Occurrence of viruses in irrigated wheat in Zambia

Surveys were conducted during the cool-dry months of June–August 1997 and June–July 1998 for the presence of viruses in irrigated wheat in Central, Copperbelt, Lusaka and Southern Provinces of Zambia in 14 commercial farms and four wheat cultivar plots. Virus symptoms were observed on nine wheat cultivars ( Triticum aestivum 'Deka', 'Gamtoos', 'Lorie II', 'MM2', 'Nata', 'Nkwazi', 'P7', 'Scan' and 'Sceptre') of South African, Zambian and Zimbabwean origin. Several viruses were identified on the basis of field symptomatology, symptoms developing on mechanically inoculated indicator plant species or cultivars and serology (DAS-ELISA). The study revealed the occurrence of Brome mosaic virus (BMV), Barley stripe mosaic virus (BSMV), Barley yellow dwarf virus and its strains (BYDV-PAV and RPV), Soil-borne wheat mosaic virus (SBWMV), Wheat dwarf virus (WDV), Wheat streak mosaic virus (WSMV) and Wheat spindle streak mosaic virus (WSSMV). DSA-ELISA tests confirmed these identifications. The prevalence of viruses varied annually and from field to field. BSMV, BYDV-PAV, SBWMV, WDV, WSMV and WSSMV were found to be the most prevalent viruses. Viruses generally occurred in mixed infections of 3–6 viruses and the most common virus complex consisted of 4 viruses (50%), viz. BYDV, SBWMV, WDV and WSSMV. Five- and six-virus complexes were relatively less common (20% each) whereas 3-virus complex was noticed in only 10% cases. SBWMV and WSSMV have been found to be new to Africa and Zambia and are reportedly vectored by a fungal protist – Polymyxa graminis . BYDV strains MAV and SGV were also tested but gave negative results against their antisera.     

Characterization and partial sequence of a new furovirus of wheat in China

A soil-borne wheat virus causing severe mosaic and stunting symptoms on wheat in China has been characterized. It had been considered to be soil-borne wheat mosaic virus (SBWMV) because of its rod-shaped virions and similarities to epidemiology and host range. In this study, the virions purified from infected wheat tissue were approximately 20 nm in diameter and of two lengths (140–160 nm and 280–300 nm), with a coat protein of 19 kDa and two RNA components of approximately 7 and 3.5 kb. A rabbit antiserum was produced against the virus and a serological relationship to SBWMV from the USA (Oklahoma) was demonstrated. However, the coat protein was not recognized by most monoclonal antibodies against Oklahoma SBWMV in either ELISA, ISEM or Western blot analysis, indicating epitope differences. In RT-PCR experiments the viral nucleotide sequences were significantly different from those of SBWMV, and this was confirmed by partial sequencing of the cloned PCR fragments generated from RNA1 ( c . 1100 nt) and RNA2 ( c . 1400 nt), which showed homologies of about 79 and 63%, respectively, to corresponding regions of SBWMV. Because of these significant differences in serology and nucleotide sequence it is suggested that it is a new furovirus for which the name Chinese wheat mosaic virus (CWMV) is proposed.     

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.     

Beet soil-borne mosaic virus: development of virus-specific detection tools

Journal of Plant Diseases and Protection - To have an opportunity for reliable detection of benyvirus Beet soil-borne mosaic virus (BSBMV) and its discrimination from Beet necrotic yellow vein...     

A generic RT‐PCR assay for the detection of Luteoviridae

This study, using RT‐PCR, is the first comprehensive assessment since 1991 of a generic detection method for the Luteoviridae. Thirteen Luteoviridae species were detected using three separate sets of low‐degeneracy generic primers with RT‐PCR to amplify 68‐, 75‐ and 129/156‐bp regions of the Luteoviridae coat‐protein gene. Species detected include all members of the genus Luteovirus [Barley yellow dwarf virus (BYDV)‐PAV, BYDV‐PAS, BYDV‐MAV (129 and/or 156 bp amplicons), Soybean dwarf virus, Bean leafroll virus (68 bp amplicon)] and eight of nine species from the genus Polerovirus [Beet western yellows virus, Beet chlorosis virus, Beet mild yellowing virus, Turnip yellows virus, Potato leafroll virus, Cucurbit aphid‐borne yellows virus, Cereal yellow dwarf virus‐RPV (68‐bp amplicon) and Sugarcane yellow leaf virus (75‐bp amplicon)]. These primers were not able to detect Carrot red leaf virus, Sweet potato leaf speckling virus (both belong to unassigned Luteoviridae) and Pea enation mosaic virus‐1 (genus Enamovirus). A synthetic positive control containing all primer sequence priming sites was designed to facilitate this method as a generic tool for use with a variety of host plants. The Luteoviridae primers described in this study present a simple infection‐detection tool of benefit to biosecurity authorities in nursery‐stock surveillance, disease management or outbreak prevention, and may also be useful in detection of as‐yet undiscovered species within the Luteovirus and Polerovirus genera.     

