Allelopathy in wheat (Triticum aestivum)

Wheat (Triticum aestivum) allelopathy has potential for the management of weeds, pests and diseases. Both wheat residue allelopathy and wheat seedling allelopathy can be exploited for managing weeds, including resistant biotypes. Wheat varieties differ in allelopathic potential against weeds, indicating that selection of allelopathic varieties might be a useful strategy in integrated weed management. Several categories of allelochemicals for wheat allelopathy have been identified, namely, phenolic acids, hydroxamic acids and short‐chain fatty acids. Wheat allelopathic activity is genetically controlled and a multigenic model has been proposed. Research is underway to identify genetic markers associated with wheat allelopathy. Once allelopathic genes have been located, a breeding programme could be initiated to transfer the genes into modern varieties for weed suppression. The negative impacts of wheat autotoxicity on agricultural production systems have also been identified when wheat straws are retained on the soil surface for conservation farming purposes. A management package to avoid such deleterious effects is discussed. Wheat allelopathy requires further study in order to maximise its allelopathic potential for the control of weeds, pests and diseases, and to minimise its detrimental effects on the growth of wheat and other crops.     

Leaf and root respiration of Lolium perenne populations selected for contrasting leaf respiration rates are affected by intra- and interpopulation interactions

Autotoxicity and allelopathy affect the yield of GL66 and GL72, two populations of perennial ryegrass (Lolium perenne L. cv. S23) that were originally selected for contrasting rates of mature leaf dark respiration, but under conditions where allelopathic effects could not occur and autotoxic effects were minimal. To investigate if the respiration properties are also affected, the populations were subjected to two conditions (monoculture and mixed culture) and two treatments (grown in `renewed', i.e. solution completely replaced every week, and `replenished', i.e. nutrients added to the solution every week, to compensate for the nutrients that had been absorbed from the solution). When plants were grown in mixed culture with a `renewed' nutrient solution, the rate of mature leaf respiration in the absence of inhibitors was higher in GL66 than in GL72. In GL66, this rate was unaffected by condition or treatment, whereas in GL72 it increased in the `replenished' cultures, due to autotoxic and allelopathic effects. In contrast with GL66, for GL72 the effect of an inhibitor of the alternative path (salicylhydroxamic acid, SHAM) differed between conditions and treatments. Effects of an inhibitor of the cytochrome path (KCN) were affected by treatment in both populations. The increase in the rate of root respiration of GL66 due to autotoxic and allelopathic effects was accompanied by a higher rate of the SHAM-resistant component, i.e. maximum activity of the cytochrome path. Roots of GL72 showed a higher control respiration rate and a higher rate of the SHAM-resistant component when long-term accumulation of root exudates was allowed to occur in mixed cultures (allelopathy). We conclude that allelochemicals can modify both leaf and root respiration and that there is no consistent correlation between yield and respiration for GL66 and GL72 in the present study. This shows that selection for low rates of mature leaf respiration is not an appropriate method to select for high-yielding cultivars in perennial ryegrass.     

Allelopathy of rice (Oryza sativa L.) root exudates and its relations with Orobanche cumana Wallr. and Orobanche minor Sm. germination

Allelopathy has been considered not only as an environmentally friendly approach for weed control but also a potential reason causing autotoxicity in crop production. In this study, the responses of seeds of lettuce, wheat, rice, clover broomrape (CB), and sunflower broomrape (SB) to the root exudates of rice cultivars were studied. Lettuce germination was promoted by root exudates of Yliangyou 3218 and I-Kung-Pao. Wheat seedling growth was inhibited by all nine rice species. I-Kung-Pao and Ganxin 203 exerted greater autotoxicity than other cultivars. Yongyou 15 and I-Kung-Pao induced the highest germination rate of CB, while Yongyou 13, Zhongzao 22, and I-Kung-Pao induced the highest germination rate of SB. A significantly correlation was noted between germination-inducing ability on broomrape seeds and allelopathic effects on target plants. It is suggested that using broomrape seeds germination is a better receptor for the identification of rice allelopathic potential.     

