Archives - Allelopathy Journal

As a survival and resource-competition strategy, submerged macrophytes are supposed to release the secondary metabolites, named allelochemicals, to affect phytoplankton development. The species-specific inhibition and easy degradation of plant allelochemicals make them possible to control the algal bloom efficiently and environment-friendly. This paper aims to review the research advances in allelopathy of submerged macrophytes on phytoplankton, which covers the following aspects: species-specific inhibition of submerged macrophytes to phytoplankton, potential allelochemicals, their inhibitory modes, physiological mechanisms, impacts of environmental factors and possibility of application in water management. Research methodology on allelopathy needs to be improved from the viewpoint of ecology. It is proposed to do more comparable bioassays, more joint laboratory and field experiments to figure out release and degradation dynamics of allelochemicals and their interactions with biotic and abiotic factors, which will be helpful to reveal the allelopathic mechanisms from gene to ecology, and provide scientific guidance for its application in aquatic ecosystem management.

We determined the chemical composition and allelopathic activity of the essential oil from Euphorbia maculata L. and to study the bioactivity of allelopathic constituents against Lolium perenne, Clitoria ternata, Portulaca oleracea and Amaranthus viridis. Results showed that 47 components were identified in the essential oil. Based on bioactivity-guided fractionation, the main active constituent was isolated and its structure was determined as diphenylamine (29.41%) by high-resolution electrospray ionization mass spectrometry and 1D nuclear magnetic resonance techniques. Both the essential oil and diphenylamine exhibited allelopathic activity. The essential oil at 0.2% (w/v) concentration inhibited the seed germination and seeding growth of Clitoria ternatea, Portulaca oleracea and Amaranthus viridis, but slightly stimulated the germination and growth of Lolium perenne weed. The bioactivity analysis of the isolated compound showed that diphenylamine and the oil at the same concentration significantly inhibited the seed germination and seedling growth of these four weeds. Thus essential oil from E. maculata inhibited the germination and growth of test weeds, hence, could be used for weeds control.

To clarify the confusion about the contents of phenolic acids in allelopathic and non-allelopathic rice accessions, various methods [4-Aminoantipyrine (4-AAP) method, Folin-Ciocalteu (FC) method, and Solid-Phase Extraction/High Performance Liquid Chromatography (SPE-HPLC)] were used. In 4-AAP method, three benzoic acid derivatives (p-hydroxybenzoic, vanillic, and syringic acid) had 29.3% - 51.2% recoveries and two were below 5% recoveries. Three cinnamic acid derivatives (caffeic, ferulic, and p-coumaric acids) gave < 4% recoveries. The recoveries of these phenolic compounds by FC method varied from 43.3% to 168.1%. The total contents of phenolic compounds at 3- 7 leaf stages were always significantly higher in the culture solution of allelopathic rice PI312777 than non-allelopathic rice Lemont. The maximum content was 710 µg/plant in the culture solution of PI312777 at the 6-leaf stage, significantly higher than 10 µg/plant/day, reported earlier by 4-AAP method. Besides, at 3- 7 leaf stages, the total contents of 7 phenolic acids exuded were significantly higher by PI312777 than Lemont. These results supported our suspicion that both benzoic acid and cinnamic acid derivatives cannot be determined accurately by the 4-AAP method. We suggested that the phenolic acids are the principal components in rice allelopathy.

