Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Plant Pathology and Crop Physiology

First Advisor

Rodrigo A. Valverde


Studies with the transmission electron microscope were used to detect and attempt to identify viruses infecting sweetpotato (Ipomoea batatas ) and other Ipomoea species. Flexuous-rods, short curved-rods, and spherical virus-like particles were observed in cells of symptomatic plants. Also, various cytopathic changes such as crystals, vesicles, fibril structures, and cylindrical inclusions were observed. Some of these cytopathic changes were associated with specific viral groups such as genus Crinivirus and Potyvirus and therefore helpful in diagnosis. Some molecular and biological properties of an isolate of Sweetpotato chlorotic stunt virus from the sweetpotato cultivar White Bunch (SPCSV-WB) were determined. Two species of whiteflies, Bemisia tabaci biotype B and Trialeurodes abutilonea, transmitted SPCSV-WB to I. nil cv. Scarlet O'Hara. Two double-stranded RNA fragments (10 and 4 kb) of SPCSV-WB were isolated from infected I. setosa plants. DNA fragments of the homologue heat shock protein 70 (HSP70) and the coat protein (CP) genes of SPCSV-WB were obtained by Reverse Transcriptase-Polymerase Chain Reaction (RT-PCR). The derived amino acid sequence of the HSP70 of SPCSV-WB was identical to that of the East and West African isolates of SPCSV. The presence of SPCSV in field-collected sweetpotato samples was not confirmed. Five viruses designated LSU-1, LSU-2, LSU-3, LSU-4, and LSU-5 were obtained from field-collected samples of I. batatas. Preliminary serological tests indicated that they were members of the family Potyviridae. RT-PCR was conducted with these viruses using specific primers for the Potyviridae. RT-PCR products corresponding to the partial 3 ' end of the nuclear inclusion B (NIb) and the partial 5 ' end of the CP genes were obtained. A DNA fragment amplified from the LSU-1 and LSU-3 potyviruses showed 98% identity to the corresponding sequence of Sweetpotato virus G. DNA fragments amplified from LSU-2 and LSU-5 were similar. Also, the amplified fragments contained various common motifs of the Potyviridae. The phylogenetic relationships based on the partial sequence of NIb and CP genes of these four viruses were determined.