南瓜组培根根系分泌物的化感效应研究

使用组织培养技术、生物测试法及室内分析相结合的方法研究了南瓜组培根在不同生长时期与不同营养谐迫下(利用正交设计调节标准B₅培养基中的大量元素、微量元素、有机质和激素)根分泌物对南瓜、萝卜和小麦3种受体的种子萌发及幼苗生长的化感作用.结果表明,南瓜具有自毒作用,南瓜组培根根系分泌物对受体幼苗生长的抑制作用呈现出高抑低促的作用表型;南瓜组培根根系分泌物产生化感作用的活性与南瓜组培根生长速度有关,南瓜组培根根系分泌物的生长抑制活性以15～17d即生长速度指数末期为最高,21d生物量最大时的南瓜组培根根系分泌物的生长抑制活性最低;营养元素的改变明显影响了南瓜根系分泌物的产生,并通过筛选出能诱导南瓜组培根对受体具有强烈抑制作用的大量元素、微量元素、维生素和激素种类和含量的最优化组合,为研究南瓜化感作用营养胁迫机理提供依据.     

三七自毒与化感作用初步研究

采用生物测定方法,对三七的自毒与化感作用进行初步研究。结果表明:(1)三七种子萌发过程中的自毒作用随其播种密度不同而有一定差异,但无明显规律性。三七种子萌发过程中的分泌物对油菜生长具有化感作用,主要表现为对油菜种子发芽率、发芽指数及苗高的抑制效应;(2)三七水浸液对不同受体植物的化感作用不尽相同,对小麦主要表现为对苗鲜重、苗干重、根鲜重、苗高及须根数有不同程度的促进或抑制作用;对油菜则表现为对其种子发芽率具有抑制作用,而对苗鲜重、苗干重、根鲜重、最长根长具有促进作用;(3)三七存在明显的化感自毒作用,其自毒物质可能为影响其连作的一个重要因素。     

Quantitative trait loci and molecular markers associated with wheat allelopathy

Wheat (Triticum aestivum L.) has been examined for allelopathic potential against annual ryegrass (Lolium rigidum). The bioassay technique, 'equal-compartment-agar-method', was employed to evaluate seedling allelopathy in a doubled-haploid (DH) population derived from cv Sunco (weakly allelopathic) and cv Tasman (strongly allelopathic). A significant difference in allelopathic activity was found among the DH lines, which inhibited the root length of ryegrass across a range from 23.7 to 88.3%. The phenotypic data showed that wheat allelopathic activity was distributed normally within this DH population and a substantial transgressive segregation for seedling allelopathic activity was also found. Analysis of restriction fragment length polymorphism (RFLP), amplified fragment length polymorphism (AFLP) and microsatellite (SSRs) markers identified two major QTLs on chromosome 2B associated with wheat allelopathy. The linkage analysis of genetic markers and the QTLs may improve genetic gains for the allelopathic activity through marker-assisted selection in wheat breeding. The development of wheat allelopathic cultivars could reduce the over-reliance of weed control on synthetic herbicides.Communicated by J. Dvorak     

