Summary. Virus isolate Y23V, obtained from squash showing leaf curl symptoms inYunnan, China, was readily differentiated from four studied Chinese begomovirus isolates in reactions with a set of monoclonal antibodies raised against begomoviruses. The complete nucleotide sequence (2714 nts) of the DNA-Alike molecule of Y23V was determined. The DNA-A of Y23V is most closely related to that of tomato yellow leaf curl Thailand virus-[1] (TYLCTHV-[1]) (84% sequence identity). However, the AC1 and AC4 gene of Y23V DNA-A resembled to Pepper leaf curl virus from Bangladesh (PepLCBDV). The DNA-A ofY23V has three distinct regions: the region from 74-2071 nts is 95% identical to TYLCTHV-[1] excluding a 27 nt deletion; the following 386 nts are 91% identical to PepLCBDV and the rest of the DNA-A is not closely related to any reported begomovirus.Y23V, therefore, is considered to have arisen by recombination. The 84%sequence identity ofY23VwithTYLCTHV-[1] allowsY23Vto be considered as a distinct begomovirus species, for which the name squash leaf curl Yunnan virus (SLCYNV) is proposed.

Sugarcane mosaic virus (SCMV)was detected in all 62 maize samples collected from eight maize-growing provinces in China showing dwarf mosaic symptoms by immunocapture reverse-transcription polymerase chain reaction (RT-PCR). Maize dwarf mosaic virus (MDMV), Sorghum mosaic virus (SrMV) and Johnsongrass mosaic virus (JGMV), however, were not detected in any of the samples by RT-PCR. Eleven cDNA fragments of approximately 0.8 kilobases covering most of the coat protein (CP) gene of SCMV were sequenced and sequence analysis indicates that these eleven isolates share 98.1 to 100% identity at the amino acid level. Sequence comparison and phylogenetic analysis of the CP genes from the eleven Chinese isolates as well as 21SCMVsubgroup virus isolates indicate that the eleven Chinese virus isolates were closely related to SCMV with 97.0 to 98.1% sequence identity at the amino acid level, while relatively lower sequence identity was found with MDWV, SrMV or JGMV. The results indicate that the Chinese isolates are members of the SCMV species, and thus, SCMV can be considered as the most common and important potyvirus infecting maize in China.

Complete DNA-A sequences of nine Pakistani geminivirus isolates from leaf curl-affected cotton (CLCuV-PK) or from okra, and the partial sequences of several additional isolates were determined. Sequences of isolates from cotton were of four types. Isolates from leaf curl-affected okra had virtually the same sequences as those from cotton. Isolates from yellow vein mosaic-affected okra were of two types (OYVMV types 201 and 301), both distinct from but closely related to the virus isolates from cotton. Of these six types, two types of CLCuVPK are the most closely related but another (CLCuVPK type 72b) is the most distinct. Of the encoded proteins, coat protein (CP) is the most strongly conserved (92-100%amino acid sequence identity), and AC4 protein the most variable (41-87%). The 5' and 3' halves of the intergenic region of some isolates had different affinities and occurred in seven combinations, suggesting that recombination had occurred and that the origin of replication was a favoured recombination site. Similarly, the first 1520 nt of CLCuV-PK type 804a DNA resembled those of OYVMV type 301 DNA but the remaining 1224 nt were very different. The AC1 (Rep) gene and 5

The VP37 protein encoded by the RNA2 of Broad bean wilt virus 2 (BBWV2) was overexpressed in Escherichia coli. The protein was purified and a polyclonal antibody specific for the protein was produced. Time course studies byWestern blot assays in BBWV2-infected Chenopodium quinoa leaves showed that the VP37 protein was present in cells of the inoculated leaves by 12 h post inoculation and in cells of systemically-infected leaves by 2 days post inoculation. The protein was able to accumulate to a high level in infected leaves at the late infection stage. Gel retardation and UV cross-linking assays demonstrated that the VP37 protein bound preferentially single-stranded (ss) RNA and DNA in a non-sequence-specific manner. The VP37 protein-RNA complex was stable in solutions containing less than 400mM NaCl, but became fully dissociated in the solutions containing 800mM NaCl. Sequence analysis of the VP37 protein and its ability to bind ssRNA and ssDNA suggest that the protein may play a role similar to the movement proteins reported for other plant viruses.

The broad bean strain of Tobacco mosaicirus (TMV-B) infects Nicotiana tabacum White Burley systemically whereas the tomato strain of Tomato mosaicirus (ToMV-S1) induces necrotic local lesions and is restricted to inoculated leaves. To examine the possible role of the viral movement protein (MP) in these symptom differences, a chimaeric virus (T/OMP) was produced in which the TMV-B MP gene was replaced by the ToMV-S1 MP gene. T/OMP induced the same symptoms as TMV-B in N. tabacum White Burley. However, in N. tabacum Samsun NN and other plants containing the N resistance gene, T/OMP caused necrotic lesions that were smaller than those produced by TMV-B but similar in size to those of ToMV-S1. We conclude that ToMV MP gene can substitute functionally for the TMV-B MP gene, and that the MP gene influences the size of necrotic local lesions on N-containing hosts.