丛枝菌根真菌对植物根腐病的抑制效应及其机制

根腐病是一类危害严重的土传病害,常常导致作物产量和品质降低。丛枝菌根(AM)真菌是一类重要的土壤微生物,通过与植物根系建立共生体而发挥重要的生理生态功能。研究表明,AM真菌通过调节宿主植物一系列生理生化响应,诱导植物增强根腐病抗性。当前,利用AM真菌开展根腐病等土传病害的生物防治是植物与微生物互作领域的研究热点。本文全面梳理了AM真菌对宿主植物根腐病病原物的抑制效应,系统总结了AM真菌改变宿主植物根系形态结构、改善植物营养水平、与病原物竞争生态位点、激活植物防御体系、调节根系分泌物等方面的研究结果,分析了AM真菌抑制根腐病危害的作用机制,展望了AM真菌抑制根腐病危害的潜在机制和AM真菌高效利用面临的现实问题,旨在为利用AM真菌开展植物根腐病的生物防治提供理论依据。     

AM真菌在植物病虫害生物防治中的作用机制

丛枝菌根(Arbuscular Mycorrhizae,AM)真菌是一类广泛分布于土壤生态系统中的有益微生物,能与大约80%的陆生高等植物形成共生体。由土传病原物侵染引起的土传病害被植物病理学界认定为最难防治的病害之一。研究表明,AM真菌能够拮抗由真菌、线虫、细菌等病原体引起的土传性植物病害,诱导宿主植物增强对病虫害的耐/抗病性。当前,利用AM真菌开展病虫害的生物防治已经引起生态学家和植物病理学家的广泛关注。基于此,围绕AM真菌在植物病虫害生物防治中的最新研究进展,从AM真菌改变植物根系形态结构、调节次生代谢产物的合成、改善植物根际微环境、与病原微生物直接竞争入侵位点和营养分配、诱导植株体内抗病防御体系的形成等角度,探究AM真菌在植物病虫害防治中的作用机理,以期为利用AM真菌开展植物病虫害的生物防治提供理论依据,并对本领域未来的发展方向和应用前景进行展望。     

菌根真菌提高杨树抗溃疡病生理生化机制的研究

以107速生杨(Populus×euramericana cv.'74/76')幼苗为材料,考察了接种丛枝菌根真菌(AMF)和外生菌根真菌(ECMF)幼苗在受到溃疡病菌侵害后生理生化指标和抗病相关蛋白的变化,初步探讨菌根真菌诱导植物抗病性的可能机制.结果表明,两种菌根真菌都能够显著降低杨树幼苗溃疡病的感病指数和发病率,显著提高杨树叶片叶绿素、树皮可溶性蛋白含量和根系活力强度;两种菌根真菌都可以显著降低杨树感病部位的丙二醛含量和提高游离脯氨酸含量,增强杨树超氧化物歧化酶(SOD)和苯丙氨酸解氨酶(PAL)的活性;丛枝菌根真菌能显著诱导提高杨树感病部位几丁质酶和β-1,3-葡聚糖酶活性,而外生菌根真菌则不能诱导或效应较低,且丛枝菌根真菌诱导杨树提高抗病性的相关指标均优于外生菌根真菌,而苗木感病指数和发病率均低于外生菌根真菌,其在幼苗期接种提高杨树抗溃疡病的效果较好.可见,在杨树受到溃疡病菌侵染时,菌根真菌可促进杨树对营养物质的吸收和生长,提高菌根苗体内保护酶活性和抗性相关化合物的含量,促使产生大量几丁质酶和β-1,3-葡聚糖酶来诱导杨树产生二次防卫反应,从而补偿病害所带来的损伤,增强抗病性.     

