Silicon application enhances resistance to xanthomonas wilt disease in banana

Silicon (Si) has been reported to be a beneficial element and shown to enhance disease resistance in many crops, although it is not regarded to be critical for plant growth and development. In this study, the potential effect of Si supplementation on resistance to banana xanthomonas wilt (BXW) disease was evaluated using various banana cultivars. Si application at a concentration of 200 mg per plant per week was found to be optimal in enhancing resistance to BXW without any detrimental effects on plant growth. The effect of varying the duration of Si application showed continuous supply of Si before and after pathogen inoculation led to a significantly higher level of resistance to BXW in all the banana cultivars tested in comparison to non‐Si‐treated inoculated plants. Banana plants treated with Si before pathogen inoculation only, also exhibited high protection against BXW similar to plants treated continuously with Si. The total Si content in leaves increased significantly in Si‐treated plants in comparison to non‐Si‐treated control plants. The amount of Si accumulation was directly correlated to the duration of application; plants treated with Si continuously showed significantly higher amounts of Si accumulation in leaves than plants where Si application was terminated following bacterial inoculation or when Si application started immediately after pathogen inoculation. The Si‐treated plants also showed higher activity of the peroxidase enzyme in comparison to non‐Si‐treated control plants. This study confirms that application of Si enhances resistance to BXW and may provide an alternative disease management strategy.     

Quantitative real-time polymerase chain reaction for bacterial enumeration and allelic discrimination to differentiate xanthomonas strains on citrus

ABSTRACT Quantitative real-time polymerase chain reaction (QRT-PCR) was developed for identification and enumeration of bacteria in citrus plant samples infected with Xanthomonas axonopodis pvs. citri and citrumelo, the cause of citrus bacterial canker (CBC) and citrus bacterial spot (CBS), respectively. Three sets of primers based on the pathogenicity gene (pth) in X. axonopodis pv. citri, a ribosomal gene in X. axonopodis pv. citrumelo, and the leucine-responsive regulatory protein (lrp) in both pathovars were combined with TaqMan probes and applied for specific strain detection and quantification. Calibration curves for bacterial abundance in plant samples obtained with the three primer-probe combinations were congruent with colony counts on plates of semiselective medium in most of the cases. However, apparent overestimation of bacterial cells by QRT-PCR indicated the presence of nonculturable or nonviable cells in some samples. In addition to quantification, the lrp primers and probes permitted differentiation by allelic discrimination of Xanthomonas strains infecting citrus tissues. This technique is based on the utilization of two probes that detect a single nucleotide difference in the target sequence between different strains and was validated with a collection of cultured Xanthomonas strains as well as tissue with CBC and CBS lesions. Allelic discrimination is demonstrated to be a more specific and sensitive protocol than previously developed PCR-based methods for strain identification and quantification.     

中国虱属分类研究 Ⅲ.分类与检索

本文是“中国虱属分类研究”系列论文的第３篇,主要介绍了目分亚目、粉亚目分组、纳组分科、虱科分属以及虱属分种团等５个目和虱属研究中常用的检索表。     

Antifungal substances produced by fungal strain Kyu-W63 from wheat leaf and its taxonomic position

Fungal strain Kyu-W63 from a wheat leaf suppressed the development of wheat powdery mildew caused by Blumeria graminis f. sp. tritici. Nuclear magnetic resonance analysis revealed that Kyu-W63 produced two volatile substances: 5-pentyl-2-furaldehyde and 5-(4-pentenyl)-2-furaldehyde. Although the two are known to be nematicidal substances, the antifungal activity of 5-(4-pentenyl)-2-furaldehyde was first confirmed in the present study. Culture experiments revealed that synthesized 5-pentyl-2-furaldehyde had antifungal activity against three other pathogens – Fusarium oxysporum f. sp. lycopersici, Colletotrichum fragariae, Botrytis cinerea – with a minimum inhibitory concentration of 2–4µg/ml. The two fractionated substances were also inhibitory against C. fragariae. Because the absence of spores in strain Kyu-W63 made its identification difficult, the sequence in the rDNA internal transcribed spacer (ITS) region of Kyu-W63 was compared with that of Irpex lacteus, which is known to produce these substances. Strain Kyu-W63 completely agreed with I. lacteus in terms of the ITS sequences, so strain Kyu-W63 was inferred to be I. lacteus. Two other strains of I. lacteus tested also produced the two furaldehydes and suppressed the growth of F. oxysporum f. sp. lycopersici. Both Kyu-W63 and additional strains produced the two furaldehydes on potato dextrose agar but not on water agar.The nucleotide sequence data reported are available in the DDBJ databases under accession numbers AB079264, AB079265, AB079266, and AB079267     