黄瓜种子及其萌发期的化感作用研究

以大白菜、萝卜、番茄和黄瓜种子为受体,采用实验室培养皿种子发芽生物测试法研究了黄瓜种子浸提液、种子萌发、胚根和芽苗分泌物、芽苗腐解物和芽苗浸提液的化感效应。结果表明:(1)黄瓜种子浸提液对大白菜、萝卜、番茄和黄瓜种子萌发均有化感抑制作用,即黄瓜种子内含有某些化感抑制物质。(2)在水浸提过的黄瓜种子萌发过程中,它不仅对其近邻套种的大白菜、萝卜和番茄种子萌发产生化感抑制作用,而且其胚根和芽苗分泌物对后茬播种的4种蔬菜种子发芽也表现出不同程度的化感抑制作用;黄瓜芽苗腐解物和芽苗水浸提液也对各受体蔬菜种子发芽与生长产生不同程度的化感抑制作用,且随着腐解芽苗量的增加或浸提液浓度的升高,各受体蔬菜种子的发芽指标值、化感效应指数值和综合效应值随之降低。(3)黄瓜种子浸提液及芽苗各器官的化感物质对黄瓜种子的萌发与生长产生了自毒作用,且黄瓜芽苗腐解物、芽苗浸提液、胚根及芽苗分泌物对受体黄瓜的自毒作用均为最大。研究发现,黄瓜种子浸提液、种子萌发时期以及芽苗各器官的化感物质主要是通过抑制受体胚根的生长而起化感抑制作用,即受体蔬菜种子胚根对化感效应最为敏感;因黄瓜种子及萌发期释放化感物质的途径有所不同,导致受体大白菜、萝卜、黄瓜和番茄的化感响应也不相同;在黄瓜种子萌发和芽苗生长的早期,化感物质即开始在芽苗体内进行合成与积累,一部分可通过胚根和芽苗分泌途径释放到环境中,另一部分可通过芽苗腐解途径释放化感物质,并对受体蔬菜种子萌发与生长表现出较强的化感抑制作用。     

甜瓜自毒相关基因CmGST的克隆及其对自毒胁迫的响应

植物谷胱甘肽硫转移酶基因(GST)在清除生物和非生物胁迫产生的氧化损伤中扮演着重要的角色,为探究GST在根系分泌物介导的甜瓜自毒胁迫中的响应机制,该实验在转录组测序基础上,以甜瓜叶片cDNA为模板,采用RT PCR技术获得了一个根系分泌物介导的甜瓜自毒作用密切相关的GST基因,命名为CmGST(GenBank 登录号：AYU66762.1);对CmGST基因进行了相关生物信息学分析,同时对自毒胁迫过程中,CmGST的差异表达情况、谷胱甘肽硫转移酶(GST)活性和谷胱甘肽(GSH)含量进行了相关测定。结果显示：(1)CmGST基因含有完整开放阅读框(ORF)654 bp,编码217个氨基酸;CmGST蛋白为酸性亲水蛋白,且较为稳定,具有GST家族Tau亚家族的2个典型的保守结构域;CmGST蛋白与黄瓜的亲缘关系较近。(2)亚细胞定位结果表明CmGST定位于细胞质中。(3)qRT PCR分析结果表明,CmGST在甜瓜根系和幼苗中均有表达,在正常生长的甜瓜幼苗中表达量相对稳定;自毒胁迫后在叶中的表达先降后升,后期迅速增加;在根系中变化趋势类似,但程度较为缓和。(4)GST活性和GSH含量分析表明,叶片中GST活性变化趋势与CmGST基因表达变化基本吻合;在根系中,GST活性呈现先升再降最后又升高的趋势;随胁迫时间增加,GSH含量在根系和叶片中均都有不同程度的增加,但根部含量低于叶片。研究认为,在自毒胁迫过程中,CmGST基因在甜瓜植株根和叶片均有相应表达水平的变化,参与了对根系分泌物介导的自毒胁迫响应。     

Modelling the effect of autotoxicity on density-dependent phytotoxicity

An established method to separate resource competition from chemical interference is cultivation of monospecific, even-aged stands. The stands grow at several densities and they are exposed to homogenously spread toxins. Hence, the dose received by individual plants is inversely related to stand density. This results in distinguishable alterations in dose-response slopes. The method is often recommended in ecological studies of allelopathy. However, many plant species are known to release autotoxic compounds. Often, the probability of autotoxicity increases as sowing density increases. Despite this, the possibility of autotoxicity is ignored when experiments including monospecific stands are designed and when their results are evaluated. In this paper, I model mathematically how autotoxicity changes the outcome of dose-response slopes as different densities of monospecific stands are grown on homogenously phytotoxic substrata. Several ecologically reasonable relations between plant density and autotoxin exposure are considered over a range of parameter values, and similarities between different relations are searched for. The models indicate that autotoxicity affects the outcome of density-dependent dose-response experiments. Autotoxicity seems to abolish the effects of other phytochemicals in certain cases, while it may augment them in other cases. Autotoxicity may alter the outcome of tests using the method of monospecific stands even if the dose of autotoxic compounds per plant is a fraction of the dose of non-autotoxic phytochemicals with similar allelopathic potential. Data from the literature support these conclusions. A faulty null hypothesis may be accepted if the autotoxic potential of a test species is overlooked in density-response experiments. On the contrary, if test species are known to be non-autotoxic, the method of monospecific stands does not need fine-tuning. The results also suggest that the possibility of autotoxicity should be investigated in many density-response bioassays that are made with even-aged plants, and that measure plant growth or germination.     