小麦对黄花叶病的抗性鉴定及典型品种的遗传分析

 本研究针对来自江苏、河南、四川、湖北、日本和美国的37个小麦品种,在进行小麦抗黄花叶病的抗病性鉴定、调查的基础上,结合分子生物学检测(RT-PCR和ELISA),证实小麦品种扬辐9311对小麦黄花叶病毒(WYMV)表现免疫。将该品种与表现高感的小麦品种进行杂交和回交,通过对其后代抗感分离的调查与分析,确定了小麦品种扬辐9311对黄花叶病的抗性受一对显性基因控制,并为寻找小麦抗黄花叶病基因的分子标记提供理论依据和实验材料。同时,本文对小麦抗黄花叶病表现的影响因素及宁麦9号的抗病性进行了分析和讨论。     

侵染西瓜的5种病毒ZYMV、WMV、TMV、SqMV和CMV的多重RT-PCR检测体系的建立与检测应用

 根据5种病毒小西葫芦黄花叶病毒(Zucchini yellow mosaic virus,ZYMV)、西瓜花叶病毒(Watermelon mosaic virus,WMV)、烟草花叶病毒(Tobacco mosaic virus,TMV)、南瓜花叶病毒(Squash mosaic virus,SqMV)和黄瓜花叶病毒(Cucumber mosaic virus,CMV)的核苷酸保守区序列,设计特异性引物对,从影响多重RT-PCR (mRT-PCR)扩增的引物浓度、Mg²⁺浓度、Taq DNA聚合酶浓度、dNTPs浓度、退火温度等方面进行反应体系的优化,建立了一种能够同时检测ZYMV、WMV、TMV、SqMV和CMV的多重RT-PCR技术体系,并进行了实际应用。在一个体系中对上述5种病毒复合侵染的西瓜材料进行多重RT-PCR扩增,得到与试验设计相符的5条特异性条带,依次是542、485、410、354和293bp。该体系实现了对侵染西瓜的5种病毒的同时检测,极大地提高了检测效率,降低了检测成本,体现了多重RT-PCR的优越性。     

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.     

黄瓜花叶病毒M株系引致烟草症状恢复的初步研究

 黄瓜花叶病毒M株系在白肋烟上具有典型的症状恢复现象,本研究用提纯病毒和DAS-ELISA建立了CMV-M病毒定量检测方法。研究发现,症状严重程度与叶片中的病毒浓度呈正相关:最早发病的黄化叶每克病组织中病毒可高达790 μg,而恢复叶片上部再发病的花叶症状病叶中每克病组织中病毒也可高达508 μg,恢复叶片中病毒含量很低,每克叶片中最高也没有超过6 μg,仅为发病叶片病毒浓度的1/85~1/135,远低于根和茎中的病毒浓度。RT-PCR和生物学检测结果表明恢复叶片中确实存在具侵染活性的病毒,而且病毒在长达半个月以上一直保持很低浓度。结果表明恢复叶中可能存在有效的病毒防御机制,其具体机理有待进一步研究。     

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.     

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.     

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.     

Natural Infection of Wheat by the Type Strain of Soil-borne Wheat Mosaic Virus in a Field in Southern Germany

Molecular analyses revealed that a virus causing a severe disease of wheat in one field in Southern Germany is closely related to the Nebraska type strain of Soil-borne wheat mosaic virus (SBWMV) and only distantly related to Soil-borne cereal mosaic virus that is widely distributed in Europe. The latter virus was not found in the SBWMV-containing leaf samples. This is the first report of the occurrence of SBWMV in Germany, and perhaps in all of Europe, which has been confirmed on the molecular level.     

