Determination of the Allelopathic Potential of Cambodia’s Medicinal Plants Using the Dish Pack Method

Plants produce several chemically diverse bioactive substances that may influence the growth and development of other organisms when released into the environment in a phenomenon called allelopathy. Several of these allelopathic species also have reported medicinal properties. In this study, the potential allelopathic effects of more than a hundred medicinal plants from Cambodia were tested using the dish pack method. The dish pack bioassay method specifically targets volatile allelochemicals. Twenty-five species were found to have significant inhibitory effects on lettuce radicle growth. Eleven different plant families, including Iridaceae (2), Apocynaceae (2), Poaceae (2), Sapindaceae, Araceae, Combretaceae, Orchidaceae, Clusiaceae, Zingiberaceae, Rutaceae and Asparagaceae had the plant species with high inhibitory effects. Allophyllus serrulatus had the highest growth inhibitory effect on lettuce radicles more than 60%, followed by Alocasia macrorrhiza, Iris pallida, Terminalia triptera, Wrightia tomentosa, Cymbidium aloifolium, Garcinia villersiana and Kaempferia parviflora. The candidate species were subjected to further studies to identify the volatile allelochemicals in the volatile constituents.

Detection and Characterization of Antibacterial Siderophores Secreted by Endophytic Fungi from Cymbidium aloifolium

Endophytic fungi from orchid plants are reported to secrete secondary metabolites which include bioactive antimicrobial siderophores. In this study endophytic fungi capable of secreting siderophores were isolated from Cymbidium aloifolium, a medicinal orchid plant. The isolated extracellular siderophores from orchidaceous fungi act as chelating agents forming soluble complexes with Fe3+. The 60% endophytic fungi of Cymbidium aloifolium produced hydroxamate siderophore on CAS agar. The highest siderophore percentage was 57% in Penicillium chrysogenum (CAL1), 49% in Aspergillus sydowii (CAR12), 46% in Aspergillus terreus (CAR14) by CAS liquid assay. The optimum culture parameters for siderophore production were 30 °C, pH 6.5, maltose and ammonium nitrate and the highest resulting siderophore content was 73% in P. chrysogenum. The total protein content of solvent-purified siderophore increased four-fold compared with crude filtrate. The percent Fe3+ scavenged was detected by atomic absorption spectra analysis and the highest scavenging value was 83% by P. chrysogenum. Thin layer chromatography of purified P. chrysogenum siderophore showed a wine-colored spot with Rf value of 0.54. HPLC peaks with Rts of 10.5 and 12.5 min were obtained for iron-free and iron-bound P. chrysogenum siderophore, respectively. The iron-free P. chrysogenum siderophore revealed an exact mass-to-charge ratio (m/z) of 400.46 and iron-bound P. chrysogenum siderophore revealed a m/z of 453.35. The solvent-extracted siderophores inhibited the virulent plant pathogens Ralstonia solanacearum, that causes bacterial wilt in groundnut and Xanthomonas oryzae pv. oryzae which causes bacterial blight disease in rice. Thus, bioactive siderophore-producing endophytic P. chrysogenum can be exploited in the form of formulations for development of resistance against other phytopathogens in crop plants.

Diversity of Epiphytic Orchids, Hoya, Dischidia and Phorophytes (Host Trees) in Bawean Island Nature Reserve and Wildlife Reserve, East Java, Indonesia

Bawean Island is a small island located between two islands (Java and Borneo). Geographically, the diversity of plants, especially epiphytic plants on this island is very interesting to be studied. This research aims to investigate the diversity of epiphytic plants, focussing on epiphytic orchids, Hoya and Dischidia in Bawean Island Nature Reserve and Wildlife Reserve. It was conducted through an inventory of epiphytic orchids and hoya growing on host trees. The results showed there were 10 species of epiphytic orchid and 3 species of epiphytic Hoya, and 1 species of Dischidia growing on-location studies. The epiphytic orchids which found in location studies included Phalaenopsis amabilis, Aerides odorata, Cymbidium aloifolium, Dendrobium anosmum, Rhynchostylis retusa, Liparis condylobulbon, Taeniophyllum biocellatum, Cymbidium sp., Eria sp. Orchid species that most often found in the study location was Phalaenopsis amabilis. In addition, this study recorded Taeniophyllum biocellatum as an endemic orchid from Java that was found on this island. The epiphytic Hoya recorded in there, i.e. Hoya diversifolia, H. verticillata, and H. amoena, and also only found 1 species of Dischidia was Dischidia imbricata. There were 12 species of trees as the host trees of epiphytic, i.e. Irvingia malayana, Tectona grandis, Diospyros buxyfolius were the host trees frequently found as the host of the epiphytic plant. Zone 3 as an area of 1/3 basal part of a total length of the branches was the most preferred zone by epiphytic orchids and hoya. The epiphytic orchid and hoya hardly found in Zone 5.