Etiology Of Papaya Leaf Curl Disease In Guangxi Province

Geminiviruses are a group of single-stranded circular DNA viruses with twinned particles occurring worldwide. Until now geminiviruses have caused significant yield losses to many economically important crops in many countries of the world. In recent years, several begomoviruses infecting tobacco, tomato and papaya have been reported in Guangdong, Guangxi, Yunnan, Fujian and Hainan provinces of China. In this thesis, etiology of papaya leaf curl disease in Guangxi province were studied.PCR detection showed most papaya leaf curl samples from Guangxi province were associated with Papaya leaf curl China virus (PaLCCNV) and Tomoto leaf curl China virus (ToLCCNV) as well as ToLCCNV DNAβ. To investigate the pathogenicity of mix-infection, infectious clones of the two viruses are constructed. Infectivity tests showed PaLCCNV alone could not induce symptoms in plants. Leaf curling symptoms could be induced in Nicotians benthamiana and N. glutinosa plants when PaLCCNV were co-inoculated with ToLCCNV DNA β . When PaLCCNV, ToLCCNV and ToLCCNV DNA β were co-inoculated, both PaLCCNV and ToLCCNV could replicate in plants with leaf curling symptoms.A recombinant DNA β molecule and a A-Rich deleted DNA β molecule were isolates in papaya sample G100. DNA β recombinant molecule was resulted from the recombination of part of the sequence from A-Rich region of ToLCCNV DNA β with part of the sequence on Cl gene of PaLCCNV. To study the pathogenecity of the recombinant and the A-Rich deleted DNA β molecules, Infectious clones of these molecules were constructed. No symptom was found when these molecules were co-inoculated with PaLCCNV or ToLCCNV. PCR detection indicated that both the recombinant and the A-Rich deleted DNA β molecules could replicate in inoculated host plants.A geminiviruses differed from PaLCCNV and ToLCCNV were identified in papaya samples G100 and G136, the full length sequence of the virus in G100 had 2742 nucleotides with typical genomic structure of the old World geminivirus. Sequence comparison show it has 98.3% sequence identity with Malvastrum leaf curl virus (MLCV) identified in Guangxi province in Malvastrum coromandelianum. According to the classification principle of geminiviruses, thisvirus is an isolate of MLCV...