| Currently, eight viruses infecting taro plants have been reported. In this study, the infectious statues of Dasheen mosaic virus (DsMV) and Cucumber mosaic virus (CMV) in taro plants grown in China was investigated. The two viruses were molecularly and biologically characterized. The efficiency of poisonous fluorine phosphorus wettable powder against the virus were evaluated. These results filled the blanks in the relative studies in China and provided technical suppots on the establishment of effient control system for taro virus diseases. The results were shown as the followings:1. Field investigation for viral diseases in taro plants showed that mosaic disease occurred commonly in taro plants. The leaf symptoms included bright yellowing spots, up-ward rolling, feathery mottle, chlorotic mottle, interveinal yellowing, margin yellowing and leaf crinkle. Two viruses DsMV and CMV in137taro samples collected from Hubei, Jiangxi, Guangxi and Fujian provinces were detected by RT-PCR. Results showed that72.3%and37.9%samples detected were positive for DsMV and CMV respectively. DsMV was frequently associated with the feathery mottle symptom.2. The CP gene of DsMV isolates from21taro samples and one Pinelia sample were amplified and sequenced. The amplified products were942,939,951,858and987bp, respectively. They shared nucleotide (nt) similarities of76.7%-100.0%with each other, and80.6%-89.7%similarity with DsMV-M13from calla and72.9%-75.0%similarity with DsMV-SY1isolated from Pinellia, respectively. Phylogenetic analysis based on nt sequences of the CP gene of DsMV isolates did not show correlation btween their phylogenetic positions and host and geographical origins. The multiple alignment for aa sequences of their cp gene revealed that there were one repeated sequence consisted of ten amino acides and and the aa deletion at the N-terminal of the CP.3. The complete genomic sequence of DsMV isolate SCS-N from a taro sample was determined by overlap RT-PCR method. Its genome consisted of10042nts excluding the poly (A) tail, and contained a large open reading frame (ORF). The genomic sequence of DsMV isolate SCS-N showed the highest identities of84.1%with that of DsMV-M13. As it was compared with DsMV-M13, among11proteins processed from the polyprotein encode the the ORF, P3, PIPO and P1showed relatively high diversity by sharing80.9%,81.7%and85.1%amino acid (aa) similarities, respectively, and other proteins of two isolates shared over94%aa similarities. 4. The mechanical inoculations showed that both DsMV and CMV could infect Cucumis sativus, calabash, Pinellia ternate, Nicotiana occidentalis, Nicotiana benthamiana and Nicotiana glutinosa. Meanwhile, DsMV was transmitted onto Nicotiana benthamian and Cucumis sativus from DsMV isolate HB-31infected taro plants by using Schizaphis piricola as a vector. The complete CP gene of DsMV was amplified from Nicotiana benthamian plants one week post inoculation. In a green house, the taro plants infeted by DsMV were propagated in pots by single tuber transplanting in two continuous years. It was found that all42plants generated from mother plants showed visible viral disease symptoms. RT-PCR analysis showed that the transmission efficiency of DsMV by tubers was100%, indicating the occurance of stable transmission of DsMV by seed tubers.5. Field tests on control efficiency of30%poisonous fluorine phosphorus wettable powder for taro viral diseases showed that30%poisonous fluorine phosphorus wettable powder determined at a500time dilution could greatly reduce the serverity of to taro virus diseases. |
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