We isolated and identified from the methanol extract of Oryza sativa straw, 4-new constituents: vanillic acid-4-O-β-D-glucopyranosyl-6'-octadec-9''-enoate (I), vanillic acid-4-O-β-D-glucopyranosyl -(6'→1'')-6'-O-β-D- glucopyranosyl-(6''→1''')-6''-O-β-D-glucopyranosyl-2'''-n-eicosanoate (II), β-D-arabinopyranosyl-(2a→1b)-2a-O-β-D-arabinopyranosyl-(2b→1c)-2b-O-β-D-arabinopyranosyl-(2c→ 1d)-2c-O-β-D-arabinopyranosyl-4a, 4b, 4c, 4d tetra-oleate (III) and β-D-glucopyranosido-1, 6-dioleate (IV). The structures of the new compounds were elucidated with spectroscopic techniques in combination with IR, ESI-MS and HRESI-FTMS. In bioassays with blue-green algae, the efficacies of the algicidal activities of these four new compounds (I-IV) were evaluated at 1, 10, and 100 mg.L-1 concentrations. Compounds II and IV were most inhibitory to the growth (95.2 ± 0.2 and 94.0 ± 0.9 %) of Microcystis aeruginosa UTEX 2388 at 100 ppm (mg.L-1) concentration. Especially the compound IV was more inhibitory to M. aeruginosa growth at the wide range of concentrations (1-100 ppm) than compounds I-III. Thus Compound IV has great potential for the eco-friendly control of weeds and harmful algae in water-logged rice.

By high performance liquid chromatography (HPLC) we determined the content of 6-phenolic acids (p-hydroxybenzoic acid, caffeic acid, p-coumaric acid, chlorogenic acid, ferulic acid and cinnamic acid) in fresh aerial parts and roots of 10-cultivars of alfalfa. The results showed that the concentrations and compositions of phenolic acids depended on the aerial part or roots of alfalfa. Bioassays were conducted with leaf litter leachates from all these cultivars on the seeding growth of Festuca arundinace and Sorghum sudanense. The growth of F. arundinace and S. sudanense was inhibited variably by different cultivars of alfalfa. At 50 mg/mL, the inhibitory effects of leaf litter leachates were higher on roots than on shoots. Our results demonstrate that the content of phenolic compounds and the allelopathic potential of 10-cultivars of alfalfa are differed from each other.

We conducted laboratory bioassay and pot experiments to find the difference in the allelopathic potentials of aqueous root leachates from 4-dominant tree species (Quercus acutissima Carruth., Robinia pseudoacacia L., Pinus thunbergii Parl. and Amorpha fruticosa L.) on seed germination and seedling growth of Rhus typhina L. in hills of Shandong Peninsula. All tree species root leachates inhibited the seed germination of R. typhina over the control (distilled water), except the P. thunbergii. Besides reducing the seed germination, Q. acutissima root leachates also significantly suppressed the root and shoot length of R. typhina seedlings. The pot experiments found that compared to the control group, the total biomass of R. typhina was significantly increased by low concentration (0.025 g/ml) aqueous root leachates from A. fruticosa. Our previous field investigations revealed that R. typhina rarely invades the Q. acutissima forests, possibly because of its allelopathic inhibition by Q. acutissima. The naturalized exotic species, such as A. fruticosa, share the same origin in North America with R. typhina. The R. typhina seedlings are less inhibited by A. fruticosa, possibly because of their allelopathic adaptability. The results showed that allelopathy plays role in the formation of community resistance to invasion.

This study aimed to examine the allelopathic potential of Eucalyptus and Calotropis species on seed germination and seedling growth of Acacia ehrenbergiana (Hayne), Acacia gerrardii (Benth.) and Acacia tortilis (Forssk.). The aqueous leaf extracts of Eucalyptus camaldulensis var. obtusa (Blakely), E. intertexta (R.T.Baker), and Calotropis procera (Aiton) inhibited the seed germination, reduced the seedlings growth, biomass yield and biomass allocation in Acacia species. It suggests the further testing at farmers’ fields to determine the allelopathic effects of Eucalyptus and Calotropis as invasive species in woodlands in central Saudi Arabia.

Although 4-hydroxybenzoic acid (4-HBA) is a model allelochemical for many plants, its biotransformation is still unexplored. Sixty grapevine (Vitis vinifera L.) rhizosphere soil samples (sterilized and non-sterilized) with 4-HBA (12C unlabeled or 13C labeled) were analyzed at 0, 0.5, 1, 2, 4, 6, 24, 50, and 68 h after incubation. Fourier transform ion cyclotron resonance mass spectrometry, combined with stable isotope probing technology data, showed that 4-HBA could be biotransformed into dimers, which was previously not known to occur, and that the allelopathic activity of 4-HBA might be maintained by depolymerization and dimer concentration. These dimers might be rapidly adsorbed or used by microbes and are a possible reason for grapevine soil autotoxicity. Hence, this study lays the foundation for future studies on phenolic acid allelochemicals, which will contribute to decipher the actively maintained allelopathy of grapevine soils and reduce its negative effects on grape and wine industries.