外来入侵植物小飞蓬化感物质的释放途径

在室内以滤纸为载体用离体生测方法测定了小飞蓬(Conyza canadesiL.)全株水浸提物、茎叶淋溶物、根系分泌物及残体土壤分解物对萝卜(Raphanussativus L.)、黄瓜(Cucumis sativus L.)、马唐(Digitarias anguinalis(L.)Scop.)油菜(Brassica campestris L.)和小麦(Triticuma estivum L.)的化感效应,同时在温室内以土壤为载体通过盆栽植物浇灌的方法测定了小飞蓬茎叶淋溶物和根系分泌物对盆栽植物生长的影响。室内生测实验结果表明,小飞蓬全株水浸提物对5种受体种子的萌发和幼苗生长均有较强的抑制作用;根系分泌物、茎叶淋溶物和残体土壤分解物对受体种子的生长抑制作用不同,根系分泌物的活性高于茎叶淋溶物和残体土壤分解物。温室盆栽实验结果也表明,小飞蓬根系分泌物对受体生长的影响高于茎叶淋溶物。这些结果说明根系分泌是小飞蓬化感物质释放的主要途径之一。     

2种杂草水提液对小麦种子萌发及幼苗生长的影响

以2种麦田伴生杂草播娘蒿(Descurainiasophia)和猪殃殃(Galiumtricorne)为供体,以关中地区15个主要的小麦(Triticumaestivum)栽培品种为受体,采用室内生物测定法,比较了2种杂草水提液对不同小麦品种种子萌发及幼苗生长的影响.结果表明:(1)播娘蒿水提液对所有小麦品种的发芽率、发芽势和发芽指数均具有显著的抑制作用,猪殃殃水提液对这3项指标的抑制作用相对较弱,甚至对某些品种的这3项指标没有影响或具有促进作用.(2)2种杂草水提液对供试15个小麦品种的活力指数,以及根长、苗高、根鲜重、苗鲜重等生长指标均表现出抑制作用,且同一种杂草水提液对不同小麦品种的影响程度存在差异.(3)以播娘蒿和猪殃殃的响应指数值(RI)为指标分别将15个小麦品种聚类为强、中、弱三组,并发现2种杂草水提液分别对小偃22和西农979的化感作用均较弱,即这2个品种对播娘蒿和猪殃殃的化感作用均具有较强抗性.     

小麦根系分泌物对黄瓜生长及土壤真菌群落结构的影响

以黄瓜为受体,以不同化感效应(促进/抑制)小麦品种为供体,采用PCR-DGGE技术,研究了小麦根系分泌物及伴生小麦对黄瓜生长及土壤真菌群落结构的影响.结果表明： 在处理第6天和第12天,化感促进效应小麦根系分泌物分别显著提高了黄瓜幼苗株高和茎粗;在处理第18天,化感促进和抑制效应小麦根系分泌物均显著提高了黄瓜幼苗株高;在处理第6天,不同化感效应小麦根系分泌物均显著降低了黄瓜幼苗根际土壤真菌群落条带数、Shannon指数及均匀度指数,有苗对照(W)显著高于无苗对照(Wn);在处理第18天,各处理的真菌群落结构条带数、Shannon指数及均匀度指数均显著高于无苗对照(Wn).伴生化感抑制效应小麦显著降低了黄瓜根际土壤真菌群落Shannon指数和均匀度指数,说明小麦根系分泌物及伴生小麦改变了土壤真菌群落结构.DGGE图谱及其主成分分析结果表明,伴生不同化感效应小麦对土壤真菌群落结构影响较大.     

