Abstract
F1 from the cross Triticum polonicum (2n=28)×T. Spelta (2n=42) was back-crossed to the tetraploid wheat. The awnless tetraploids could be obtained in the offspring of this back-cross. An awnless plant with long glumes (PP) was crossed to T. dicoccoides (2n=28) and another tetraploid with short glumes (pp) to T. persicum (2n=28).
1) In F2 of these crosses long glume (P), awnless (A), hairy glume (Hg) and red coleoptile (Rc) were found to differ from short glume (p), awned (a), glabrous glume (hg) and green coleoptile (rc) respectively by only a single gene. P and p are linked to Rc and rc with a cross-over value of 20.3%.
2) P gene for the long glume of T. polonicum with the manifold effects inhibits the awn length, the glume hair, the coleoptile color and the awn color in its homozygous condition.
3) Two abnormalities have been observed in crosses between tetraploid wheats. The first, apparent failure to segregate, was reported by Biffen (1916) in a cross between a white chaffed T. polonicum and a grey chaffed T. turgidum. Similar phenomenon on the chaff color and hair was found by Backhouse (1918) and Engledow (1920) in the cross T. polonicum×T. durum. The author supposes from the present studies that these abnormalities are due to the inhibition of P- gene.
4) The second case was studied on the glume length by Engledow (1920, 1923) in a cross T. polonicum×T. durum, who termed the phenomenon “shift”. This abnormality could be explained also by the major gene P and the multiple modifyers.
5) Darlington (1927, 1928) and Watkins (1940) consider that in tetraploid wheats these two abnormalities are examples of the result of autosyndesis in the polyploid plants. The present work shows, however, the contrary results.
6) The characters waxy and waxless differ by an allelomorphic pair W-w and their inhibitor Iw-iw. The genotype of waxless T. dicoccoides is wwIwIw and in F2 the ratio 13 waxless: 3 waxy is ordinarily observed. W and Iw show an independent segregation to the genes P, A and Hg respectively.
