Unterschiedliche Formen der Resistenz gegen bodenbürtige Viren des Weizens

In Germany the furovirus Soil-borne cereal mosaic virus (SBCMV) and the bymovirus Wheat spindle streak mosaic virus (WSSMV) occur often together particularly in several rye production areas. Soil-borne wheat mosaic virus (SBWMV), a wheat infecting furovirus, has so far been found only in one field near Heidelberg. Each of these viruses is transmitted by Polymyxa graminis. The cultivation of resistant varieties is the only promising measure to prevent yield losses caused by soil-borne viruses. Resistance of wheat against the bymovirus WSSMV is comparable to the immunity of barley to the bymoviruses Barley yellow mosaic virus and Barley mild mosaic virus. In case of immunity no virus multiplication is observed in resistant cultivars. In contrast, all wheat cultivars are hosts of the furoviruses. All cultivars – including the resistant ones – can be infected following mechanical inoculation with SBWMV and SBCMV. Resistance to furoviruses is based on reduced levels of virus multiplication in roots and on inhibition of virus movement from roots to leaves. Because of the inhibited virus movement from roots to aerial parts of plants this type of resistance is referred to as translocation resistance. In spite of the different resistance mechanisms the absence of virus symptoms on the leaves is a common selection criterion for both immunity and translocation resistance. Therefore, the symptom free development of plants on uniformly infested fields is the best criterion for selecting wheat lines with resistance to soil-borne viruses. The limited suitability of other selection methods is discussed.     

The effects of postplanting environment on the incidence of soilborne viral diseases in winter cereals

ABSTRACT Soilborne wheat mosaic virus (SBWMV) and Wheat spindle streak mosaic virus (WSSMV) are putatively transmitted to small grains by the obligate parasite Polymyxa graminis, but little is known about environmental requirements for transmission and the resulting disease incidence. We planted susceptible wheat and triticale cultivars in field nurseries on different autumn dates in 3 years and observed the incidence of symptomatic plants in each following spring. Autumn postplanting environment explained most of the variation in disease caused by both viruses. Little apparent transmission, based on eventual symptom development, of either virus occurred after the average soil temperature dropped below 7 degrees C for the remainder of the winter. To forecast disease, we tested an SBWMV transmission model in the field, based on laboratory results, that predicts opportunities for transmission based on soil temperature and soil moisture being simultaneously conducive. This model was predictive of soilborne wheat mosaic in 2 of 3 years. Zoospores of P. graminis have optimal activity at temperatures similar to those in the SBWMV transmission model. Furthermore, the matric potential threshold (as it relates to waterfilled pore sizes) in the SBWMV transmission model fits well with P. graminis as vector given the size restrictions of P. graminis zoospores. Conditions optimal for SBWMV transmission in the laboratory were not conducive for WSSMV transmission in the laboratory or for wheat spindle streak mosaic development in the field. This differential response to environment after emergence, as indicated by disease symptoms, may be due to virus-specific environmental conditions required to establish systemic infection via the same vector. Alternatively, the differential response may have been due to the involvement of a different vector in our WSSMV nursery than in our SBWMV nursery. Our results suggest that, as a control tactic for SBWMV or WSSMV, earliness or lateness of planting is less important in determining virus transmission and disease than the specific postplanting environment. Improved models based on the postplanting environment might predict virus-induced losses of yield potential, and in some cases, growers might avoid purchase of spring inputs such as pesticides and fertilizer for fields with greatly reduced yield potential.     

A novel putative member of the family Benyviridae is associated with soilborne wheat mosaic disease in Brazil

