Showing papers on "Allelopathy published in 2006"

Allelopathy : a physiological process with ecological implications

Abstract: Preface.- List of contributors.- 1. Introduction to allelopathy Chou,C-H.- 2. Basic pathways for the origin of allelopathic compounds Seigler, D.S.- Methodological aspects. 3. Clues in the search of new herbicides Dayan, F.E., Duke, S.O.- 4. Distinguishing allelopathy from resource competition: the role of density Weidenhamer, J.D.- 5. Toxicity in allelopathy: in silico approach Lo Piparo, E. et al.- Physiological aspects of allelopathy. 6. Allelochemicals and photosynthesis Zhou, Y.H., Yu, J.Q.- 7. Cell cycle analyses for understanding growth inhibition Sanchez-Moreiras, A.M. et al. 8. Detoxification of allelochemicals. The case of bezoxazolin-2(3H)-one (BOA) Schulz, M. et al.- 9. Allelopathy and abiotic stress Pedrol, M.N. et al.- 10. Allelopathy and biotic stresses Gawronska, H., Golisz, A.- 11. Plant secondary metabolites. Targets and mechanisms of allelopathy Lotina-Hennsen, B. et al.- 12. Mitochondria as a site of allelochemical action Ishii-Iwamoto, E.L. et al.- Ecophysiology and allelopathy. 13. Weed germination, seedling growth and their lesson for allelopathy in agriculture Aliotta, A. et al.- 14. Allelopathy: A soil system perspective Blum, U.- 15. Microorganisms and allelopathy: A one-sided approach Vokou, D. et al.- Ecological aspects of allelopathy. 16. Ecological relationships and allelopathy Sinkkonen, A.- 17. Resistance and susceptibility of plant communities to invasion:revisiting rabotnov's ideas about community homeostasis Callaway, R.M., Hierro, J.L.- Allelopathy in different environments. 18. Allelopathy in marine ecosystems Graneli, E., Pavia, H.- 19. Allelopathy in aquatic environments Erhard, D.- 20. Forest ecosystems and allelopathy Reigosa, M.J., Gonzalez, L.- 21. Allelopathic interactions in agroecosystems Kohli, R.K. et al.- Applied aspects of allelopathy. 22. Playing with chemistry: studies on Orobanche spp. germination stimulants Macias, F.A. et al.- 23. Modes of action of phytotoxins from plants Duke, S.O., Dayan, F.E.- 24. Allelopathy in ecological sustainable agriculture Narwal, S.S.- 25. Parasitic weeds and allelopathy: from the hypothesis to the proof Qasem, J.R.-

Leaf and root extracts of the invasive shrub, Lonicera maackii, inhibit seed germination of three herbs with no autotoxic effects

Abstract: In addition to effects mediated by resource competition, some invasive plants may impact surrounding vegetation by secreting compounds that are directly inhibitory to growth. Lonicera maackii, an invasive Asian shrub of forests and open areas in eastern and midwestern North America, has devastating effects on understory vegetation, some of which persist even after this shrub is removed. In this study, we explored the potential of aqueous extracts of the leaves and roots of this plant to inhibit seed germination of Impatiens capensis, Alliaria petiolata, Arabidopsis thaliana, and L. maackii in Petri dish bioassays. Both L. maackii root and leaf extracts significantly decreased germination in the three herb species. This inhibitory effect generally increased with increasing extract concentration and was more pronounced with application of leaf extract than root extract. However, when the same extracts were applied to seeds of L. maackii itself, germination was delayed in some cases, but was not significantly reduced by the end of the experiment. Germination of L. maackii seeds even reached significantly higher levels in some extract treatments than in no-extract controls. This implies that L. maackii can successfully inhibit the germination of other plants with few autotoxic effects and may even promote the germination of its own seeds.

Allelopathy in Harmful Algae: A Mechanism to Compete for Resources?