明孢盘菌属分类进展及其重要的病原菌种类

明孢盘菌属(Neofabraea)中很多种类是重要的植物病原菌。该属真菌分类历史较为复杂,系统发育关系也长期存在较大的争议。本文对明孢盘菌属的分类学研究历史做了系统回顾,包括属的建立、物种组成及其命名更替和系统发育,概述了该属重要的植物病原菌种类地理分布和经济为害性,讨论了该属真菌物种的传统分类方法及分子研究方法,指出了存在的问题及今后的研究方向。     

A polyetic modelling framework for plant disease emergence

Plant disease emergences have dramatically increased recently as a result of global changes, especially with respect to trade, host genetic uniformity, and climate change. A better understanding of the conditions and processes determining epidemic outbreaks caused by the emergence of a new pathogen, or pathogen strain, is needed to develop strategies and inform decisions to manage emerging diseases. A polyetic process-based model is developed to analyse conditions of disease emergence. This model simulates polycyclic epidemics during successive growing seasons, the yield losses they cause, and the pathogen survival between growing seasons. This framework considers one immigrant strain coming in a single event into a system where a resident strain is already established. Outcomes are formulated as probability of emergence, time to emergence, and yield loss, resulting from deterministic and stochastic simulations. An analytical solution to determine a threshold for emergence is also derived. Analyses focus on the effects of two fitness parameters on emergence: the relative rate of reproduction (epidemic speed), and the relative rate of mortality (decay of population between seasons). Analyses revealed that stochasticity is a critical feature of disease emergence. The simulations suggest that: (a) emergence may require a series of independent immigration events before a successful invasion takes place; (b) an explosion in the population size of the new pathogen (or strain) may be preceded by many successive growing seasons of cryptic presence following an immigration event; and (c) survival between growing seasons is as important as reproduction during the growing season in determining disease emergence.     

A method to test wheat leaves for their reactions to inoculation with Septoria species

The construction and application is described of a polystyrol humidity box in which wheat leaves, while continuing to function as parts of living plants, can be tested for their reactions toSeptoria spp. in an atmosphere nearly saturated with water, as is required for successful infection. The method is simple, accurate ans inexpensive.Samenvatting Voor dit doel is een z.g. vochtdoos geconstrueerd (Fig. 1A). Het te toetsen blad wordt daar doorheen geleid en in de doos geïnoculeerd met een druppel conidiën-suspensie van de schimmel. Onder het blad staat wat water in de doos (Fig. 1B). Na afsluiting ontstaat in de doos de hoge luchtvochtigheid van bijna 100% die nodig is voor de infectie. Dit wordt op deze wijze eenvoudig en goedkoop gerealiseerd. De bladeren die zo worden getoetst blijven onbeschadigd functioneren aan de plant. Na enkele dagen kan de doos worden geopend en kan de symptoom-ontwikkeling worden afgewacht en gevolgd (Fig. 3A, 3B en 4). De methode leent zich voor nauwkeurig werk en vereist zeer weinig infectiemateriaal. De Technische en Fysische Dienst voor de Landbouw (TFDL), Wageningen, ontwierp en construeerde een statief voor het gebruik van de vochtdozen in serie (Fig. 2).     

A taxonomic study of the host ranges of tymoviruses

Published data on the susceptibility of plant species to 18 tymoviruses were collated. These data showed that tymoviruses infected more species from the family of their natural field host than species from other families. The data also indicated that tymoviruses infected a greater proportion of species from the same primary division of the dicotyledons (crassinucellate or tenuinucelate) as their natural host than other species, but the correlation was not statistically significant.
The susceptibility of 18 crassinucellate and 18 tenuinucellate test plant species to 10 tymoviruses was determined. The viruses infected about three times more plant species from the primary taxonomic division that contained the family of their field host than species from the other division; this difference was statistically significant.
The separation of tymoviruses into two groups based on the taxonomic division containing their natural hosts and most of their experimental hosts correlates broadly with a classification of the tymoviruses based on the serological relationships of their particle coat proteins.     