Soilborne wheat mosaic disease (SBWMD), originally attributed to infections by Soilborne wheat mosaic virus (SBWMV) and Wheat spindle streak mosaic virus (WSSMV), is one of the most frequent virus diseases and causes economic losses in wheat in southern Brazil. This study aimed to characterize molecularly the viral species associated with wheat plants showing mosaic symptoms in Brazil. Wheat leaves and stems displaying mosaic symptoms were collected from different wheat cultivars in Passo Fundo municipality, Rio Grande do Sul State, southern Brazil. Double-stranded RNA was extracted and submitted to cDNA library synthesis and next-generation sequencing. No sequences of SBWMV and WSSMV were detected but the complete genome sequence of a putative new member of the family Benyviridae was determined, for which the name wheat stripe mosaic virus (WhSMV) is proposed. WhSMV has a bipartite genome with RNA 1 and RNA 2 organization similar to that of viruses belonging to Benyviridae. WhSMV RNA 1 has a single open reading frame (ORF) encoding a polyprotein with putative viral replicase function. WhSMV RNA 2 has six ORFs encoding the coat protein, the major protein (read-through), triple gene block movement proteins (TGB 1, 2 and 3) and ORF 6 (hypothetical protein). In addition to the genomic organization and nucleotide and amino acid sequence identities, phylogenetic analyses also corroborated that WhSMV is a virus species of the Benyviridae. However, isolates of WhSMV formed a clade distinct from members of the genus Benyvirus. It was also demonstrated that the plasmodiophorid Polymyxa graminis is associated with wheat roots showing SBWMD symptoms and infected by WhSMV.     

Common reed (Phragmites communis) is a natural host of important cereal viruses in the Trakya region of Turkey

Common reed (Phragmites communis Trin.), a perennial grass, is a widespread weed in the Trakya region of Turkey. Reed leaf samples were collected in 2004 and 2005, and tested for the presence of theMaize dwarf mosaic virus (MDMV),Sugarcane mosaic virus (SCMV),Barley yellow dwarf virus-PAV (BYDV-PAV),Cereal yellow dwarf virus-RPV (CYDV-RPV) andWheat dwarf virus (WDV) by DAS-ELISA, PTA-ELISA and Western blot analysis. MDMV was identified in five out of sixP. communis samples that exhibited characteristic virus-like symptoms in 2004. The remaining sample was co-infected with MDMV and BYDV-PAV. Transmission electron microscopy confirmed the presence of flexuous rod-shaped virus particles in four samples that reacted positively for MDMV in ELISA. In 2005, ELISA revealed that nine out of 234 samples that were collected in two different locations were infected with MDMV, nine with SCMV, and three with BYDV-PAV. No sample contained CYDV-RPV, JGMV and WDV. Our results confirm that the common reed is a host of BYDV-PAV and indicate, for the first time, that it is also a natural host of MDMV and SCMV.P. communis most likely acts as a reservoir of these three viruses in the Trakya region in Turkey. http//www.phytoparasitica.org posting Sept. 13, 2006.     

Untersuchungen zum Infektionsverlauf und zur biologischen Differenzierung von bodenbürtigen Viren in Roggen, Triticale und Weizen

Abstract In the frame of the investigation of epidemiology of soil-borne viruses, like the Soil-borne cereal mosaic virus (SBCMV), Soil-borne wheat mosaic virus (SBWMV) and the Bymovirus Wheat spindle streak mosaic virus (WSSMV), which were transmitted by fungal vector Polymyxa graminis Ledingham, the infection progress in different cereals was observed. The detection of furovirus and bymovirus in field plants was depending on temperature conditions during the vegetation period and the kind of cereals. The furoviruses tolerate a broad temperature spectrum and once established infection is detectable until the harvest time. In contrast to this observation, the propagation of WSSMV seems to be restricted to lower temperatures. Consequently, this virus is detected best at the end of February until the middle of April. Among the tested cereals, rye becomes more early infected than wheat and triticale. Both furoviruses could be differed by variable virulence reactions on cereal hosts and indicator plants. The SBCMV infects rye, triticale and wheat but not barley. The SBWMV is able to contaminate beside these cultures barley too. Both viruses are distinguished in the infection typ in Nicotiana benthamiana. Whereas SBCMV isolates spread out in the whole plant and cause yellowing and the die back of plants, the SBWMV infects the inoculated leaves only.     

Reservoirs of plant virus disease: Occurrence of wheat dwarf virus and barley/cereal yellow dwarf viruses in Sweden

