The relation of mansonones to resistance against dutch elm disease and their accumulation,as induced by several agents

No evidence was found that mansonones E and F, which accumulated in elms after infection withCeratocystis ulmi, were responsible for resistance against Dutch elm disease inUlmus hollandica cl. 390. Furthermore, production of mansonones inU. americana was only about one-fifteenth of that inU. hollandica cl. Belgica. Yet both are susceptible to Dutch elm disease.Induction of these compounds was not specific, for accumulation occurred not only after introduction of crude toxin ofC. ulmi, but also after inoculation withVerticillium albo-atrum and after introduction of H₂SO₄ or ethanol.The dark discolouration of the wood after toxin treatment was restricted to the lower part of the stem. No mansonones could be detected in the non-discoloured higher parts of the stem or from the necrotic or wilted leaves.Samenvatting Er werd geen aanwijzing gevonden dat mansononen E en F, die na infectie metC. ulmi gevormd worden, verantwoordelijk zijn voor de resistentie tegen de iepziekte inU. hollandica cl. 390 (Tabel 1). U. americana bevat ongeveer 15 maal zo weinig van deze stoffen alsU. hollandica cl. Belgica, terwijl beide vatbaar zijn.De inductie van de synthese van deze stoffen bleek niet specifiek te zijn, omdat bij chemische beschadiging met H₂SO₄ of ethanol ook mansononen gevormd werden.De donkere verkleuring van het hout bleek na toxine toediening beperkt tot het onderste gedeelte van de stam. Geen mansononen werden gevonden in hoger gelegen, niet verkleurde stamgedeelten of in de necrotische en verwelkte bladeren.     

Induction of disease resistance against Botrytis cinerea by heat shock treatment in melon (Cucumis melo L.)

The present study investigated resistance against Botrytis cinerea after heat shock treatment in melon plants. Heat shock at 50 °C for 20 s 0–24 h before inoculation resulted in maximal B. cinerea symptom reduction and peroxidase gene expression, which peaked 12 and 72 h post-treatment and decreased 24–48 h post-treatment, suggesting pathogenesis-related protein expression priming. Hot water dipping did not directly inhibit mycelia growth. Plants treated with 2-benzisothiazol-3(2H)-one 1,1-dioxide, which induces systemic acquired resistance, demonstrated higher peroxidase gene expression but no B. cinerea resistance, indicating possible involvement of additional novel mechanisms in heat shock-activated resistance of melon against B. cinerea.     

冠菌素诱导田间灌浆期冬小麦抗高温的生理效应研究

采用化学调控的方法,研究了新型植物生长调节剂冠菌素对缓解冬小麦灌浆期高温胁迫的作用。结果表明:在高温胁迫条件下,于灌浆前期喷施0.1 μmol/L的冠菌素,可维持小麦旗叶较高的相对含水量,降低叶片质膜的透性,从而维持细胞膜的完整性,同时冠菌素处理还可增强小麦旗叶的光合能力,最终使千粒重提高了9.1%,每公顷理论产量提高了495.75 kg,显著降低了因高温胁迫造成的产量损失。     

Barley traits associated with resistance to fusarium head blight and deoxynivalenol accumulation

ABSTRACT Fusarium head blight (FHB) or scab is a destructive disease of barley in many countries. A better understanding of the interrelationships between plant traits and FHB resistance should help in the development of effective and efficient breeding strategies for FHB-resistant cultivars. Recent mapping studies indicate that many of the quantitative trait loci (QTL) for FHB resistance coincide with the QTL for plant height, heading date, and spike characteristics. Therefore, a study was conducted to investigate the relationship of morphological and physiological traits to FHB infection and deoxynivalenol (DON) accumulation in a barley doubled-haploid (DH) population derived from a Léger x CI9831 cross. Approximately 190 DH lines were grown at Ottawa (Ontario) for 2 years, Charlottetown (Prince Edward Island) for 1 year, and Hangzhou (Zhejiang) for 2 years. The field plots were inoculated with Fusarium graminearum at each location. FHB incidence was positively correlated with DON content. Resistance to FHB was associated with two-row spike, purple lemma, long glume awn, tall stature, and resistance to lodging, but it was not associated with long rachilla hairs, rough lemma awn, or heading date. Two-row spike was associated with tall stature and resistance to lodging. These associations as well as its spike characteristics helped reduce FHB infection and DON accumulation in two-row lines compared with six-row lines. The association between long glume awn and FHB resistance could be due to genetic linkages. Therefore, trait associations should be taken into consideration when breeding for FHB resistance and interpreting data from FHB experiments.     