Abstract: Some phytoplankton species produce and release secondary metabolites that negatively affect the growth of other organisms; i.e., they are allelopathic (e.g., Rizvi and Rizvi 1992). The production of such allelopathic chemicals by phytoplankton is known among several different algal groups: cyanobacteria, dinoflagellates, prymnesiophytes, and raphidophytes (Table 15.1). Some reports suggest that allelochemicals are also produced in diatoms and green algae (e.g., Subba Rao and Smith 1995; Chiang et al. 2004). A comprehensive list of freshwater and marine algae suspected of production of allelopathic substances was compiled by Legrand et al. (2003). In this chapter, we focus on unicellular organisms (protists and cyanobacteria) as target cells, because many so-called phytoplankton cells actually are mixotrophic or heterotrophic, and because many so-called protozoa functionally are mixotrophic. This requires that we address the negative effects of allopathic marine phytoplankton on both competitors and grazers.

Allelochemicals released by rice roots and residues in soil

Abstract: A few rice (Oryza sativa L.) varieties or rice straw produce and release allelochemicals into soil in which interfere with the growth of neighboring or successive plants. Allelopathic rice PI312777 and Huagan-1 at their early growth stages released momilactone B, 3-isopropyl-5-acetoxycyclohexene-2-one-1, and 5,7,4′-trihydroxy-3′,5′-dimethoxyflavone into soil at phytotoxic levels, but non-allelopathic rice Huajingxian did not. Both allelopathic and non-allelopathic rice residues released momilactone B and lignin-related phenolic acids (p-hydroxybenzoic, p-coumaric, ferulic, syringic and vanillic acids) into the soil during residue decomposition to inhibit successive plants. The results indicated that allelochemicals involved in rice allelopathy from living and dead plants are substantially different. Interestingly, the concentrations of the allelochemicals released from the allelopathic rice seedlings in soil increased dramatically when they were surrounded with Echinochloa crus-galli. The concentrations of the allelochemicals were over 3-fold higher in the presence of E. crus-galli than in the absence of E. crus-galli. However, the same case did not occur in non-allelopathic Huajingxian seedlings surrounded with E. crus-galli. In addition to allelochemical exudation being promoted by the presence of E. crus-galli, allelopathic rice seedlings also increased allelochemical exudation in response to exudates of germinated E. crus-galli seeds or lepidimoide, an uronic acid derivative exuded from E. crus-galli seeds. These results imply that allelopathic rice seedlings can sense certain allelochemicals released by E. crus-galli into the soil, and respond by increased production of allelochemicals inhibitory to E. crus-galli. This study suggests that rice residues of both allelopathic and non-allelopathic varieties release similar concentrations and types of allelochemicals to inhibit successive plants. In contrast, living rice plants of certain allelopathic varieties appear to be able to detect the presence of interspecific neighbors and respond by increased allelochemicals.

Allelopathic effects of sunflower extracts on mustard seed germination and seedling growth

Abstract: The allelopathic potential of two cultivars of sunflower (Helianthus annuus L.) Lech and Ogrodowy was studied. Leaf aqueous extracts of sunflower at 2.5, 5, and 10 % (m/v) concentrations were applied to determine their effect on mustard (Sinapis alba) seed germination and seedlings growth under laboratory conditions. Increasing concentration of aqueous extracts of sunflower inhibited seed germination, up to almost complete failure of germination, observed in the presence of 10 % extract from sunflower cv. Ogrodowy. The decrease in germinability was well correlated with increased membrane deterioration, assayed as electrical conductivity and enhanced lipid peroxidation, detected as increased malondialdehyde content.

Potencial alelopático de espécies nativas na germinação e crescimento inicial de Lactuca sativa L. (Asteraceae)

Abstract: Allelopathy is characterized by harmful or beneficial effects on vegetation development, caused by chemical substances produced and released into the environment by the plant. Aiming to assess the allelopathic potential of Brazilian species, aqueous leaf extracts of Cecropia pachystachya Trec. (Urticaceae), Peltophorum dubium (Spreng.) Taub. (Fabaceae), Psychotria leiocarpa Cham. & Schltdl (Rubiaceae), Sapium glandulatum (Vell.) Pax (Euphorbiaceae), and Sorocea bonplandii (Baill.) Burger, Lanj. & Boer (Moraceae) were tested on lettuce using germination and growth bioassays. In these bioassays, aqueous leaf extracts were used at concentrations of 2 and 4%, prepared by static maceration with cold and hot water. The five species extracts delayed lettuce germination and produced toxic effects on seedling growth, with root reduction and debility. The results point to the presence of inhibitorychemical substances in the extracts, indicating an allelopathic potential for the five species evaluated.

