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.

A Review on the Nematicidal Activity of Volatile Allelochemicals against the Pinewood Nematode

The pinewood nematode (PWN), Bursaphelenchus xylophilus, induces shoot yellowing and wilting by injuring pine vascular tissues and resin canals. In Asia, it has devastated wide forests of susceptible pine with drastic ecological, economic and cultural repercussions. In 1999, it reached Europe (Portugal) and despite the actions of the authorities, it rapidly advanced to the border areas of Spain, threatening other European pine forests. Chemical control has been used in Asia with remarkable success, yet most nematicides are dangerous to human health and the environment. Natural volatile allelochemicals (VA) and derivatives are sustainable alternatives, providing many advantages to commercial nematicides. The present work summarizes available bibliographic information on VAs with activity against the PWN and reviews the chemical properties leading to nematoxicity. Published works have reported over 250 VAs in direct contact assays. Compounds highly active against the PWN belong to monoterpenoid, phenylpropanoid and aliphatic alcohols; aldehydes, ketones, carboxylic acids, esters and sulphide groups. The presence of highly electronegative elements in these structures appears to increase activity. Trisulphides, coumarins, medium carbon chain length aliphatic alcohols and derivatives comprise the top five most active allelochemicals. An indication of their mechanisms of action can be obtained from studying the reported structure–activity relationships.

Evaluation of Potential Volatile Allelopathic Plants from Bangladesh, with Sapindus mukorossi as a Candidate Species

This study focuses on identifying volatile emissions from plants with potential plant growth inhibitory activity. The aim of this study was to evaluate plant species from the Asian country Bangladesh for new, potential volatile allelopathic species. A total of 103 plant samples from 40 different families were assessed with the dish pack (DP) method. About 25% of the evaluated plant samples influenced (inhibited or stimulated) the growth of lettuce, due to the presence of potentially volatile allelochemicals. The pericarp of Sapindus mukorossi Gaertn. caused the lowest radicle elongation (3% of control) of the lettuce. This was followed by the leaves of Cassia nodosa Roxb. (34.4%) and the root of Kaempferia galangal L. (43.4%), in that order. Therefore, the pericarp of S. mukorossi is reported from this study as a new potential volatile allelopathic species. On the contrary, the leaves of Gynostemma pentaphyllum Thunb. had a stimulatory effect on the hypocotyl elongation of lettuce seedlings (156% of control). The single petri dish (SPD), a new method, was also adapted to justify the potentiality of the growth control of particular allelopathic species. This study revealed that the new potentially volatile allelopathic plant species could be further explored in sustainable weed management.

Identification of Volatile Compounds Released by Leaves of the Invasive Plant Croftonweed (Ageratina adenophora, Compositae), and their Inhibition of Rice Seedling Growth

Several volatile allelochemicals were identified and characterized from fresh leaf tissues of the invasive croftonweed. A simple bioassay was used to demonstrate the release of volatile allelochemicals from leaf tissues. The bioassays revealed that foliar volatile components of croftonweed exhibited significant effects on the seedling growth of upland rice. Peroxidase (POD) activity, superoxide dismutase (SOD) activity, and root oxidizability rose as the concentration of volatiles increased. Activity for both POD and SOD significantly increased with exposure to 15 g and 20 g of croftonweed leaf tissue for 5 d. Root activity was significant at 10 g compared to the control. The volatile components also stimulated the development of the aerenchyma tissue and inhibited lateral root formation. Leaf volatiles of croftonweed were identified by gas chromatography coupled with mass spectrometry (GC–MS). Some of the compounds identified included α-phellandrene, camphene, ρ-cymene, 2-carene, α-pinene, limonene, and (z)-3-hexen-1-ol. Bioassays showed that four of these compounds could account for the observed phytotoxicity imparted by total leaf volatiles. Limonene, 2-carene, α-pinene and camphene had no phytotoxic effect on shoot elongation. Phellandrene did cause inhibition in shoot growth at all concentrations. Both (z)-3-hexene-1-ol and ρ-cymene inhibited both shoot elongation and root elongation, but the effects of the two compounds on root length were more significant than on the shoot length.