小麦化感作用物的提取、分离及其对白茅的杀除效果

小麦颖壳提取物经3520树脂分离后,对所得甲醇洗脱物离心,分得油类似物、上清液及沉淀物。前两个组分在300mg/L的浓度下,对白茅生长抑制率分别为100％和98％。上清液经硅胶柱分离,得7个亚组分,其中第1、3和7号亚组分在500mg/L浓度下对白茅生长的抑制率分别为95％、91％和95％。第3亚组分经葡聚糖凝胶柱分离,又分得A、B、C 3个组分,褐色粉末状的B组分在1000mg/L浓度下使白茅的生长量下降81％。从而证明小麦颖壳对白茅的化感作用是由多个化感物共同作用的结果。室内和温室及大田的测定结果表明,小麦颖壳中的甲醇洗脱物在24mg/株的剂量下对白茅生长的抑制率可达90％以上。这暗示,小麦颖壳中的甲醇可溶物可望开发成为防治白茅的生物除草剂。

植物生化他感作用及其在生产实践中的应用

本文从化感作用的普遍性、化感作用物产生的部位、释放方式、化感作用物的种类。

Interspecific competition and allelopathic interaction between Karenia mikimotoi and Dunaliella salina in laboratory culture

Algal allelopathy is a manifold ecological/physiological phenomenon that is focused on chemical interactions and autotoxicity. We investigated the allelopathic interactions between Karenia mikimotoi and Dunaliella salina in laboratory cultures based on different temperature （15℃, 20℃, and 25℃） and lighting （40,80, and 160 umol/（m2·s）） conditions. The growth of D. salina in bi-algae culture （1：1 size/density） was significantly restrained. The results of cell-free filtrate culture indicate that direct cell-to- cell contact was not necessary in interspecific competition. Further experimental results demonstrated that allelochemicals released from K. miMmotoi were markedly influenced by both temperature （P=0.013） and irradiance （P=0.003）, resulting in different growth characteristics olD. salina in filtrate mediums. Compared with the plateau period, K. mikimotoi exudates in the exponential phase had a stronger short-term inhibition effect on D. salina in normal conditions. A clear concentration-dependent relationship was observed in the effect of allelochemicals released from K. mikimotoi with low-promoting and high-repressing effects on D. Salina in a short time-scale. In addition, allelopathic substances remain stable and effective under high temperature and pressure stress. Many flocculent sediments adhering with D. salina cells were observed in all filtrate mediums, while the quantity and color depended on the original culture conditions.

Allelopathic effects of Lantana camara on germination and growth behavior of some agricultural crops in Bangladesh

An experiment was conducted to understand the growth inhibitory effects of aqueous extracts derived from Lantana camara L. （a globally recognized invasive alien weed） on six popular agricultural crops of Bangladesh. The test was conducted in sterilized petridishes with a photoperiod of 24 hours and an average temperature of 29℃. The effect of different concentrations ofL. camara leaf extracts were recorded and compared with control （i.e., distil water）. Result showed different concentrations of aqueous leaf extracts caused significant inhibitory effect on germination, root and shoot elongation and development of lateral roots of receptor crops. Bioassays also indicated that the inhibitory effect was proportional to the concentrations of the extracts and higher concentration had the stronger inhibitory effect whereas the lower concentration showed stimulatory effect in some cases. The inhibitory effect was much pronounced in root and lateral root development rather than shoot and germination.

Application of Box-Behnken Design in Optimization of Allelopathic Effects of Potamogeton Pectinatus Against Microcystis Aeruginosa

Allelopathic effects of submerged macrophytes against algae are affected by many environmental factors which can only be measured one by one by traditional methods. Box-Behnken design of response surface methodology was used to optimize three environmental factors （temperature, light intensity and total dissolved solids） of allelopathic effects of Potarnogeton pectinatus against Microcystis aeruginosa at the same time. By solving the regression equation and analyzing the response surface contour plots, the optimal conditions of the relatively inhibitory rate of Microcystis aeruginosa were that the temperature was 23℃, the light intensity was 2 700 lx and the total dissolved solids were 4 415 mg/L. Under these conditions, the optimal value of relatively inhibitory rate of Microcystis aeruginosa was 81.9%. According to validation experiments, the results of analysis indicated that the experimental values fitted well with the predicted ones.

