番茄斑萎病毒对云南莴苣类蔬菜的侵染为害

莴苣类蔬菜是常见的食用蔬菜。近年在云南发现生菜、莴笋、油麦菜有症状表现为叶片黄化、褪绿、坏死斑的病害流行危害,为确定其病原,通过电子显微镜观察、回接试验、ELISA检测、病毒基因分析,在典型症状病样组织粗汁液和超薄切片中均观察到有类似番茄斑萎病毒属病毒的粒体,该病毒粒体为球形,直径80～85 nm; ELISA检测和病毒基因分析显示,侵染莴苣类蔬菜的病毒为番茄斑萎病毒。     

Molecular Characterization of <Emphasis Type="Italic">Bean yellow mosaic virus </Emphasis>from Vegetatively Propagated Dwarf <Emphasis Type="Italic">Gentiana </Emphasis>Plants

The causative virus (isolate No. 4) of gentian (Gentiana spp.) mosaic, which had been identified previously as Clover yellow vein virus (C1YVV) on the basis of host range and serological reactions, was re-identified as Bean yellow mosaic virus (BYMV) on the basis of the nucleotide sequences of the gene for the coat protein (CP) and the 3′-noncoding region, as well as the predicted amino acid sequence of CP. Received 16 April 2002/ Accepted in revised form 19 June 2002     

Characteristics for Practical Use of Attenuated Isolate UA-Fukushima of <Emphasis Type="Italic">Tomato mosaic virus</Emphasis>

L₁₁A-Fukushima (L₁₁A-F) derived from attenuated isolate LuA of Tomato mosaic virus (ToMV) has the highest ability to cross protect against virulent ToMV among LuA and its derivatives and is stably inherited. Growth, yield, fruit quality and symptom attenuation of inoculated tomato plants did not differ significantly between L₁₁A-F and L₁₁A. The infectivity of progeny viruses in tomato infected with LuA-F was less than 4% of that with virulent ToMV. From these results, L₁₁A-F appears to possess the properties necessary for practical use. To manage L₁₁A-F strictly, a PCR-based assay to detect trace contamination of virulent ToMV in L₁₁A-F preparations was established. Received 10 June 2002/ Accepted in revised form 30 October 2002     

Incidence of viruses in <Emphasis Type="Italic">Alstroemeria</Emphasis> plants cultivated in Japan and characterization of <Emphasis Type="Italic">Broad bean wilt virus-2, Cucumber mosaic virus</Emphasis> and <Emphasis Type="Italic">Youcai mosaic virus</Emphasis>

Alstroemeria plants were surveyed for viruses in Japan from 2002 to 2004. Seventy-two Alstroemeria plants were collected from Aichi, Nagano, and Hokkaido prefectures and 54.2% were infected with some species of virus. The predominant virus was Alstroemeria mosaic virus, followed by Tomato spotted wilt virus, Youcai mosaic virus (YoMV), Cucumber mosaic virus (CMV), Alstroemeria virus X and Broad bean wilt virus-2 (BBWV-2). On the basis of nucleotide sequence of the coat protein genes, all four CMV isolates belong to subgroup IA. CMV isolates induced mosaic and/or necrosis on Alstroemeria. YoMV and BBWV-2 were newly identified by traits such as host range, particle morphology, and nucleotide sequence as viruses infecting Alstroemeria. A BBWV-2 isolate also induced mosaic symptoms on Alstroemeria seedlings.     

Analysis of genetic relations between <Emphasis Type="Italic">Broad bean wilt virus 1</Emphasis> and <Emphasis Type="Italic">Broad bean wilt virus 2</Emphasis>

