Cytology and fertility of an intergeneric orchid hybrid

Abstract

The orchid, Aranda Lucy Laycock, is an intergeneric hybrid between Arachnis hookerana and Vanda tricolor. It is well known among breeders because of its unusually high fertility among the over 200 existing Aranda hybrids, but only when used as a maternal parent in crosses. Melotic and sporad analysis of one fertile and one infertile clones of this hybrid were made. The fertite clone was found to produce 47.1 percent dyads of unreduced spores. Cytological studies revealed that 66.4 percent of its pollen mother cells (PMCs) showed noncongressed chromosomes at Ml. Failure of disoriented chromosomes in many of these PMCs to move apart at AI gave rise to first division restitution nuclei. On the other hand, most PMCs of the Infertile clone showed some degree of alignment of chromosomes at the equatorial region at Ml even though most chromosomes remained as unpaired unlvalents. It appeared that the formation of three or more blvalents were necessary to Induce some degree of chromosome alignment at Ml. © 1987, American Genetic Association.