Plant growth promoting rhizobacteria as alternative to chemical crop protectors from pathogens (review)

The review analyses data on physiological and biochemical influence of rhizospheric and endophytic plant growth promoting rhizobacteria (PGPR) on induced the mechanisms of resistance of plants and the possibility of their using in agricultural for to protect crop from pathogens and phytophages. Resistance of plants promoted by PGPR due to their endosymbiotic interrelationships is directly achieved by producing peptide antibiotics and hydrolases of chitin and glucan and also because plants form their own system of induced resistance, accompanied by changes in the balance of defensive proteins, phytohormones, and pro-/antioxidant status.     

Photosynthetic bacterium Rhodopseudomonas palustris GJ‐22 induces systemic resistance against viruses

Photosynthetic bacteria (PSB) have been extensively used in agriculture to promote plant growth and to improve crop quality. Their potential application in plant disease management, however, is largely overlooked. In this study, the PSB strain Rhodopseudomonas palustris GJ‐22 was investigated for its ability to induce resistance against a plant virus while promoting plant growth. In the field, a foliar spray of GJ‐22 suspension protected tobacco plants against tobacco mosaic virus (TMV). Under axenic conditions, GJ‐22 colonized the plant phyllosphere and induced resistance against TMV. Additionally, GJ‐22 produced two phytohormones, indole‐3‐acetic acid and 5‐aminolevulinic acid, which promote growth and germination in tobacco. Furthermore, GJ‐22‐inoculated plants elevated their immune response under subsequent TMV infection. This research may give rise to a novel biological agent with a dual function in disease management while promoting plant growth.     

Effects of jasmonic acid, ethylene, and salicylic acid signaling on the rhizosphere bacterial community of Arabidopsis thaliana

Systemically induced resistance is a promising strategy to control plant diseases, as it affects numerous pathogens. However, since induced resistance reduces one or both growth and activity of plant pathogens, the indigenous microflora may also be affected by an enhanced defensive state of the plant. The aim of this study was to elucidate how much the bacterial rhizosphere microflora of Arabidopsis is affected by induced systemic resistance (ISR) or systemic acquired resistance (SAR). Therefore, the bacterial microflora of wild-type plants and plants affected in their defense signaling was compared. Additionally, ISR was induced by application of methyl jasmonate and SAR by treatment with salicylic acid or benzothiadiazole. As a comparative model, we also used wild type and ethylene-insensitive tobacco. Some of the Arabidopsis genotypes affected in defense signaling showed altered numbers of culturable bacteria in their rhizospheres; however, effects were dependent on soil type. Effects of plant genotype on rhizosphere bacterial community structure could not be related to plant defense because chemical activation of ISR or SAR had no significant effects on density and structure of the rhizosphere bacterial community. These findings support the notion that control of plant diseases by elicitation of systemic resistance will not significantly affect the resident soil bacterial microflora.     

木本植物木质部的冻融栓塞应对研究进展

冻融栓塞在中高纬度地区木本植物中普遍存在。抗冻融栓塞能力对在寒冷环境中木本植物的生长和安全越冬十分关键, 这直接决定植物分布范围。冻融栓塞是由于冰中气体溶解度低, 木质部水分在低温下冷冻, 使之前水中溶解的气体逸出到导管中, 随后木质部中的冰融化又使气泡扩张而引发的栓塞现象。木质部解剖结构的差异会影响植物的抗冻融栓塞能力, 植物还可以通过调节木质部正压、代谢耗能等方式主动修复冻融栓塞, 也可通过增加树液溶质含量等逃避冷冻, 以减少低温损伤。然而, 与干旱栓塞相比, 目前对木质部冻融栓塞的形成以及植物响应和调节机制的理解不足。为此, 该文首先综述了木质部冻融栓塞的形成机制和植物的逃避、忍耐、修复等3种冻融栓塞的应对策略, 然后总结了木质部抗低温胁迫能力的生理表现、影响因子和评价指标, 并在此基础上讨论了低温抗性、干旱抗性和水力效率之间的多元权衡关系, 最后提出今后该领域中的5个优先研究问题: (1)不同植物冰冻的最低温度阈值; (2)是否存在应对低温胁迫的水力脆弱性分割机制; (3)冻融栓塞修复与代谢消耗的关系; (4)低温抗性、干旱抗性和水力效率之间的权衡关系; (5)抗冻融栓塞性状是否能够纳入经济性状谱系。     