Non-crop plants such as grasses and volunteer plants are an inseparable part of the flora of crop fields and can influence virus incidence in crop plants. The presence of grasses as virus reservoirs can lead to a higher probability of virus incidence in crop plants. However, the role of reservoirs as an inoculum source in agricultural fields has not been well studied for many viral diseases of crops. Grasses have been found to constitute potential reservoirs for cereal-infecting viruses in different parts of the world. This study revealed that cereal-infecting viruses such as wheat dwarf virus (WDV), barley yellow dwarf viruses (BYDVs), and cereal yellow dwarf virus-RPV (CYDV-RPV) can be found among ryegrass growing in or around winter wheat fields. Phylogenetic analysis showed that a WDV isolate from ryegrass was a typical WDV-E isolate that infects wheat. Similarly, a ryegrass isolate of barley yellow dwarf virus-PAV (BYDV-PAV) grouped in a clade together with other BYDV-PAV isolates. Inoculation experiments under greenhouse conditions confirmed that annual ryegrass of various genotypes can be infected with WDV to a very low titre. Moreover, leafhoppers were able to acquire WDV from infected ryegrass plants, despite the low titre, and transmit the virus to wheat, resulting in symptoms. Information from the grass reservoir may contribute to improving strategies for controlling plant virus outbreaks in the field. Knowledge of the likely levels of virus in potential reservoir plants can be used to inform decisions on insect vector control strategies and may help to prevent virus disease outbreaks in the future.     

Serological relationships of geminivirus isolates from Gramineae in Australia

Three distinct viruses, named chloris striate mosaic virus (CSMV), paspalum striate mosaic virus (PaSMV) and digitaria didactyla striate mosaic virus (DDSMV), have been identified among the five Gramineae-infecting geminiviruses from Australia using polyclonal antisera. An isolate from Microlaena was confirmed as a strain of CSMV, and an isolate from Bromus catharticus was identified as PaSMV-BC. Enzyme-linked immunosorbent assay (ELISA) detected relationships between all but one of the viruses tested, the exception being miscanthus streak virus (MiSV) from Japan. The Australian viruses proved to be distantly related to similar viruses from Africa, digitaria streak virus (DSV) from Vanuatu, and wheat dwarf virus (WDV) from Europe. Three distinct groups of viruses from Africa, Australia and Europe were distinguished by phylogenetic analysis.     

Molecular characterization and detection of European isolates of Soil-borne wheat mosaic virus

Sequencing of a recently identified isolate of Soil-borne wheat mosaic virus (SBWMV) from the UK confirmed its identity as a European strain of the species and provided further evidence for taxonomic divisions in the group. Two RT–PCR protocols were developed for the detection of all SBWMV strains and for the specific detection of the European SBWMV strain, and were tested successfully on 21 isolates of SBWMV from a range of countries. Both protocols worked well using either purified total RNA in one- or two-step RT-PCR, or immunocapture (IC) RT–PCR. The sensitivity of IC RT-PCR was 100 times greater than ELISA. Neither set of primers produced any PCR product with either Wheat spindle streak mosaic virus or Wheat yellow mosaic virus which are frequently associated with SBWMV, or with the related viruses Indian peanut clump virus , Potato mop-top virus , Beet soil-borne virus and Beet necrotic yellow vein virus . This new diagnostic protocol will improve disease management by enabling correct identification of the causal pathogen and earlier detection than is possible serologically.     

Response of UK winter wheat cultivars to <Emphasis Type="Italic">Soil-borne cereal mosaic</Emphasis> and <Emphasis Type="Italic">Wheat spindle streak mosaic viruses</Emphasis> across Europe.

Twenty-one UK winter wheat cultivars were grown over three seasons at sites with natural inoculum sources of Soil-borne cereal mosaic virus (SBCMV) and Wheat spindle streak mosaic virus (WSSMV) located in France, Italy and the UK. Plants were assessed visually for virus symptoms and leaf extracts were tested for the presence of each virus using enzyme-linked immunosorbent assays (ELISA). Cultivars showing little or no foliar symptoms and low levels of virus in leaf tissue were classified as resistant to each virus. All the trials were taken to harvest and agronomic data collected. At the most heavily infected sites, severe symptoms of SBCMV were observed in all UK cultivars except Aardvark, Charger, Claire, Cockpit, Hereward and Xi 19. The latter cultivars exhibited either light or no symptoms and little or no SBCMV infection in leaves. In fields with WSSMV, the virus failed to develop in Italy, but was detected in the leaves of all the susceptible control cultivars at a site in France. However, no UK cultivar tested positive for WSSMV. Multi-site analysis indicated that the presence of WSSMV did not increase the impact of SBCMV on the height, thousand-grain weight or yield of UK cultivars. The wheat cultivars on test gave a similar response to SBCMV across three European countries. Possible sources of SBCMV resistance are discussed.     

