd, ts2 ts2, sk sk, has a papyrescent ear that is highly branched and female fertile.
Other genetic systems to confer female fertility upon Pn Pn, bd bd are being explored. It is hoped that an F1 hybrid between two papyrescent lines each with a different recessive system for female fertility will give a hybrid uniform for sterile "cauliflower ears". This would represent a new vegetable comparable to the cauliflower variety of Brassica oleracea.
Walton C. Galinat
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