Mango malformation disease and the associated fusarium species

ABSTRACT Mango malformation disease (MMD) occurs in Asia, Africa, and the Americas and was first reported in India in 1891. The vegetative form of MMD was first reproduced in 1966 with Fusarium moniliforme and the floral form with isolates of F. moniliforme var. subglutinans from both vegetative shoots and floral tissue. The fungi were subsequently recognized as F. subglutinans. In 2002, a new species, F. mangiferae, was established based on nuclear and mitochondrial DNA sequences; it included strains of F. subglutinans from Egypt, Florida, Israel, Malaysia, and South Africa, some of which had been shown to cause MMD by artificial inoculation. At least three additional taxa have been associated with MMD: F. sterilihyphosum from Brazil and South Africa, and Fusarium sp. nov. and F. proliferatum (teleomorph: Gibberella intermedia) from Malaysia. To date, Koch's postulates have not been completed with them. In the future, gene sequencing will be essential to identify the Fusarium spp. that are associated with MMD. Work remains to be done on the morphology, sexual compatibility, pathogenicity, and toxigenicity of these taxa.     

Role of reactive oxygen species and antioxidants in plant disease resistance

Membrane damage caused by the non-specific fungal toxin fusaric acid was less on pretreated than on control leaves when tobacco leaves were pretreated with anti-senescence plant hormones, such as kinetin, benzyladenine or the anti-ozonant N-[2-(2-oxo-1-imidazolidinyl)]ethyl-N'-phenylurea. Similarly, the necrosis caused by mercuric chloride was reduced by the above anti-senescence agents. In addition, in in vitro tests, leaves from selected paraquat-tolerant tobacco plants were less sensitive to Alternaria alternata (Fr) Keissler infection than those of the control paraquat-sensitive tobacco leaves. Paraquat-tolerant Conyza canadensis (L) Cronq weeds naturally selected in vineyards in Hungary showed similar inhibition of senescence to paraquat-tolerant tobacco, expressed as more green leaves and slower development. In accordance with this, the paraquat-tolerant Conyza leaves remained almost symptomless, while paraquat-sensitive plants showed severe symptoms after infection with Botrytis cinerea Pers. Oxidative burst (accumulation of hydrogen peroxide) was attenuated in TMV-infected leaves of Xanthi-nc tobacco as a result of treatment with salicylic acid or in leaves where systemic acquired resistance (SAR) had been induced by a previous TMV infection. Accordingly, superoxide dismutase (SOD) activity was higher in Xanthi tobacco leaves with SAR than without SAR. However, in NahG tobacco, in which SAR cannot develop, there was no augmentation of SOD activity. All the above data support the significance of delayed senescence and antioxidants in the resistance of plants to biotic and abiotic necrosis-inducing agents.     

Paclobutrazol and other plant growth-retarding chemicals increase resistance of melon seedlings to fusarium wilt

Studies were made of plant growth retardation and effects on resistance of melon to fusarium wilt by soil application of paclobutrazol, other ergosterol biosynthesis inhibitors, the fungicide benomyl and the herbicide dinitramine. Paclobutrazol and ancymidol delayed the onset of wilting and were the most effective in reducing wilt incidence. A relationship between effectiveness in retarding seedling elongation and increasing resistance to fusarium wilt was observed. No chemical had a significant effect on pathogen population level in the plant, as determined by stem colonization and direct assessment tests in seedlings grown in soil treated with the chemicals. Excluding benomyl, and to a lesser extent dinitramine, leaf and stem extracts had no inhibitory effect on conidial germination. Gibberellins GA₄₊₇, when applied to seedlings inoculated after germination in paclobutrazol-treated soil, nullified growth retardation and increased disease incidence. We suggest that disease incidence reduction by paclobutrazol is due to an effect on plant metabolic processes and not to direct fungitoxicity of the compound.     

