Testing the systemic induced resistance hypothesis with Austrian pine and Diplodia sapinea

Systemic induction of defenses (e.g. phenolic metabolites) is considered vital in conifer resistance to pathogens and insects, and forms the mechanistic basis of the systemic induced resistance hypothesis (SIRH). In this study, the SIRH was tested on juvenile Austrian pine. Main stems expressed SIR in a manner that was consistent with the SIRH, while shoots became uniformly more susceptible to subsequent inoculations, demonstrating clear organ specificity in the tree's response. The majority of phenolic metabolites were poorly correlated with phenotype. Thus, the defensive system of Austrian pine is highly plastic and organ specific, and cannot be predicted by phenolic profiles alone.     

Comparison of induced resistance activated by benzothiadiazole, (2R,3R)‐butanediol and an isoparaffin mixture against anthracnose of Nicotiana benthamiana

Resistance in Nicotiana benthamiana against anthracnose caused by the hemibiotrophic fungus Colletotrichum orbiculare was activated by benzothiadiazole (BTH), (2R,3R)­butanediol or PC1, an isoparaffin‐based mixture. In inoculation experiments, BTH, (2R,3R)­butanediol and PC1 reduced the number of lesions per leaf area caused by C. orbiculare by 98%, 77% and 81%, respectively. Foliar application of BTH induced expression of genes for the acidic pathogenesis‐related (PR) proteins, NbPR‐1a, NbPR‐3Q and acidic NbPR‐5. In contrast, soil application of (2R,3R)­butanediol or PC1 primed expression of genes for the basic PR proteins, NbPRb‐1b, basic NbPR‐2 and NbPR‐5dB. These results are consistent with the activation of salicylic‐acid‐dependent systemic acquired resistance (SAR) by BTH and that of jasmonate/ethylene‐dependent induced systemic resistance (ISR) by (2R,3R)­butanediol or PC1, and show that (2R,3R)­butanediol and PC1 can affect gene expression similarly to plant growth‐promoting rhizobacteria. However, the effects of (2R,3R)‐butanediol and PC1 were not identical. In addition to priming, (2R,3R)‐butanediol induced expression of basic NbPR‐2, whereas PC1 treatment induced expression of both NbPRb‐1b and basic NbPR‐2. Although a number of microbial products, such as (2R,3R)­butanediol, have been shown to produce ISR, this is the first demonstration that an isoparaffin‐based mixture, not derived from a microorganism, can produce ISR.     

Fitness costs associated with insecticide resistance

Insects are exposed to a variety of stress factors in their environment, and, in many cases for insect pests to agriculture, those factors include toxic chemical insecticides. Coping with the toxicity of insecticides can be costly and requires energy and resource allocation for adaptation and survival. Several behavioural, physiological and genetic mechanisms are used by insects to handle toxic insecticides, sometimes leading to resistance by constitutive overexpression of detoxification enzymes or inducing mutations in the target sites. Such actions are costly and may affect reproduction, impair dispersal ability and have several other effects on the insect's fitness. Fitness costs resulting from resistance to insecticides has been reported in many insects from different orders, and several examples are given in this mini‐review. Copyright © 2012 Society of Chemical Industry     

Enhanced tomato resistance to bacterial canker by application of turtle oil

Pretreatment with oil of sea turtle Caretta caretta protected tomato plants against bacterial canker caused by Clavibacter michiganensis subsp. michiganensis (Cmm). The turtle oil was ineffective in inhibiting Cmm in an agar diffusion test, suggesting a mechanism of induced resistance. Under controlled conditions in the greenhouse, turtle oil lowered the disease index and had reduced the growth of bacteria up to 50.4% by 7 days after inoculation. Applying turtle oil to the foliage of tomato plants increased per-oxidase and lipoxygenase activities. Gas chromatography analyses of turtle oil indicated the presence of polyunsaturated fatty acids such as eicosapentaenoic acid and docosahexaenoic acid. These fatty acids may lead to the higher activity of the enzymes and probably induced plant resistance against the pathogen.     