We determined the complete nucleotide sequence of RNA-1 and the 5-terminal region of RNA-2 from Broad bean wilt virus 1 (BBWV-1) isolate PV132. This report is the first analysis of the genome organization of BBWV-1. We also determined the complete nucleotide sequence of RNA-1 from Broad bean wilt virus 2 (BBWV-2) isolate IP and analyzed the genetic relations between BBWV-1 and BBWV-2. Similar to the BBWV-2 isolates, both RNAs of PV132 encoded a single large polyprotein, which was predicted to contain some functional proteins in a manner similar to those of comovirus. With respect to the deduced amino acid sequences of the mature proteins, PV132 and IP had only 20%–40% homology to comovirus. On the other hand, IP was 73%–98% homologous to BBWV-2 isolates, but PV132 was 39%–67% homologous to the isolates. Although the extent of the homologies differed, the homologies were limited between BBWV-1 and BBWV-2 not only for the coat protein but also for the other proteins. These results clearly support the placement of BBWV-1 and BBWV-2 in the genus Fabavirus as distinct species, proposed on the basis of double immunodiffusion tests.The nucleotide sequence data reported are available in the DDBJ/EMBL/GenBank databases under the accession numbers AB084450 (RNA-1 of isolate PV132), AB084451 (RNA-2 of isolate PV132), and AB023484 (RNA-1 of isolate IP)     

<Emphasis Type="Italic">Physalis ixocarpa</Emphasis> and <Emphasis Type="Italic">P. peruviana</Emphasis>, new natural hosts of <Emphasis Type="Italic">Tomato chlorosis virus</Emphasis>

Tomato chlorosis virus causes yellow leaf disorder epidemics in many countries worldwide. Plants of Physalis ixocarpa showing abnormal interveinal yellowing and plants of Physalis peruviana showing mild yellowing collected in the vicinity of tomato crops in Portugal were found naturally infected with ToCV. Physalis ixocarpa and P. peruviana were tested for susceptibility to ToCV by inoculation with Bemisia tabaci, Q biotype. Results confirmed that ToCV is readily transmissible to both species. The infection was expressed in P. ixocarpa by conspicuous interveinal yellow areas on leaves that developed into red or brown necrotic flecks, while P. peruviana test plants remained asymptomatic. Infected plants of both P. ixocarpa and P. peruviana served as ToCV sources for tomato infection via B. tabaci transmission. This is the first report of P. ixocarpa and P. peruviana as natural hosts of ToCV.     

Expression of <Emphasis Type="Italic">Xanthomonas oryzae </Emphasis>pv. <Emphasis Type="Italic">oryzae hrp</Emphasis> Genes in XOM2, a Novel Synthetic Medium

To analyze the regulation of hrp expression and to detect and identify hrp-dependent secretion proteins of plant-pathogenic bacteria, an appropriate hrp-inducing medium is indispensable. In this study, two efficient hrp-inducing media for Xanthomonas oryzae pv. oryzae were designed by assaying the expression of a hrcU (the first gene of the hrpC operon) and a gus (β-glucuronidase) fusion gene. We modified XVM2, which is a hrp-inducing medium for X. campestris pv. vesicatoria, by adding 0.01% xylose in place of fructose and sucrose (0.18 and 0.34%, respectively) as a sugar source. The resulting medium induced approximately 15-fold more GUS activity from transformants containing a hrcU::gus gene than did XVM2. Moreover, a methionine-containing synthetic medium with 0.18% xylose as a sugar source was able to induce much stronger expression of HrcU::GUS, with GUS activity approximately 100-fold greater than that in XVM2. Induction depended on a regulator, HrpXo, and the PIP (plant-inducible-promoter) box, suggesting that HrcU::GUS was expressed in a hrp-dependent manner. The induction of operons hrpA to hrpF in XOM2 was also confirmed. These results suggest that both media, especially XOM2, are highly efficient hrp-inducing media for X. oryzae pv. oryzae. Received 7 October 2002/ Accepted in revised form 22 November 2002     

Alternaria Leaf Spot on Mealycup Sage (<Emphasis Type="Italic">Salvia farinacea </Emphasis>Benth.) Caused by <Emphasis Type="Italic">Alternaria alternata </Emphasis>(Fr.) Keissler