Antimicrobial activity of catechol and pyrogallol as allelochemicals.

Abstract: Catechol and pyrogallol are allelochemicals which belong to phenolic compounds synthesized in plants. Their antimicrobial activities were investigated on three bacteria (Pseudomonas putida, Pseudomonas pyocyanea, Corynebacterium xerosis) and two fungi (Fusarium oxysporum, Penicillium italicum) phytopathogenic species as test organisms using the disc diffusion method. Both catechol and pyrogallol were found to have antibacterial effects on all the bacteria used in the study at 5 and 10 mM concentrations. Catechol has also been found to have an antifungal effect on the fungi used in the study, whereas no antifungal effects of pyrogallol were observed. The most sensitive species among the bacteria was P. putida which was inhibited by the allelochemicals even at 1 mM concentration.

Potential allelopathic effect of Pinus halepensis in the secondary succession: an experimental approach

Abstract: Recent economic and social changes in north Mediterranean regions have led to an important rural depopulation. Consequently, meadows developed on abandoned agricultural lands (characterized by high species richness) undergo reforestation. These former fields are mainly colonized by Pinus halepensis Miller, which is known to syn-thetize a wide range of secondary metabolites, among these, some could influence plant succession through allelopathy. The allelopathic potential of P. halepensis, was tested against two target species (Lactuca sativa L. and Linum strictum L.) with aqueous extracts obtained from different organs (root and needle) taking into account the individual age (±10, ±30 and >60 years old). Root and needle extracts affected differently germination and growth of the two target species, the responses varying with concentration of extracts, age and organs tested. The strongest inhibitory effect was observed on the germination and growth of L. strictum, exposed to needle extracts of young P. halepen-sis (±10 years old), and root extracts of older P. halepensis (>30 years old). These extracts contained several phenolic acids (e.g. 4-hydroxybenzoic acid and p-coumaric acid), which are known as allelochemicals and their concentrations vary with age and organ tested. Hence, P. halepensis could influence secondary succession through the release of potential allelochemicals in the environment by leaf leachates or root exudates.

Cyanide in the Chemical Arsenal of Garlic Mustard, Alliaria petiolata

Abstract: Cyanide production has been reported from over 2500 plant species, including some members of the Brassicaceae. We report that the important invasive plant, Alliaria petiolata, produces levels of cyanide in its tissues that can reach 100 ppm fresh weight (FW), a level considered toxic to many vertebrates. In a comparative study, levels of cyanide in leaves of young first-year plants were 25 times higher than in leaves of young Arabidopsis thaliana plants and over 150 times higher than in leaves of young Brassica kaber, B. rapa, and B. napus. In first-year plants, cyanide levels were highest in young leaves of seedlings and declined with leaf age on individual plants. Leaves of young plants infested with green peach aphids (Myzus persicae) produced just over half as much cyanide as leaves of healthy plants, suggesting that aphid feeding led to loss of cyanide from intact tissues before analysis, or that aphid feeding inhibited cyanide precursor production. In a developmental study, levels of cyanide in the youngest and oldest leaf of young garlic mustard plants were four times lower than in the youngest and oldest leaf of young Sorghum sudanense (cv. Cadan 97) plants, but cyanide levels did not decline in these leaves with plant age as in S. sudanense. Different populations of garlic mustard varied moderately in the constitutive and inducible expression of cyanide in leaves, but no populations studied were acyanogenic. Although cyanide production could result from breakdown products of glucosinolates, no cyanide was detected in vitro from decomposition of sinigrin, the major glucosinolate of garlic mustard. These studies indicate that cyanide produced from an as yet unidentified cyanogenic compound is a part of the battery of chemical defenses expressed by garlic mustard.

Control of parthenium hysterophorus l., by aqueous extracts of allelopathic grasses

Abstract: Both the root and shoot extracts of the three allelopathic grasses viz., Dicanthium annulatum Stapf., Cenchrus pennisetiformis Hochest and Sorghum halepense Pers., reduced germination and suppressed early seedling growth of exotic weed Parthenium hysterophorus L. Aqueous extracts of D. annulatum and C. pennisetiformis were more inhibitory than extracts of S. halepense. The highest suppressive ability was exhibited by extracts of C. pennisetiformis where 20% shoot and 25% root extract completely inhibited the germination of P. hysterophorus. In general shoot extracts were more inhibitory than the root extracts.

