We performed reciprocal crosses between the tetraploid Selenicereus megalanthus and the diploid Hylocereus species, H. undatus and H. polyrhizus. S. megalanthus X H. undatus gave rise to viable hexaploids and 6x-aneuploid hybrids rather than to the expected triploids. No genuine hybrids were obtained in the reciprocal cross. The pollen diameter of the tetraploid S. megalanthus varied widely, indicating the occurrence of unreduced gametes, while that of H. undatus pollen was very uniform, indicating an extremely low frequency of unreduced gametes. This finding suggests that the hexaploids were formed by chromosome doubling after the formation of the hybrid triploid zygote rather than by fusion of unreduced gametes of the two species.
Bibliographical noteFunding Information:
This study was partially supported by the UCLA-BGU Program of Academic Cooperation. The authors thank Prof. G. Ladizinsky for the many instructive discussions in the course of this study and for his valuable comments on the manuscript. We extend our gratitude to Ms. Hadassa van Oss (Hebrew University of Jerusalem) and Mr. Joseph Mouyal (Ben-Gurion University of the Negev) for their skillful technical assistance and to Ms. Dorot Imber for her constructive criticism and for editing the manuscript.