ABSTRACTExtraction, thin layer chromatography, and gas chromatography-mass spectrometry of leaf surface waxes of Polygonum orientale L. (Polygonaceae) weed revealed 16, 19 and 15 n-alkanes between n-C15 and n-C33 in the young, mature and senescent leaves, respectively. In the young, mature and senescent leaves, the predominant alkanes were (heptacosane, nonacosane and nonacosane) were 11.92, 15.95 and 14.83 %, respectively. Heneicosane, dotriacontane and tritriacontane were absent in the young and senescent leaves, whilst eicosane was absent only in the senescent leaves. The role of cuticular alkanes to the female insect, Galerucella placida Baly (Coleoptera: Chrysomelidae) was evaluated in the Y-shaped glass tube olfactometer bioassay under laboratory conditions. The cuticular alkanes from the young, mature and senescent leaves, and the synthetic blends comparable to the cuticular alkanes of three types of leaves were attractive to G. placida at 4, 1-2 and 4 leaf equivalent alkanes, respectively. Females were attracted to the individual synthetic n-C15, n-C16, n-C17, n-C18, n-C20, n-C21, n-C23, n-C24, n-C25, n-C26, n-C28 and n-C31 alkanes at the minimum concentrations of 4, 2, 1, 20, 40, 2, 4, 8, 6, 14, 14 and 50 µg in a dose-dependent bioassay, respectively. A synthetic blend of 1.60, 0.86, 11.90, 17.79, 1.82, 1.54, 12.06, 6.60, 6.55 and 25.45 µg of n-C16, n-C17, n-C18, n-C20, n-C21, n-C23, n-C24,

n-C26, n-C28 and n-C31, respectively, indicated highest attraction of the insect, and provide a basis in developing a lure to monitor field population.

Intercropping is a crucial agroecosystem to alleviate the autotoxicity in crops. For this, 5- crops were tested for their compataibility with muskmelon. Of these, root exudates of fennel (Foeniculum valgare), onion (Allium cepa) and rape (Brassica campestris) inhibited the growth of Fusarium oxysporum f. sp. melonis, and stimulated the seed germination and seedling growth of muskmelon. Field experiments showed that muskmelon + fennel, muskmelon + onion and muskmelon + rape intercropping systems could alleviate the Fusarium wilt. Phenolics in fennel, onion and rape root exudates were detected by HPLC and the benzyl benzoate, dibutyl phthalate and p-tolyl benzoate were identified in all the 3-plants root exudates. These phenolics suppressed the growth of Fusarium oxysporum f. sp. melonis and promoted the growth and development of muskmelon.

The leaf extracts of bamboo (Shibataea chinensis Nakai) and its fractions (Ethyl acetate, n-butanol and water) obtained after extraction with petroleum ether, were assayed on seed germination and seedling growth of lettuce (Lactuca sativa L. var. ramosa Hort.) and cucumber (Cucumis sativus L.). The leaf extract showed the lowest phytotoxic activity, while, the n-butanol fraction was most bioactive on germination and seedling growth of both target plants. A bioassay-guided fractionation of the n-butanol fraction led to the isolation of five phytotoxic compounds. The chemical structures of these substances were elucidated by nuclear magnetic resonance as apigenin (I), quercetin (II), daucosterol (III), 3, 3’, 4’, 5-tetrahydroxy-7-methoxyflavone (IV) and p-methoxybenzoic acid (V). The Quercetin, apigenin and daucosterol were more phytotoxic to germination (IC50=7.26-7.95 ppm), root (IC50= 2.97-6.33 ppm) and shoot elongation (IC50=4.89-7.74 ppm) of lettuce than glyphosate (IC50 values >20 ppm). In cucumber, the p-methoxybenzoic acid showed similar phytotoxic activity (IC50 = 20 ppm, 6.93 ppm, 10.45 ppm, respectively) to glyphosate (IC50=20 ppm, 7.71 ppm, 10.84 ppm, respectively). Our research suggested that the leaves of S. chinensis have potent allelochemicals and their potential as herbicide should be further investigated.