The Brachypodium distachyon UGT Bradi5gUGT03300 confers type II fusarium head blight resistance in wheat

Fusarium head blight (FHB), caused by fungi belonging to the Fusarium genus, is a widespread disease of wheat (Triticum aestivum) and other small-grain cereal crops. The main causal agent of FHB, Fusarium graminearum, produces mycotoxins mainly belonging to type B trichothecenes, such as deoxynivalenol (DON), that can negatively affect humans, animals and plants. DON detoxification, mainly through glucosylation into DON-3-O-glucose, has been correlated with resistance to FHB. A UDP-glucosyltransferase from the model cereal species Brachypodium distachyon has been shown to confer resistance both to initial infection and to spike colonization (type I and type II resistances, respectively). Here, the functional characterization of transgenic wheat lines expressing the Bradi5g03300 UGT gene are described. The results show that, following inoculation with the fungal pathogen, these lines exhibit a high level of type II resistance and a strong reduction of mycotoxin content. In contrast, type I resistance was only weakly observed, although previously seen in B. distachyon, suggesting the involvement of additional host-specific characteristics in type I resistance. This study contributes to the understanding of the functional relationship between DON glucosylation and FHB resistance in wheat.     

Effects of plant height on type I and type II resistance to fusarium head blight in wheat

By carefully separating type I and type II resistances, the possible effects of plant height on fusarium head blight (FHB) resistance in wheat were assessed using near‐isogenic lines (NILs) for several different reduced‐height (Rht) genes. Tall isolines all gave better type I resistance than their respective dwarf counterparts when assessed at their natural heights. These differences largely disappeared when the dwarf isolines were physically raised so that their spikes were positioned at the same height as those of their respective tall counterparts. The effects of plant height on type II resistance was less clear. For those NIL pairs which showed significant differences, it was the dwarf isolines which gave better resistance. As the Rht genes involved in these NILs locate at different genomic regions, the differences in FHB between the dwarf and tall isolines are unlikely to be the result of linkages between each of the different Rht loci with a beneficial or a deleterious gene affecting type I or type II resistance. Rather, the different FHB resistances are probably caused by direct or indirect effects of height difference per se, and microclimate may have contributed to the better type I resistance of the tall plants. Thus, caution should be exercised when attempting to exploit any of the FHB resistant loci co‐located with Rht genes.     

Reactions of various plant species to inoculation with potato virus S

In total 98 plant species belonging to 15 families were tested on their possible value as indicator hosts for potato virus S. Plants were sap-inoculated with six virus isolates respectively. In only three families (Amaranthaceae, Chenopodiaceae and Solanaceae) suspectible species were found. The susceptible Chenopodiaceae reacted with local lesions. Seven of those Chenopodiaceae were not mentioned before as local lesion hosts for PVS, viz.Chenopodium ambrosioides, C. hybridum, C. murale, C. opulifolium, C. polyspermum, C. rubrum andC. urbicum.Samenvatting In totaal 98 plantesoorten behorende tot 15 families werden onderzocht als mogelijke toetsplanten van het aardappelvirus S. De planten werden met respectievelijke zes verschillende isolaten van het aardappelvirus S in bladsap geïnoculeerd. Slechts in de plantefamilies Amaranthaceae, Chenopodiaceae en Solanaceae werden soorten gevonden, die vatbaar zijn voor één of meer isolaten van het virus. De vatbare Solanaceae werden systemisch geïnfecteerd, terwijl de Amaranthaceae en Chenopodiaceae met lokale vlekken reageerden. De vatbaarheid van de lokale-vlekkenplanten was zeer ongelijk voor de zes isolaten van het aardappelvirus S (Tabel 3). Chenopodium album, C. polyspermum enC. quinoa (I.P.O.) reageerden met lokale vlekken na inoculatie met elk van de zes isolaten, de andere Chenopodiaceae deden dit na inoculatie met slechts enkele isolaten. Ook de herkomst van één en dezelfde Plantesoort (Chenopodium quinoa) had invloed op het al of niet verschijnen van lokale vlekken op de waardplant na inoculatie met de verschillende virusisolaten.     

