中文摘要：

针对已公布的18个甘蔗花叶病毒（SCMV）全基因组序列,利用MEGA 5.1分析了其11个蛋白（P1、HC-Pro、P3、6K1、CI、6K2、VPg、NIa-Pro、Nib、CP-C和多聚蛋白）编码基因所受的选择压,并结合其编码蛋白的功能,预测了部分基因在SCMV进化过程中的角色和变异位点.结果显示：P1和CP-N端的变异性程度较大,P1蛋白多样性最高;CP-C端变异性和多样性均较低;PIPO受到的选择压最小,但多样性最低,可能是由于PIPO与P3共用一段编码序列.来源于甘蔗的SCMV多聚蛋白的第2 853、2 897和2 904个氨基酸位点（在CP中部）分别为T、R和E,而来源于玉米的SCMV多聚蛋白对应的氨基酸位点分别为S、K和D,表明这3个位点具有寄主依赖性.

英文摘要：

The population structure and phylogenetic analysis were conducted on 18 fully sequenced Sugarcane mosaic virus（ SCMV）isolates. MEGA 5. 1 was applied to evaluate the selective pressure of 11 genes encoding regions,i. e. P1,HC-Pro,P3,6K1,CI,6K2,VPg,NIa-Pro,Nib,CP-C and polyprotein. Basing on the known function of genes from Potyvirus genome,we predicted the potential roles and nucleotide substitutions sites of the 11 genes. The results were as following： P1 and N terminal of CP（ CP-N） demonstrated the maximum variability while P1 showed the highest diversity among the tested SCMV isolates. However,the C terminal of CP（ CP-C） displayed the minimum variability and diversity. PIPO was under the lowest selective pressure and diversity,which may be attributed to PIPO sharing the same encoding region with P3. Also,the 2 853 th,2 897 th and 2 904 th amino-acid residues of the polyprotein from SCMV sugarcane isolates presented different patterns comparing to the isolates from maize. The corresponding aminoacid residues were T,R and E in the polyprotein of SCMV isolated from sugarcane,but S,K and D for those isolated from maize,respectively. The distinguished pattern of these three amino-acid residues sites demonstrated strong host preference.