The H2O2 content increased in Fabaceae (pea, vetch and broad bean) plants after aphid herbivory and reached the highest level at 6 h post-infestation. Prolonged aphid feeding decreased the H2O2 content, but it was still higher in infested plants than in control ones. The maximum increase of H2O2 concentration was noted in A. pisum pea plants. A. pisum feeding reduced the CAT activity in infested plants. CAT was inhibited until 48 h after infestation in pea and vetch and until 24 h in broad bean. The pea plants drastically inhibited the CAT. Initial feeding of A. pisum (1 h, 2 h) slightly increased the APX activity in seedlings of pea and broad bean. Thus the changes in enzyme activity were dependent on plant species. The strongest inhibition and induction of APX was noted in tissues of broad bean. Our results indicated that H2O2 and H2O2-scavenging enzymes may play a significant role in the defence mechanisms of Fabaceae plants towards the pea aphid.

In Petri plate Lab. bioassays, we studied the effects of aqueous extracts (0, 5 and 10%) of nettle (Urtica dioica L.), chamomile (Matricaria chamomilla L.) and dandelion (Taraxacum officinale L.) as donor species on germination and seedling growth of wild mustard (Sinapis arvensis L.), common mallow (Malva neglecta Waller.) and canary grass (Phalaris minor Retz.) as recipient species. We found that weed species differed from each other in terms of germination and seedling growth. The aqueous extracts inhibited the seed germination and seedling growth of weeds. The 10% chamomile extract significantly reduced germination percentage, root length and seedling dry weight in all weeds. The effect inhibitory of nettle extract on seed germination and seedling growth was more pronounced than dandelion extract

Root rot of Ginseng caused by Fusarium solani is one of the major factors reducing the yield and quality of ginseng. We determined the inhibitory effects of total ginsenosides present in the stem and leaves of Panax ginseng (TGSL) on the spore germination and growth of F. solani using the disc diffusion method. Spore germination and mycelial growth inhibition were found to be concentration dependant and the EC50 was 3.0377 mg/mL and 3.5302 mg/mL respectively. The TGSL altered the membrane permeability of hyphal cells, adversely affecting the growth

Root knot nematode (Meloidogynae incognita) infestation and low magnesium use efficiency are serious constraints in polyhouse cultivation of cucumber. Novel combination formulations of Tagetes patula root extract containing the nematicidal alpha terthienyl (a-T) and magnesium sulfate were prepared, using the biopolymeric hydrogel as carrier. The test products slowly released the nematicidal a-T with half life (t1/2) of 22.97 and 36.87 days, in water and soil, respectively. Magnesium showed fast release till 3rd Day. Compared with commercial formulations (carbofuran, Furadan 3G®), these formulations showed significantly higher mortality of M. incognita population under in vivo and polyhouse conditions. In 3-months polyhouse study conducted on cucumber crop during 2011-12, the application of formulations containing Mg alone or Mg in combination with root extract significantly increased the crop yield and showed 83% correlation with the magnesium content of leaves. Besides the morphological and physiological parameters of the crop were also improved.

Thirteen genotypes of tuberose (Polianthes tuberosa L.) were evaluated against root knot nematode (Meloidogyne incognita) to understand the relative resistance, phenol and polyphenol oxidase (PPO) activities. Results revealed that Shringar, Suvasini, Prajwal and Phule Rajani were found resistant against M. incognita race 2, had least galls and reduced the nematode population per 200 cm3 soil + 5g root, while Calcutta single, Calcutta double, Vaibhav and Hyderabad double were susceptible. Estimation of phenol and (PPO) content in healthy and infected plant’s roots of 13-tuberose genotypes revealed that nematode infected genotypes (Shringar, Suvasini, Prajwal and Phule rajani) contained high phenol and PPO activities than healthy ones. The high phenol and PPO activities imparted resistance against the M. incognita race 2. While infected Calcutta single, Calcutta double, Vaibhav and Hyderabad double showed low phenol and PPO activity, thus, were susceptible.