Phenolic compounds in plant disease resistance

We propose that an important first line in plant defense against infection is provided by the very rapid synthesis of phenolics and their polymerization in the cell wall. This rapid synthesis, which leaves no time forde novo enzyme synthesis, is regulated by the extreme pH-dependence of the hydroxylase, catalyzing the formation of caffeoyl-CoA from 4-coumaroyl-CoA. We further propose that elicitor treatment or infection causes rapid membrane changes leading to a decrease in cytoplasmic pH. This decrease would have the effect of activating the hydroxylase.     

Over-expression of the citrus gene CtNH1 confers resistance to bacterial canker disease

Citrus canker is a devastating disease, caused by Xanthomonas axonopodis pv. citri (Xac). It is well established that the NPR1 gene plays a pivotal role in systemic acquired resistance (SAR) in Arabidopsis. In this study, we report the isolation and characterization of an NPR1 homolog from citrus, namely Citrus NPR1 homolog 1 (CtNH1). Sequence alignment and phylogenetic analysis indicate that CtNH1 is closely-related to the Arabidopsis NPR1 gene and its orthologs from rice, grapevine, and cacao. When over-expressed in citrus, CtNH1 confers resistance to Xac and leads to constitutive expression of the pathogenesis-related (PR) gene chitinase 1 (Chi1), suggesting that CtNH1 is orthologous to NPR1.     

3%植物激活蛋白诱导蚕豆抗病性应用技术

从苗期开始间隔30d或始花期开始间隔20d喷施1次植物激活蛋白1000倍液能显著增强蚕豆的抗病性,尤其是苗期开始使用的效果更明显,对蚕豆赤斑病、根腐病、病毒病的诱抗效果分别为59.1%、76.4%和85.6%,增产率达26.6%。激活蛋白制剂500～1000倍对3种病害的诱抗效果为50%~70%,浓度间诱抗效果无显著差异。根据蚕豆生产实际,以苗期开始叶面喷雾1000倍植物激活蛋白,间隔30d使用最好。若从始花期开始,则每间隔20d叶面喷施。     

香石竹不同品种对镰刀菌枯萎病的抗性评价

连续2年以土壤接种方法对30个香石竹品种进行田间镰刀菌枯萎病抗性鉴定。结果表明,品种间抗性存在明显差异。30个品种中没有发现免疫品种,其中高抗品种占所鉴定总数的16.7%,中抗占40.0%,中感占13.3%,高感占30.0%。在所有鉴定的品种中,红色品种抗性较低,70%属感病品种;复色品种抗性较高,89%为抗病品种。依相对抗性指数,两个年度间的相对抗性无显著差异,鉴定结果可靠,建议将此方法作为我国香石竹对镰刀菌枯萎病田间抗性评价的基本方法。     

Recovery from inhibition of photosynthesis by metamitron in various plant species

Inhibition of photosynthesis by metamitron in the rooting medium and its subsequent recovery after transfer of the roots to herbicide-free nutrient solution was measured in eight plant species. Fast and complete recovery within a few hours after treatment showed that metamitron, once absorbed, was rapidly and completely inactivated in the leaves of sugar beet (Beta vulgaris L.). Inactivation in perennial ryegrass (Lolium perenne L.) was slower and incomplete. It was low in Echinochloa crusgalli (L.) P.B., Amaranthus retroflexus L., Alopecurus myosuroides Huds. and bean (Phaseolus vulgaris L.), and undetectable in maize (Zea mays L.) and Portulaca oleracea L. From the transpiration rate and the concentration of metamitron in the nutrient solution that just did not cause inhibition of photosynthesis in sugar beet, uptake and inactivation rates per unit leaf area were calculated to be at least 18·5 ng/cm²/h. The same external concentration markedly depressed photosynthesis in the other more susceptible species. After leaf sprays sugar beet plants gradually resumed the normal rate of photosynthesis, but bean plants did not recover.     

