Archives - Allelopathy Journal

We evaluated the effects of aqueous extracts of H. bacciferum root, leaves and inflorescences on seed germination and seedling growth of maize and faba bean and identified the Allelochemicals using GC-MS. The seed germination of both test plants was inhibited and the lower germination was recorded at the highest extract concentration (75%). Maize was more sensitive to the phytotoxicity of the tested soluble extracts than faba bean. Root extract was more toxic to seed germination followed by leaves and inflorescences extracts. Similar trend was observed for radical and plumule length and seedling dry biomass of both test plants. The maize was more sensitive than faba bean and root extract was the most toxic. In GC-MS analysis, 19-compounds were identified in each H. bacciferum extract and classified into 4-classes (alkaloids, phenols, organic acids and flavonoids). In root extract, the major constituents were phenols (78.13%). While in leaves and inflorescences extracts, alkaloids were more dominant 33.787% and 24.79%, respectively. As a total relative values, roots had the highest 86% content compared to 45% in leaves and inflorescences. This is the first report on the allelochemicals constituents of H. bacciferum.

The Charles Elton?s book „The Ecology of Invasions by Animals and Plants?, started the systematic study of biological invasions. The biological invasions have attracted much attention and now the Invasion Ecology has become an important multi-disciplinary subfield of ecology. Allelopathy plays an important role in many aspects of plant invasion and is regarded as a novel weapon in plant invasion. Most studies on invasiveness of exotic species and ecological impacts of invasive plants, are associated with allelopathy. In recent years, more attention is paid to understand resistance of native species to invasive plants through allelopathy and on how to control or manage the invasive plants and restore the invaded ecosystem through allelopathy.

Allelopathy plays important role in many aspects of plants invasion (plant invasiveness, resistance to invasive plants of native community and control of invasive plants). There is urgent need to understand the integrative role of allelopathy in plant invasion, resistance of native community and management/ control of invasive plants. This review summarizes the role of allelopathy in plant invasion: (i). Facilitating the exotic plant invasion as indicated by “Novel Weapon” hypothesis, (ii). Used by native plants as weapon against invasive plants, (iii). Its potential to control exotic plant invasion by regulating the native species allelopathic effects on invasive species. It is crucial for the ecological restoration of invaded communities, to understand how the allelopathic effects of invasive and native plants counteract and which allelochemicals produced by natives are effective against invasive plants. We suggest that exotic plants invasion may be controlled by eliminating the allelopathic effects of invasive species or by enhancing the allelopathic effect of native species

Allelopathy helps in the success of some invasive plants (i.e. Novel Weapons Hypothesis). The invasive plants exert allelopathic inhibitory effects on natives, but it is unclear, how the invaders are affected by the allelochemicals released by native plants. We have developed a GC-MS based approach to analyze the phenolic acids in forest soil and their allelopathic effects on three worst invasive plants (Ipomoea triloba L., Mikania micrantha Kunth and Wedelia trilobata (L.) Hitchc.) in South China. We identified eight phenolic compounds (benzoic acid, p-hydroxybenzal- dehyde, trans-cinnamic acid, p-hydroxybenzoic acid, vanillic acid, 3,4-dihydroxybenzoic acid, p-coumaric acid and ferulic acid) in the forest soil, and found that individual phenolic acids were seldom strong enough to effectively inhibit the growth of invasive plants, however, their mixtures had inhibitory effects on invaders. Our work provides an evidence, how the native forest community resists the exotic plant invasion through allelopathy.

During the screening of soil microorganisms with potential allelopathic activity, a fungus strain H13 Aspergillus flavus was isolated from Solanum rostratum Dunal. invaded soil, it was identified as per its morphological characteristics and ITS region of rDNA. The PDB (Potato Dextrose Broth) fermentation broth of H13 was extracted by ethyl acetate and subjected to column chromatography purification procedure, which led to the isolation of 5-hydroxy-2-hydroxymethyl4H-pyran-4-one (kojic acid) as the most active compound. In Bioassay, the kojic acid at low concentration (2 µg/ml) stimulated (<15%) the receiver plants (Amaranthus retroflexus L., Thlaspi arvense L. and Poa annua L.) but was inhibitory at higher concentrations (10~1000 µg/ml) in a dose-dependent manner. At 1 mg/ml concentration the seed germination of T. arvense was completely inhibited, while the root and shoot length of A. retroflexus and Poa annua were reduced to 36.4% and 49.6%, and 3.6%, 79.4% of the control, respectively. Pyrosequencing analysis results indicated that Aspergillus flavus and other Aspegillus fungi significantly increased in the invaded soil, and the possible physiological and ecological consequences of this phenomenon are worth further investigation