An isolate of Wheat streak mosaic virus from foxtail overcomes Wsm2 resistance in wheat

Wheat streak mosaic virus (WSMV) is an economically important pathogen of wheat (Triticum aestivum) causing major yield losses in regions where severe infection occurs. To detect the presence of any new virus or new WSMV isolates, green foxtail (Setaria viridis) plants exhibiting virus-like symptoms were sampled in a summer-fallowed wheat field at the Agricultural Research Center-Hays, Kansas State University, Hays, Kansas. These plants were tested serologically for four wheat viruses: WSMV, Triticum mosaic virus (TriMV), High Plains wheat mosaic virus (HPWMoV) and Foxtail mosaic virus (FoMV). Among 38 plant samples exhibiting virus-like symptoms, 29 contained WSMV as indicated by ELISA. Four isolates from samples with relatively strong reactions were transferred to healthy wheat seedlings by mechanical inoculation in a growth chamber for pathogenicity testing. Three isolates were avirulent to a wheat variety RonL, which contains Wsm2, a gene providing temperature-sensitive resistance to currently prevalent isolates of WSMV. However, one isolate, KSH294, was able to infect RonL and showed more virulence on two other varieties/lines containing Wsm2. Further sequence and phylogenetic analysis of KSH294 confirmed that this isolate displays a sequence homology with WSMV, but has sequence differences making it distinct from previously identified WSMV isolates included in the phylogenetic analysis.     

Investigation of soilborne mosaic virus diseases transmitted by <Emphasis Type="Italic">Polymyxa graminis</Emphasis> in cereal production areas of the Anatolian part of Turkey

Polymyxa graminis is the vector of several important viruses, including Soilborne cereal mosaic virus, Wheat spindle streak mosaic virus, Barley yellow mosaic virus and Barley mild mosaic virus, of winter cereals worldwide. Surveys were carried out to detect these viruses and their vector P. graminis in 300 soil samples from the main wheat and barley production areas of the Anatolian part of Turkey collected in May 2002, June 2004 and May 2005. For these surveys, various susceptible wheat and barley cultivars were pot grown in the collected soil samples in a greenhouse and then analysed using ELISA and RT-PCR to detect the presence of different virus species. In addition, a combination of light microscopy following roots staining with acid fuchsin and PCR was used for detection of P. graminis. All soil samples analysed were found to be free of these soilborne viruses and their vector.     

Genome-wide association analysis of resistance to wheat spindle streak mosaic virus in bread wheat

Wheat spindle streak mosaic virus (WSSMV) is a major concern for cereal crops in Europe and North America. A strong increase in the occurrence of WSSMV has been observed in each French region where susceptible cultivars are cultivated. Most European bread wheat cultivars are resistant, but assessing the status of newly registered cultivars or breeding lines regarding WSSMV resistance is of importance. This paper describes a genome-wide association study carried out on a panel of 163 cultivars and tested for their resistance to WSSMV. Two regions on chromosomes 5B and 7D showed minor effects on WSSMV resistance. More importantly, a large genomic region on chromosome 2D explained most of the resistance to WSSMV. More than 99% of the cultivars carrying the AA genotype at the most associated marker (Excalibur_c15426_661) were resistant to WSSMV, while 100% of the cultivars showing the GG genotype were susceptible. This large genomic region of 45.8 Mb was found distal to the centromere and showed very high linkage disequilibrium. It is hypothesized that this region may be an alien introgression originating from a wild related species. This region contains a total of 2605 predicted genes based on the Chinese Spring IWGSC RefSeq v. 1.0 including genes potentially involved in plant disease resistance. A kompetitive allele-specific PCR (KASP) single-nucleotide polymorphism (SNP) marker was designed in order to identify breeding lines or registered cultivars resistant to WSSMV.     