In June 1995, a disease causing round to irregular-shaped, water-soaked, brown to blackish brown spots on mealycup sage (Salvia farinacea Benth.) was found in Atsugi-shi, Kanagawa Prefecture, Japan. The symptoms were seen only on leaves, not on neither flower petals or stems. The disease was also found in Setagaya-ku, Tokyo, Memambetsu-cho, Hokkaido and Shimoda-shi and Matsuzaki-cho, Shizuoka. An Alternaria sp. was frequently isolated from these diseased plants. The isolates were severely pathogenic to mealycup sage and caused lesions on the inoculated leaves. The isolates were also weakly pathogenic on scarlet sage (S. splendens Sellow ex Roem. and Schult.) but not on any other Labiatae plants tested. Based on morphological characteristics, such as size of conidia, chain number, and the short beak on conidia, the causal fungus was identified as Alternaria alternata (Fr.) Keissler. This report is the first on a mealycup sage disease caused by A. alternata. Because the symptom was restricted to the leaf, the common name of Alternaria leaf spot was proposed. Received 30 August 2002/ Accepted in revised form 18 November 2002     

Validation of the specificity and sensitivity of species-specific primers that provide a reliable molecular diagnostic for <Emphasis Type="Italic">Xiphinema diversicaudatum</Emphasis>, <Emphasis Type="Italic">X. index</Emphasis> and <Emphasis Type="Italic">X. vuittenezi</Emphasis>

Xiphinema diversicaudatum and X. index are vector nematode species of economic importance in viticulture regions as they can transmit Arabis Mosaic, Grapevine Fanleaf and Strawberry Latent Ringspot viruses to grapevine. Wang et al. (2003) designed species-specific diagnostic primers from ribosomal genes for both these vector species as well as a vector and a non-vector species X. italiae and X. vuittenezi, respectively. Our study aimed to confirm the specificity and determine the sensitivity and reliability of the primers for the two vector species, X. diversicaudatumand X. indexwhen challenged with closely related longidorid species and general nematode communities typical of vineyard soil. With one exception, no PCR product was observed when the primers were tested against six Longidorus, one Paralongidorus and one Xiphinema non-target species. Occasionally (three out of eight replicate PCR reactions) a weak PCR product was noted when primers for X. index were tested with L. elongatus. Furthermore, when challenged with a range of non-target nematode species comprising the nematode community typical of viticulture soil, no PCR product was amplified. An experimental dilution series of extracted DNA rigorously demonstrated that DNA from an equivalent single specimen of the target virus-vector species, X. diversicaudatum and/or X. index, could be detected amongst 1000 equivalent non-targetX. vuittenezi. Also, extracted DNA from an equivalent single target specimen was detected when added to DNA extracted from the overall soil nematode community. The primers were assessed further by using serial mixtures of actual nematodes rather than extracted DNA to simulate field soil. Using this method, a single target nematode could be detected amongst 200 non-target specimens. Given their specificity, sensitivity and reliability, it appears that these diagnostic primers will be of great benefit to phytosanitary/quarantine services related to the viticulture industry.     

Suppression of Fusarium wilt of spinach with hypovirulent binucleate <Emphasis Type="Italic">Rhizoctonia</Emphasis>

 Four isolates of hypovirulent binucleate Rhizoctonia (HBNR) were evaluated for their ability to control Fusarium wilt of spinach (FWS) caused by Fusarium oxysporum f. sp. spinaciae (FOS). Fourteen-day-old spinach seedlings grown in paper pots with HBNR-amended soil (1% w/w ground barley grain inoculum) were transferred to artificially pathogen-infested soil. Treatments with HBNR isolates significantly (P = 0.05) reduced disease and discoloration severity by 56%–100% and 52%–100%, respectively. The numbers of colony-forming units of FOS per gram fresh weight in petioles or roots were reduced significantly (P = 0.01) in the plants treated with HBNR. HBNR isolates were well reisolated from the roots inside paper pots where they were inoculated, whereas inconsistent colonization of HBNR was recorded from the roots outside paper pots where only pathogen was inoculated. Root extracts from HBNR-treated and pathogen-challenged plants significantly inhibited germination and germling length of FOS. The fresh weight of spinach leaves in the HBNR-treated plants increased significantly (P = 0.01), as much as 53%–63%, over the untreated and pathogen-challenged plants. This is the first report of biocontrol of FWS by HBNR. Received: July 18, 2002 / Accepted: October 22, 2002 Acknowledgments We are grateful to Dr. Komada for providing nonpathogenic Fusarium F13. The senior author (A.M.) thanks the Ministry of Education, Culture, Sports, Science, and Technology (Monbukagakusho) Japan, for financial assistance.     