丛枝菌根菌诱导植物抗病的内在机制

应用菌根真菌诱导植物抗病性是近年化学生态学和病害生物防治研究的热点．研究表明,丛枝菌根真菌(AMF)对土传病原物具有一定拮抗或抑制作用,能提高植物对土传病害的抗／耐病性．在菌根根际,各种菌群不断产生相互作用,AMF在其中起着抑制病原菌、促进有益菌生长的作用,可与其他桔抗菌结合,用做生防菌．AMF提高植物抗病性的机制还有这样几种假设：(1)植物营养得到改善;(2)竞争作用;(3)根系形态结构改变;(4)根际微生物区系变化;(5)诱导抗性及诱导系统抗性,即AMF侵染植物根系后,诱导植物体内酚酸类代谢产物增加,使植物产生局部或系统防御反应．深人研究AMF提高植物抗病性的机制,有助于正确理解菌根的抗病作用,使其能尽快地成为植物病害生物防治中的一种新方法,在生态农业中发挥作用。     

Rhizobacterial salicylate production provokes headaches!

Background

Salicylic acid (SA) is produced in significant amounts by certain plant growth promoting rhizosphere bacteria, and some of these rhizobacteria have the ability to induce systemic resistance against diseases in plants. Exogenous application of SA to plants has long been known to lead to protection against a range of plant pathogens through the elicitation of systemic acquired resistance. Thus, it is reasonable to assume that the SA producing plant beneficial rhizobacteria elicit induced resistance through the production of SA.

Scope and conclusions

However, we discuss here that bacterial secretion of SA in vitro appears to be an artifact and that the bacteria will normally incorporate SA into SA-containing metabolites, mainly SA-based siderophores, under environmental conditions. Therefore, we argue that rhizobacteria do not likely excrete free SA into the rhizosphere thereby not inducing resistance in plants through this metabolite. SA detected in the rhizosphere is most likely produced by the plant and we discuss the impact of this phenolic compound on microbial interactions.     

小麦体内生化物质在抗蚜中的作用

综述了小麦体内生化物质的抗蚜作用 ,主要包括不同抗性品种对麦蚜的影响、小麦体内氨基酸、糖类、酚类物质、生物碱和非蛋白氨基酸等与抗蚜性的关系 ,以及蚜虫对小麦体内抗虫生化物质的诱导作用 ,并提出了深入研究小麦生化物质与抗蚜性关系的前景和意义。     

Endophytic bacteria enhancing growth and disease resistance of potato (Solanum tuberosum L.)

Priming plants by non-pathogenic bacteria allows the host to save energy and to reduce time needed for development of defense reaction during a pathogen attack. However, information on the role of endophytes in plant defense is limited. Here, the ability of endophytic bacteria to promote growth and resistance of potato plants towards infection by the necrotroph Pectobacterium atrosepticum was studied. A Pseudomonas sp. strain was selected due to antagonism towards bacterial pathogens and a Methylobacterium sp. strain because of efficient plant colonization. The aim of this study was to find if there is any correlation between plant growth promotion and induction of resistance by endophytes of potato, as well as to study the putative mechanisms of endophytes interacting with the plant during resistance induction. Both tested strains promoted growth of potato shoots but only the Pseudomonas sp. increased potato resistance towards the soft rot disease. Induction of disease resistance by the Methylobacterium sp. was inversely proportional to the size of bacterial population used for inoculation. The plant antioxidant system was moderately activated during the induction of resistance by the biocontrol strains. qPCR data on expression of marker genes of induced systemic resistance and acquired systemic resistance in endophyte-infected Arabidopsis plants showed activation of both salicylic acid and jasmonate/ethylene-dependent pathways after challenge inoculation with the pathogen. We suggest that some endophytes have the potential to activate both basal and inducible plant defense systems, whereas the growth promotion by biocontrol strains may not correlate with induction of disease resistance.     