Herbicidal potential of allelochemicals from Lantana camara against Eichhornia crassipes and the alga Microcystis aeruginosa

Abstract: In the field, the growth of the aquatic weed Eichhornia crassipes and the alga Microcystis aeruginosa may be inhibited by fallen leaves of Lantana camara. This study showed that extracts of L. camara leaves and their fractions reduced the biomass of E. crassipes and M. aeruginosa within 7 days under laboratory conditions. Two fractions with highly inhibitory activity from the extract were isolated and subsequently identified as the pentacyclic triterpenoids, lantadene A and lantadene B. Both compounds significantly inhibited E. crassipes and M. aeruginosa growth, even at a low concentration. At all concentrations tested, their inhibitory activities were much higher than that of salicylic acid, a putative allelochemical from L. camara. The results indicated that the predominant allelochemicals involved in L. camara against either E. crassipes or M. aeruginosa are not phenolic acids, but lantadene A and lantadene B. Field trials showed that released levels of lantadene A and lantadene B were significantly correlated with amounts and decomposition periods of L. camara leaves floated in water. The amount released from 5 kg L. camara leaves was over the inhibition threshold of both E. crassipes and M. aeruginosa and reached a maximum at days 15-20. This study suggested that allelochemicals of L. camara could potentially be used to improve the management of weeds and algae in aquatic systems.

Effect of allelopathic compounds produced by Cistus ladanifer on germination of 20 Mediterranean taxa

Abstract: In order to analyze the extent to which allelopathic action of Cistus ladanifer may influence the successional progression towards Mediterranean sub-climacic shrublands and the geographical distribution of other species, the inhibitory effect of Cistus ladanifer extracts on the germination of 20 Mediterranean species was analyzed. Five of the species tested were characteristic of maquis sub-climacic shrublands: Arbutus unedo, Adenocarpus argyrophyllus, Phillyrea angustifolia, Phillyrea latifolia, and Rhamnus alaternus. Tests were also carried out on 6 Cistaceae species in order to evaluate the auto-toxicity rate of allelopathic extracts: Halimium umbellatum subsp. viscosum, Halimium ocymoides, Cistus ladanifer, Cistus salvifolius, Cistus monspeliensis, and Cistus populifolius. Nine herbaceous species sharing the natural habitat with C. ladanifer were also examined. Results confirmed a clear inhibitory and delaying effect of aqueous C. ladanifer-leaf extracts on the germination of P. angustifolia, P. latifolia, R. alaternus, H. ocymoides, C. populifolius, Erysimum lagascae, Brassica barrelieri, Silene tridentata, and Moricandia moricandioides. Assays with soil collected below the canopy of the C. ladanifer community showed more pronounced inhibitory effect on sub-climacic shrub species than the aqueous extracts. In contrast, the opposite pattern was detected when analyzing the allelopathic effect of natural soil on Cistaceae and herbaceous species. Allelopathic compounds produced by C. ladanifer showed little auto-toxicity. The inhibitory effect of phytotoxic compounds accumulated in the jaral soil upon germination of A. unedo, B.␣barrelieri, and M. moricandioides was eliminated by heating soil at 150 °C for 10 min. Phenolic compounds (i.e. ferulic, p-hydroxybenzoic, vanillic, p-coumaric, and caffeic acids) and terpenes (i.e. α and β-pinene) with allelopathic documented effect were detected in the aqueous extracts and soil samples used in the analyses. We suggest that the allelopathic effect of C. ladanifer may influence the composition and structure of Mediterranean communities where the species is present, since it hinders the establishment of some sub-climacic species and may reduce the area occupied by numerous herbaceous species.