Biofilm formation and resistance to bactericides of <Emphasis Type="Italic">Pseudomonas syringae</Emphasis> pv. <Emphasis Type="Italic">theae</Emphasis>

Biofilm-grown cells of Pseudomonas syringae pv. theae (P.s.theae) wild-type strain K9301 on abiotic surface had remarkable resistance to kasugamycin in comparison to planktonically grown cells; however, the biofilm-grown cells of K9301 had the same sensitivity to copper sulfate. Because both the lesser biofilm-forming strain K9301S3 and enhanced biofilm-forming strain K9301-6 also had remarkable biofilm resistance to kasugamycin just as K9301 did and because epigallocatechin gallate, which enhanced biofilm formation of P.s.theae, had no effect on biofilm resistance to kasugamaycin, the degree of biofilm formation was not correlated with the antibiotic susceptibilities. In addition, K9301 and K9301S3 had less sensitivity to kasugamycin but had high sensitivity to copper sulfate on nonwounded leaf surfaces. These results indicate a possibility that the mechanism of P.s.theae biofilm resistance to bactericide functions on both abiotic and nonwounded leaf surfaces.     

Susceptibility and resistance of <Emphasis Type="Italic">Beta vulgaris</Emphasis> subsp. <Emphasis Type="Italic">maritima</Emphasis> to foliar rub-inoculation with <Emphasis Type="Italic">Beet necrotic yellow vein virus</Emphasis>

Four lines (designated MR0, MR1, MR2, and M8) from 13 accessions of Beta vulgaris subsp. maritima were selected on the basis of phenotypes produced after foliar rub-inoculation with Beet necrotic yellow vein virus (BNYVV). The susceptible phenotype developed bright yellow local lesions, whereas the resistant phenotype had symptoms ranging from no visible lesions to necrotic lesions at the inoculation site. MR1 and MR2 lines had a resistant phenotype depending on the isolate and the MR0 line was susceptible to all isolates of BNYVV tested. The M8 line was highly susceptible; the virus spread systemically and caused severe stunting. These plant lines will be useful for distinguishing BNYVV isolates having different pathogenicities, especially those controlled by RNA3 and/or RNA5.     

Occurrence of <Emphasis Type="Italic">Phaeoacremonium</Emphasis> spp. and <Emphasis Type="Italic">Phaeomoniella chlamydospora</Emphasis> in grape propagation materials and young grapevines

During a 6-year study, grapevine propagation materials and young grapevines were analysed to evaluate the presence of internal wood discolouration and the occurrence of fungal species involved in Petri disease. The intensity of wood discolouration increased with the ageing of the plants. The maximum incidence of dark streaks was observed in the rootstock while necrosis originating from buds or nodes were notably present in the trunk and cordon of older vines. In contrast, the highest levels of brown-red halo symptoms, defined as discoloured areas around the pith, were recorded in the early growth stages. Phaeoacremonium spp. and Phaeomoniella chlamydospora were usually isolated from the rooted-grafts and the 3-year old plants, respectively. The number of infected grapevines increased with age. Most of the P. chlamydospora strains were isolated from dark streaks or dots, while Phaeoacremonium spp. were detected in brown-red halo symptoms and other symptomatic or asymptomatic wood. The greatest incidence of the two fungal taxa was recorded in the lower parts of the grapevine, including the roots and rootstock.     

Characteristics of a <Emphasis Type="Italic">Plasmopara angustiterminalis</Emphasis> isolate from <Emphasis Type="Italic">Xanthium strumarium</Emphasis>

Leaves of Xanthium strumarium infected with downy mildew were collected in the vicinity of a sunflower field in southern Hungary in 2003. Based on phenotypic characteristics of sporangiophores, sporangia and oospores as well as host preference the pathogen was classified as Plasmopara angustiterminalis. Additional phenotypic characters were investigated such as the size of sporangia, the number of zoospores per sporangium and the time-course of their release. Infection studies revealed infectivity of the P. angustiterminalis isolate to both X. strumarium and Helianthus annuus. Inoculation of the sunflower inbred line, HA-335 with resistance to all known P. halstedii pathotypes, resulted in profuse sporulation on cotyledons and formation of oospores in the bases of hypocotyls. Infections of sunflower differential lines often led to damping-off. Molecular genetic analysis using simple sequence repeat primers and nuclear rDNA sequences revealed clear differences to Plasmopara halstedii, the downy mildew pathogen of sunflower.     