Sources of resistance in Musa to Xanthomonas campestris pv. musacearum,the causal agent of banana xanthomonas wilt

It is claimed that, with the exception of Musa balbisiana, all banana varieties are susceptible to bacterial wilt caused by Xanthomonas campestris pv. musacearum (Xcm). Despite being resistant to Xcm infection, M. balbisiana is not preferred for breeding because it belongs to the BB genome subgroup, while most edible bananas are of the A genome. To identify potential sources of resistance to Xcm, 72 banana accessions representing the Musa genetic diversity were evaluated in an outdoor confined potted trial. The midribs of the youngest leaf of 3-month-old banana plants were inoculated with 10⁸ CFU mL⁻¹ of Xcm isolate USY13P, and symptom development assessed weekly for 4 months. Results confirmed that M. balbisiana genotypes are indeed resistant to Xcm. Varieties within the Musa acuminata subsp. zebrina (AA) set were further identified as potentially useful sources of Xcm resistance. These findings reveal the potential to develop banana and plantain varieties with tolerance to Xcm.     

A test of taxonomic predictivity: resistance to early blight in wild relatives of cultivated potato

Host plant resistance offers an attractive method of control for early blight (caused by the foliar fungus Alternaria solani), a widespread disease that appears annually in potato crops worldwide. We tested the assumed ability of taxonomy to predict the presence of early blight resistance genes in wild Solanum species for which resistance was observed in related species. We also tested associations to ploidy, crossing group, breeding system, and geography. As in a prior study of Sclerotinia sclerotiorum (white mold) resistance, tremendous variation for resistance to early blight was found to occur within and among species. There was no discernable relationship between the distribution of resistant phenotypes and taxonomic series (based on an intuitive interpretation of morphological data), clade (based on a cladistic analysis of plastid DNA data), ploidy, breeding system, geographic distance, or climate parameters. Species and individual accessions with high proportions of early blight resistant plants were identified, but high levels of inter- and intra-accession variability were observed. Consequently, the designation of species or accessions as resistant or susceptible must take this variation into account. This study calls into question the assumption that taxonomic or geographic data can be used to predict sources of early blight resistance in wild Solanum species.     

有害生物危险性综合评价方法的研究

本文对植物有害生物危险性综合评价指标体系的建立,指标值和权重的确定,以及综合评价模型等问题作了方法论的初步探讨     

A mixed methodology framework for the assessment of the Voluntary Initiative

The Voluntary Initiative (VI) is a UK programme of measures aimed at reducing the adverse effects of pesticides on the environment. It was initiated in 2001 and will be evaluated during 2006 following a five-year trial period. To assess such a complex scheme, a mixed methodology approach is appropriate, encompassing the assessment of objective deliverables and issues raised by the farming community. A series of focus groups examined the perceptions of the VI by the farming community. Farmer attitudes to the VI appeared to be influenced by the belief that the UK government will, eventually, introduce some form of pesticide tax regardless of the outcome of the VI. Most farmers expressed that they already followed the principles of the VI. It was also evident that the scheme may become more acceptable and better understood as it becomes incorporated into existing farm assurance schemes. This paper proposes a framework for evaluation of the VI that takes into account these perceptions of the VI by the farming community. Based on the analysis of available data, key questions are identified that should be addressed within the final evaluation. These key questions cover the general themes of completion of VI targets and projects, uptake of the VI, environmental impact of the VI and economic implications. To answer the questions, four methods are proposed: a review of literature, a survey of farmers, questions to agencies and environmental modelling.     

暴雨和洪灾对湖北稻区稻白叶枯病

水稻白叶枯病是湖北稻区中、晚稻常发病害.80年代平均年发生面积达180. 8khm2,平均年自然损失达19.05万t.发生区域主要集中在江汉平原、鄂东北、鄂东南及鄂北稻区.其间发生规律表现为:初夏、盛夏大风、暴雨多的年份流行面广,为害重,淹过水的中稻和秧田淹过水的双季晚稻发生受害重.90年代湖北稻白叶枯病的发生一直处于较低水平,年平均发生面积104.2khm2,年平均自然损失万吨,为害较80年代明显减轻.作者收集了有关气象资料,并对稻白叶枯病的侵染规律进行了试验研究,弄清了90年代白叶枯病发生水平降低的原因,为稻白叶枯病的风险预报提供了新的依据.     