Beta-cyanoalanine synthase as a molecular marker for induced resistance by fungal glycoprotein elicitor and commercial plant activators

ABSTRACT The biocontrol agent Pythium oligandrum produces glycoprotein elicitor in the cell wall fraction, designated CWP, and induces resistance to a broad range of pathogens. To understand the mechanism of CWP-induced resistance to pathogens, gene expression at the early stage of CWP treatment in tomato roots was analyzed using a cDNA array. At 4 h after CWP treatment, 144 genes were up-regulated and 99 genes were down-regulated. In the 144 up-regulated genes, nine genes exhibited about eightfold increased expression. Analysis of the response of these nine genes to three commercial plant activators indicated that a high level of one gene, beta-cyanoalanine synthase gene (LeCAS) encoding hydrogen cyanide (HCN) detoxification enzyme, was stably induced in tomato roots by such treatment. However, expression of LeCAS was not significantly induced in tomato roots at 4 h by abiotic stresses, whereas only a very low level of induction of such expression by cold stress was observed. This LeCAS expression was also induced after exogenous treatment with a low level of 1-amino-cyclopropane-1-carboxylate as the precursor of ethylene, but not with either salicylic acid or methyl jas-monate. The induction of LeCAS expression in CWP-treated and plant activator-treated roots is likely to be caused by the detoxification of HCN during ethylene production. Transient activation of LeCAS expression caused by ethylene production in tomato roots may be a general phenomenon in fungal elicitor-induced and synthetic plant activator-induced resistance. LeCAS seems to be useful for screening possible novel plant activators for plant protection against pathogens.     

Allelism of theFcu-1 andFoc genes conferring resistance to fusarium wilt in cucumber

The inheritance of resistance toFusarium oxysporum f.sp.cucumerinum race 1 was determined in the cucumber cv. WIS-248 by analyzing segregation of F₁, F₂, and BC populations of crosses with the susceptible cv. Straight-8. Resistance was conferred by a single dominant gene. In an allelism test, it was proven that theFcu-1 gene, which confers resistance toF. oxysporum f.sp.cucumerinum races 1 and 2 in cucumber cv. SMR-18 and theFoc gene, which confers resistance toF. oxysporum f.sp.cucumerinum race 2 in cucumber cv. WIS-248, are indistinguishable.     

Fusarium species and chemotypes associated with fusarium head blight and fusarium root rot on wheat in Sardinia

Environmental conditions in Sardinia (Tyrrhenian Islands) are conducive to fusarium root rot (FRR) and fusarium head blight (FHB). A monitoring survey on wheat was carried out from 2001 to 2013, investigating relations among these diseases and their causal agents. FHB was more frequently encountered in the most recent years while FRR was constantly present throughout the monitored period. By assessing the population composition of the causal agents as well as their genetic chemotypes and EF‐1α polymorphisms, the study examined whether the two diseases could be differentially associated to a species or a population. Fusarium culmorum chemotypes caused both diseases and were detected at different abundances (88% 3‐ADON, 12% NIV). Fusarium graminearum (15‐ADON genetic chemotype) appeared only recently (2013) and in few areas as the causal agent of FHB. In F. culmorum, two haplotypes were identified based on an SNP mutation located 34 bp after the first exon of the EF‐1α partial sequence (60% adenine, 40% thymine); the two populations did not segregate with the chemotype but the A‐haplotype was significantly associated with FRR in the Sardinian data set (P = 0·001), suggesting a possible fitness advantage of the A‐haplotype in the establishment of FRR that was neither dependent on the sampling location nor the sampling year. The SNP determining the Sardinian haplotype is distributed worldwide. The question whether the A‐haplotype segregates with characters facilitating FRR establishment will require further validation on a specifically sampled international data set.     

植物诱导抗病性研究进展

从植物诱导抗病性的诱导因子及诱导机制等方面综述了近年来国内外植物诱导抗病性的研究进展。     

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.     

