GENES FOR DWARFING AND PHOTOPERIOD FLOWERING RESPONSE IN PHARBITIS-NIL CHOISY

Dwarfing and sensitivity to the duration of a single inductive dark pe riod for flowering of Pharbitis nil in F2 progeny of a cross between t he tall strain Tendan, and the dwarf, Kidachi appear to be controlled by the alleles at two independent loci. Progeny of a similar cross bet ween the tall strain Violet and the dwarf Kidachi at F2 and F3 also sh owed single locus segregation for tall: dwarf plants. In this cross, d ifferences in photoperiodic response could be identified in F3 familie s but they were not simply inherited. There was some evidence of diffi culties with classification of the F2 plants, but also, the flowering of the F1 between the two less sensitive strains Tendan and Violet ind icated complex inheritance of their photoperiodic response. Complement ary dominant alleles at three independent loci may be necessary for fl owering in even shorter dark periods with the sensitive strain Kidachi . The dwarf strain Kidachi has a reduced gibberellin (GA) content (Bar endse and Lang 1972), it flowers in a short dark period without termin al flowering, and it responds positively to GA application both for fl owering and growth. However, since control of dwarfing and photoperiod ic sensitivity can be separated genetically, there is no strict link b etween the gibberellin responsiveness of Kidachi for its growth and fl owering. Despite the complexity of flowering genetics in Violet X Kida chi, a short-dark-period-sensitive, terminal flowering and tall F7 lin e was obtained in a pedigree previously held heterozygous for the dwar f: tall character but not selected for flowering time. Thus, flowering in a short dark period can also be obtained in the presence of the no n-dwarfing allele from strain Violet, again demonstrating genetic inde pendence.