丛枝菌根真菌防治尖孢镰孢枯萎病的效应、机制及其应用研究进展

尖孢镰孢(Fusarium oxysporum)所引起的植物枯萎病是农业生产中广泛存在且难以防治的一种土传病害,严重影响作物的产量和品质。丛枝菌根(arbuscular mycorrhiza,AM)真菌能够与大部分陆生植物形成互惠共生关系,在促进植物生长、增强宿主植物抗病性等方面具有重要作用。本文收集整理了2001-2021年期间发表的相关文献,评述了AM真菌防治尖孢镰孢枯萎病的研究进展,并分析了AM真菌菌剂组成及应用方式对病害发生情况和尖孢镰孢丰度的影响。根据AM真菌在土壤-植物连续体的空间位置及其影响范围,从土壤、根系、植株等作用层面对AM真菌增强植物抵抗尖孢镰孢的直接和间接作用机制进行总结,包括影响土壤微环境、调节植物根际微生物群落结构、与病原菌竞争生态位、强化根系机械保护屏障、促进宿主植物养分吸收和生长、诱导植物系统性抗性等。此外,综合讨论了AM真菌与其他手段联合应用防治尖孢镰孢枯萎病的应用研究进展。本文可为推进AM真菌生物防治病害相关基础与应用研究的发展提供借鉴和参考。     

丛枝菌根真菌提高植物抗病性的作用机制*

近年来, 人们越来越重视丛枝菌根（AM）真菌对植物病原物的影响和提高植物抗病性的效应。当前建立在分子生物学、免疫学和组织化学技术上的基础研究, 可以从分子水平上深入了解AM真菌提高植物抗病性的作用机制。本文主要探讨AM真菌拮抗植物土传病原物、提高抗病性的可能机制和研究途径。1 AM真菌对植物土传病原物的拮抗作用自然条件下,绝大多数植物都能形成菌根。菌根围（Mycorrhizosphere）内的主要成员：根系、细菌、真菌、线虫等之间往往通过协同和/或拮抗作用达到动态平衡。其中植物—植物间、植物—微生物间、微生物—微生物间、…     

丛枝菌根对植物根际逆境的生态学意义

近年来,我国在菌根分子生物学、菌根营养学、菌根分类学和菌根生态学等方面取得了令人瞩目的研究成果,其中对丛枝菌根真菌(AMF)的研究居多。AMF能与大部分陆地植物根系形成共生关系,促进植物生长发育,提高植物抗逆性,在保持生态平衡、保护生态环境等方面发挥重要作用。本文主要从非生物胁迫(干旱胁迫、重金属污染、盐碱胁迫)和生物胁迫(致病菌和线虫侵染)方面介绍了AMF在植物根际逆境中发挥的生态功能及作用机制,提出了该研究领域尚存的不足之处和研究前景,为AMF后续研究提供参考。     

禾草内生真菌对其它微生物的影响研究进展

禾草内生真菌在宿主植物的茎叶等地上组织中普遍存在,不仅能够提高禾草对生物与非生物逆境的抗性,而且能够对周围环境中的不同微生物类群产生影响。主要总结了禾草Neotyphodium/Epichlo内生真菌对病原真菌、丛枝菌根真菌和土壤微生物的影响及其作用机理。发现禾草内生真菌普遍存在对病原真菌的抑制作用,而对丛枝菌根真菌存在不对称的竞争作用,且因种类而异。禾草内生真菌对土壤微生物群落的作用则会随着土壤类型和时间等外界因素发生变化。禾草内生真菌对不同类群微生物的影响机制主要包括:通过生态位竞争、抑菌物质分泌、诱导抗病性等对病原真菌造成影响;通过根系化学物质释放、营养元素调节、侵染条件差异等对丛枝菌根真菌造成影响;通过根际沉积物和凋落物等对土壤微生物群落造成影响。禾草内生真菌产生的生物碱能提高宿主植物对包括昆虫在内草食动物采食的抗性,影响病原菌的侵入、定殖和扩展;根组织分泌物中包含次生代谢产物能够抑制菌根真菌、土传病原真菌及其它土壤微生物的侵染与群落组成;也可能通过次生代谢物影响禾草的其它抗性。因此,禾草内生真菌在植物-微生物系统中的作用应该给予更多的关注和深入研究。     

茉莉酸介导丛枝菌根形成及其诱导抗病性研究进展

丛枝菌根真菌(arbuscular mycorrhizal fungi,AMF)与大多数植物共生可增强植株对病原菌的抗性,而茉莉酸(jasmonic acid,JA)在丛枝菌根(arbuscular mycorrhiza,AM)的形成以及植物对病原菌的抗性方面具有积极的作用。因此,该文旨在讨论茉莉酸介导的丛枝菌根诱导的植物抗病性可能机理,以期为抗病性应用提供尽可能多的理论支撑。首先,总结了茉莉酸与丛枝菌根的相关性;其次,对茉莉酸介导的丛枝菌根诱导的抗病性研究进展及可能机理做出归纳;最后,对未来的研究方向及方法进行了展望。     

