| Summary: | 碩士 === 國立臺灣大學 === 植物病理與微生物學研究所 === 103 === Papaya ring spot caused by Papaya ring spot virus (PRSV) , one of the most destructive diseases in papaya. PRSV belonging to the genus Potyvirus, family Potyviridae. PRSV-infected papaya trees show mosaic, distorted and shoestring-like symptoms on the leaves, and sunken ring spots on the fruits. PRSV categorized into 2 types, PRSV-P type and PRSV-W type. The P type infects both papayas and cucurbits whereas the W type only infects cucurbits. Based on the incited symptoms, the PRSV-P type further devided into SM (severe mottling), SMN (severe mottling with necrosis) and DF (deformation) strains. Between these 3 strains have apparently differences on pathological and molecular. This study investigate the genomic variations and find the key genomic areas associated with pathogenicity among different PRSV strains through the research with artificially recombinant infectious clones infecting papaya hosts. Based on the previously constructed infectious clones of PRSV SMN and DF strains, two new recombinant infectious named 5’-DF(P1)-SMN and 5’-SMN(P1)-DF clones were further made. The 5’-DF(P1)-SMN clone has a head of DF (5’UTR and P1 fragment of DF) followed by the SMN fragment, and the 5’-SMN(P1)-DF clone has a head of SMN (5’UTR and P1 fragment of SMN) followed by the DF fragment. The recombinant genomic RNA trascripts were synthesized through in vitro transcription, and they were used to individually inoculate the TN2 papayas. The results showed that symptom express of both two recombinant clones similar to PRSV-DF. It revealed that P1 gene contribute part of pathogenicity, but not the only one gene affect symptom express.
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