Allelopathic, Autotoxic, and Hormetic Effects of Postharvest Sugarcane Residue

Abstract: With green sugarcane (interspecific hybrids of Saccharum spp.) harvesting, 6 to 24 Mg ha -1 of postharvest residue is deposited on the field surface covering the sugarcane stubble that must reemerge for several ratoon crops. The objectives of this research were to: (i) determine if postharvest residue possesses allelopathic, autotoxic, and hormetic properties; (ii) determine the interaction of soil type with possible autotoxic effects; and (iii) identify a reliable indicator species. Extract concentrations consisted of 0, 0.1, 10, 25, and 100% of the original solution of a 1:28 tissue to water extract. The higher concentrations of residue extracts exhibited autotoxicity by delaying early leaf development. The lower extract concentration of 10% increased sugarcane bud germination by 45% compared with the control, indicating hormetic effects. Allelopathic activity on tall morninglory (Ipomoea hederacea Jacq.) was more pronounced on a light soil; germination and radical length were reduced by all concentrations by an average of 42% and 8 mm, respectively, compared with the control. Seedling dry weights were reduced by an average of 10 mg by the 10, 25, and 100% extract concentrations relative to the control. On the heavy soil, only the 100% concentration reduced radical length and weight by 5 mm and 4 mg, respectively, relative to the control. Extract effects on oat (Avena nuda L.), rye (Secale cereale L.), and tomato (Lycopersicon esculentum Mill.) showed poor correlation with effects on sugarcane. Chemical analysis by gas chromatography/ mass spectrotometry indicated the extract contained benzoic acid. Further studies are needed to establish the impact of benzoic acid in natural settings.

Allelopathic Potentialities of Gliricidia sepium and Acacia auriculiformis on the Germination and Seedling Vigour of Maize (Zea mays L.)

Abstract: Decline in crop yield in cropping and agroforestry system in recent years has been attributed to allelopathic effects. Plants may favourably or adversely affect other plants through allelochemicals, which may be released directly or indirectly from live or dead plants. The objective of this study was to examine and quantify the nature of interference of leaf leachates of Gliricidia sepium and Acacia auriculiformis on seed germination and seedling vigour of maize and to identify morphological trait for allelopathic interference assessment of maize seedlings. Leaf leachates of both Gliricidia and Acacia significantly decreased germination percentage and increased mean germination time (P

Weed suppression by Passiflora edulis and its potential allelochemicals

Abstract: Summary Passion fruit (Passiflora edulis) is grown in the tropics for its edible fruits and for its many ethno-pharmacologic and pharmacological properties. Our study revealed that the plant contains a strong allelopathic potential. In a bioassay, aqueous extracts of P. edulis strongly suppressed germination and growth of lettuce, radish and two major paddy rice weeds, Echinochloa crusgalli and Monochoria vaginalis. In glasshouse and field experiments, P. edulis also strongly inhibited the growth of paddy rice weeds. Application of 2 t ha−1 dry plant material of P. edulis reduced weed biomass by 70% and increased rice yield by 35% compared with the unweeded control. Ten newly identified substances in P. edulis extracts, including coumarin, long-chain fatty acids and lactones, may be responsible for the inhibitory activity of P. edulis. Coumarin and the lactones showed greater inhibition of germination and growth of E. crusgalli than the fatty acids. The authors suggest that P. edulis may be used as a natural herbicide to reduce the dependency on synthetic herbicides.

Structure-activity relationship (SAR) studies of benzoxazinones, their degradation products, and analogues. Phytotoxicity on problematic weeds Avena fatua L. and Lolium rigidum Gaud.

Abstract: Avena fatua L. (wild oat) and Lolium rigidum Gaud. (rigid ryegrass) are highly problematic weeds affecting a wide variety of cereal crops worldwide. The fact that both of these weeds have developed resistance to several herbicide groups made them optimal candidates as target organisms for ongoing research about the potential application of allelochemicals and analogue compounds as natural herbicide models. Benzoxazinones, a family of natural allelochemicals present in corn, wheat, and rye, including 2,4-dihydroxy-(2H)-1,4-benzoxazin-3(4H)-one and 2,4-dihydroxy-7-methoxy-(2H)-1,4-benzoxazin-3(4H)-one, together with some degradation products, found in crop soils as well as in other systems, and some synthetic analogues of them were tested on wild oat and rigid ryegrass seeds; the results were statistically treated, and some structure-activity relationships, useful in further development of natural herbicide models, were elucidated. The most active compounds were the synthetic benzoxazinone 2-acetoxy-(2H)-1,4-benzoxazin-3(4H)-one and the degradation product 2-aminophenoxazin-3-one, with highly significant inhibition on the development of both weeds. The ecological role of these compounds is discussed by considering both degradability and phytotoxicity. The bioactivity of aminophenoxazines has been correlated by their aqueous solubility-lipophilicity predicted by means of computational methods.