植物抗病激活剂诱导植物抗病性的研究进展

植物抗病激活剂本身及其代谢物无直接的杀菌活性,但可刺激植物的免疫系统而诱导植物产生具有广谱性、持久性和滞后性的系统获得性抗病性能(SAR).植物抗病激活剂的诱导除了可以引起植物富含羟脯氨酸糖蛋白(HRGP)的变化,导致木质素在细胞壁沉积,使植物形成物理防御机制外,经植物抗病激活剂诱导后的植株能导致内源水杨酸(SA)的累积、形成氧化激增,植物局部细胞程序化死亡而产生过敏反应(HR),植物抗病激活剂诱导后产生的抗病信号经内源信号传导物质SA、茉莉酸(JA)、乙烯(Et)和一氧化氮(NO)可传导到达整个植株,经过一系列抗病相关基因的调控和表达可引起寄主防御酶系如苯丙氨酸解氨酶(PAL)、β-1,3-葡聚糖酶(β-1,3-glucanase)、几丁质酶(chitinase)、过氧化物酶(POX)等以及抗病物质如木质素与植保素等的变化及病程相关蛋白(PRP)的调控与表达.文中讨论了植物抗病激活剂概念和种类及其诱导抗病作用的主导机制,指出了植物抗病激活剂的应用前景和发展方向及使用和研究开发中可能存在的问题与对策.     

pHBA对菜心炭疽病的诱导抗性及植株生理特性的影响

 以菜心品种为材料,设置不同浓度对羟基苯甲酸(pHBA)处理,并通过人工接种炭疽病菌,研究pHBA对菜心炭疽病的诱导抗性作用机理。结果表明,在菜心生长发育过程中根系可以分泌出pHBA。pHBA对菜心的生长、产量形成和炭疽病的发生有明显的影响。适宜浓度的pHBA处理可促进菜心生长,提高植株对炭疽病的抗性,显著地降低病情指数(DI),提高菜薹产量,但当pHBA积累到一定浓度时,就对菜心植株产生自毒作用,提高DI和降低菜薹产量。炭疽病菌的感染破坏了植株细胞膜,增强细胞膜透性水平,诱导产生病程相关蛋白(几丁质酶、β-1,3-葡聚糖酶)和细胞壁物质(木质素、富含羟脯氨酸糖蛋白(HRGP))。适宜浓度的pHBA处理可抑制炭疽病菌对细胞膜透性的伤害,加强诱导提高几丁质酶活性、β-1,3-葡聚糖酶活性、木质素含量和HRGP含量,引起细胞壁木质化加强,增加了菜心植株对炭疽病的诱导抗病能力,从而阻止病原菌进一步侵入和扩散,抑制炭疽病菌对菜心产量造成的损失。     

The use of Verticillium dahliae and Diplodia scrobiculata to induce resistance in Pinus halepensis against Diplodia pinea infection

The pathogenic fungi Verticillium alboatrum and Diplodia scrobiculata were assayed for biological control of Diplodia pinea on Aleppo pine (Pinus halepensis) in Catalonia (north-eastern Spain). Young shoots were pre-treated with inoculations of either V. dahliae or D. scrobiculata, by placing colonized agar plugs on wounds made by removing a single needle fascicle. An inoculation with D. pinea was performed 15 days later. Two months after the shoot inoculations, the canker length on the stems was measured and the percentage of shoot dieback calculated. Verticillium dahliae and D. scrobiculata were found to significantly reduce the canker length of D. pinea (P < 0.05) when compared with positive controls. Diplodia pinea was slightly more sensitive to V. dahliae than to D. scrobiculata, but no significant differences (P > 0.05) were observed in the mean canker length between the two treatments. Trees pre-inoculated with V. dahliae resulted in 31.12% shoot dieback, while those pre-inoculated with D. scrobiculata resulted in 32.18% shoot dieback, compared with positive controls (42.85%).     

Fitness costs associated with milbemectin resistance in the two-spotted spider mite Tetranychus urticae

The two-spotted spider mite Tetranychus urticae Koch is one of the most important pests of a wide range of crops worldwide. Its control is still largely based on the use of acaricides. However, due to its short life-cycle, high fecundity and arrhenotokous reproduction, it is able to develop resistance to these compounds very rapidly. Preliminary studies for milbemectin resistance in T. urticae showed that, under laboratory conditions, such resistance was unstable in the absence of a selection pressure. The aim of this study was to evaluate the possible fitness costs associated with milbemectin resistance in T. urticae. Comparison of biological traits between resistant and susceptible strains indicated the occurrence of fitness costs associated with milbemectin resistance. The resistant strain showed a longer juvenile development period for females, lower fecundity and a higher proportion of males among the progeny. The figures for net reproductive rate (R ₀), intrinsic rate of natural increase (r _m) and finite rate of increase (λ) were higher in the susceptible strain. The instability of milbemectin resistance can be exploited in resistance management programmes.     

