侵染中国甘蔗和玉米的SCMV CP基因序列多样性分析

Sequence Diversity in the CP Coding Region of Sugarcane Mosaic Virus Isolates Infecting Sugarcane and Maize in China

【目的】揭示侵染中国甘蔗及玉米的甘蔗花叶病毒(Sugarcanemosaicvirus,SCMV)的遗传多样性,为抗病品种培育及病害综合防治提供依据。【方法】以病株叶组织总RNA抽提物为模板,通过RT-PCR扩增及扩增产物直接测序获得了华南地区SCMV26个甘蔗及玉米田间分离物的近全长CP基因序列,结合GenBank中已公布的部分相应序列,采用序列比对及分子系统进化树重建方法,对SCMVCP基因序列的变异性进行分析。【结果】中国SCMV可分为3个分子组群,各组群分别对应于各自来源的寄主,即杂种甘蔗(糖用甘蔗,Saccharuminterspecifichybrids)、玉米(Zeamays)和高贵甘蔗(果用甘蔗,Saccharumofficinarum)。CP基因核苷酸同一性,不同组群之间为78%～84%,同一组群内部各分离物之间大于91%。在分子系统进化树中,这3个分子组群各自聚集成簇,前两个组群分别隶属于Alegria等(2003)建立的甘蔗组(sugarcanegroup,SCE组)和玉米组(maizegroup,MZ组),第3个组群为本研究首次发现,命名为高贵甘蔗组(noblesugarcanegroup,NSCE组)。侵染杂种甘蔗的SEC组不存在明显的地域分化,而侵染玉米和高贵甘蔗的MZ组和NSEC组则可对应地理来源分为若干亚组,前者可分为华东华中亚组、西北西南亚组及华南亚组,后者至少包括华南亚组和浙江亚组。在玉米、杂种甘蔗及高贵甘蔗混栽区,不同作物上的SCMV可以通过蚜虫传播而交叉侵染,但各组群间依寄主种类存在相对隔离现象。本研究还发现中国华南地区,SCMV可自然侵染甘蔗近缘属杂草河八王(Narengasp.)和芒(Miscanthussp.)。【结论】在中国,SCMV存在丰富的遗传多样性,其分化与寄主类型密切相关,可分为杂种甘蔗组、玉米组和高贵甘蔗组,其中玉米组和高贵甘蔗组又可根据地理来源分为若干亚组。在抗病品种的选育及病害综合防治中,必须充分考虑到病毒的这种分化现象。

[Objective] The study was conducted to reveal genetic diversity of Sugarcane mosaic virus （SCMV） isolates infecting sugarcane and maize and to provide theoretical references for resistance breeding and integrated management of mosaic disease in China. [Method] 26 fragments of the near-full-length SCMV coat protein （CP） gene were obtained by reverse-transcription polymerase chain reaction （RT-PCR） using total RNA extracted from diseased sugarcane and maize leaves from south China as templates. Their nucleotide sequences were determined directly by Sanger＇s method, and then the obtained sequences, together with partial corresponding sequences of SCMV-CP available in GenBank （mainly from China）, were used for nucleotide identity analysis and molecular phylogenetic reconstruction. [Result] SCMV isolates in China could be divided into three molecular groups that coincidently correlated to their respective original hosts, hybrid sugarcane （Saccharum interspecific hybrids, for sugar milling）, maize （Zea mays） and noble sugarcane （Saccharum officinarum, for chewing）. Nucleotide identities among the groups were 78%-84%, and 〉91% within the group. Molecular phylogenetic reconstruction based on the SCMV-CP gene sequences showed a strong correlation, forming three host-species-dependent clusters. The first and second cluster corresponded with the sugarcane group （SCE group） and maize group （MZ group）, which were reported previously, whereas the third cluster was founded first in this study. We designed it as the noble sugarcane group （NSCE group） according to the isolate host origin. In China, no significant geographical divergence was found among SCMV isolates from hybrid sugarcane, whereas the MZ group and NSCE group could be further divided into some subgroups based on the identities of SCMV-CP, which correlated with geographical origin. MZ group included subgroups of East and Middle China, Northwest and Southwest China and South China, while in NSCE group, there were at lest two subgroups of Zhejiang and South China. Notwithstanding the phenomenon of host species-dependent population structure of SCMV, field investigation indicated that the cross-infection among SCMV population via aphid-transmission occurred occasionally in mixed growing areas of maize and sugarcane. In addition, our results show that Narenga sp. and Miscanthus sp., two species of weeds closely related to sugarcane, could be infected by SCMV in the nature. [Conclusion] A great genetic variability of SCMV was observed in China. It appears that the population of SCMV from sugarcane and maize in China contains three genotypes according to their respective host： SEC group from Saccharum interspecific hybrids, MZ group from maize and NSCE group from Saccharum oJficinarum. Meanwhile the MZ group and NSCE group could be divided several subgroups according to isolate geographical origin. This situation should be taken into consideration in resistance breeding program and disease integrated management.