瘿螨传播植物病毒病害的研究进展

瘿螨是植物病毒病的一类传播媒介。根据国内外大量最新资料,从瘿螨生物学,为害和病毒不的角度较为详尽地分析了小麦线条花叶病毒,小麦斑点花叶,黑麦草花叶病,冰草花叶病,葱属植物病毒,小麦糜疯病,黑醋栗退化病,无花果花叶病,桃花叶病,樱桃斑驳花叶,蔷薇丛簇病和木豆不孕花叶病这１２种已被确认为瘿螨所传播的病毒病的特点,症状,病毒特性和防治方法,帮助人们进一步了解螨传病毒。     

Yield Effects of Barley yellow dwarf virus in Soft Red Winter Wheat

ABSTRACT Three cultivars of soft red winter wheat were evaluated to determine the relationship between the incidence and time of infection by Barley yellow dwarf virus (BYDV) and yield. Wheat was planted in 1995, 1996, and 1997 in a split-plot design with six replicates at sites in Indiana and Illinois. Yield plots were infested with different amounts of viruliferous aphids, and the incidence of BYDV in each plot was measured. In a 2-year study in Illinois with cv. Clark and the PAV-IL isolate of BYDV, yields were assessed following aphid infestation in fall, early spring, and late spring. Early spring infections resulted in larger yield reductions than late spring infections in both years and larger than fall infections in one year. Regression analyses to relate incidence of infection and yield with data from fall and early spring infections provided R(2) values of 0.89 and 0.51 for the 1996 to 1997 and 1997 to 1998 seasons, respectively. An additional study at the same site in the 1996 to 1997 season compared the yield responses of cvs. Clark, Y88-3e, and PT8935b. Increases in the incidence of BYDV correlated with decreases in yield, with R(2) values of 0.80, 0.78, and 0.90 for the three cultivars, respectively. Estimated yield losses in both studies and all cultivars ranged from 27 to 45 kg/ha or 0.34 to 0.55% for each percent increase in virus infection. In a third study over a 2-year period in Indiana with the same three wheat genot ypes and a second BYDV isolate (PAV-P), BYDV treatments resulted in significant reductions in yield, but yield loss and the incidence of BYDV were not linearly correlated. Given the differences in yield reductions caused by the two BYDV isolates, PAV-P may be an attenuated strain of BYDV and may cross-protect plants from naturally occurring strains of the virus.     

小麦矮缩病毒外壳蛋白基因的原核表达、抗体制备及应用

 小麦矮缩病毒(Wheat dwarf virus,WDV)引起的小麦矮缩病是近年来我国小麦生产中的一种重要病毒病害,急需研发快速精准的检测技术用于预测预报和病毒-介体相互作用的研究。本研究应用Gateway重组技术构建了外壳蛋白基因(Coat protein, CP)的原核表达载体,将重组表达载体转化大肠杆菌Rosetta,经IPTG诱导获得CP基因原核表达蛋白。以重组蛋白为抗原免疫新西兰大白兔制备得到了相应的抗体,Western blot检测表明制备的抗体能与CP重组蛋白、感病小麦和带毒叶蝉特异性结合,说明获得的抗体特异性高。用获得的抗体进行免疫荧光标记,观察到病毒分布在介体叶蝉的前中肠和中中肠部位,为WDV的预测预报和介体条沙叶蝉传毒机制的研究奠定了基础。     

Phylogenetic relationships within the family potyviridae: wheat streak mosaic virus and brome streak mosaic virus are not members of the genus rymovirus

ABSTRACT The complete nucleotide sequence of wheat streak mosaic virus (WSMV) has been determined based on complementary DNA clones derived from the 9,384-nucleotide (nt) RNA of the virus. The genome of WSMV has a 130-nt 5' leader and 149-nt 3'-untranslated region and is polyadenylated at the 3' end. WSMV RNA encodes a single polyprotein of 3,035 amino acid residues and has a deduced genome organization typical for a member of the family Potyviridae (5'-P1/HC-Pro/P3/6K1/CI/6K2/VPg-NIa/NIb/CP-3'). Because WSMV shares with ryegrass mosaic virus (RGMV) the biological property of transmission by eriophyid mites, WSMV has been assigned to the genus Rymovirus, of which RGMV is the type species. Phylogenetic analyses were conducted with complete polyprotein or NIb protein sequences of 11 members of the family Potyviridae, including viruses of monocots or dicots and viruses transmitted by aphids, whiteflies, and mites. WSMV and the monocot-infecting, mite-transmitted brome streak mosaic virus (BrSMV) are sister taxa and share a most recent common ancestor with the whitefly-transmitted sweet potato mild mottle virus, the type species of the proposed genus "Ipomovirus." In contrast, RGMV shares a most recent common ancestor with aphid-transmitted species of the genus Potyvirus. These results indicate that WSMV and BrSMV should be classified within a new genus of the family Potyviridae and should not be considered species of the genus Rymovirus.