Importance of nutrient competition and allelopathic effects in suppression of the green alga Scenedesmus obliquus by the macrophytes Chara, Elodea and Myriophyllum

Abstract: Possible allelopathic effects of substances released from the macrophytes Chara globularis, Elodea canadensis, Myriophyllum spicatum on the common green alga Scenedesmus obliquus were tested in the laboratory with plastic plants and untreated medium as controls. A two-phase approach was used in which first the effects of physical presence of plants was studied (phase I) followed by the effects of plant culture filtrates (phase II). In the presence of plastic plants growth was reduced only marginally, but strong growth inhibition of Scenedesmus occurred in the physical presence of all macrophytes. In contrast, filtrates from Chara had no growth inhibitory effect on Scenedesmus. Myriophyllum filtrate reduced particle-based growth rate by 7% compared to filtration controls, while Elodea culture filtrate reduced volume-based growth by 12%, chlorophyll-based growth by 28% and particle-based growth by 15%. Photosystem II-efficiency of Scenedesmus was reduced in all three macrophyte treatments in phase I, but not in filtrates from macrophyte cultures (phase II). Thus, while enzyme activity or other physiological aspects may have been affected, the current study yielded no proof for allelopathically active compounds being directed at photosynthesis. Mean particle volume (MPV) of Scenedesmus was not influenced by macrophyte exudates and cultures remained dominated by unicells. The strong growth inhibitory effects found for Scenedesmus in the physical presence of macrophytes, but not in plastic controls, and no or weaker response in nutrient-enriched filtrates, suggest nutrient competition was a more powerful driving factor than allelochemicals. However, the experimental design does not exclude disappearance of allelochemicals during the filtration process.

Assessment of allelopathic interference of Chenopodium album through its leachates, debris extracts, rhizosphere and amended soil

Abstract: A study conducted to assess the allelopathic interference of invasive weed Chenopodium album indicated that aqueous leachates of C. album plant parts (roots, whole plant, and leaves), debris extracts and rhizosphere soil deleteriously affected the germination and initial growth of two test plants – Cassia occidentalis (a weed) and Phaseolus aureus (a crop). Further, the plant growth in terms of height, biomass, chlorophyll and protein content was significantly lesser in soil amended with C. album debris. Aqueous leachates, debris extracts, rhizosphere soil and debris amended soil were found to contain significantly higher amounts of water-soluble phenolics – the known phytotoxins. These phytotoxins in root, above-ground parts and leaves were phenolic acids, namely gallic, chlorogenic, caffeic, vanillic, p-coumaric, syringic and ferulic. Among these, chlorogenic acid was present in the maximum amount in the leaves and roots. The study concludes that C. album releases phenolics into the soil and th...

Experimental complexities in evaluating the allelopathic activities in laboratory bioassays: A case study

Abstract: Soil is the major player in deciding allelopathic activities. A study was designed to examine experimental complexities in determining the allelopathic behavior of soil amended with water-soluble leachates from Chenopodium murale . Chenopodium murale interferes with the growth and establishment of crop seedlings. The present study examined the role of water-soluble organic substances, if any, in the shoot growth suppression of rice ( Oryza sativa L.). Rice seeds were grown on C. murale leaf leachate-amended soil to investigate the phytotoxic effects of C. murale leachates. Any modification of C. murale phytotoxic activities was studied through using abiotic soil, activated charcoal and nitrogen (N) fertilization. Chemical and microbiological analysis of C. murale -amended soil was made to evaluate the role of soil components in C. murale phytotoxicity. Significant inhibition in the shoot growth of rice was observed when abiotic or biotic soil was amended with full-strength leaf leachate (T1) of C. murale compared to unamended soils. The inhibitory effect of T1 is maintained when rice seeds were placed on T1-amended soil after 0, 24 or 48 h; however, the inhibitory effects were eliminated when seeds were placed on amended soil after 72, 96 h or 1 wk of incubating soil with T1. Activated charcoal (1, 2 or 4 g) could not eliminate the inhibitory effects of T1-amended soil to the shoot length of rice. The phytotoxic effects of T1-amended soil to the shoot length of rice, however, were largely eliminated after the addition of N fertilization. Interference of C. murale leaf leachate to rice shoot growth could be due to number of effects that could be misconstrued as allelopathy effects.