Differential belowground allelopathic effects of leaf and root of Mikania micrantha

This study evaluates the relative contributions of leaves and roots to the belowground allelopathic effects of Mikania micrantha. The hypothesis that leaves contribute more to the allelopathic effect than roots was experimentally tested. We assessed the allelopathic effects of aqueous extracts from Mikania leaves and roots on the seed germination and seedling growth of two co-occurring woody plants in southern China, Lagerstroemia indica L. and Robinia pseudoacacia L. The results showed that the aqueous extracts from Mikania leaves and roots had inhibitory effects on the woody species. Allelopathic activity depended on the concentration of the extracts, target species, and the extract sources (i.e., leaves vs. roots of Mikania). Leaf extract showed stronger allelopathic effects than root extract on germination percentage, initial germination time, speed of germination, and shoot height; while root extract had greater allelopathic effects on roots than leaf extract. The latter phenomenon might greatly promote the invasion success of Mikania due to more direct and effective allelopathy of root. Our results suggest that allelopathy of root extract on belowground biomass might be greater than that of leaf extract for some species in contrast allelopathy of leaf extract on belowground biomass might also be greater than that of root extract for other species, at least for their effects on root growth of the target species.     

The chemical-mediated allelopathic interaction between rice and barnyard grass

Aims

The possible involvement of the chemical-mediated interaction in allelopathy between rice and barnyard grass was investigated.

Methods

Effcts of rice seedlings and rice root exudate on the alleloapthic activity of barnyard grass were determined and a key compound invovled in the allelopathic interaction between rice and barnyard grass was isolated.

Results

Allelopathic activity of barnyard grass was increased by the presence of rice seedlings. Rice root exudates also elevated the allelopahtic activity of barnyard grass. A key compound, which increased the allelopathic activity of barnyard grass, in the rice root exudates was isolated and determined as momilactone B. Momilactone B increased the allelopathic activity of barnyard grass at concentrations greater than 3 μM, and increasing the momilactone B concentration increased the activity.

Conclusions

Momilactone B is known to act as a potent rice allelochemical and to possess strong growth inhibitory activity against barnyard grass. The present research suggests that barnyard grass may response to the presence of neighboring rice by sensing momilactone B in rice root exudates and increase allelopathic activity. Thus, momilactone B may not only act as a rice allelochemical but also play an important role in rice-induced allelopathy of barnyard grass. The induced-allelopathy may provide a competitive advantage for barnyard grass through the growth inhibition of competing plant species including rice. Barnyard grass allelopathy may be one of the inducible defense mechanisms by chemical-mediated plant interaction between rice and barnyard grass. Rice allelopathy was also reported to be increased by the presence of barnyard grass through increasing production and secretion of momilactone B into surrounding environments. During the evolutional process, rice and barnyard grass may have developed the chemical cross talk to activate the defense mechanisms against some biotic stress conditions by detection of certain key compounds.     

Autotoxic potential of cucurbit crops

Soil sickness is often observed in cucurbit crops such as Citrullus lanatus, Cucumis melo and Cucumis sativus, but not in cucurbit crops such as Cucurbita moschata, Lagenaria leucantha and Luffa cylindrica. Results showed that root aqueous extracts of Citrullus lanatus, Cucumis melo and Cucumis sativus were autotoxic, but those of Cucurbita moschata, Momordica charantia and Luffa cylindrica were less autotoxic to the radicle elongation of respective species. Plant growth of Citrullus lanatus, Cucumis melo and Cucumis sativus were greatly inhibited by autotoxic substances released from powered root tissue at a rate of 1 g per seedling. Root exudates of Citrullus lanatus, Cucumis melo and Cucumis sativus were autotoxic to radicle elongation and seedling growth of respective species. However, root exudates of Citrullus lanatus did not inhibit radicle elongation of Cucurbita ficifolia, which is commonly used as rootstock for the grafting of Citrullus lanatus, Cucumis melo and Cucumis sativus to decrease soil-borne diseases in commercial production. It seems possible to overcome autotoxicity in cucurbit crops by grafting on Cucurbita ficifolia. This revised version was published online in June 2006 with corrections to the Cover Date.     