Occurrence of yellowing viruses (Beet pseudo-yellows virus, Cucurbit yellow stunting disorder virus and Cucurbit aphid-borne yellows virus) affecting cucurbits in Greece

A survey of the incidence of yellowing viruses in Greek glasshouse (and occasional field) cucumber and melon crops was carried out during 2000–03. In most cases disease incidence ranged from 50 to 80%. Simplex RT-PCR was used for the detection of Beet pseudo-yellows virus (BPYV) and Cucurbit yellow stunting disorder virus (CYSDV), and DAS-ELISA for the detection of Cucurbit aphid-borne yellows virus (CABYV). The results showed that BPYV was the predominant virus in cucumber and melon crops, whereas CYSDV, reported for first time in Greece, was isolated only in three regions of southern Greece: Rhodes, Crete and Arkadia. CABYV was detected only in three cucumber glasshouses in Pella (Macedonia). A simplified triplex RT-PCR method using a simple sample-preparation protocol was developed to allow rapid, sensitive and simultaneous detection of the three viruses. Sequence comparisons of the PCR products of BPYV and CYSDV revealed 98·7 and 100% amino acid identity, respectively, with previously reported sequences. The arable weed species Amaranthus retroflexus , Selosia cristata , Sonchus oleraceus and Sonchus sp. were identified as potential BPYV reservoirs.     

Response of Hard Red Winter Wheat to Soilborne wheat mosaic virus Using Novel Inoculation Methods

ABSTRACT Soilborne wheat mosaic virus (SBWMV) is an agronomically important pathogen of wheat that is transmitted by the soilborne plasmodiophorid vector Polymyxa graminis. In the laboratory, attempts to generate SBWMV-infected plants are often hampered by poor infectivity of the virus. To analyze the mechanism for virus resistance in wheat cultivars, we developed novel inoculation techniques. A new technique for foliar inoculation of SBWMV was developed that eliminated wound-induced necrosis normally associated with rub inoculating virus to wheat leaves. This new technique is important because we can now uniformly inoculate plants in the laboratory for studies of host resistance mechanisms in the inoculated leaf. Additionally, wheat plants were grown hydroponically in seed germination pouches and their roots were inoculated with SBWMV either by placing P. graminis-infested root material in the pouch or by mechanically inoculating the roots with purified virus. The susceptibility of one SBWMV susceptible and three field resistant wheat cultivars were analyzed following inoculation of plants using these novel inoculation techniques or the conventional inoculation technique of growing plants in P. graminis-infested soil. The results presented in this study suggest that virus resistance in wheat likely functions in the roots to block virus infection.     

Monoclonal antibodies detect a single amino Acid difference between the coat proteins of soilborne wheat mosaic virus isolates: implications for virus structure

ABSTRACT Four monoclonal antibodies (MAbs) were prepared against an isolate of soilborne wheat mosaic furovirus from Oklahoma (SBWMV Okl-7). Three MAbs had different reactivities in tests on SBWMV isolates from Nebraska (Lab1), France, and Japan. One MAb (SCR 133) also reacted with oat golden stripe furovirus. None of the MAbs cross-reacted with other rod-shaped viruses including beet necrotic yellow vein furovirus, potato mop-top furovirus, and tobacco rattle tobravirus. Sequence analysis of nucleotides between 334 and 1,000 of RNA 2, the region that encodes the coat protein (CP) and the first 44 amino acids of a readthrough protein, of the four SBWMV isolates revealed up to 27 base changes from the published sequence of a Nebraska field isolate of SBWMV. Most changes were translationally silent, but some caused differences of one to three amino acids in residues located near either the N- or C-terminus of the CPs of the different isolates. Two further single amino acid changes were found at the beginning of the readthrough domain of the CP-readthrough protein. Some of these amino acid changes could be discriminated by MAbs SCR 132, SCR 133, and SCR 134. Peptide scanning (Pepscan) analysis indicated that the epitope recognized by SCR 134 is located near the N-terminus of the CP. SCR 132 was deduced to react with a discontinuous CP epitope near the C-terminus, and SCR 133 reacted with a surface-located continuous epitope also near the C-terminus. Predictions of CP structure from computer-assisted three-dimensional model building, by comparison with the X-ray fiber diffraction structure of tobacco mosaic virus, suggested that the three CP amino acids found to differ between isolates of SBWMV were located near the viral surface and were in regions predicted to be antigenic.