植物诱导抗病机制的研究进展

植物诱导抗病性是植物抵御病害侵染的重要机制,并且作为一种经济有效的抗病策略,在农林业可持续病害防控中具有广阔应用前景,受到人们的日益关注.从组织结构、生理生化乃至分子生物学的一系列变化,阐述了植物诱导产生抗病性的机制.同时,指出了植物诱导抗病性研究中有待进一步研究加以解决的问题和发展前景.     

Costs and trade-offs associated with induced resistance

Plants resist attack by pathogens and herbivorous insects through constitutive and inducible defences. Based on differences in signalling pathways and spectra of effectiveness, different types of induced resistance have been defined. Systemic acquired resistance (SAR) occurs in distal plant parts following localized infection by a necrotizing pathogen. It is controlled by a signalling pathway that depends upon the accumulation of salicylic acid (SA) and the regulatory protein NPR1. In contrast, induced systemic resistance (ISR) is induced by selected strains of non-pathogenic plant growth promoting bacteria (PGPR). ISR functions independently of SA, but requires NPR1 and is regulated by jasmonic acid (JA) and ethylene (ET). It is generally believed that induced resistance evolved to save energy under pathogen or insect-free conditions, although costs still arise when defences are activated following attack. Costs can arise from the allocation of resources to defence and away from plant growth and development, and there are also ecological costs which result from trade-offs between induced resistance and the plant's interaction with beneficial organisms e.g. mycorrhizal fungi. To date, few studies have examined the costs and trade-offs associated with induced resistance to pathogens. There is a clear need for long-term studies of costs and trade-offs associated with induced resistance in crops under commercial conditions. Without such information, the potential offered by induced resistance is unlikely to be realized.     

Engineering flax with increased flavonoid content and thus Fusarium resistance

Flavonoids are a group of secondary plant metabolites important for plant growth and development, and thus the regulation of their biosynthesis is of special interest. We used a transgenic approach for flavonoid content manipulation. The multigene construct contained the cDNAs for chalcone synthase (CHS), and chalcone isomerase (CHI) and dihydroflavonol reductase (DFR) were prepared. Following flax plants transformation, the levels of the products of the enzyme overproduction were assessed in leaves and seeds. The simultaneous expression of genes resulted in a significant increase in the levels of flavanones, flavones, flavonols and anthocyanins, suggesting those three overproducing enzymes efficiently control the flavonoid route of the phenylpropanoid pathway.The increase in the flavonoid content in the transgenic flax plants might be the reason for observed, enhanced antioxidant capacity of those plants. The increased antioxidative properties of transgenic plants lead to improved resistance to Fusarium, the main pathogen of flax.The changes in phenylpropanoids accumulation in transgenic plants affect cell wall carbohydrate content. Immunochemical studies revealed significant increase in carbohydrates, constituents of pectin and hemicellulose. Since pectins contribute to flax stem retting, the compounds increase might affect fibre production. An increase in pectin and hemicellulose content leads to enhanced disease resistance of those plants.     

Mediation of partial resistance to rice blast through anaerobic induction of ethylene

ABSTRACT The correlation between anaerobic soil conditions and increased resistance to rice blast disease has long been observed without benefit of an adequate explanation. We researched flood depth, dissolved oxygen (DO), and ethylene relative to expression of partial blast resistance in cvs. M-201, Newbonnet, LaGrue, Mars, and Cypress. Cultivar blast index (BI) and flood DO decreased with increasing flood depth. BIs were positively correlated with DO. Total leaf blast lesions were 3.4 and 3.2 times greater in cvs. M-201 and LaGrue growing in a 5.0-mul liter(-1) DO nutrient solution than when growing in a 0.1-mul liter(-1) DO solution. Treatment with 0.25 mM ethephon, which releases ethylene, lowered BIs of Newbonnet, LaGrue, and Cypress growing upland when applied drench, foliar, or foliar-drench. If flooded, BIs of ethephon-treated cultivars were decreased by drench and foliar-drench applications only. BIs of upland plants were unchanged, whereas BIs of analogous flooded plants increased following treatment with 0.31 mM aminoethoxyvinylglycine (AVG), an ethylene biosynthesis inhibitor. We hypothesize that varying anaerobic conditions mediate production of phytohormones, particularly ethylene, which modify expression of inherent partial blast resistance in these rice cultivars.     