Locating quantitative trait loci associated with Orobanche crenata resistance in pea

Orobanche crenata (broomrape) is a root parasite that represents the major constraint for pea (Pisum sativum) cultivation in the Mediterranean area and the Middle East. The efficacy of available control methods is minimal and breeding for O. crenata resistance is considered the most promising strategy of control. Only moderate levels of incomplete resistance are available in pea germplasm. In order to identify and map the quantitative trait loci (QTL) controlling the trait, 115 F₂ plants derived from the cross between a susceptible and a resistant parent were analysed using isozymes, random amplified polymorphic DNA and sequence tagged site markers. F₂‐derived F₃ lines were studied for O. crenata resistance under field conditions. The linkage map was constructed with MAPMAKER V2.0. Of 217 markers, 120 could be mapped into 21 linkage groups. Linkage groups consisted of 13 to two marker loci covering 1770 cM. The mean inter‐marker distance was 17.64 cM. Simple interval mapping (SIM) and composite interval mapping (CIM) were performed using QTL Cartographer. The CIM approach using five cofactors was clearly the most efficient way to locate putative QTL. Two QTL for O. crenata resistance (Ocp1 and Ocp2), explaining only a moderate portion of the observed variation (9.6% and 11.4% respectively), were detected.     

Homology modelling of Drosophila cytochrome P450 enzymes associated with insecticide resistance

BACKGROUND: Overexpression of the cytochrome P450 gene Cyp6g1 confers resistance against DDT and a broad range of other insecticides in Drosophila melanogaster Meig. In the absence of crystal structures of CYP6G1 or complexes with its substrates, structural studies rely on homology modelling and ligand docking to understand P450–substrate interactions. RESULTS: Homology models are presented for CYP6G1, a P450 associated with resistance to DDT and neonicotinoids, and two other enzymes associated with insecticide resistance in D. melanogaster, CYP12D1 and CYP6A2. The models are based on a template of the X‐ray structure of the phylogenetically related human CYP3A4, which is known for its broad substrate specificity. The model of CYP6G1 has a much smaller active site cavity than the template. The cavity is also ‘V’‐shaped and is lined with hydrophobic residues, showing high shape and chemical complementarity with the molecular characteristics of DDT. Comparison of the DDT–CYP6G1 complex and a non‐resistant CYP6A2 homology model implies that tight‐fit recognition of this insecticide is important in CYP6G1. The active site can accommodate differently shaped substrates ranging from imidacloprid to malathion but not the pyrethroids permethrin and cyfluthrin. CONCLUSION: The CYP6G1, CYP12D1 and CYP6A2 homology models can provide a structural insight into insecticide resistance in flies overexpressing P450 enzymes with broad substrate specificities. Copyright © 2010 Society of Chemical Industry     

植物诱导抗病性与诱抗剂研究进展

以糖、蛋白和糖蛋白三大类生物源激发子为重要的植物诱抗剂,本文分析了植物诱抗剂作用于植物后所发生的一系列信号识别与信号传导过程及植物典型的防卫反应,为植物诱抗剂的研发和植物诱导抗病性分子机理的探讨提供参考。     

Multiple forms of carboxylesterase from Leptinotarsa decemlineata haemolymph associated with permethrin resistance

For the first time, it has been unequivocally shown that multiple-feed second-generation anticoagulant rodenticides were ineffective against a population of rats in N.W. Berkshire, UK because of an unusually high prevalence and high degree of resistance. Use of the non-anticoagulant rodenticide calciferol led to a substantial reduction in the population, although primary poisoning of small birds appeared to be greater than with anticoagulant baits. There was strong evidence that many of the surviving rats had developed an aversion towards calciferol-treated bait. A reduction in the degree of anticoagulant resistance in the population was evident after a period of 17 months without anticoagulant use. The long-term strategy to manage the resistant population should integrate non-anticoagulant and anticoagulant rodenticide use to take advantage of possible pleiotropic costs of resistance.     

The Ecological Concept of Costs of Induced Systemic Resistance (ISR)

Plant defence is thought to provide benefits for the defended plants. Theoretical concepts must, therefore, explain why there is variation in defensive traits, which naively might be assumed to be present constitutively in fixed high amounts. Explanations are mainly based on the assumption of fitness costs. Investment in defence is thought to reduce the fitness of plants in enemy-free environments. Fitness costs often result from allocation costs, i.e. allocation of limited resources to defence, which then cannot be used for growth or other fitness-relevant processes. This theoretical concept can provide a useful tool for the interpretation of induced plant responses against pathogens, named induced systemic (or systemic acquired) resistance (ISR or SAR). Phenotypic plasticity, leading to induced responses, might have evolved mainly to reduce costs, since investment in defence is restricted to situations actually requiring defence. ISR can incur allocation costs and other, indirect costs, which ultimately may lead to fitness costs. Evolution of any defensive trait depends on both what a plant ideally 'should do and what it actually 'is able to do. Costs of defence constrain its expression. This might have important influences on the evolution of plant defensive traits, as well as on the exploitation of natural defences in agricultural crop protection.