Allelopathic Potentials of Some Crop Residues on the Germination and Seedling Growth of Chromolaena Odoratum L.

The allelopathic effects of aqueous extracts of rice husk （Orza sativa L.） and sorghum stem （Sorghum bicolor L.） on the germination and seedling growth of Chromolaena odoratum L. were investigated. The extracts of the two crop residues exhibited inhibitory effects on the germination and seedling growth of Chromolaena odoratum L. The degree of retardation demonstrated in both extracts was concentration dependent. However the results obtained revealed that the retardation was more pronounced in the rice husk extract-treated seeds. However statistical analysis （P 〈 0.05% level） revealed that the degrees of inhibition of radicle and plumule obtained from various extracts treated seeds of both extracts were not significantly different when compared to those obtained from the control experiments as well as those obtained from the varying extract concentrations.

Phytochemical Constituents and Allelopathic Effects of Some Medicinal Plants Extract on the Soil Algal Diversity

Phytochemical constituents of the shoots and roots extract of chosen eight medicinal plants （Plantago major, Verbesina encelioides, Glinus lotoides, Helotropium supinum, Mentha microphylla, Euphorbia hirta, Juncus subulatus and Convolvulus arvensis） were estimated using standard qualitative analysis. The extract contained alkaloids, glycosides, saponins, phenols, tannins, f[avonoids and terpenoids in some medicinal plants while others contain some only of these phytochemical components. Allelopathic effect of the various concentrations of the extracts on the soil algal diversity was also investigated. Wollea saccata was the only algal species disappeared from all applied investigated plant extracts. Phormidium richardsii, Monoraphidium braunii, Eunotia verneris and Nitzschia bilobata were the highly sensitive algal species to all applied shoot and root extract from all tested plants, they disappeared from most of the studied plants. On the other hand, Phormidium animale and Chlorella neustonice were highly tolerant algal species to all applied extracts. Counts of Cyanophyceae, Chlorophyceae and Bacillariophyceae were decreased by addition of some investigated medicinal plants extracts such as Juncus subulatus, Convolvulus arvensis and Euphorbia hirta. So the authors can use these plants extracts in biocontrol of the nuisance of algal bloom or any other microorganisms. Also, these plants may be useful to recover eutrophic water which needs further investigation.

A New Bioassay Method for Evaluation Allelopathic Potential of Rice Germplasm

Allelopathy was defined in 1996 by IAS （international allelopathy society） as any process involving secondary metabolites produced by plant, algae, bacteria and fungi that influences the growth and development of agricultural and biological systems. Rice allelopathy against weeds was reported since 1989, which offers an integrated weed management with substantially reduced herbicide usage. Application of allelopathic rice cultivars is thought a resources conservation and environmental friendly way of weed bio-control, and could promote the sustainable development of agriculture. Screening or evaluating the allelopathic potential rice variety is the first step. In this paper, a new bioassay method was set up by the allelopathic potential of 9 rice lines on the target weed barnyardgrass （Echinochloa crusgalli）, and comparing with bioassay methods such as relay seeding in filter paper （RSF） and relay seeding in agar （RSA）. The results indicated that three methods had a same tendency in evaluating the allelopathic potential of rice; there existed a significant difference among different bioassay methods, and an interaction between bioassay methods and rice lines. The method of root exudates （RE） with the highest value and a correlation efficiency of 0.98 was considered as ideal bioassay method for evaluation of allelopathic potential.

Management of Chenopodium album L. through the Allelopathic Effect of Mangifera indica L.

