Chromosome Numbers and Genome Relationships of Some Species in the Nigrohirsutae Section of Dendrobium

Abstract

Chromosome numbers and meiotic behavior of species and hybrids in the Nigrohirsutae section Dendrobium were investigated. The chromosome number of the Philippine species, D. schuetzei and D. sanderae was 2n=40, while that of the extra-Philippine species, D. formosum and D. draconis, was 2n=38.
The chromosomes of D. formosum were about twice as large as those of D. sanderae, and those of D. draconis were intermediate in size.
Meiosis in D. schuetzei and its hybrids with D. sanderae and D. dearei was regular with the formation of 20 bivalent chromosome at metaphase I. The triploid hybrid, D. sanderae×D. dearei, formed 19-13 trivalents and 7-1 bivalents and univalents. D. dearei×D. formosum, having 39 chromosomes, exhibited 19-11 bivalents with a mean of 15.9, most of which were heteromorphic.
It can be concluded that the Philippine species are very closely related to each other while D. formosum is more distantly related.