Seeds of selected European and Japanese winter wheat cultivars were grown at two experimental sites in China, namely Yaan, Sichuan province (YA), and Yangzhou, Jiangsu province (YZ), where wheat yellow mosaic bymovirus (WYMV) was severe. There were some differential responses of the cultivars to the virus isolates present at the two sites. The complete nucleotide sequence of both RNAs of both virus isolates was determined. Their genome organization was identical to that reported for a Japanese isolate and the sizes were very similar. Nucleotide comparisons demonstrated that parts of the CI and NIa coding regions on RNA1 and the N‐terminal part of the P2 coding region on RNA2 were particularly variable, while substantially conserved regions occurred in the 3′ UTR of RNA2, the 7K, one part of the CI and parts of the NIb and coat protein. It seems unlikely that differences in the 7K and NIa‐VPg proteins are responsible for virulence differences and the CI and NIb regions were considered the most promising for further study.

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.

A sequence of 942 nucleotides, located in the helicase gene of RNA1 of a French isolate of soil-borne wheat mosaic virus (SBWMV), is presented. This sequence was compared with the corresponding sequences published for Nebraskan and Chinese isolates and showed a 74.8% and 73.4% identity, respectively, with these isolates, whereas the Nebraskan and Chinese isolates shared a 78.2% identity. A set of primers specific to the French SBWMV isolate was designed on the basis of this sequenced 942 nucleotide fragment. A primer set for wheat spindle streak mosaic virus (WSSMV) was designed from the published partial sequence of a French isolate. Both sets of primers were combined into a two-step multiplex reverse-transcription polymerase chain reaction, allowing simultaneous detection of both viruses in leaves of infected wheat samples. The amplification specificity of the two sets of primers was checked against isolates of SBWMV from Oklahoma and China, Indian peanut clump virus strains H, L and D from India, barley mild mosaic virus and barley yellow mosaic virus from France. SBWMV primers were specific for French isolates of this virus, whereas the primers designed from the sequence of a French isolate of WSSMV could also faintly detect barley yellow mosaic virus in barley plants. The RT-PCR technique was also compared with ELISA (enzyme-linked immunosorbent assay) on 100 wheat leaf samples collected from the field on the basis of symptoms, and was shown to be reliable and reproducible.

The complete sequences of both RNAs of an isolate of barley yellow mosaic virus from Yancheng, Jiangsu province, China, were determined. The sequences resembled those of an isolate from Japan (96.8% identical nucleotides for RNA1; 95.7% for RNA2) more closely than one from Germany (93.9 and 91.0%, respectively). The greatest differences between the Chinese and Japanese isolates were in the 5′-UTRs of RNAs 1 and 2 (88.9 and 91.6% identical nucleotides, respectively) and there were also some other regions of difference in P1 (RNA2) and P3, CI, NIa and the 5′ end of the coat protein (CP) (RNA1). Molecular differences between isolates from ten sites widely distributed in Eastern China were studied by sequencing RNA regions coding for the CP (RNA1) and the N-terminus of the P2 protein (RNA2). The P2 fragment was more variable than the CP, and phylogenetic analysis of both regions showed that Asian and European isolates formed distinct clusters. Differences between isolates were also revealed by single-strand conformation polymorphism of reverse transcription-polymerase chain reaction products, spanning the full lengths of both RNA1 and RNA2. However, molecular variations between isolates could not be linked to earlier results showing differences in cultivar response.