| 1. Identification of the viral pathogen of maize dwarf mosaic disease in ZhejiangA virus isolate ZJ1 was obtained from maize showing dwarf mosaic symptoms in Hangzhou, Zhejiang. The purified virus particles were flexuous rods with the size of 740 X 14nm, and pinwheels and laminated aggregates were found in the cytoplasm of the infected maize leaf tissues. Virus coat protein migrated as a single component in SDS-PAGE with MW of ~33kDa. RT-PCR was conducted with RNA purified from ZJ1 infected maize as template using primers specific to Sugarcane mosaic virus (SCMV), Maize dwarf mosaic virus (MDMV), Sorghum mosaic virus (SrMV) and Johnsongrass mosaic virus (JGMV), respectively. A fragment of about 0.8kb was amplified only with SCMV specific primer pair. Sequence analysis shows that the fragment covers nearly full-length CP region with 781 nucleotides (nt) encoding 260 deduced amino acids (aa). The 260 aa sequence of ZJ1 was compared with the counterpart of the related potyviruses. A high sequence identity (97.8%) was observed with SCMV, whereas lower sequence identities (60.6- 78.8%) were found with SrMV, MDMV, and JGMV. According to the taxonomy criterion of species and strain in Potyvirus, ZJ 1 is identified as SCMV.2. Production of monoclonal antibodies against sugarcane mosaic virus ZJ1 isolate and virus detection3 monoclonal antibodies (MAbs) were produced against Sugarcane mosaic virus ZJ1 isolate. These MAbs were found to be specific to SCMV isolates, while no serological reaction was found with Maize rough dwarf v/ras(MRDV), SrMV, Potato virus A (PVA), Wheat yellow mosaic virus (WYMV) , Zucchini yellow mosaic virus (ZYMV) , Bean common mosaic virus (BCMV) and Turnip mosaic virus (TuMV) . The titres of ascitic fluids of 3 MAbs ranged from 1: 32000 to 1: 2048000 when measured by indirect ELISA. The MAb 2B5 could detect SCMV in plant sap with 1:10240 dilution, and the detection sensitivity for purified virus particles was 0.7ng.3. Detection and identification of the pathogen of maize dwarf mosaic disease in 12 provinces in China176 maize samples showing dwarf mosaic symptoms from 15 sites in 12 provinces in China, were collected and detected with SCMV MAb 2B5 by indirect ELISA. SCMV was detected in all of samples. Some selected samples were then detected by immunocapture reverse-transcription PCR (IC-RT-PCR) with SCMV, MDMV, SrMV and JGMV specific primers, respectively. SCMV was detected in all the test samples, while no other potyviruses was observed. The results show that SCMV is probably the only potyvirus infecting maize in China. 4.Variability and evolution of coat protein gene of SCMV isolates from 11provinces in ChinaThe nearly full-length coat protein (CP) gene of 14 maize and 1 sorghum isolates of SCMV from 11 provinces in China were cloned and sequenced. It had 781 nucleotides encoding 260 amino acids. These 15 SCMV isolates formed two groups based on determined nucleotide sequence. Sequences of 11 maize isolates from Zhejiang, Jiangsu, Shanghai, Shandong, Henan, Hebei, Shanxi and Shannxi provinces have 98.8-99.8% identity on nucleotide level and 98.1-100% identity on amino acid level,respectively, whereas 3 maize isolates from Gansu, Sichuan and Yunnan province and 1 sorghum isolate from Shanxi province have 94.5-99.6% identity on nucleotide sequence level and 99.2-100% identity on amino acid sequence level, respectively. Isolates between the 2 groups have only 90% identity on nucleotide sequence level and 97% identity on amino acid sequence level. Phylogenetic analysis shows that SCMV isolates from China is closely related to SCMV isolates from Europe, and relatively less related to isolates from USA, Australia and South Africa. 5. Pathogenicity of Sugarcane mosaic virus isolatesPathogenicity of SCMV isolates ZJ1 and GS was tested on 13 maize cultivars. GS induced higher disease incidence with a shorter incubation period in some cultivars (Taiwan2,Taiwan3,Danyul3) when compared with ZJ1. Virus concentration in GS-infected plants was usually higher than that in ZJ1-infecte...
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