A taxonomic study ofNorbanus Walker (Hymenoptera: Pteromalidae) from China

The Chinese species of the pteromalid genusNorbanus Walker are reviewed. Six valid species, including four newly recorded species, are recognized. Diagnoses and a key to species are provided. The specimens are deposited in the Zoological Museum, Institute of Zoology, Chinese Academy of Sciences.     

A malathion-tolerant strain of the spiderChiracanthium mildei and its response to chlorpyrifos

Chiracanthium mildei L. Koch (Araneae: Clubionidae) spiders, from two populations, were collected and reared in the laboratory. One originated from a citrus grove at Kibbutz Afeq and the other from an experimental cotton field at the Newe Ya’ar Experiment Station. Laboratory evaluation indicated that the Afeq strain was more tolerant to malathion than the Newe Ya’ar strain (resistance factor of x3.3). When spiders of the Afeq strain were exposed to chlorypyrifos (Dursban) and malathion residues, chlorpyrifos was much more toxic.     

A strain ofPseudomonas syringae which does not belong to pathovarphaseolicola produces phaseolotoxin

A bacterial strain, CFBP 3388, isolated from Vetch (Vicia sativa, L.) was identified asP. s. pv.syringae on the basis of nutritional and biochemical patterns which were obtained with classical tests and the Biolog system. It caused necrotic symptoms typical ofP. s. pv.syringae on bean leaves and pods after artificial inoculation. However, the isolate caused a citrulline-reversible inhibition ofE. coli in phaseolotoxin bioassay. Furthermore, with CFBP 3388 DNA as template a 1900 bp DNA fragment, specific for the phaseolotoxin DNA cluster ofP. s. pv.phaseolicola, was amplified by PCR. This is the first demonstration that an isolate ofP. syringae that is not pv.phaseolicola can produce phaseolotoxinAbbreviations bp base pair - kb kilobase - OCT Ornithine Carbamoyl Transferase     

A contribution to the knowledge of nematophagous species of Verticillium

Nine nematophagous species and two varieties ofVerticillium (Verticillium sect.Prostrata), occurring either as parasites of free-living nematodes or as parasites of cysts and eggs, are revised and keyed out.V. catenulatum is reduced to a variety ofV. chlamydosporium A similar fungus is distinguished asV. suchlasporium n. sp. (including a var.catenatum). Spicaria coccospora Drechsler is transferred toVerticillium. All species have been studied in pure culture. Ecological data are reviewed for each species.Samenvatting Negen nematofage soorten en twee variëteiten vanVerticillium (Verticillium sectieProstrata), die óf als parasieten van vrijlevende aaltjes óf als parasieten van cysten en eieren optreden, worden gereviseerd en er wordt een determinatiesleutel van gepresenteerd.V. catenulatum wordt gereduceerd tot een variëteit vanV chlamydosporium. Een hierop lijkende schimmel wordt onderscheiden als.V. suchlasporium n.sp. (incl. een variëteitcatenatum. Spicaria coccospora Drechsler wordt naarVerticillium overgebracht. Alle soorten werden in reincultuur onderzocht. Voor iedere soort worden oecologische gegevens vermeld.     

Characterization of a new viroid strain from hops: evidence for viroid speciation by isolation in different host species

A new viroid was detected in hops cultivated in Akita Prefecture, Japan where it is prevalent in many hops fields. In a survey of hop samples collected during the 1986–2002 growing seasons, the new viroid was present in the major Japanese hop-cultivating areas as early as the 1980s. A single-stranded circular RNA of 368–372 nucleotides that assume a highly basepaired, stable, rod-like secondary structure, shares 93%–98% sequence homology with Apple fruit crinkle viroid (AFCVd) isolated from apple and 85%–87% with Australian grapevine viroid (AGVd) isolated from grapevine. Taking into account the present concept of viroid species, we conclude that the viroid is AFCVd. Circumstantial evidence suggests that AFCVd from apples and hops were endemic in Japan only where cultivation of the two host plants overlapped, thereby strongly supporting the possibility that AFCVd (or an ancestral viroid) was transmitted across the species barrier from apples to hops or hops to apples somewhere in the region. Phylogenetic analysis of AFCVd from hops, AFCVd from apples, and AGVd together with the other members of the genus Apscaviroid revealed that the Akita isolates of AFCVd from hops (AFCVd-hop) formed a cluster that is distinct from AFCVd-apple and AGVd. Accumulation of host-specific sequence variation following their isolation in different host species may be leading to the formation of two viroid species from a common ancestor.