Allelochemicals: biological control of plant pathogens and diseases

Abstract: Allelochemicals: biological control of plant pathogens and diseases , Allelochemicals: biological control of plant pathogens and diseases , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

Benzoxazinoid Allelochemicals in Wheat: Distribution among Foliage, Roots, and Seeds

Abstract: In this study, the distribution of eight allelochemicals among the foliage, roots, and seeds of different wheat varieties is reported for two different sampling campaigns, corresponding to two consecutive years. The determination of benzoxazinoid derivatives was performed by combining pressurized liquid extraction--solid-phase extraction followed by liquid chromatography--electrospray mass spectrometry. To the authors' knowledge, there are no previous works about the content of allelochemicals in seed tissue of germinated wheat seedlings. Allelochemicals found in seeds were detected at levels similar to those found in foliage and roots. The results showed that the type of metabolites detected depends strongly on the working up procedure of the plant material, as well as of plant growth stage. A general decrease of the total amount of allelochemical content in the plants was observed with plant age. There was a significant difference in the total amount of benzoxazinoid derivatives in the different wheat varieties analyzed.

Allelopathic effects of extracts from Solidago canadensis L. against seed germination and seedling growth of some plants.

Abstract: To investigate the potential role of allelopathy in plant interference and in the successful invasion of alien species Solidago canadensis, aqueous an d ethanolic extracts from rhizomes, stems and leaves of S canadensis were prepa red and used as treatment solutions to assess their effects on seed germination and seedling growth in four target species, mulberry (Morus alba); morning glory (Pharbitis nil), wheat(Triticum aestivum) and rape(Brassica campestris) Reducti on and/or growth in germination and growth of the target plant species in the pr esence of both aqueous and ethanolic extracts at different concentrations indica ted that the responses were species-specific and concentration-dependent Genera lly, ethanolic extracts(especially from leaves) imposed stronger effects on both seed germination and seedling growth Extracts with lower concentration at 000 1 g/ml dw could stimulate the seedling growth of rape and morning glory, whereas extracts at any given concentrations have inhibitory effects on wheat and mulbe rry It is suggested that the aqueous and ethanolic extracts of all the three pa rts of S canadensis have significant allelopathic effects Although both inhibi tion and stimulation occurred in the germination and growth of the target specie s, extracts with higher concentrations definitely inhibit seed germination and s eedling growth of all target plants We suggest that allelopathy plays a more im portant role than other mechanisms do in the out-competition of S canadensis ov er other plants, and make it invasive in new habitats

Herbicidal Effects of Soil-Incorporated Wheat

Abstract: The hydroxamic acid 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA) and the benzoxazolinones benzoxazolin-2-one (BOA) and 6-methoxybenzoxazolin-2-one (MBOA) have been identified as important allelochemicals in wheat. This study examines the possibility of exploiting the allelopathic properties of wheat as a weed control strategy by cultivating wheat as a precrop and incorporating plant residues into the soil before the next crop is sown. Different wheat varieties were cultivated in field plots during two seasons in both conventional and organic farming systems. Plants were sampled at various growth stages, and their contents of DIMBOA, MBOA, and BOA were determined by chemical analyses. The wheat samples were incorporated into soil, and the effect on germination and growth of 12 different weed species was examined in pot experiments under controlled conditions. In some cases significant effects were obtained, but the results were inconsistent and the effects were not correlated to the content of DIMBOA, MBOA, and BOA in the incorporated wheat plants. ED50 doses of the pure compounds were estimated in dose-response experiments in Petri dishes, and these turned out to be much higher than the predicted maximum concentrations of DIMBOA, MBOA, and BOA in the soil water following incorporation. The study shows that a prerequisite for exploiting the incorporation of wheat residues as a weed control strategy is the development of wheat varieties with an increased content of allelochemicals.

An evaluation of the allelopathic potential of selected perennial groundcovers: foliar volatiles of catmint (Nepeta x faassenii) inhibit seedling growth.