Evaluation of the durability of the <Emphasis Type="Italic">Barley yellow dwarf virus</Emphasis>-resistant <Emphasis Type="Italic">Zhong ZH</Emphasis> and <Emphasis Type="Italic">TC14</Emphasis> wheat lines

Serial passage experiments (SPE) of a Barley yellow dwarf virus-PAV (BYDV-PAV) isolate were performed on Zhong ZH and TC14 wheat lines to evaluate the durability of their resistance to BYDV. At different passage numbers (from the 2nd to the 114th), biological properties of the produced isolates were recorded either by monitoring infection percentages and virus titers of the first 3 weeks of viral infection or by measuring their impact on yield components. Statistical analyses using the area under pathogen progress curves and the area under concentration progress curves demonstrated that these two resistant lines induce, after only a few passages, a selection of variant(s) with significantly modified infection abilities. Isolates resulting from SPE performed on these lines induced important decreases of yield components. These results indicate that the use of Zhong ZH and TC14 lines in BYDV-resistant breeding programmes should be approached with caution.     

Genetics of host-pathogen interactions in the <Emphasis Type="Italic">Pyrenophora teres</Emphasis> f. <Emphasis Type="Italic">teres</Emphasis> (net form) – barley (<Emphasis Type="Italic">Hordeum vulgare)</Emphasis> pathosystem

The genetics of host-pathogen interactions in the Hordeum vulgare – P. teres f. teres pathosystem was studied in twelve resistant barley accessions, i.e. CI 9825, CI 9819, Diamond, CI 4922, CI 5401, Harbin, c-8755, c-21849, c-8721 c-23874, c-19979, c-15811. F₂ analyses of crosses with susceptible genotypes employing various isolates (from Europe, USA, Canada, and Australia) revealed that resistance is mostly isolate-specific and controlled by one or two genes. Segregation in ascospore progeny from two crosses between isolates of different origin revealed that avirulence in P. teres is also determined by one or two genes. An epistatic effect of suppressor genes on avirulence genes is proposed for the genetics of virulence to Diamond, Harbin, CI 5401 and c-8721 in the fungal crosses D (181-6 × A80) and F (H-22 × 92-178/9). Segregation in F₂ of crosses of three new sources of resistance (c-23874, c-19979, c-15811) to the susceptible cv. Pirkka was studied in laboratory and greenhouse tests by using seven P. teres isolates, i.e. 181-6, d8-3, d8-4, d9-1, d9-4, F4 and F74. In addition, virulence to these barley accessions of ascospore progeny from crosses of the same isolates was studied. Based on these studies it was concluded that depending on the isolate used, resistance of c-23874 is determined at least by two genes and in c-19979 and c-15811 by three genes. The results of this parallel analyses of genetics of resistance and genetics of virulence allows the postulation of a gene–for–gene interaction in the P. teres – H. vulgare pathosystem.     

Development of a semi-selective medium for isolation of <Emphasis Type="Italic">Xanthomonas campestris</Emphasis> pv<Emphasis Type="Italic">. musacearum</Emphasis> from banana plants