丛枝菌根真菌对茄子黄萎病的防治效果和茄子植株生长的影响

研究了接种丛枝菌根真菌(AMF)对茄子生长和对黄萎病的影响,并且探讨了AMF诱导植物抗病性的生理生化变化。结果表明:接种AMF能促进茄子的生长,明显降低茄子黄萎病的发病率和发病指数;与只接黄萎菌处理比较,在先接种AMF然后接种黄萎病原菌的情况下,可以降低茄子叶内脯氨酸含量和相对电导率,提高根系活力,提高过氧化物酶(POD)、多酚氧化酶(PPO)和苯丙氨酸解氨酶(PAL)的活性。试验显示,AMF对茄子黄萎病具有一定的生防效果。这种抗性可能来源于AMF提高了茄子营养水平,激活了植物抗病机制。     

内蒙古中部地区马铃薯根际和根系丛枝菌根真菌类群的多样性

【背景】丛枝菌根真菌(arbuscular mycorrhizal fungus,AMF)是菌根真菌中分布最广泛的一类真菌,能够与90%以上的植物形成菌根共生体,并通过调节宿主体内的代谢活动增强植物的抗逆性。【目的】揭示内蒙古马铃薯主产区土壤中AMF的结构与组成,解析马铃薯不同发育阶段以及连作对AMF类群的影响。【方法】以内蒙古中部地区大井村、徐麻夭村和红格尔图村采集的马铃薯根系及根际土为材料,通过PCR扩增建立18S rRNA基因文库,研究不同地点、不同马铃薯生育阶段以及连作对马铃薯根系内和根际土中的AMF类群组成和多样性的影响。【结果】大井村和红格尔图村马铃薯根际土中的AMF的类群多样性优于徐麻夭村,其中Glomus为大井村和红格尔图村马铃薯根际土样本中AMF的优势菌群,而徐麻夭村样本根际土中的优势类群为Diversispora。马铃薯根系中的AMF多样性的研究结果表明,3个供试地点根系内AMF类群的类型没有显著差异,但是AMF类群的比例却不同。大井村根系样本中AMF的优势菌为Diversispora,而Rhizophagus是红格尔图村和徐麻夭村根系样本中的优势AMF类群。同一供试地点马铃薯苗期和块茎膨大期根际土中的AMF类群的类型多于块茎形成期,其中Glomus是马铃薯不同发育阶段根际土中的优势类群;而Rhizophagus是3个不同发育阶段根系内的优势类群。2015和2016年马铃薯连作地块中根际土和根系内AMF类群的类型完全相同,但是不同的AMF类群的相对丰度随着马铃薯的连作呈现出显著的变化。其中,根际土样本中Glomus和Archaeospora类群的相对丰度随着连作有所上升,相应的Entrophospora和Diversispora相对丰度有所下降;根系样本中AMF的优势类群随着连作从Glomus转变为Rhizophagus。AMF多样性测定结果表明,连作对马铃薯根际土中AMF多样性的影响显著高于对根系内类群的影响。【结论】AMF类群的多样性会因土壤组成成分、马铃薯生育期和连作效应而呈现不同变化。     

Arbuscular mycorrhiza‐mediated resistance in tomato against Cladosporium fulvum‐induced mould disease