Chenopodium album is an invasive weed in wheat fields in Egypt. The present study indicated the potentials for utilization of MILAE （Mangifera indica leaves aqueous extract） at different concentrations （5%, 10%, 15% and 25%） to suppress the germination and growth of C. album in Petri dish experiment Results indicated that predictable degrees of inhibition in C album germination and growth rate of seedlings were accompanied with the increase in the concentration of MILAE. PL （Plumule） and RL （radicle） lengths of C. album were negatively affected as the concentration of MILAE increased and the effect was prominent at 25% extract concentration. This study recommended the use of MILAE as strong phytotoxic potential allelochemicals. an alternative bioherbicides, since its leaves extract possess

Allelopathic Effects of Aqueous and Ethanolic Leaves Extracts of Schinus molle L. under Different Kinds of Pruning

Secondary metabolites produced by plants can be used in popular medicine, as well they can interact with plants and other organisms, in which case they are called allelochemicals and influence the neighboring ecosystem. This work aimed to evaluate the allelopathic effects of Schinus molle L. species widely used in reforestation and urban afforestation. Therefore, leaves of S. Molle were collected from different populations located at Alfenas and Nepomuceno in Minas Gerais, Brazil. Cypselae of lettuce （Lactuca sativa L.） were germinated in biochemical oxygen demand （BOD） chamber at 25 ℃ with a photoperiod of 12 h under different extracts concentrations. The experiment was performed in factorial design （2 × 4） with two kinds of extracts （aqueous and ethanol） and four concentrations （2.5, 5, 10 and 20 mg/mL） in randomized blocks. The variables analyzed were germination （%）, germination speed index （GS1）, % of normal seedlings, root length, fresh biomass and dry biomass. Changes in the cell cycle in meristematic cells of the used model were also evaluated. Concentration-dependent effect on all parameters was observed, with the exception of dry biomass exposed to ethanol extract. The root elongation parameter was different between the extracts even in lower concentrations, thus indicating that this is the most sensitive parameter of this species. Toxic effect from S. rnolle extracts was observed in all parameters regardless the kind of pruning management or method of extraction （water or ethanol）.

Allelopathic Effects of Different Organs of Redroot Pigweed （Amaranthus retroflexus L.） on Cucumber and Wheat Plants

Allelopathy is one of the most important interactions between plants. Weeds are famous plants from this viewpoint, which can decrease crop production in farms by their allelopathic effects. Research has shown that different plant organs have different allelopathic effects. Redroot pigweed （Amaranthus retroflexus L.） is one of the most common weeds with well-known allelopathic potential. This experiment aimed to study the allelopathic effects of different organs＇ leachate of redroot pigweed on germination and growth of cucumber （Cucumis sativus L.） and wheat （Triticum aestivum L.） as two important crop species. The effect of different organs＇ leachate on seed germination and seedlings growth parameters of tested plants was significantly different. In addition, the effects on cucumber were not the same as wheat. According to the results, wheat plant was more resistant at both seed germination and seedling growth stages in comparison to cucumber. Cucumber only showed normal growth potential when treated with the stem leachate, while wheat showed measurable growth potential in all treatments and leaf leachate showed the highest negative effect on wheat. Accordingly, allelopathic effects of redroot pigweed are dependent not only on leachate concentration and plant species, but also on plant organ from which the leachate was released. Therefore, understanding the altelochemical source （organ） of a donor plant is essential for accurate evaluation ofallelopathic interactions between plants.

Allelopathic Effects of Corrigiola Telephiifolia Root Extracts on Germination and Seedling Growth of Raphanus Sativus and Triticum Aestivum

The allelopathic potential of aqueous and organic solvent extacts from Corrigiola telephiifolia Pour which is an aromatic and medicinal plant in mediterranean regions, was investigated under laboratory conditions on two plant species： Raphanus sativus and Triticum aestivum. The aqueous extract of Corrigiola telephiifolia roots had an important inhibitory effect on the seed germination of the two tested plant species. The dichloromethane and the methanol extracts significantly reduced the growth of radish roots up to 84.44% and 68.85% respectively. The butanol, the dichloromethane and the ethyl acetate extracts had a high inhibitory effect on seed germination and roots growth of wheat. The presence of saponins in butanol extracts and tanins in dichlorometane and ethyl acetate extracts may be responsible of these allelopathic activities. These results suggest that Corrigiola telephiifolia Pour have allelopathic effects and contains potent allelochemicals which should be used for weeds management.

