Archives - Allelopathy Journal

In Laboratotry bioassays, the extracts of 136 plant species (40 families) in Jordan were collected and investigated for their phytotoxicities on wheat (Triticum durum L. cv. Stork). All aqueous extracts reduced the wheat seed germination and shoot (except Smilax aspera L.) and root growth (except Launaea nudicaulis (L.) Hook.) than control. There was variability in the effects of extracts on wheat. Some completely prevented or severely reduced the crop seed germination, inhibited seedlings growth and imbalanced shoot/root growth ratio. Extracts of Ranunculus arvensis L., Sinapis arvensis L., Ecballium elaterium (L.) A. Rich., Crambe orientalis L., Salvia syriaca L., Rumex cyperius Murb., Calotropis procera Ait. Fit and Aristolochia maurorum L. completely prevented the wheat seed germination. In contrast, S. aspera extract stimulated the shoot and root growth and that of Launea nudicaulis stimulated the root growth of wheat seedlings than control. In general, the effects of extracts were more pronounced on roots than on shoots and the severity of phytotoxic effects was plant species-dependent. The different extracts had variable effects on shoots and roots growth and on shoot/root ratio.

In green house, the effects of rice residue and water deficit were evaluated on accumulation of proline in leaves of wheat (Triticum aestivum L.). Different doses of rice residues were applied to wheat with or without water deficit. The activities of enzymes involved in proline metabolism (glutamate dehydrogenase, pyrroline-5-carboxylate synthetase, pyrroline-5-carboxylate reductase and ornithine-δ-aminotransferase) were significantly enhanced in the leaves under allelopathic stress with and without water deficit, while the activities of proline dehydrogenase decreased with increase in stress. This study showed that crop residues and drought stress enhanced the proline levels in wheat seedlings with glutamate pathway playing the dominant role.

Under the laboratory conditions, we evaluated the effects of ginsenosides extracted from the Panax ginseng on development and life span parameters of Asiatic corn borer (ACB), Ostrinia furnacalis. Five concentrations of ginsenosides at 0, 1, 5, 10, 20 and 40 mg/g were fed with artificial diet to different life stages of O. furnacalis. The O. furnacalis fed on higher concentration (40 mg/g) of ginsenosides had significantly longer developmental time (3.2 d longer) than control. While, the immature survival decreased significantly (42.94 % lower) than control, particularly the 3rd instar. The ovipositional period and the adult longevity were shortened and fecundity of female O. furnacalis adult was decreased, with the increase in total ginsenosides concentration. Furthermore, when fed on 40 mg/g ginisenosides, the net reproductive (R0), intrinsic increase rate (rm) and finite increase rate (λ) of O. furnacalis were 43, 25 and 22 % lower respectively than control. The mean generation time (T) and population doubling time (DT) were significantly longer (20 and 33 %, respectively) than control. Our results indicated that ginsenosides effectively inhibited population and development of O. furnacalis.

The 4, 8-Dihydroxy-1-tetralone (4, 8-DHT) exert allelopathic effects as an allelochemical on various plant species. To evaluate the toxicity of 4, 8-DHT enantiomers to plants and promote the use of pure active enantiomers, a direct high-performance liquid chromatography (HPLC) method for enantio-separation of 4, 8-DHT with coated cellulose tris (3,5-dimethyl-phenylcarbamate) (CDMPC) chiral stationary phase (CSP) was developed. The satisfactory enantio-separation was done by using the mobile phase consisting of a mixture of n-hexane and iso-propanol (95:5, v/v) containing 0.1% acetic acid (AcA) under a flow rate of 0.8 mL·min-1 at 200C. The calibration ranges of quantification for (R)-(-) regiolone and (S)-(+) isosclerone were 10-150 and 10-90 μg·mL-1, respectively. The limit of detection (LOD) and limit of quantitation (LOQ) of the (R)-(-) regiolone and (S)-(+) isosclerone were 0.86 μg·mL-1, 2.9 μg·mL-1 and 0.97 μg·mL-1, 3.4 μg·mL-1 for the 20 μL of injection volume, respectively. All the validation results of quantitative determination methods were satisfactory. The proposed method was successfully used to separate the (R)-(-) regiolone and (S)-(+) isosclerone from 4, 8-DHT.