To find the relationship between different pathways of diterpenoid biosynthesis and rice allelopathic effects, two over-expressed transgenic lines oe-OsCPS2 and oe-OsCPS4 were developed. Over-expression of OsCPS4 led to accumulation of momilactone A and B, and enhanced the inhibitory effects of rice on root growth of lettuce seedlings. Over-expression of OsCPS2 decreased the accumulation of momilactones and stimulated the lettuce seedlings. qRTPCR analyses demonstrated that over-expressed OsCPS4 down-regulated the OsGA20X2 and OsZEP, but up-regulated the OsIPT4, suggesting that over-expression of OsCPS4 may compromise the biosynthesis of gibberellins and auxins and increased the biosynthesis of abscisic acid

We tested the effects of allelochemicals phytotoxicity from Eugenia dysenterica leaf extracts on the gravitropism in radish and sesame plants. We also investigated the morphoanatomical, ultrastructural aspects of sesame and radish seedlings exposed to E. dysenterica extracts. The roots underwent structural modifications with severe structural abnormalities when exposed to E. dysenterica extracts. Hence, these roots bended upwards, the hypocotyl thickened, root tip malformations and showed early lateral root development. Internally, tissue oxidation, faster damage to xylem and root caps. Furthermore, the gravitropic response of roots was altered due to abnormalities in columella cells ultrastructure. Thus, allelochemicals may interfere with the differentiation and positioning of statoliths, which is a determining factor for a proper gravitropic response in plants.

We evaluated the effects of aqueous and ethanolic extracts from 3-Baccharis species (B. dentata, B. uncinella and B. anomala) on the germination and seedlings growth of Lactuca sativa (model specie) and Bidens pilosa (weed) and by chemical analysis determined the phenolic compounds present in extracts. Aqueous and ethanolic extracts of B. dentata, B. uncinella and B. anomala were tested at 2.5, 5, 7.5 and 10% concentrations. Allelopathic effects of three Baccharis species were variable. The B. pilosa was more sensitive to the extracts than L. sativa and germination was inhibited with ethanolic extracts of B. anomala and B. uncinella from 5 to 10%. Aqueous extract of B. dentata and B. uncinella at 10% concentration reduced the germination of B. pilosa by 80%. The ethanolic extracts of B. uncinella (2.5 to 10%) and B. anomala (5 to 10%) caused 100% mortality of seedlings. Total phenolic compounds were more abundant in aqueous extracts. Amongst the phenolics, catechin was most abundant (1.61 to 6.16 mg g-1 DM) in aqueous and ethanolic extracts of Baccharis species tested. This study showed that Baccharis uncinella may be used as an alternative bioherbicide to control the weeds in agroecosystems

We studied the allelopathic effects of sunflower on the succeeding mungbean crop and also identified and quantified the allelochemicals present in different plant parts of sunflower using HPLC. Phenolic compounds present in leaves of sunflower were : Chlorogenic acid (18.53±0.66 mg/100 g) > trans-ferulic acid (17.96 ±1.15 mg/100 g) > caffeic acid (17.32±1.59 mg/100 g) > vanillic acid (15.34±1.07 mg/100 g), while stem contained trans-ferulic acid (17.92±1.57 mg/100 g) > chlorogenic acid (16.31±0.95 mg/100 g) > vanillic acid (15.15±0.91 mg/100 g) and root contains only trans-ferulic acid (13.6±1.2 mg/100 g). The seed yield of mungbean was significantly higher in fallow-mungbean rotation (716 kg/ha) than in sunflowermungbean sequence (593 kg/ha). Among the sowing periods, the crop sown on June 14 gave significantly higher seed yield (904 kg ha-1) than other sowing dates except June 21 (837 kg ha1). The seed yield of mungbean in fallow-mungbean rotation sown on June 14 was 1038 kg ha-1 than sunflower-mungbean rotation sown on June 14 (770 kg ha-1).