Effects of herbivory and plant conditioning on the population dynamics of spider mites

Plants vary in their resistance to tetranychid spider mites, and this can have profound effects on spider-mite population dynamics. Such variation can be attributable to many factors. In this review, however, we focus on how previous or concurrent feeding by phytophagous hervivores influences expression of plant resistance to spider mites.Induced resistance is a change in the host plant in response to extrinsic stimuli, resulting in reduced host suitability for the population growth of spider mites. We begin our review by summarizing the different ways in which spider mites and plants interact to produce induced resistance-like phenomena. We then discuss a number of hypotheses which address the mechanisms underlying induced resistance and end by suggesting agricultural applications. Although the potential use of induced resistance to manage spider mites is apparent, progress in this area will depend on a better understanding of the mechanisms involved and their associated costs and benefits to the plant.     

A two-strain mixture of rhizobacteria elicits induction of systemic resistance against Pseudomonas syringae and Cucumber mosaic virus coupled to promotion of plant growth on Arabidopsis thaliana

We evaluated a commercial biopreparation of plant growth-promoting rhizobacteria (PGPR) strains Bacillus subtilis GB03 and B. amyloliquefaciens IN937a formulated with the carrier chitosan (BioYield) for its capacity to elicit growth promotion and induced systemic resistance against infection by Cucumber Mosaic Virus (CMV) and Pseudomonas syringae pv. tomato DC3000 in Arabidopsis thaliana. The biopreparation promoted plant growth of Arabidopsis hormonal mutants, which included auxin, gibberellic acid, ethylene, jasmonate, salicylic acid, and brassinosteroid insensitive lines as well as each wild-type. The biopreparation protected plants against CMV based on disease severity in wild-type plants. However, virus titre was not lower in control plants and those treated with biopreparation, suggesting that the biopreparation induced tolerance rather than resistance against CMV. Interestingly, the biopreparation induced resistance against CMV in NahG plants, as evidenced by both reduced disease severity and virus titer. The biopreparation also elicited induced resistance against P. syringae pv. tomato in the wild-type but not in NahG transgenic plants, which degrade endogenous salicylic acid, indicating the involvement of salicylic acid signaling. Our results indicate that some PGPR strains can elicit plant growth promotion by mechanisms that are different from known hormonal signaling pathways. In addition, the mechanism for elicitation of induced resistance by PGPR may be pathogen-dependent. Collectively, the two-Bacilli strain mixture can be utilized as a biological inoculant for both protection of plant against bacterial and viral pathogens and enhancement of plant growth.     

Endophytic fungi promote plant growth and mitigate the adverse effects of stem rot: an example of Penicillium citrinum and Aspergillus terreus

Disease resistance is a highly desirable crop trait in the sustainable agricultural industry. Endophytic fungi with gibberellins-secreting potential are now widely known for their ability to stimulate plant growth, but their role in promoting disease resistance in plants has rarely been reported. We have studied the role of Penicillium citrinum LWL4 and Aspergillus terreus LWL5 in time-dependent manner on sunflower (Helianthus annuus L.) growth, disease resistance and their capacity for the regulation of hormone signaling networks involved in plant defense against the stem rot caused by Sclerotium rolfsii for 3, 6 and 12 days after treatment (DAT). Our results show that plant growth characteristics (i.e. shoot length, shoot diameter, shoot fresh/dry weight, transpiration, stomatal conductance, photosynthesis and chlorophyll content) were promoted in fungi-treated plants with or without the disease caused by Sclerotium rolfsii as compared to their respective controls in 3, 6 and 12 DAT. The negative impacts of stem rot in endophyte-treated diseased plants were greatly reduced in comparison to control diseased plants shown by low disease severity in 3, 6 and 12 DAT. Similarly, fungal endophytes in diseased plants relieved the biotic stress in time-dependent manner (3, 6 and 12 DAT) as shown by low level of endogenous salicylic acid and jasmonic acid contents and were significantly higher in control diseased plants. Furthermore, we observed that the Penicillium citrinum LWL4 association had a greater positive effect on sunflower plants than Aspergillus terreus LWL5. It was concluded that inoculation with fungal endophytes reprogramed plant growth during disease incidence by regulating responses associated with host plant defense. Management strategies involving endophytic symbiosis can help achieve sustainability in agriculture in an eco-friendly manner by reducing excessive fungicide use.     