This study evaluated the allelopathic activity of ethanol extracts from the roots, root bark, stems and stem bark of C. pachystachya on seed germination and seedling growth of Lactuca sativa. The ethanol extracts were prepared from dried powdered plant parts and dissolved in solvent mixture water and DMSO (0.1%). The concentration of each extract was calculated according to its solubility. The chemical composition of extract was determined using HPLC-DAD analysis. All extracts had allelopathic effects on lettuce seed germination and seedling growth. Stem and root bark extracts were very inhibitory to the development of radicle; the stem extract was also inhibitory to the development of hypocotyl. The stem bark and stem extracts were very inhibitory to germination. Chromatographic analysis showed the presence of quercetin, catechin and tormentic acid in the root, epicatechin and tormentic acid in the root bark, catechin, quercetin and tormentic acid in the stem and quercetin and tormentic acid in the stem bark extracts. At the tested concentrations, only epi-catechin and catechin inhibited the radicle development.

Under laboratory conditions, we assayed the phytotoxic potential of L. leucocephala seed leachates from (1 to 5 d after start of imbibitions) on germination and seedling growth of tomato (Solanum lycopersicum L.) and rice (Oryza sativa L.). The chemical composition of L. leucocephala seed leachates was also determined. The L. leucocephala seed leachates did not affect the germination, while root and shoot lengths were significantly reduced. In the beginning of imbibition the mimosine, abscisic acid, sugars, phenolics, proteins and amino acids were found in L. leucocephala seed leachates. The mimosine was very inhibitory to seedling growth of tomato than rice. The presence of mimosine in seed leachates could explain the high toxicity of L. leucocephala on the development of assayed crops.

The Festuceto-Potentilletum arenariae steppe community is dominated by Festuca vallesiaca Schleich. We investigated its allelopathic influences on seed germination and seedling growth of neighbouring plants (Cynodon dactylon and Lolium perenne), by determining the amount of total phenolics and phenolic acids in the aboveground parts of F. vallesiaca, litter and soil. An aqueous extract of the aboveground parts of F. vallesiaca, hydroponic growth solution in which F. vallesiaca grew, root exudates, its litter, soil and the phenolic-containing fraction from the soil inhibited the seed germination and seedling growth of neighbouring plants. Total phenolic compounds contents followed the order: vegetative F. vallesiaca parts > litter > soil. The same phenolic acids detected in the aboveground parts of the dominant F. vallesiaca were also found in plant litter and soil, but in significantly lower amounts. Phenolics produced in its tissue accumulated in the litter and soil, reaching toxic concentrations, thus inhibiting the seed germination and seedling growth. In addition to other ecological factors, the dominance of F. vallesiaca mainly resulted from its negative allelopathic effects on other species due to the synthesis and secretion of phenolics, which accumulate in the litter and soil.

We studied the allelopathic effects of Artemisia sacrorum on vegetation succession in typical grassland on Yunwu Mountain. The effects of root exudates, rhizosphere soil extracts and leaf and stem extracts from A. sacrorum were assayed on seed germination, radicle length, and coleoptile length of 4-dominant grassland species (Stipa bungeana, S. grandis, Thymus mongolicus, and Leymus secalinus) and for autotoxicity on A. sacrorum. The grassland species showed different responses to the extracts and root exudates of A. sacrocum. At the same concentration, the methanol extracts had greater effects on Acceptor planta than aqueous extracts. The effects of the alkaloids obtained from A. sacrorum leaf and stem extracts were significantly differed than other fractions. Our results suggested that allelopathy of A. sacrorum shapes the botanical composition of grasslands on Yunwu Mountain.