We evaluated the potential of essential oil (EO) of basil Ocimum micranthum Willd as an insecticide against whitefly Aleurodicus cocois (Curtis, 1846) (Hemiptera, Aleyrodidae) and determined its chemical composition using GCMS. The E.O. toxicity was analyzed by spraying it on insects present on dwarf cashew seedlings. EO at 1% concentration exhibited the highest toxicity against A. cocois and faster mortality (6.82 h with a confidence interval of 6.34-7.30 h). Eugenol, elemicin, and beta-caryophyllene were the major allelochemicals found in the EOs of O. micranthum. We found that the EOs of O. micranthum are very promising in controlling the whitefly A. cocois.

Casuarina equisetifolia L. is major windbreak specie in the south-eastern islands of China, but it facing the great problem of heavy decline due to ageing of forest. To explore the possibility of developing a mixed forest of C. equisetifolia and H. nymphaeifolia, we in laboratory bioassays, studied the effects of aqueous litter leachate of C. equisetifolia (15-20 y old trees) on the germination, photosynthesis parameters and antioxidative activity of H. nymphaeifolia seedlings. The leachate of C. equisetifolia significantly reduced the net photosynthetic rate, stomatal conductance, transpiration rate, light saturation point, light compensation point, maximal RuBP regeneration rate, apparent quantum yield and carboxylation efficiency on the seedlings of H. nymphaeifolia. The higher concentrations (0.125 and 0.25 g/mL) of C. equisetifolia leachate, markedly inhibited the activities of superoxide dismutase (SOD) and peroxidase (POD) in the seedlings of H. nymphaeifolia. However, the content of malondialdehyde (MDA) and the activity of glutathione (GR) increased with the increasing leachate concentration. The activities of ascorbate peroxidase (APX) and catalase (CAT) were improved at lower leachate concentrations than control but were inhibited at the highest concentration (0.25g/mL). The changes in the antioxidative activity may be an adaptive regulatory mechanism in H. nymphaeifolia seedlings in response to the allelochemicals of C. equisetifolia.

Hulless barley (Hordeum vulgare L.) is alpine crop grown only in the Qinghai-Tibetan Plateau. The allelopathic effects of its 66-varieties were evaluated on rape by the relay-seeding co-culture in agar and in Pot culture. Two varieties (Qing 0039 and Qing 0415) significantly inhibited the root length (66.67% and 71.81%, respectively) in Brassica campestris L. The results of Response index (RI) values were similar to the relay-seeding co-culture in agar test. The leachates of its 5-varities (Tibet 1295, Qing 0079, Qing 0373, Tibet 0921 and Qing 0230) inhibited the rape seedlings growth. Their inhibition was drastic (100% inhibition) in root length and shoot length but was less (< 80% inhibition) on dry weight. In Cluster analysis, varieties in Group 1 (Qing 0415 and Qing 0039) were inhibitory to root length and dry weight of rape. In the relay-seeding co-culture in agar and leachate experiments the variety Qing 0039 proved most allelopathic. Its roots significantly inhibited the rape seedlings growth up to 5-7 cm distance. The extracts from its whole plants contained 9 compounds (tricin 4'-O-(threo-β-guaiacylglyceryl) ether (I), tricin 4'-O-(erythro-β-guaiacylglyceryl) ether (II), salcolin C (III), methyl ferulate (IV), dibutylphthalate (V), (+)-syringaresinol (VI), (+)-(7R, 7'R, 7"S, 7'''S, 8S, 8'S, 8''S, 8'''S)-4'', 4'''-dihydroxy-3, 3', 3'', 3''', 5, 5'- hexamethoxy-7, 9'; 7', 9-diepoxy-4, 8''; 4', 8'''-bisoxy-8, 8'-dineolignan-7'', 7''', 9'', 9'''-tetraol (VII), tricin (VIII) and chlorogenic acid (IX)), in which compounds I, II and V were most allelopathic.