| Maize dwarf mosaic disease (MDM) is one of the most widespread viral diseases of maize in the world. The viruses that cause MDM in China were identified as Sugarcane mosaic virus (SCMV) and Pennisetum mosaic virus (PenMV). There were more reports on SCMV than PenMV in China.We collected maize and sorghum samples with dwarf mosaic symptoms from11cities of5provinces of the huang-huai-hai region in2010and2011, and identified PenMV from19samples with RT-PCR, among which eight maize samples from Chengde of Hebei province,9maize and2sorghum samples from Anze of Shanxi province. Their complete genomic sequences were amplified with five RT-PCR reactions and5’-RACE.The PenMV genome comprised9613nucleotides (nt), excluding the3’-terminal poly (A) tail. Their5’-untranslated region (UTR) and3’-UTR were183nt and241nt, respectively, and the single open reading frames (ORF) were9189nt. The putative proteinase cleavage sites of PenMV polyprotein were almost identical at most sites except two of them. The P3/6K1cleavage sites were E/G in the Chengde isolates, while they were E/H in the Shanxi isolates; the NIa-Pro/NIb cleavage sites were Q/A in the Chengde isolates, while they were Q/G in the Shanxi isolates. Some conserved motifs of potyviruses could be found in the polyprotein of different PenMV isolates.The P1gene of PenMV shared the lowest identities of70.0%-98.1%at nt level and70.0%-96.7%at amino acid (aa) level, while the PIPO gene shared the highest identities of95.5%-100%at nt level and93.9%-100%at aa level. The complete genomic sequences shared identities of84.0%-99.5%at nt level and the polyprotein shared identities of93.2%-99.5%at aa level. The CP gene of PenMV shared identities of89.9%-100%at nt level and97.0%-100%at aa level.Recombination events occurred frequently in the PenMV population, especially in the Chengde isolates. The P1gene region and the CI-6K2region were the hotspots of recombination. In the phylogenetic trees calculated with complete genomic sequences and putative polyproteins, all the PenMV isolates were clustered to two groups related to their geographical origin. Similar trees were caculated with6K1, P1, and VPg gene, while the tree showed more branches calculated with other genes.Different genes of PenMV shared nt diversities of0.028-0.249. The P1gene had the highest nt diversity, while the PIPO gene had the lowest one. The dN/dS ratios were less than1for most genes except the CP gene, indicating positive (or diversifying) selection on the CP gene, while negative (or purifying) selection exerting on most genes. The values of the Ks*, Kst*were significant and the Snn values were1or very close to1, suggesting high degree of differentiation between Chengde and Shanxi subgroups. Most of FST values between the two PenMV subpopulations of Chengde and Shanxi were＞0.33, indicating the gene flow was infrequent. In the neutrality test, the values of Tajima’s D, Fu&Li’s D, Fu&Li’s F and Fu’s Fs were negtive, suggesting the populations had low polymorphysim, and may in a state of expanding. The mismatch distribution of different PenMV genes were in multimodal and ragged shapes, indicating the two subgroups were long-existing and no new emergent appeared.Seventeen maize cultivars were mechanically inoculated with CD2and CD9. Systemic chlorisis and mosaic symptoms were observed in some cultivars four weeks after inoculation. The isolate CD2could infect Denghai3, Denghai6213and Nonghua101with incidences of14.3%,19.0%and28.6%. CD9could only infect Denghai6213with incidence of8.7%. Masking of symptom was found with RT-PCR when we detected the Luyu850, Liyu35, Chengyu10, Ludan9032, and Zhenjie3cultivars plants with no symptom. |
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