Root colonization with arbuscular mycorrhizal fungi (AMF) enhances plant resistance particularly against soil‐borne pathogenic fungi. In this study, mycorrhizal inoculation with Glomus mosseae (Gm) significantly alleviated tomato mould disease caused by the air‐borne fungal pathogen, Cladosporium fulvum (Cf). The disease index (DI) in local leaves (receiving pathogen inoculation) and systemic leaves (just above the local leaf without pathogen inoculation) was 36.4% and 11.7% in mycorrhizal plants, respectively, whereas DI was 59.6% and 36.4% in the corresponding leaves of AMF non‐inoculated plants, after 50 days of Gm inoculation, corresponding to 15 days after Cf inoculation by leaf infiltration. Foliar spray inoculation with Cf also revealed that AMF pre‐inoculated plants had a higher resistance against subsequent pathogen infection, where the DI was 41.3% in mycorrhizal plants vs. 64.4% in AMF non‐inoculated plants. AMF‐inoculated plants showed significantly higher fresh and dry weight than non‐inoculated plants under both control (without pathogen) and pathogen treatments. AMF‐inoculated plants exhibited significant increases in activities of superoxide dismutase and peroxidase, along with decreases in levels of H₂O₂ and malondialdehyde, compared with non‐inoculated plants after pathogen inoculation. AMF inoculation led to increases in total chlorophyll contents and net photosynthesis rate as compared with non‐inoculated plants under control and pathogen infection. Pathogen infection on AMF non‐inoculated plants led to decreases in chlorophyll fluorescence parameters. However, pathogen infection did not affect these parameters in mycorrhizal plants. Taken together, these results indicate that AMF colonization may play an important role in plant resistance against air‐borne pathogen infection by maintaining redox poise and photosynthetic activity.     

Mycorrhizal fungi suppress aggressive agricultural weeds

Plant growth responses to arbuscular mycorrhizal fungi (AMF) are highly variable, ranging from mutualism in a wide range of plants, to antagonism in some non-mycorrhizal plant species and plants characteristic of disturbed environments. Many agricultural weeds are non mycorrhizal or originate from ruderal environments where AMF are rare or absent. This led us to hypothesize that AMF may suppress weed growth, a mycorrhizal attribute which has hardly been considered. We investigated the impact of AMF and AMF diversity (three versus one AMF taxon) on weed growth in experimental microcosms where a crop (sunflower) was grown together with six widespread weed species. The presence of AMF reduced total weed biomass with 47% in microcosms where weeds were grown together with sunflower and with 25% in microcosms where weeds were grown alone. The biomass of two out of six weed species was significantly reduced by AMF (?66% & ?59%) while the biomass of the four remaining weed species was only slightly reduced (?20% to ?37%). Sunflower productivity was not influenced by AMF or AMF diversity. However, sunflower benefitted from AMF via enhanced phosphorus nutrition. The results indicate that the stimulation of arbuscular mycorrhizal fungi in agro-ecosystems may suppress some aggressive weeds.     

Role of 2,4-diacetylphloroglucinol-producing fluorescent Pseudomonas spp. in the defense of plant roots

Plants have evolved strategies of stimulating and supporting specific groups of antagonistic microorganisms in the rhizosphere as a defense against diseases caused by soilborne plant pathogens owing to a lack of genetic resistance to some of the most common and widespread soilborne pathogens. Some of the best examples of natural microbial defense of plant roots occur in disease suppressive soils. Soil suppressiveness against many different diseases has been described. Take-all is an important root disease of wheat, and soils become suppressive to take-all when wheat or barley is grown continuously in a field following a disease outbreak; this phenomenon is known as take-all decline (TAD). In Washington State, USA and The Netherlands, TAD results from the enrichment during monoculture of populations of 2,4-diacetylphloroglucinol (2,4-DAPG)-producing Pseudomonas fluorescens to a density of 10 (5) CFU/g of root, the threshold required to suppress the take-all pathogen, Gaeumannomyces graminis var. tritici. 2,4-DAPG-producing P. fluorescens also are enriched by monoculture of other crops such as pea and flax, and evidence is accumulating that 2,4-DAPG producers contribute to the defense of plant roots in many different agroecosystems. At this time, 22 distinct genotypes of 2,4-DAPG producers (designated A - T, PfY and PfZ) have been defined by whole-cell repetitive sequence-based (rep)-PCR analysis, restriction fragment length polymorphism (RFLP) analysis of PHLD, and phylogenetic analysis of PHLD, but the number of genotypes is expected to increase. The genotype of an isolate is predictive of its rhizosphere competence on wheat and pea. Multiple genotypes often occur in a single soil and the crop species grown modulates the outcome of the competition among these genotypes in the rhizosphere. 2,4-DAPG producers are highly effective biocontrol agents against a variety of plant diseases and ideally suited for serving as vectors for expressing other biocontrol traits in the rhizosphere.     