Variation for resistance to kernel infection and toxin accumulation in winter wheat infected with Fusarium graminearum

Host resistance is the main way to control Fusarium head blight (FHB) in wheat. Despite improved levels of resistance to infection and spread in vegetative tissue, the toxin deoxynivalenol (DON) can still accumulate to unacceptable concentration levels. In this study, our objectives were to assess the genetic variation for resistance to kernel infection (RKI) and resistance to toxin accumulation (RTA) and their role in controlling DON. We collected spikes with different levels of visual symptoms from each of 32 wheat genotypes and at four environments and determined DON and fungal biomass (FB) from each sample. We assessed RKI by regressing FB on the level of visual symptoms and RTA by regressing DON on FB for each genotype. Significant genetic effects were found for RKI and RTA. Some genotypes consistently had low FB in their grain despite increasing visual symptoms suggesting RKI. Additionally, some genotypes consistently had low DON in their grain despite increasing FB levels suggesting a higher RTA in these genotypes. The variation for RKI and RTA explained a significant fraction of the variation for DON among genotypes with moderate visual symptoms using independent grain samples. Although RKI and RTA were significantly correlated (r = 0.58, P = 0.05), RTA was more predictive of DON accumulation because it modeled 32 to 44% of the genotype sum of squares for DON, while only 9 to 10% were predicted using RKI. Thus, variation for RTA was important in explaining variation for DON among genotypes with acceptable levels of resistance to fungal infection and spread. This work indicates that there is a need to develop a better understanding of RTA and rapid screening methods for this trait.     

水杨酸和乙烯在烟草抗黑胫病中的作用

5mmol/L水杨酸或1g/L乙烯外源处理可诱导烟草对黑胫病的抗性，推迟植株死亡。不能积累水杨酸的转nahG基因植株和不表现乙烯应答反应的转etr1-1基因植株对黑胫病的抗性显著弱于野生型植株。组成性积累高水平水杨酸的转entC和pmsB基因植株对黑胫病的抗性明显强于野生型植株。这些结果说明水杨酸和乙烯增强烟草对黑胫病的抗性，减缓黑胫病的扩展。0．5mmol/L KCN连续浇灌植株4天或浸溃叶片2，4h均不能恢复转nahG基因植株丧失的对黑胫病的抗病性。此结果进一步支持关于KCN处理不能恢复转nahG基因植株丧失的对真菌病害抗病性的假说。     

苯并噻二唑诱发水稻对纹枯病的抗性

研究了苯并噻二唑(B1H)诱发水稻产生对纹枯病的抗性。离体条件下，1．0mmol／L BTH对纹枯病菌菌丝生长无明显抑制作用。BTH叶面或灌根处理四叶一心期水稻幼苗，并将植株第2、3和4叶离体接种纹枯病菌，水稻叶片纹枯病病斑长度明显下降，BTH诱发苗期水稻产生抗性的最佳诱导期在处理后的3—5天，最佳浓度为0．1mmol／L，BTH灌根处理诱发抗性的效果较好。用BTH溶液叶面喷雾处理成株期水稻倒二叶后离体接种纹枯病菌，倒二叶、倒一叶和剑叶上病斑长度显著低于对照，最佳诱导期在处理后3—5天。用BTH处理苗期水稻第2叶或成株期倒二叶，可使未经处理的苗期水稻第3和4叶以及成株期水稻倒一叶和剑叶上纹枯病病斑长度显著下降。     

Association of dhurrin levels and post-flowering non-senescence with resistance to stalk rot pathogens in Sorghum bicolor

European Journal of Plant Pathology - Aflatoxin contamination is common in several crops, including maize, in warm agricultural areas. For over 40 years, there have been many efforts to...     

Induction of heat resistance in Fusarium oxysporum and Verticillium dahliae caused by exposure to sublethal heat treatments

The effects of sublethal heat treatments on heat resistance were studied forFusarium oxysporum f.sp.dianthi (Fod) andVerticillium dahliae (Vd), one isolate of each pathogen. Treatments of propagule suspensions of Fod at 55°C and of Vd at 45°C for 30 min were survived by less than 0.001% and 0.01% of the propagules, respectively. Pretreatment of suspensions of Fod at 45°C increased survival of the 55°C treatment up to 0.73% of the propagules and pretreatment of suspensions of Vd at 40°C increased survival of the 45°C treatment up to 0.40%. Induction of heat resistance was dependent on duration of the exposure to the sublethal temperature. With Fod, this duration was shorter for propagules from old cultures than for those from young cultures. Pretreatment at 45°C of a suspension of an 1-week-old culture of Fod induced resistance when lasting 30 min or longer, but not when 20 min or shorter. With Vd, the duration of the pretreatment inducing heat resistance depended on type of culture — white or black — due to differences in microsclerotia formation. Implications of induced heat resistance for control of plant diseases by thermotherapy are discussed.     