植物的诱导抗虫性

植物对植食性昆虫的抗性可包括两个方面,即植物的组成抗性（constitutiveresistance）和诱导抗性（inducedresistance）。组成抗性是指植物在遭受植食性昆虫进攻前就已存在的抗虫特性;而诱导抗性是指植物在遭受植食性昆虫进攻后所表现出来的一种抗虫特性[1,2]。根据作用世代的不同,诱导抗性又分为迅速的诱导抗性（rapidlyinducedre－sistance,RIR）和滞后的诱导抗性（delayedinducedresistance,DIR）。前者是指对当前世代的植食性昆虫的影响,而后者是指对后续的1～几个世代的植食性昆虫的影响[2]。研究植物的诱导抗虫性,不仅能在…     

Specificity of induced resistance in wild radish: causes and consequences for two specialist and two generalist caterpillars

Inducible plant resistance against herbivores is becoming a paradigm of plant–herbivore ecology. Fundamental to understanding induced resistance and its evolutionary ecology is specificity of "induction" and "effects". Specificity in the induction of resistance refers to whether plant damage by various herbivores causes the same response in plants. Specificity in the effects of induced resistance refers to whether induction has the same consequences (i.e., reduced preference or performance) for various herbivores. I examined both specificity of induction and effect employing four lepidopteran herbivores and wild radish plants, a system for which fitness benefits and costs of induction have been documented for the plant. Variation in the specificity of induction and effects of induced plant resistance was found; however, this variation was not associated with diet specialization in the herbivores (i.e., specialists vs generalists). Induction caused by Plutella (specialist) and Spodoptera (generalist) resulted in general resistance to all of the herbivores, induction caused by Pieris (specialist) induced resistance only to Spodoptera (generalist) and Pieris , and plant damage by Trichoplusia (generalist) failed to induce resistance and reduce the performance of any of the herbivores. To the contrary, plants damaged by Trichoplusia supported enhanced growth of subsequently feeding Trichoplusia compared to uninduced controls. These results add a novel level of complexity to interactions between plants and leaf chewing caterpillars. Within the same guild of feeders, some herbivores cause strong induced resistance, no induced resistance, or induced susceptibility. Similarly, caterpillar species were variable in the level to which induced resistance affected their performance. Such interactions limit the possibility of pairwise coevolution between plants and herbivores, and suggest that coevolution can only be diffuse.     

Drought stress affects constitutive but not induced herbivore resistance in apple plants

Plant–herbivore interactions are influenced by chemical plant traits, which can vary depending on the plants’ abiotic and biotic environment. Drought events, which are predicted to become more frequent and prolonged due to climate change, may affect primary and secondary plant metabolites contributing to constitutive resistance. Furthermore, the ability of plants to respond to herbivore attack in terms of induced resistance may be altered under drought conditions. We assessed the effects of drought stress on constitutive and induced apple plant resistance to a generalist insect herbivore by quantifying plant and herbivore responses in concert. Plants were exposed to different drought stress intensities (constitutive resistance) and subsequently to herbivore damage treatments that included different damage durations (induced resistance). As drought stress intensified, plant growth and concentrations of the leaf phenolic phloridzin decreased, whereas leaf glucose concentrations increased. Changes in fructose concentrations and in herbivore feeding preferences indicated a non-monotonic shift in constitutive resistance. Moderately stressed plants showed reduced fructose concentrations and were consumed least, while severely stressed plants were fructose-enriched and consumed most compared to well-watered control plants showing intermediate fructose concentrations and palatability. We found no evidence for effects of drought stress on induced resistance, as herbivore feeding preferences for undamaged over damaged plants were independent of drought intensity. Our results suggest a strong role of primary metabolites for drought-dependent variation in constitutive plant resistance and offer novel experimental insights into the effects of drought stress on induced plant resistance across a gradient of water deprivation.     

