CHROMOSOME HOMOLOGY IN SOME INTERCONTINENTAL HYBRIDS IN HIBISCUS SECT. FURCARIA

Ten kinds of interspecific hybrids were obtained involving the following species: H. surattensis L. (2x, genome constitution BB), H. sudanensis Hochr. (2x, GG), and H. rostellatus Guill. and Perr. (4x, GGHH) from Africa; H. furcatus Roxb. non Willd. (8x) from India and Ceylon; H. furcellatus Lam. and H. bifurcatus Cav. (both 4x, PPQQ) from South America; and H. heterophyllus Vent. (6x) from Australia. Chromosome pairing in pollen mother cells (PMC's) at metaphase I in the 4x hybrids H. bifurcatus-rostellatus and H. furcellatus-rostellatus indicated that the parents have one genome in common (Q = G or H). Hibiscus furcatus was shown earlier to have a B genome; hybrids of H. surattensis-sudanensis F₁ X furcatus were hexaploid, having received an unreduced gamete from their hybrid parent, and had approximately 36 II, 36 I in PMC's. The genome formula of H. furcatus may therefore be designated BBGGWWZZ. The hybrid H. rostellatus-furcatus (BGGHWZ) confirmed that H. furcatus has a G genome in common with H. rostellatus; pairing of the other three genomes was inconsistent, as was that in H. rostellatus-heterophyllus. Some samples of the latter approached 36 II, 36 I, expected if H. heterophyllus were GGHHJJ; other samples had less pairing. Hibiscus furcatus-heterophyllus hybrids apparently arose from unreduced gametes of H. heterophyllus and originated as decaploids rather than heptaploids; chromosome number was unstable in PMC's. Nevertheless, multivalents, especially trivalents, were frequent enough to suggest that H. furcatus and H. heterophyllus share G genomes. On the other hand, an 8x H. bifurcatus-furcatus hybrid, which apparently arose from an unreduced gamete of H. bifurcatus, had a low multivalent frequency. Hybrids were obtained of H. heterophyllus X sudanensis and H. surattensis-sudanensis X heterophyllus, but the plants were weak and were not analyzed cytologically. We suggest that the New World, African, Indian, and Australian genomes which retain a considerable degree of homology (G or H or both) were distributed by land prior to separation of the southern continents by continental drift.