Ornamental Orchid Research Articles

Contribution of militarine and dactylorhin A to the plant growth‐inhibitory activity of a weed‐suppressing orchid, Bletilla striata

The methanol extract of Bletilla striata, an ornamental orchid in eastern Asia, exhibited plant growth‐inhibitory activity. It was purified by continuous chromatography, based on the inhibitory activity against the growth of lettuce seedlings, resulting in two glycosidic compounds, militarine and dactylorhin A. The EC50 values of militarine and dactylorhin A against the radicle elongation of the lettuce seedlings were 0.28 and 0.88 mmol L−1, respectively. The amount of militarine and dactylorhin A in the methanol extract of the aerial part of B. striata was calculated to be 5.6 and 7.5 mg g−1 fresh weight, respectively. The inhibitory activity of militarine and its content in the methanol extract revealed that the plant growth‐inhibitory activity of the extract of B. striata was mainly related to militarine. The inhibitory activity of militarine against the growth of Italian ryegrass and timothy were of the same level as that of lettuce.

MORPHOLOGICAL AND MOLECULAR CHARACTERIZATION OF INTERGENERIC HYBRIDS BETWEEN THE ORCHID GENERA RENANTHERA AND VANDA

The Indo-Burmese mega-biodiversity 'hotspot' houses a number of ornamental orchids belonging to rare, endangered, threatened and vulnerable species possessing highly attractive flowers. However, till date, many of these beautiful orchids growing in the pristine forests of north-east India have remained largely unexplored and unexploited. Renanthera imschootiana Rolfe is an IUCN red-listed rare and endangered orchid classified under Appendix-I of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). This orchid is renowned for its bright crimson, long-lasting floriferous spikes which bloom during spring every year. Vanda coerulea Griff. ex. L., and Vanda testacea (L.) Reichb.f. are simultaneously deeply coloured flowers with high aesthetic values. Using Renanthera imschootiana as the female parent, we have crossed it with the Vanda species and intergeneric hybrids have been synthesized, viz., Renantanda Kebisana Shija (R. imschootiana × V. coerulea) and Renantanda Prof GJ Sharma (V. testacea x R. imschootiana). These hybrids have been registered in The International Orchid Register of the Royal Horticultural Society, London. We have also developed in vitro propagation protocols for these parents and their hybrids keeping in view of their conservational and eco-restorative considerations. The synthesized hybrids produced beautifully coloured flowers with shelf-lives lasting from 1 to 1 1 / 2 months. Morphological as well as molecular characterizations of these hybrids have been made for confirmation of hybridity and other genetic information.

Evidence that Cymbidium mosaic virus (CymMV) isolates divide into two subgroups based on nucleotide diversity of coat protein and replicase genes

The genetic diversity of Cymbidium mosaic virus (CymMV, family Flexiviridae) was assessed by analysing the nucleotide sequences of coat protein (CP) and partial RNA-dependent RNA polymerase (RdRp) genes. Thirty CymMV sequences from vanilla isolates, obtained in this work by direct sequencing of RT-PCR products, were compared to the sequences from ornamental orchid isolates available in GenBank. The CymMV population exhibited overall low genetic diversity (pi=0.054 and pi=0.053 for CP and RdRp genes, respectively). Phylogenetic analyses of the 85 CP and 37 RdRp sequences revealed the segregation of the isolates into two congruent monophyletic clusters; however these two subgroups did not cluster in amino sequence analysis because most of the nt mutations were synonymous. Nevertheless, the subgrouping was confirmed by highly significant Kst tests for the CP and RdRp genes. Analysis of population genetic parameters and distribution of synonymous and nonsynonymous mutations revealed that both genes were under negative selection with no recombination events. These results suggested that the CymMV isolates found in cultivated orchids worldwide have a dual origin and are expanding as if following bottlenecks.

AFLP fingerprinting and conversion to sequence-tag site markers for the identification of Oncidium cultivars

SummaryOncidium is one of the most popular ornamental orchids. However, it is difficult to differentiate one cultivar from another based only on phenotypic traits. As Plant Breeders’ Rights evolve, in particular since the advent of essential derivations, the importance of early differentiation of crop cultivars increases. In this report,AFLP markers were used, with 21 primer pair combinations, to fingerprint two cultivars from Oncidium Gower Ramsey hybrids and two cultivars from O. Sweet Sugar hybrids with the restriction endonucleases Eco RI and Mse I. A total of 1,091 AFLP bands were obtained. More polymorphic bands (209) were detected between the two hybrids than between the two cultivars of O. Gower Ramsey (25 bands), or between the two cultivers of O. Sweet Sugar (18). The most significant polymorphic AFLP bands (11) were cloned and sequenced for conversion into 12 sequence-tagged site (STS) markers. These STS markers were then applied to the identification of 49 cultivars from four Oncidium hybrids including O. Gower Ramsey, O. Sweet Sugar, O. Kaizumic Delight and O. Sharry Baby. Three STS markers (P03A, P03B and P10) were successfully identified to differentiate the three hybrids (O. Gower Ramsey, O. Sweet Sugar, and O. Sharry Baby) and three cultivars of O. Sweet Sugar (‘Angel’, ‘Emperor’ and ‘Million Coin’). In conclusion, STS molecular markers, developed through AFLP fingerprinting, could prove useful to distinguish new cultivars of Oncidium orchid.

Application of furanyl carbamate cycloadditions toward the synthesis of hexahydroindolinone alkaloids.

A convenient synthesis of various substituted hexahydroindolinones has been achieved by an intramolecular Diels--Alder cycloaddition reaction (IMDAF) of furanyl carbamates bearing tethered alkenyl groups. The initially formed [4 + 2]-cycloadduct undergoes nitrogen-assisted ring opening followed by deprotonation of the resulting zwitterion to give the rearranged ketone. The stereochemical outcome of the IMDAF cycloaddition has the sidearm of the tethered alkenyl group oriented syn with respect to the oxygen bridge. A synthetic route to (+/-)-mesembrane and (+/-)-crinane was accomplished using this methodology. It was possible to carry out a stereoselective reduction of the initially formed hexahydroindolinone ring to produce the cis-3a-aryl-hydroindole skeleton. A related [4 + 2]-cycloaddition/rearrangement sequence was also used for a formal synthesis of the Chinese ornamental orchid (+/-)-dendrobine. The tricyclic alkaloid core was formed stereoselectivity from the thermolysis of N-[(2-methyl-2-cyclopentenyl)methyl]-N-(4-isopropyl-furan-2-yl)carbamic acid tert-butyl ester. Kende's advanced intermediate 33 was prepared in seven additional steps by standard transformations, thereby completing a formal synthesis of (+/-)-dendrobine.