Banana Xanthomonas wilt, caused by Xanthomonas campestris pv. musacearum, is a new threat to banana cultivation in eastern Africa. The causal bacterium grows slowly in culture and is easily overgrown by contaminants. A selective culture medium for isolation of X. c. pv. musacearum will facilitate disease study. A medium that suppressed saprophytic growth and possessed diagnostic characters for the pathogen was developed. Various carbon sources were tested with two isolates of X. c. pv. musacearum, and sucrose was selected as main carbon source. The susceptibility of X. c. pv. musacearum and other bacterial strains was tested with 29 different antibiotics. Cephalexin and cycloheximide had no effect on X. c. pv. musacearum but cephalexin inhibited most of the saprophytes and cycloheximide inhibited the fungal contaminants. Based on these studies, we have developed a semi-selective medium YTSA-CC containing yeast extract (1%), tryptone (1%), sucrose (1%), agar (1.5%), cephalexin (50 mg l⁻¹) and cycloheximide (150 mg l⁻¹), pH 7.0. The pathogen X. c. pv. musacearum was easily identified as yellowish, mucoid and circular colonies on YTSA-CC medium. This simple semi-selective medium was effective for isolation of X. c. pv. musacearum from infected banana tissues and soil, and it should be a valuable tool in ecological and epidemiological studies.     

Indirect interactions between rust (<Emphasis Type="Italic">Melampsora epitea</Emphasis>) and leaf beetle (<Emphasis Type="Italic">Phratora vulgatissima</Emphasis>) damage on<Emphasis Type="Italic">salix</Emphasis>

Willows (Salix spp.) are beneficial as a potential source of renewable energy, riparian barriers and riverbank control, yet are considered invasive weeds when they clog watercourses and lead to erosion and flooding. Interactions between willow rustMelampsora epitea (Thüm.) (Uredinales: Melampsoraceae) and leaf beetlePhratora spp. (Coleoptera: Chrysomelidae) feeding damage have an impact on effective pest management and biological control. The present study investigated the effects of(a) prior mechanical leaf damage on rust development, and(b) rust infection on beetle feeding under laboratory conditions for different time intervals and levels of damage. Willow rust infection significantly reduced the amount of leaf area consumed by beetles. The result was similar when a compatible or an incompatible rust pathotype was sprayed ontoSalix viminalis (L.) ‘Mullatin’ plants. There were no overall significant effects of mechanical damage on rust development, although the lowest level of rust infection was found with the incremental damage treatment. There were, however, differences of significance for leaf position and damage status, with damaged leaves at all positions having fewer pustules and a smaller pustule area than the corresponding undamaged leaves. There was no detectable effect of possible volatile emissions from crushed willow leaves on rust infection and development, although the volatile compoundcis-3-hexenyl acetate significantly reduced pustule diameter and overall pustule area. The results are discussed in terms of the implications for pest management and biological control. Corresponding author http://www.phytoparasitica.org posting April 6, 2003.     

Virulence and diversity of <Emphasis Type="Italic">Blumeria graminis</Emphasis> f.sp. <Emphasis Type="Italic">hordei</Emphasis> in East China

Four hundred and sixty-one isolates of Blumeria graminis f.sp. hordei were obtained from eight populations occurring on cultivated barley (Hordeum vulgare) at four geographically distant locations in China during 2003 and 2004. Their virulence frequency was determined on 30 differential lines. No isolate was virulent on differential lines possessing the resistance genes Mla1, Mla3, Mla6, Mla7, Mla9, Mla12, Mla13, Mlat, Mlg, Mla10, Mla22, Mla23, Mlp1, Ml(N81) and Mlmw. Virulences to the first nine resistance genes are prevalent in Europe and constitute the main part of genetic distance between Chinese and European populations. Conversely, no isolate was avirulent on the differential lines possessing the genes Mla8 and Ml(Ch). The frequencies of isolates overcoming the genes Mla2, Mla11, Mlk1 and Mlk2 were .4–9.3%, and frequencies of isolates overcoming the genes Mlh, MlLa, Ml(Bw), Mlra, Ml(Ru2), mlw, MlGa, MlWo and Mlnn ranged from 18.2% to 98.7%. Based on reactions of differential lines possessing the genes Mlk1, Mlh, MlLa, Ml(Bw), Mlra and Ml(Ru2), pathotypes were identified and diversity parameters calculated. Eleven of 22 detected pathotypes were found in both years and comprised 94.6% of isolates. Generally, the populations from different locations in 1 year were more closely related than populations collected from the same locations in different years. Complete effectiveness of the resistance genes, for which no corresponding virulences were found, will allow Chinese breeders to access many modern European barley cultivars that are fully resistant to powdery mildew in China, including those possessing the non-host resistance gene mlo.