Paraphyly Study of Remusatia vivipara (Roxb.) Schott (Araceae) by Morphology, Molecular and Bulbil Development Traits
Date Issued
2015
Date
2015
Author(s)
Huang, Chi-Tung
Abstract
Remusatia vivipara (Lodd.) Schott is listed as a Vulnerable (VU) species in the Red Lists of Taiwan. Remusatia species are among the few tropical aroids which can have both sexual flowers and asexual bulbils growing in their life cycle. Within Remusatia, R. vivipara is the most widespread in tropical Asia and Africa, while the other species restricted to S and SE Asia except R. yunnanensis which is endemic in Yunnan, China. However, this taxonomic grouping solely based on the existence of bulbil as the genus single diagnostic character has been widely argued, because the morphological characters of inflorescence (especially the spathe) are very different. This dissertation focuses on phylogenetic and taxonomic studies of Remusatia species. There are six chapters in this study: In Chapter 1, the taxonomical status of Remusatia vivipara in Taiwan was introduced. Other chapters dealed with phylogenetic analysis, bulbil development, microsporogenesis and flowering induction of R. vivipara. In Chapter 2, we sequenced two plastid (trnL-trnF and psbA-trnH) and two nuclear (ITS and phyC) DNA regions in resolving the phylogenetic relationships. The genus Remusatia is not monophyletic and could be divided into three subgroups in which R. vivipara and R. yunnanensis formed a clade, R. pumila sistered with Studnera species in another group, while R. hookeriana was sistered to Colocasia species. Based on the phylogenetic trees and morphology of Remusatia species, R. pumila seems to belong to Remusatia and R. yunnanensis is genetically not different from R. vivipara. It is suggested that R. pumila is probably better restored to the genus Gonatanthus. In Chapter 3, we document the discovery of Remusatia yunnanensis (H. Li & A. Hay) A. Hay from Nantou County in central Taiwan. R. yunnanensis has before been considered endemic to Yunnan, China. Remusatia yunnanensis is similar to R. vivipara and only distinguishable by the difference in spathe limb color. The spathe limb of R. yunnanensis is distinctly purple red while that of R. vivipara is yellow. The description and illustration of R. yunnanensis, including a dichotomous key description for Remusatia in Taiwan were provided. In Chapter 4, the reproductive strategies between Remusatia vivipara and R. pumila were compared. Both species can produce sexual flowers and asexual bulbils. However, R. vivipara rarely sets seeds and appears largely on asexual reproduction by bulbils and tubers, whereas R. pumila has regular seed set. This chapter tried to understand the asexual mode of bulbil development and the reasons for sexual failure in R. vivipara. The developments of asexual bulbils from stolons were observed in R. vivipara by using scanning electron microscope and light microscope. Results showed that the bulbils of R. vivipara occurred on independent bulbiliferous shoots rather than on inforescences, and were different from other bulbiliferous plants. Each bulbil was covered with hooked scales which were actually an elongation of bulbil top cells. These hooked scales on bulbils appeared to be unique in Araceae. With the hooked scales, the bulbils might be easily dispersed by birds and mammals in long distance. This might be reflected by the widespread distribution of R. vivipara in Taiwan, SE Asia and Eastern Africa. In addition, chromosome counting was performed to confirm R. vivipara as triploid species. In Chapter 5, the effect of applying Gibberellic acid (GA3) to promote inflorescence initiation and elongation in R. vivipara was evaluated. Tubers of various sizes (average 2.67 cm in diameter) were treated with different concentrations of GA3 (0, 25, 50, 75 and 100 mg L-1). Our results showed the induction of flowering by GA3 at and above 25 mg L-1. However, no significant differences were observed among different GA3 concentrations in terms of inflorescence characteristics and vegetative growth. To produce R. vivipara as an ornamental plant, it is recommended to drench plants with 25 mg L-1 GA3. The present study also revealed that large tuber size made more significant contributions to the prediction of flowering, and the magnitude of inflorescence characteristics (inflorescence length, male zone length, female zone length, spathe length and sterile zone length) and vegetative growth (fresh and dry bulbil stolons) mostly increased with increasing tuber size. The final chapter draws an overall conclusion from the research findings, which could shed light on the reproductive biology of Remusatia vivipara, the unique bulbil developmental pattern and its phylogenetic affinity. Further examinations on pollen meiosis, stamen and ovule developments in R. vivipara are necessary. The application of nuclear DNA markers may also provide a remarkable contribution to the revision of the genus Colocasia and its relationship with R. hookeriana.
Subjects
Araceae
Remusatia
Pollen mother cell
Hooked scale
Pollen viability
Phylogeny
Polyploidy
Gibberellin acid
Tuber
Inflorescence characteristics
Bulbil stolon
Type
thesis
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