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

Dwarfing and sensitivity to the duration of a single inductive dark period for flowering of Pharbitis nil in F2 progeny of a cross between the tall strain Tendan, and the dwarf, Kidachi appear to be controlled by the alleles at two independent loci. Progeny of a similar cross between the tall strain Violet and the dwarf Kidachi at F2 and F3 also showed single locus segregation for tall: dwarf plants. In this cross, differences in photoperiodic response could be identified in F3 families but they were not simply inherited. There was some evidence of difficulties with classification of the F2 plants, but also, the flowering of the F1 between the two less sensitive strains Tendan and Violet indicated complex inheritance of their photoperiodic response. Complementary dominant alleles at three independent loci may be necessary for flowering in even shorter dark periods with the sensitive strain Kidachi. The dwarf strain Kidachi has a reduced gibberellin (GA) content (Barendse and Lang 1972), it flowers in a short dark period without terminal flowering, and it responds positively to GA application both for flowering and growth. However, since control of dwarfing and photoperiodic sensitivity can be separated genetically, there is no strict link between the gibberellin responsiveness of Kidachi for its growth and flowering. Despite the complexity of flowering genetics in Violet X Kidachi, a short-dark-period-sensitive, terminal flowering and tall F7 line was obtained in a pedigree previously held heterozygous for the dwarf: tall character but not selected for flowering time. Thus, flowering in a short dark period can also be obtained in the presence of the non-dwarfing allele from strain Violet, again demonstrating genetic independence.