Molecular genetic relationship of some Aeschynanthus in Thailand

Abstract

Aeschynanthus is an epiphyte genus with c.160 species wide spreading in SE Asia. They have brightly red or orange tubular flowers and therefore are commercially cultivated. Literature reviews and herbarium visiting indicated that there are approximately 20ׄ species in Thailand. Most of these plants have not yet been studied in both cellular and molecular genetics. Thus this thesis had studied genetic relationship of Aeschynanthus especially on sequences of ITS regions of nuclear ribosomal DNA gene. First, plant sample collections were done by having an expedition, buying from a plant market, and asking from foreign organisation. DNA of the plant specimens were extracted and ITS regions were amplified with PCR before sequenced and aligned with a previously data to reconstruct a phylogenetic tree. The result confirms a division of Aeschynanthus into two major groups. Most of Thai species were placed in the clade I while only A. radicans and A. parvifolius were in the clade II. Aeschynanthus andersonii, A. humilis and A. hiidebrandii, the three supposingly synonymous species, were found from molecular phylogenetic and PCR-RAPD studies that A. andersonii and A. humilis should be the same species. Almost all additional samples having the same name but different in accession number to their investigated counterparts were clustered together. Lacks of morphological information of some Aeschynanthus species limited a discussion on their seed evolutionary patterns. This thesis also used molecular techniques to identify cultivated and wild samples successfully. Interestingly, one species with unusual pink flowers showed unique ITS sequence and may be a new undescnbed species. Furthermore, a cytogenetic investigation of six Aeschynanthus species indicated that chromosomes of these plants were too small to do karyotyping. Aeschynanthus radicans, A. obconicus and A. sp. JJ_001 have chromosome numbers of 2n= 32 whereas A. andersonii, A. humilis and A. hiidebrandii have 2n=28. This chromosome number counting supports the suggestion to place A. andersonii, A. humilis, A. hiidebrandii into the section X.