We investigated the chemical composition and phytotoxicity of essential oils isolated from different Malaysian local plants, [Cupressus macrocarpa Hartweg, Murraya koenigii (L.) Spreng, Plectranthus amboinicus (L.) Spreng, Persicaria odorata (L.) Sojak, and Pelargonium radula (Cav.)] against major weeds [Amaranthus hybridus (L.) (Dicot) and Dactyloctenium austral (L.)(Monocot)]. Gas chromatography-Flame ionization detector (GC-FID) and Gas chromatography-Mass spectrometry (GC-MS) analyses showed qualitative and quantitative differences in the Chemical composition of essential oils. The essential oils from C. macrocarpa and P. radula inhibited the seed germination and suppressed the seedling development of both weeds than oils from other plants. The essential oils at 5 µL/ml concentration significantly suppressed the seed germination. We explored the phytotoxicity mechanism in terms of chlorophyll content, relative electrolyte leakage and cellular respiration. Essential oils with high content of monoterpenes were most inhibitory. Results showed that C. macrocarpa and P. radula essential oils could be used as effective and safe alternative to conventional synthetic herbicides to control D. australe and A. hybridus weeds.

Growth and development of Arabidopsis thaliana seedlings treated with the essential oil component citral have been severely affected. We analyzed whether citral can enter and accumulate into the roots and we found that it interferes with the plant metabolism accumulating mainly in the differentiation zone. Besides, the distribution of stained zones varied with the experimental time.

The combined activities of mixtures of nine phenolic acid autotoxins (PCM), [trans-cinnamic acid, p-coumaric acid, ferulic acid, vanillic acid, vanillin, salicylic acid, syringic acid, benzoic acid and p-hydroxybenzoic acid] were investigated on embryo and seedling growth of American ginseng (Panax quinquefolium L.). Both root and shoot growth of American ginseng embryo were considerably inhibited by PCM at 0.55-4.4 mg/mL concentrations. The PCM solution at 0.02-0.5 mg/mL significantly reduced the ginseng seedlings growth by inhibiting the leaf photosynthesis. However a weak autotoxicity was observed, when plants were grown in soil due to degradation of the applied PCM. Our results demonstrated that phenolic acids are autotoxic against the American ginseng embryo and seedling growth in vitro, but the autotoxicity can be altered by soil conditions.

We investigated the allelopathic effects of wheat crop residues, cadmium and activated charcoal on biophysical and biochemical parameters of Vigna radiata L. Phenolic contents of growing medium increased with increase in dose of residue incorporated in soil and decreased with the addition of activated charcoal. Seed germination and seedlings growth decreased, with increase in dose of added residue. Pigment and protein contents decreased under allelopathic stress. Activated charcoal increased the pigment and protein content of mungbean seedlings. The combined stresses (allelopathic and cadmium stress) incresed the toxic effects of wheat residue and decreased the pigment and protein contents. Residue with and without cadmium increased the sugar and proline contents. The allelopathic and cadmium stress significantly enhanced the malondialdehyde content (MDA) and electrolyte leakage (EL) of mungbean seedlings. Activated charcoal decreased the MDA content and maintained the electrolyte leakage to control level. Both these stresses increased the activities of antioxidant enzymes (superoxide dismutase, catalase, ascorbate peroxidase and guaiacol peroxidase). A dose-dependent increase in ascorbic acid (AsA) and non protein thiol (NPSH) contents was recorded under allelopathic stress alone and allelopathic + cadmium stresses. Cadmium also increased the AsA and NPSH level. However, residues with activated charcoal significantly declined the AsA concentration than only residues. In combined treatments, toxicity increased but the magnitude of increase was lower than toxicity caused by cadmium alone and allelopathic stress alone. Activated charcoal played important role in minimizing the toxicity of residues, as it decreased the phenolic content of incorporated soil residue.