Effects of water extract from Cornus controversa on the expression levels of DiSOC1-b and DiCCoAOMT1 genes related with the growth of dove tree seedlings

Although characterization of plant interactions has become a research hotspot to assess the adaptability of endangered plants,the underlying molecular basis remains elusive.Dove tree(Davidia involucrata)seedlings were watered with distilled water(CK),leaf water extract(0.025 g mL^(-1))and branch water extract(0.1 g mL^(-1))from Cornus controversa,respectively.Subsequently,the morphology,biomass and gene expression levels of DiSOC1-b and DiCCoAOMT1 were analyzed.The results showed that morphological traits and biomass accumulation of D.involucrata seedlings were decreased by the addition of leaf water extracts,and increased by branch water extracts.Moreover,the gene expression level of DiSOC1-b was signifcantly down-regulated,while the gene expression level of DiCCoAOMT1 was signifcantly up-regulated in the stems and roots of D.involucrata upon treatment with leaf water extracts of C.controversa.In contrast,the gene expression level of DiSOC1-b was signifcantly up-regulated in the leaves and stems,while the gene expression level of DiCCoAOMT1 was signifcantly down-regulated in the roots of D.involucrata upon treatment with branch water extracts of C.controversa.In addition,the expression level of DiSOC1-b was positively correlated with most of morphological traits and total biomass(P<0.05),while DiCCoAOMT1 was negatively correlated with the majority of morphological traits in D.involucrata seedlings(P<0.05).Taken together,these results suggest that water extracts from the leaves and branches of the C.controversa exhibit opposite allelopathic effects and affect the expression levels of genes related to growth(DiSOC1-b)and environmental adaptability(DiCCoAOMT1)in D.involucrata seedlings.

Soil microbes alleviate allelopathy of invasive plants

Soil microbes are one of the most important determinants of allelopathic effects in the field. However, most studies testing the role of allelopathy in biological invasions did not consider the roles of soil microbes. Here we tested the hypothesis that soil microbes which can degrade allelochemicals may accumulate in soils over time by adaptation and therefore increase the degradation of allelochemicals and alleviate the allelopathic effects in biological invasions. As expected, soil microbes signifi- cantly decreased the allelopathic effects of leaf leachates of eight in the nine invasive plant species studied. In addition, Ageratina adenophora showed lower allelopathic effects in soil with long or intermediately invasion history than those in soil with short invasion history. The two main allelo- chemicals of the invader were degraded more rapidly with increasing invasion history in the soil. Correspondingly,biomass and activity of the soil microbes were higher in the soils with long invasion history than in that with short invasion history. Our results indicate that soil microbes may graduaUy adapt to the allelochemicals of Ageratina and alleviate its allelopathic effects and thus support the above hypothesis. It is necessary to consider the effects of soil microbes when testing the roles of allelopathy or the novel weapons hypothesis in biological invasions.

PERSISTENCE, EXTINCTION AND STABILITY FOR NONLINEAR PLANKTON ALLELOPATHY MODEL WITH DELAYED NEGATIVE FEEDBACKS

By the techniques of comparison argument and Lyapunov-like functionals, some criteria about persistence and extinction of the species are obtained. And then, with the help of constructing Lyapunov functionals and some new analysis method, sufficient conditions, provided with the form of average value of a function, to guarantee the stability of the system are derived. Finally, some examples together with their numerical simulations show the feasibility of these main results. Our conclusions are different from many existing forms for nonlinear competitive systems.