We studied the mechanism of allelopathic effects of fresh persimmon (Diospyros kaki) leaves extract on: (i). seed germination, seedling growth and chlorophyll content of seedlings of receptor plant and (ii). analysed the activity of superoxidedismutase (SOD), peroxidase (POD), catalase (CAT) and root activity of receptor plants and content of malondialdehyde (MDA). The aqueous extracts of persimmon leaves had variable allelopathic effects on the receptor plants. All aqueous extracts significantly inhibited the lettuce and cabbage than control, but only high concentrations (50 mg and 100 mg) were inhibitory to mung bean, millet, rapeseed and corn. The extracts at 100 mg concentration were most inhibitory to lettuce and cabbage than other receptor plants. The growth and development of plants were significantly affected and the roots activity decreased with the increasing extracts concentration. The effects of extracts from persimmon leaves on activities of CAT, SOD, POD and the content of MDA of receptor plants were determined during the lettuce and cabbage seedling growth. The extracts had significant effects on the activities of CAT, SOD and POD in receptor plants, which in vivo first increased and then decreased. Of all the enzymes assayed (SOD, POD, CAT), the SOD and the POD activity cooperated to remove the reactive oxygen radicals. The allelopathy affected the activity of protective-enzymes of receptor plants and broke the structure and function of membrane. So the balance of activate oxygen metabolism was broken, the cell membrane was destroyed and the content of MDA increased.

We investigated (i). the composition of soil bacterial communities in continuous monoculture and rotation in 3-cropping systems (continuous maize monoculture for 3 years, continuous peanut monoculture for 3 years, maize - peanut rotation), (ii). if soil bacterial communities in the rhizosphere were affected by the addition of chemical soil amendments (mixture of biochar and silicon powder) and biological soil amendments (Kuai-rui-song) in continuous monoculture peanut. The Analysis of the V4 16S rRNA gene region on the Illumina MiSeq platform, identified the changes in bacterial diversity and community structure. Although the composition of predominant taxa was similar in all 5-treatments, but there were few differences in the least-abundant phyla such as Synergistetes, Tenericutes, GAL15 and WS2. There were four unique phyla [Synergistetes, GAL15, WS2 and Kazan-3B-28] in peanut fields in continuous monoculture. Four phyla [Tenericutes, WS2, OP3 and FCPU426] were significantly different (p < 0.05) in the peanut monoculture field and in the maize-peanut rotation field. Continuous monoculture with peanut had the highest bacterial community richness, as indicated by high Chao index and Ace index. In maize-peanut rotation, the rhizosphere bacteria belonged to 500 genera. Among the bacteria, Bradyrhizobium, Rhodospirillum, Burkholderia, Candidatus Koribacter, Candidatus, Solibacter and Koribacteraceae were more frequent. Although there was no improvement in bacterial diversity at the generic level, but the addition of soil amendments slightly altered the bacterial diversity than in peanut monoculture and the addition of biological soil amendment was slightly better than the chemical additive.

We assessed the antifungal efficacy of the essential oil and extracts of Daucus carota seeds against Alternaria triticina, Bipolaris sorokiniana and Ustilago segetum var. tritici. The essential oil of carrot seeds was obtained by hydrodistillation of hexane, dichloromethane and methanol by Soxhlet extraction. The major and minor compounds identified in carrot seed oil were carotol (52.73), daucol (5.10), daucene (5.68), (E)-ß-farnesene (5.40), ß-cubebene (3.19), longifolenaldehyde (3.23), ß-elimene (3.23), (E)-caryophyllene (1.22), ß-bisabolene (2.95) etc. The chemical composition of hexane, dichloromethane and methanol extracts was different. Carotol was the common compound in carrot seed essential oil and extracts. Major compounds were isolated from the carrot seed essential oil by column chromatography. Carrot seed essential oil, isolated compounds and extracts had strong inhibitory effects on spore germination of all tested plant pathogens at 100 to 1000 mg/ml concentrations.