植物微生物组的功能及应用研究进展

健康的植物中生活着多种多样但分类学结构不同的微生物群落,它们在所有可接触到的植物组织中定殖.这些微生物群落赋予植物宿主健康优势,包括促进宿主植物生长、营养吸收、抗逆性和对病原菌的抵抗力等.植物菌群及其相互作用具有高度的多样性,多种因素决定着群落的组成和功能.虽然从19世纪开始植物菌群就被人们所认识,但对其功能及应用的相...     

植物内生菌增强植物对生物胁迫抗性的研究进展

植物在生长发育过程中因遭遇多种逆境的威胁而出现营养流失、产量大幅下降等问题，而使用传统的化学农药调控植物抗逆作用会对环境造成严重污染甚至危及人类健康，因此需要从天然成分中寻找合适的农药代替品。生活在每种植物体内的内生菌几乎都是植物微生态系统中的天然成分，因其特殊的生态位而可能对植物具有更加积极和直接的影响。然而目前，关于内生菌在提高宿主生物胁迫抗性等方面的作用机制还知之甚少。该文就植物内生菌的来源、多样性和对生物胁迫的抗性展开叙述。首先，总结了植物内生菌传播的主要方式，即水平传播和垂直传播；其次对内生菌种类的多样性以及在植物中的分布多样性进行了归纳与分析；最后，详细阐述了植物内生菌增强植物对生物胁迫应激耐受性(抗致病菌病害、抗虫害)的基本特点与作用机制，即植物内生菌可利用生态位竞争或营养位竞争产生的诱导抗性遏制病原菌感染，或合成抗生素类、生物碱类、几丁质类等次生代谢产物抑制病原菌或线虫的生长，从而防治病虫害。此外，基于内生菌增强植物生物胁迫抗性的研究现状进行了展望，为更加环保的生物防治制剂的开发与利用提供了参考。     

The presence of generalist plant pathogens might not explain the long-term coexistence of plant species

Pathogens have been shown to contribute to the possibility of coexistence of competing plant species by creating ecological distinction between the coexisting species. This coexistence promoting mechanism resembles intra-specific density dependence as found in Lotka-Volterra models. However, plant species adapt in their level of resistance against pathogen infection and this adaptation has been shown to be traded-off by a reduction in growth rate. A model is developed to show that taking into account the possible adaptation of plant species to increase their resistance against pathogen infection by generalist pathogens has consequences for the coexistence of the plant species. The results show that in systems where plants adapt to the pathogen infection, coexistence becomes impossible. The implication of this finding is that plant pathogens might contribute less to the coexistence of plant species than is commonly thought.     

In vitro induction of lipo-chitooligosaccharide production in Bradyrhizobium japonicum cultures by root extracts from non-leguminous plants

Bradyrhizobium japonicum can form a N2-fixing symbiosis with compatible leguminous plants. It can also act as a plant-growth promoting rhizobacterium (PGPR) for non-legume plants, possibly through production of lipo-chitooligosaccharides (LCOs), which should have the ability to induce disease resistance responses in plants. The objective of this work was to determine whether non-leguminous crop plants can induce LCO formation by B. japonicum cultures. Cultures treated with root extracts of soybean, corn, cotton or winter wheat were assayed for presence and level of LCO. Root extracts of soybean, corn and winter wheat all induced LCO production, with extracts of corn inducing the greatest amounts. Root washings of corn also induced LCO production, but less than the root extract. These results indicated that the stimulation of non-legume plant growth by B. japonicum could be through the production of LCOs, induced by materials excreted by the roots of non-legume plants.     

Plant-aphid interactions: molecular and ecological perspectives

Many aphids are major agricultural pests because of their unparalleled reproductive capacity and their ability to manipulate host plant physiology. Aphid population growth and its impact on plant fitness are strongly influenced by interactions with other organisms, including plant pathogens, endophytes, aphid endosymbionts, predators, parasitoids, ants, and other herbivores. Numerous molecular and genomic resources have recently been developed to identify sources of aphid resistance in plants, as well as potentially novel targets for control in aphids. Moreover, the same model systems that are used to explore direct molecular interactions between plants and aphids can be utilized to study the ecological context in which they occur.