The plant growth‐promoting fungus Fusarium equiseti and the arbuscular mycorrhizal fungus Glomus mosseae stimulate plant growth and reduce severity of anthracnose and damping‐off diseases in cucumber (Cucumis sativus) seedlings

To alleviate the environmental contamination due to persistent chemical usage, approaches to integrated pest management were conceived. In this perspective, microbe–microbe interactions such as mycorrhizal relationships with other soil microbiota in the rhizosphere like the plant growth‐promoting fungi (PGPF) are particularly important. Better understanding of the interactions between beneficial microbial groups is imperative in the identification of possible synergistic or antagonistic effects to improve their practical usage as biocontrol agents or biofertilizers. In this study, the consequence of co‐inoculation of the arbuscular mycorrhizal fungus (AMF) Glomus mosseae (Gm) and the PGPF Fusarium equiseti (isolates GF18‐3 and GF19‐1) in terms of plant growth enhancement, root and rhizosphere colonisation, and development of anthracnose (Colletotrichum orbiculare) and damping‐off (Rhizoctonia solani AG‐4) diseases in cucumber plants was investigated under controlled conditions. The amendment of either GF18‐3 or GF19‐1 singly or in combination with Gm indicated a general tendency to significantly enhance the shoot dry weight (SDW) of cucumber plants at 4 weeks after planting (WAP). Similarly, Gm alone significantly enhanced SDW at 4 WAP. Gm showed a tendency to depress root colonisation by F. equiseti but such antagonistic effect was not observed in the rhizosphere soil. Both GF18‐3 and GF19‐1 significantly reduced percent root colonisation of Gm. However, these general tendencies may vary with the inoculum densities of AMF and PGPF. Both F. equiseti and Gm inoculated singly significantly increased percent of protection against anthracnose, but the combined inoculation was more effective in controlling the disease compared to single inoculation. The inoculation of the cucumber seedlings with GF18‐3, GF19‐1 or Gm, 6 or 12 days prior to damping‐off pathogen inoculation, increased percent of protection against damping‐off disease. This study shows that the co‐inoculation of F. equiseti and Gm resulted in additive effect on the suppression of anthracnose disease in cucumber.     

Early responses of wild plant seedlings to arbuscular mycorrhizal fungi and pathogens

Many plants form associations with arbuscular mycorrhizal fungi (AMF) because they profit from improved phosphorus nutrition and from protection against pathogens. Whereas mycorrhiza-induced pathogen protection is well understood in agricultural plant species, it is rarely studied in wild plants. As many pathogens infest plants in the first days after germination, mycorrhiza-induced pathogen protection may be especially important in the first few weeks of plant establishment.Here, we investigated interacting effects of AMF and the seedling pathogen Pythium ultimum on the performance of six- to seven-week-old seedlings of six wild plant species of the family Asteraceae in a full factorial experiment.Plant species differed in their response to AMF, the pathogen and their interactions. AMF increased and the pathogen decreased plant biomass in one and three species, respectively. Two plant species were negatively affected by AMF in the absence, but positively or not affected in the presence of the pathogen, indicating protection by AMF. This mycorrhiza-induced pathogen protection is especially surprising as we could not detect mycorrhizal structure in the roots of any of the plants.Our results show that even seedlings without established intraradical hyphal network can profit from AMF, both in terms of growth promotion in the absence of a pathogen and pathogen protection. The function of AMF is highly species-specific, but tends to be similar for more closely related plant species, suggesting a phylogenetic component of mycorrhizal function. Further studies should test a wider range of plant species, as our study was restricted to one plant family, and investigate whether plants profit from early mycorrhizal benefits in the long term.     

Arbuscular mycorrhizal fungi-enhanced resistance against Phytophthora sojae infection on soybean leaves is mediated by a network involving hydrogen peroxide, jasmonic acid, and the metabolism of carbon and nitrogen

The arbuscular mycorrhizal fungi (AMF) enhance the resistance to pathogen infection in host plant. However, it is unclear how the AMF are involved in the systemic acquired resistance of host plant against pathogen. Here, an experiment was carried out to clarify the role of the AMF in soybean’s defense against the infection from pathogen Phytophthora sojae. It was found that the AMF contributed to the resistance of soybean against Phytophthora sojae by the release of hydrogen peroxide and by the accumulation of jasmonic acid in response to pathogenic invasion. Furthermore, the trade of nitrogen (N) from the fungus for carbon from the host was accelerated in the AM symbiosis in the defense reaction, which was indicated by the increased soluble sugar level, NO content and enzyme activities involved in N metabolism in the AM symbiosis.     