不同百合品种对百合灰霉病的抗病性鉴定

为明确不同百合品种对灰霉病的抗病能力,本试验采用离体叶片菌丝块接种和田间孢子液喷雾2种方法测定了百合7个不同品种对百合灰霉病的抗病性。离体测定结果表明,供试的7个品种对百合灰霉病的抗病性存在显著差异,其中‘法兰西’和‘罗蒂娜’为高感品种,‘康斯坦萨’和‘索邦’为高抗品种,‘马可波罗’、‘提拔’和‘西伯利亚’为中抗品种;田间接种发病的测定结果除‘西伯利亚’为高抗品种外其余结果与离体接种结果一致;离体接种和田间接种发病情况的系统调查分析得知,感病品种‘法兰西’和‘罗蒂娜’发病早,病情发展速度快,病情指数高;‘提拔’、‘康斯坦萨’、‘西伯利亚’和‘索邦’等抗病品种发病晚,病情发展缓慢,病情指数低;随着品种抗病性的增强,发病速度和病情指数逐渐降低。     

Identification of fusarium head blight resistance related metabolites specific to doubled-haploid lines in barley

Fusarium head blight (FHB) and deoxynivalenol (DON) mycotoxin produced by Fusarium graminearum reduce barley yield and quality worldwide. Hundreds of quantitative trait loci (QTLs) have been identified in wheat and barley but their functions are largely unknown. Metabolic profiling was applied to better understand the mechanisms of resistance and to identify potential FHB resistance biomarker metabolites in barley. Four FHB resistant (H15-2, H148-3, H203-2 and H379-2) and one susceptible (H97-2), two-row, purple, doubled-haploid (DH) lines of barley were inoculated with either the pathogen or mock-solution. The disease severity quantified as the area under the disease progress curve (AUDPC) significantly varied between the resistant and susceptible genotypes, but not among the resistant genotypes. Neither the amount of DON nor the detoxified product, proportion of total DON, was significant among lines. The resistance related (RR, higher in abundance in resistant than in susceptible) metabolites varied in numbers and fold changes among the DH resistant lines. A total of 144 RR constitutive (RRC) and 167 RR induced (RRI) metabolites were selected, of which 39 and 37, respectively, were putatively identified. These RR metabolites mainly belonged to six chemical groups: phenylpropanoids, hydroxycinnamic acid amides, flavonoids, fatty acids, terpenoids, and alkaloids. The specific RR metabolites identified in each DH line, the possible mechanisms of resistance in each and their use as potential biomarkers are discussed.     

植物抗病研究进展与展望

植物在其整个生活史中随时经受多种病原的侵袭,在进化过程中植物发展出多种对抗病原的机制。植物抗病性研究是当前植物病理学研究的热点问题之一。培育具有广谱而持久抗性的植物品种是育种学家追求的目标。目前,关于植物非寄主抗性、抗病基因介导的抗性、microRNA相关的抗性、感病基因的研究以及基因编辑在植物抗病性中的应用等方面已取得了大量新的研究成果。本文就以上几个方面综述了近年来植物抗病研究中的最新进展,并提出今后研究和育种中的应用展望。     

The novel elicitor COS‐OGA enhances potato resistance to late blight

Phytophthora infestans is the causal agent of potato late blight. This pathogen is usually controlled by fungicides, but new European regulations have imposed changes in crop protection management that have led to a search for alternative control measures. The induction of plant defence responses by elicitors is a promising new strategy compatible with sustainable agriculture. This study investigated the effect of eliciting a defence response in potato against P. infestans using a formulation of the COS‐OGA elicitor that combines cationic chitosan oligomers (COS) and anionic pectin oligomers (OGA). Trials were conducted under greenhouse conditions to assess the ability of COS‐OGA to control P. infestans. The results showed that three foliar applications with this elicitor significantly increased potato protection against late blight in controlled conditions. The activation of potato defence genes was also evaluated by RT‐qPCR during these trials. Two pathogenesis‐related proteins, basic PR‐1 and acidic PR‐2, were rapidly and significantly up‐regulated by the elicitor treatment. Therefore, these results suggest that the COS‐OGA elicitor increases the protection of potato against P. infestans and that this protection could be explained by an increase in the expression of potato defence genes rather than by biocide activity.