Autotoxicity Against Germination and Seedling Emergence in Cistus ladanifer L

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.     

Allelopathic substance in rice root exudates: rediscovery of momilactone B as an allelochemical

Much research on rice allelopathy has been directed toward the selection of allelopathic rice strains and the identification of allelochemicals in rice. This paper briefly summarizes recent progress in the rice allelopathy and focuses on rediscovery of momilactone B as an allelochemical. A large number of rice varieties were found to inhibit the growth of several plant species when grown together under field and/or laboratory conditions. These findings suggest that rice probably produces and releases allelochemical(s) into the environment. The putative compound causing the inhibitory effect of rice was recently isolated from rice root exudates, and the chemical structure of the inhibitor was determined by spectral data as momilactone B. In addition, it has been found that momilactone B is released from rice roots into the neighboring environment, and the release level of momilactone B from rice may be sufficient to cause growth inhibition of neighboring plants. These findings suggest that momilactone B may play an important role in rice allelopathy.     

蕨类植物的化感作用及其对生物多样性的影响

植物化感作用是植物通过向环境中释放化学物质从而对同种植株和繁殖体或与其他植物之间产生的直接或间接、有益或有害的作用,它影响植物分布、群落形成与演化、作物间作等,与生物多样性保护以及农林和园艺生产实践关系密切,在国际上受到越来越多的关注。但国内这方面的研究起步相对较晚,研究范围有限,对蕨类植物化感作用的报道更少。本文系统介绍了蕨类植物化感作用的研究进展,包括蕨类植物种内的化感作用(即自毒效应)、常见的蕨类植物种间的化感作用(即孢子体对配子体的化感作用和配子体对配子体的化感作用)及蕨类植物对种子植物的化感作用(蕨类植物可通过化感作用与种子植物争夺更多的资源和生长空间)。还介绍了种子植物对蕨类植物的化感作用(主要表现为抑制作用)以及蕨类植物化感作用与动物侵食、微生物侵染的关系,研究发现昆虫侵食能增强或减弱蕨类植物的化感作用,微生物的活动可能增强某些蕨类植物的化感作用。本文从上述不同角度说明蕨类植物化感作用对生物多样性的影响,希望有助于促进我国学者对该领域的深入研究。     

大量元素胁迫下南瓜化感作用研究

研究采用水培实验、生物测试及室内分析相结合的方法,研究在不同大量元素(N、P、K、Ca、S、Mg)营养胁迫下幼苗期南瓜根系分泌物及其提取物对南瓜幼苗生长的化感作用。结果表明：南瓜具有自毒作用,不同大量营养元素胁迫对其胚根和胚芽生长均产生了抑制作用。不同的营养条件对其根系分泌物的影响不同,营养元素的合理搭配可以减轻自身的自毒作用。南瓜根系分泌物经乙酸乙酯提取的活性有机物埘南瓜胚根牛长亦表现出抑制作用,且抑制作用程度较大。南瓜幼苗期根系十物质水浸液巾存在着抑制南瓜幼苗生长的化感物质：筛选出南瓜根系分泌物对自身幼苗生长产生抑制作用最弱的大量元素水平优化组合,为南瓜的营养胁迫机理提供依据。     

Allelopathic Substance Exuded from a Serious Weed, Germinating Barnyard Grass (Echinochloa crus-galli L.), Roots

The allelopathy of a serious weed, barnyard grass (Echinochloa crus-galli L.), was investigated. Root exudates of young barnyard grass showed allelopathic effects and plant-selective activity and inhibited root elongation of all plants tested. With respect to shoot growth, the exudates did not show inhibition of barnyard grass only. The allelopathic substance was isolated and identified as p-hydroxymandelic acid by NMR. p-Hydroxymandelic acid strongly inhibited shoot growth and root elongation of all plants tested. The effects of three congeners of p-hydroxymandelic acid were tested on rice shoot growth. In the biological activity exhibited in rice, shoot growth was related to the hydroxyl groups. Received October 7, 1998; accepted March 29, 1999