| The system appears as follows : A. In vulgare (Q present) : Irrespective of presence or absence of other genes, the vulgare factor Q determines normal flower formation in the first and subsequent flowers. B. In speltoids (Q absent) : ( i ) In the presence of a dominant gene, A, the second, and subsequent, flowers are normal. ( ii ) The development of the first flower is conditioned by a polygenic series, presumably linked with A, with its plus (or minus) alleles determining the frequencies of normal (or abnormal) development of the first flower, between the extremes of " fertile " (StF) and " 1st flower sterile " (St1). ( iii ) In the absence of the A allele, i.e. in plants with the aa genotype, formation of the second and subsequent flowers is also conditioned by a polygenic series. There is evidence that this is identical with that conditioning first flower development. In crosses between the speltoid series and unrelated vulgare wheats, it has been shown that all vulgare wheats tested so far possess some alleles which impair normal flower formation in the speltoid state. This has been confirmed by Mac Key (1954) in X-ray induced speltoids. We conclude from the observations so far adduced that in the diploid ancestral genomes of hexaploid wheat, flower formation may have been conditioned by these gene systems now revealed in speltoids, and that under the cover of the later acquired Q factor these systems have become disused and are now in a state of gradual disintegration. To test further our interpretations, we are continuing the studies of the crosses already mentioned. Recent work includes crosses between our speltoid series and selected tetraploid and hexaploid wheats. |
| <-- Back |