Chemical defense,mycorrhizal colonization and growth responses in <Emphasis Type="Italic">Plantago lanceolata</Emphasis> L.

Allelochemicals defend plants against herbivore and pathogen attack aboveground and belowground. Whether such plant defenses incur ecological costs by reducing benefits from plant mutualistic symbionts is largely unknown. We explored a potential trade-off between inherent plant chemical defense and belowground mutualism with arbuscular mycorrhizal fungi (AMF) in Plantago lanceolata L., using plant genotypes from lines selected for low and high constitutive levels of the iridoid glycosides (IG) aucubin and catalpol. As selection was based on IG concentrations in leaves, we first examined whether IG concentrations covaried in roots. Root and leaf IG concentrations were strongly positively correlated among genotypes, indicating genetic interdependence of leaf and root defense. We then found that root AMF arbuscule colonization was negatively correlated with root aucubin concentration. This negative correlation was observed both in plants grown with monocultures of Glomus intraradices and in plants colonized from whole-field soil inoculum. Overall, AMF did not affect total biomass of plants; an enhancement of initial shoot biomass was offset by a lower root biomass and reduced regrowth after defoliation. Although the precise effects of AMF on plant biomass varied among genotypes, plants with high IG levels and low AMF arbuscule colonization in roots did not produce less biomass than plants with low IG and high AMF arbuscule colonization. Therefore, although an apparent trade-off was observed between high root chemical defense and AMF arbuscule colonization, this did not negatively affect the growth responses of the plants to AMF. Interestingly, AMF induced an increase in root aucubin concentration in the high root IG genotype of P. lanceolata. We conclude that AMF does not necessarily stimulate plant growth, that direct plant defense by secondary metabolites does not necessarily reduce potential benefits from AMF, and that AMF can enhance concentrations of root chemical defenses, but that these responses are plant genotype-dependent.     

Modulation of host immunity by beneficial microbes

In nature, plants abundantly form beneficial associations with soilborne microbes that are important for plant survival and, as such, affect plant biodiversity and ecosystem functioning. Classical examples of symbiotic microbes are mycorrhizal fungi that aid in the uptake of water and minerals, and Rhizobium bacteria that fix atmospheric nitrogen for the plant. Several other types of beneficial soilborne microbes, such as plant-growth-promoting rhizobacteria and fungi with biological control activity, can stimulate plant growth by directly suppressing deleterious soilborne pathogens or by priming aboveground plant parts for enhanced defense against foliar pathogens or insect herbivores. The establishment of beneficial associations requires mutual recognition and substantial coordination of plant and microbial responses. A growing body of evidence suggests that beneficial microbes are initially recognized as potential invaders, after which an immune response is triggered, whereas, at later stages of the interaction, mutualists are able to short-circuit plant defense responses to enable successful colonization of host roots. Here, we review our current understanding of how symbiotic and nonsymbiotic beneficial soil microbes modulate the plant immune system and discuss the role of local and systemic defense responses in establishing the delicate balance between the two partners.     

Cultivation of high-biomass crops on coal mine spoil banks: can microbial inoculation compensate for high doses of organic matter?

Two greenhouse experiments were focused on the application of arbuscular mycorrhizal fungi (AMF) and plant growth promoting rhizobacteria (PGPR) in planting of high-biomass crops on reclaimed spoil banks. In the first experiment, we tested the effects of different organic amendments on growth of alfalfa and on the introduced microorganisms. While growth of plants was supported in substrate with compost amendment, mycorrhizal colonization was suppressed. Lignocellulose papermill waste had no negative effects on AMF, but did not positively affect growth of plants. The mixture of these two amendments was found to be optimal in both respects, plant growth and mycorrhizal development. Decreasing doses of this mixture amendment were used in the second experiment, where the effects of microbial inoculation (assumed to compensate for reduced doses of organic matter) on growth of two high-biomass crops, hemp and reed canarygrass, were studied. Plant growth response to microbial inoculation was either positive or negative, depending on the dose of the applied amendment and plant species.