Laboratory and greenhouse experiments were conducted to assess the allelopathic potential of Leucaena leucocephala leaf and seed on the germination and growth of Ageratum conyzoides, Tridax procumbens and Emilia sonchifolia. The allelopathic activity of L. leucocephala was evaluated using the Sandwich Method, Dish Pack Method and Plant Box Method. The germination, root growth, hypocotyl growth and fresh weight of A. conyzoides, T. procumbens and E. sonchifolia decreased with increasing concentrations of L. leucocephala leaf and seed debris incorporated into the soil. At the highest concentration (66.7 g/L) of aqueous seed extract the germination of A. conyzoides, T. procumbens and E. sonchifolia was reduced by 74%, 76% and 75% of the control, respectively. Leaf and seed litter leachate showed strong inhibitory activity on the radicle growth of A. conyzoides, T. procumbens sand E. sonchifolia. Root exudates of L. leucocephala also inhibited the root growth of T. procumbens. Thus L. leucocephala leaf, seed and root proved allelopathic to germination and seedling growth of the tested bioassay species.

We investigated the effects of four Larix gmelini (larch) phenolic acids (2, 4-2 hydroxy benzoic acid, 7-hydroxyl coumarin, ferulic acid, abietic acid) on soil phospholipid fatty acid (PLFA) composition in Fraxinus mandshurica (Manchurian ash) soil. Sixteen combinations of 4- phenolic acids of larch rhizosphere and bulk soil were added to one year old Manchurian ash seedling pot cultured soil during Spring, Summer and Autumn 2011. We found that some of the larch rhizosphere and bulk phenolic acids combinations out of 16 groups acted as allelochemicals which stimulated and inhibited the Manchurian ash seedlings and microbial biomass of the soil. Larch rhizosphere phenolic acids combination significantly increased the seedling biomass and microbial biomass than control.. Specific phenolic acids were responsible to affect the abundance of specific microbe in the soil. Thus some phenolic acids in larch rhizosphere soil have stimulatory potential, which improved the productivity of Manchurian ash in inter-planting with larch. It is thus concluded from the experiment that the establishment and management of Manchurian ash can be improved by inter-planting with larch in northeast of China.

We studied the allelopathic potential of Nepeta rtanjensis Diklić and Milojević essential oil and pure α- and β-pinene on seed germination of 4-crops (Lepidium sativum L., Lactuca sativa L. cv. ‘May Queen’, Lotus corniculatus L. cv. Bokor and Brassica napus L. cv. napus) and 3-weed species (Stellaria media (L.) Vill., Rumex crispus L. and Arabidopsis thaliana (L.) Heynh. ecotype Columbia). Nepetalactones are dominant compounds in essential oil of N. rtanjensis (88%), while α- and β- pinene were present in low concentrations (3% and 0.4%, respectively). We found the species-specific and dose-dependent effects of essential oils and pure compounds on seed germination of test species. Among tested crops, L. sativa proved to be the most sensitive, while B. napus was most tolerant to both essential oil and pure monoterpenoids. S. media weed was the most susceptible, while R. crispus was most tolerant. Due to its high allelopathic potential, of nepetalactones, N. rtanjensis essential oil could be developed as promising natural bioherbicide to control weeds.

Truffles (Tuber sp.) are the underground ectomycorrhizal fungi associated with numerous trees and shrubs. They produce metabolites, which interacts with plants. More than 200 volatile organic compounds (VOCs) and many non-volatile compounds have been identified from various truffles. The VOCs are mixtures of alcohols, aldehydes, acids, ethers, esters, ketones, terpenes, thiols, sulfur compounds, terpenoids and phenolics. The metabolites released by truffles in the rhizosphere are involved not only in host-plant interaction but also in other interactions viz., defence or competition with other organisms. Some metabolites are phytotoxic to non-host plants in the barren zone around or near the host plant, where the vegetative cover is scarce. The volatiles released by the fruiting bodies inhibited the development (seed germination, root morphogenesis, plant hormonal balance, hypocotyl leaves size, and also induce strong bleaching of the seedlings) of neighbouring plants. In the barren zone, there is high toxicity from native rhizospheric microflora as indicated by the inhibition.