In laboratory conditions, we studied the influence of two preparations (i). Formulation based on effective microorganisms (EM) and (ii). Asahi SL biostimulator, applied to winter wheat on the secretion of flavonoids, foraging and development of cereal leaf beetle (Oulema melanopus L.). The level of secretion of flavonoids, induced by the applied preparations and the short-time damage in cereal leaf beetle was evaluated. The undamaged wheat plants grown in soil incorporated with stubble from the previous crop excreted more quantity of flavonoids [expressed as amount of quercetin (0.613 % DM)] than those earlier exposed to cereal leaf beetle (O. melanopus) foraging (0.599 % DM). No significant differences were observed in the foraging and development of O. melanopus in plants treated with EM preparation and Asahi SL biostimulator. The linear correlation coefficients between the level of flavonoids secreted by wheat and the extent of cereal leaf beetle foraging or development were negative and relatively low.

To prevent the schistosomiasis disease is to control the intermediate host (snail, Oncomelania hupensis Gredler). We developed and tested an environment-friendly approach to control this snail by preparing the plant molluscacide, camptothecin granules and tested its molluscacidal activity. Aqueous solution (prepared from dissolved granules) of 0.60 g/L concentration of camptothecin showed 100% molluscacidal effect after submerging the O. hupensis for 4-5 days. It reduced the glycogen content, total protein and liver alanine aminotransferase activity in the treated snails. Camptothecin proved safe to fish, at 1.0 g/L for 96 h or 0.40 g/L concentration for 30 days. It prevented the schistosomiasis in schistosomiasis epidemic area in China by controlling the snails growth, that carry the worms causing schistosomiasis.

We compared the ability of physiological and morphological adaptations of the invasive Bidens pilosa L. and the native Bidens bipinnata L. under different light intensities (LI). The morphological and physiological characteristics of the invasive B. pilosa were compared with B. bipinnata at 3-Light intensities (Control (100% full sunlight), 40% full sunlight and 10% full sunlight) for 64 days. Decreased LI significantly decreased the germination and root and shoot biomasses but significantly increased the leaf biomass of both plant species. Under the same LI the invasive species B. pilosa higher leaf mass ratio (LMR), total leaf area (LA), relative growth rate (RGR), maximum net photosynthesis rate (Pmax), light saturation point (LSP), light compensation point (LCP) and dark respiration (Rd) and lower root mass ratio (RMR), stem mass ratio (SMR) and root mass/crown mass (R/C) than in B. bipinnata. Decrease in LI significantly reduced the photosynthesis efficiency of the non-invasive B. bipinnata compared with the invasive B. pilosa. The higher photosynthetic response of B. pilosa to variable lighting conditions also indicated its better competitive ability. Our results provide key information concerning the effects of light intensity on the growth and photosynthetic characteristics of B. pilosa and B. bipinnata and indicated that former exhibits greater physiological and morphological adaptation to different light intensities, which facilitates its further invasion.

The allelopathy of Heracleum sosnowskyi Manden fruit exudates had variable effects on tested plant species depending on the temperature and duration of the incubation period. Results demonstrated the importance of placement of fruits (incorporated in/on the soil surface) on their allelopathic performances. When fruits covered the soil surface, concentration of octanol, octanal and octyl acetate in the soil was not significant. In contrast, significantly high concentrations of these compounds were detected, when fruits were incorporated in soil. The exudates of H. sosnowskyi fruits had little effects on the radicle growth of Lolium multiflorum and Trifolium repens than on Lactuca sativa and Raphanus sativus seedlings. A strong positive relationship was found between the octanol concentration in the soil and the plant growth inhibition of L. sativa, T. repens and L. multiflorum seedlings, as well as between the octanal concentration and the radicle growth inhibition of L. sativa and L. multiflorum seedlings. Results proved that allelochemicals from the fruits of H. sosnowskyi have the potential to suppress the growth of surrounding plants. However, these inhibitory properties were variable and depended on temperature, temporal factor and fruit placement method in soil.