Cytogenetics of domestication and improvement of garden Gladiolus and Bougainvillea

摘要

The ornamental crops being of recent origin offer excellent opportunity to unravel the cytogenetical mechanisms involved in their cultivation. It is worthwhile to know how the major cytogenetical events changed these plants from insignificant elemental species to conspicuous and attractive ornamentals. Gladiolus and Bougainvillea represent slightly different pathways which are reflected in their genetic systems. Gladiolus possesses a very plastic genome where interspecific hybridization is possible irrespective of ploidy level or species designation. The elemental species range from diploid to hexaploid and the first critical cross took place between a 2x and a 6x species to produce a highly heterozygous tetraploid hybrid. The present day garden cultivars have further undergone many cycles of hybridization involving some other species resulting in tremendous variability. Bougainvillea has comparatively simpler genetic system as all the three elemental species are diploid and the hybrids between them are either completely sterile or semi sterile. This interspecific hybridization has produced intermediate morphological and phenological characters and entirely novel bract colours in the three hybrid groups. The fertility in these hybrid groups could be restored by induced polyploidy and this expanded germplasm was used to produce tetraploid and triploid hybrids with highly positive horticultural traits. The hybridization under cultivation in both these ornamentals was aided by their strictly out-crossing nature supplemented by the presence of self-incompatibility. Furthermore, the novelty which arose could be fixed by vegetative multiplication.