The glutamate dehydrogenase gene gdhA increased the resistance of tobacco to glufosinate

The gene gdhA from Escherichia coli, that encodes a NADPH‐dependent glutamate dehydrogenase (GDH), directs a novel pathway in transgenic plants that allows an increase in ammonium assimilation. Glufosinate leads to plant death by the irreversible inhibition of glutamate synthetase (GS) leading to a disruption of subsequent GS‐related processes resulting in elevated ammonium and disruption of photorespiration. Therefore, it was speculated that the gdhA‐transformed plants may exhibit a novel mechanism of resistance to glufosinate by altered activity of the GDH‐directed pathway(s) and subsequently related processes. Studies were conducted in the greenhouse to evaluate the resistance of tobacco plants containing the gdhA gene to glufosinate. Five tobacco genotype lines were investigated including a non‐transformed control line, a positive control line and three transformed lines with levels of increasing GDH activity directed by the gdhA gene. Plants transformed with the gdhA gene expressed up to six times increased level of resistance (GR₅₀) to glufosinate compared with the non‐transformed control, which is 100 times less resistant than plants transformed with the bar gene. The GDH activity among lines was highly correlated (r² = 0.9903) with the level of herbicide resistance. Thus, the use of the E. coli gdhA gene in plant transformations can provide an additional mechanism for resistance to glufosinate.     

两种化合物联合诱导黄瓜的抗性效应及田间防治试验

用草酸钾和硫酸亚铁两种化合物联合诱导,可使黄瓜同时产生对霜霉病和白粉病的抗性效应.但不同组合方式的诱导所产生的抗性效应明显不同.其中两种化合物分别诱导的抗性效应最低;混合诱导的抗性效应较高;相继诱导的抗性效应最高.田间试验表明,先喷有效浓度60 mmol/L的草酸钾诱导物,间隔3 d再喷有效浓度20 mmol/L的硫酸亚铁诱导物,10 d后以同样顺序进行第2轮相继诱导,对霜霉病的防治效果达82.73%,显著高于70%代森锰锌WP 800倍液的防治效果;对白粉病的防治效果达78.64%,接近50%多菌灵WP 800倍液的防治效果.     

Antioxidant,ethylene and membrane leakage responses to powdery mildew infection of near-isogenic barley lines with various types of resistance

Leaves of powdery mildew-susceptible barley (Hordeum vulgare cv. Ingrid) and related near-isogenic lines bearing various resistance genes (Mla12, Mlg or mlo5) were inoculated with Blumeria graminis f. sp. hordei race A6. Fungal attack induced several-fold increases in ethylene emission and electrolyte leakage in leaves of susceptible Ingrid beginning 3 days after inoculation. Activities of peroxidase, superoxide dismutase, glutathione S-transferase, ascorbate peroxidase and glutathione reductase enzymes were induced markedly in susceptible leaves 5–7 days after inoculation. Similar, but less pronounced pathogen-induced changes were detected in inoculated leaves of Mla-type resistant plants that show hypersensitive cell death upon inoculation, and, to an even lesser extent, in the Mlg and mlo lines, where no visible symptoms accompanied the incompatible interaction. Glutathione content increased only in susceptible barley 7 days after inoculation. Catalase activity, total ascorbate content and redox state were not influenced by inoculation in any of the genotypes. The activity of dehydroascorbate reductase was significantly reduced 3–5 days after inoculation in the susceptible parental plants and after 5 days in Mla and Mlg lines, while it was stable in the mlo barley. Slightly elevated levels of H₂O₂ were observed in the inoculated resistant plants. In contrast, H₂O₂ content decreased in the susceptible line 7 days after pathogen attack. These data indicate that high levels of antioxidants are involved in the compatible interaction of susceptible barley and powdery mildew by protecting the pathogen from oxidative damage.     

Association of stomatal frequency and morphology in Lycopersicon species with resistance to Xanthomonas campestris pv. vesicatoria

Study of the stomata and leaf epidermis of eight Lycopersicon species has revealed a relationship between frequency of stomata, stomatal size and some morphological leaf characteristics, and resistance to bacterial leaf spot caused by Xanthomonas campestris pv. vesicatoria. Significant correlations were found between the stomatal frequency in both adaxial and abaxial leaf epidermis and the number of bacterial lesions per leaf area ( r = 0.70 and 0.68, respectively) and the frequency of stomata in both adaxial and abaxial epidermis and disease incidence (percentage of diseased plants) ( r =0.87 and 0.80, respectively) for all the Lycopersicon species and one hybrid tested. A correlation was also found between disease incidence and number of bacterial lesions per leaf area ( r = 0.85). The length and width of stomata were correlated with frequency of stomata in adaxial and abaxial epidermis ( r = 0.85, 0.75, 0.89 and 0.90, respectively). The stomatal width was correlated with the number of bacterial lesions per cm² ( r =0.82; P = 0.0065). Scanning electron microscopic studies of the leaf surface and stomata indicated that other morphological features such as the raised stomatal complex in L. hirsutum and persistent, hydrophobic waxy coating of the epidermis in L. peruvianum may also be relevant in disease response.     

水杨酸诱导烟草对TMV的抗性和PAL活性变化研究

 植物内源水杨酸(SA)可能是诱导植物产生系统抗病性(SAR)的信号物质,它在植物体内具有多种生理调节作用。