Chromosome number variation and polyploidy in 19 Kaempferia (Zingiberaceae) taxa from Thailand and one species from Laos

Abstract

© 2017 Institute of Botany, Chinese Academy of Sciences Several Kaempferia species, endemic to Thailand, are rare and therefore entitled to conservation status; other species are widely cultivated. We conducted extensive cytogenetic investigation of this genus to elucidate the botanical and taxonomic characterization of these plants. The study included 42 accessions belonging to 15 Kaempferia species and four undescribed taxa from regions throughout Thailand, and one species from Laos. We determined chromosome numbers from root-tip cells collected from germinating rhizomes ex situ, but examined meiosis in flowers collected from the wild. The mitotic analyses verify that 2n chromosome numbers range from 22 (diploid, 15 taxa), 33 (triploid, three species), 44 (tetraploid, five taxa) to 55 (pentaploid, one species). Four taxa included accessions with different ploidy levels. The meiotic analyses demonstrated that all 14 diploid accessions investigated displayed normal meiosis, forming 11 bivalents, indicating the base chromosome number x = 11 for this genus. Meiotic figures were obtained from one triploid and four tetraploid accessions. The triploid showed 11 trivalents, most likely indicating autotriploidy. Two tetraploid accessions showed regular meiotic figures consisting of 22 bivalents, probably indicating allopolyploidy originating from interspecific hybrids, a hypothesis that is consistent with observations of plant morphology. The other two tetraploid accessions belong to the same species and show mostly irregular meiotic figures. Cytogenetic information is useful for evaluating fertility and hybridity in the genus. Good seed set was observed among diploid and tetraploid accessions. Triploid and pentaploid plants, on the other hand, do not set seeds, but produce large clusters of vegetatively-propagated rhizomes.