Abstract: Six perennial groundcovers including Alchemilla mollis, Nepeta x faassenii, Phlox subulata, Sedum acre, Solidago cutleri, and Thymus praecox were investigated for the allelopathic potential of their respective foliar tissues via evaluation of volatile constituents produced by foliage. These groundcovers were selected for further laboratory evaluation because of superior performance as weed-suppressive groundcovers in previous field experiments. Foliar volatile components of N. x faassenii exhibited the strongest inhibitory effects on seedling growth of curly cress (Lepidium sativum), but S. cutleri also showed allelopathic potential by reducing shoot growth of curly cress seedlings with extracted volatiles. Although A. mollis and P. subulata exhibited strong weed-suppressive traits in past field experiments, weed suppression is apparently associated with either competition for resources or other allelopathic mechanisms rather than an allelopathic effect caused by volatiles. Volatiles of N. x faassenii were further evaluated with gas chromatography coupled to mass spectrometry (GC-MS). A total of 21 chemical constituents were identified in the volatile cocktail; 17 components were identified from a direct crude leaf sample extraction, including sabinene, beta-pinene, beta-myrcene, 2-(2-ethoxyethoxy)-ethanol, 1,8-cineole, ocimene, neryl Acetate, 4aalpha,7alpha,7aalpha-nepetalactone, alpha-copaene, trans-caryophyllene, alloaromadendrene, 4abeta,7alpha,7abeta-nepetalactone, germacrene D, beta-farnesene, chi-cadinene, germacrene B, and beta-sesquiphellandrene. Five additional constituents were identified in a methanolic extract of dried of N. x faassenii foliage, but not the volatile cocktail collected from N. x faassenii foliage. These included methyl benzoate, 2,4-decadienal, neryl acetate, isodihydronepetalactone, and caryophyllene oxide. Three components, 2-(2-ethoxyethoxy)-ethanol, alloaromadendrene, and chi-cadinene, were not only detected in both the volatile mixture and the methanolic extract, but also in an aqueous foliar extract that exhibited potential allelopathic activity.

Allelopathic effects of extracts from Solidago canadensis L.against seed germination and seedling growth of some plants

Abstract: 在植物干扰并且在相异的种类 Solidago canadensis 的成功的侵略调查他感酌的潜在的角色，水并且从 S 的根茎，茎和叶子的 ethanolic 摘录。canadensis 被准备并且用作处理答案在四目标种在种子萌芽和幼苗生长上估计他们的效果，桑树(妈妈白长袍的一) ；牵牛花(Pharbitis 无) ，小麦(Triticum aestivum ) 和强奸(Brassica campestris ) 。在萌芽的 Reductionand/or 生长和目标的生长种种面对水并且在显示的不同集中的 ethanolic 摘录 werespecies 特定的回答和集中依赖者。通常， ethanolic 提取(特别从叶子) 种子萌芽和幼苗生长上的强加的更强壮的效果。有在 0.001 g/ml dw 的更低的集中的摘录能刺激强奸和牵牛花的幼苗生长，而在任何给定的集中的摘录在小麦和桑树上有禁止的效果。这被建议水并且 S 的所有三部分的 ethanolic 摘录。canadensis 有重要 allelopathic 效果。尽管抑制和刺激发生在目标种类的萌芽和生长，有更高的集中的摘录毫无疑问禁止所有目标植物的种子萌芽和幼苗生长。我们比另外的机制在 S 的外面比赛做建议他感酌起一个更重要的作用。在另外的植物上的 canadensis，并且在新产地使它侵略。

Autotoxicity against germination and seedling emergence in Cistus ladanifer L

Abstract: Autotoxic species are those which adversely affect their own seeds’ germination and/or seedling development. Cistus ladanifer L (labdanum or jara) has been shown to have a pattern of allelopathic behaviour against the herbs that share its habitat. The present work studied whether an autotoxic effect also exists. The aqueous solution obtained from washing jara leaves was found by itself to inhibit germination and cotyledon emergence of the species’ seeds. When these same trials were carried out in soils, autotoxicity was observed only from leaves and soils collected in winter. This was so both in soils collected away from the influence of the jaral to which was added the greatest concentration of aqueous extract prepared from the leaves, and in soils collected within the jaral, except that in the latter group of soils germination was inhibited with or without the addition of C. ladanifer extracts. This autotoxic behaviour could be involved in the species’ own population control, and would explain the scant self-regeneration within established C. ladanifer stands.