Title page for ETD etd-03092006-163704

Type of Document Dissertation
Author Kokkinos, Charalambos D.
Author's Email Address ckokkin@lsu.edu
URN etd-03092006-163704
Title Assessment of Interactions among Viruses Infecting Sweetpotato
Degree Doctor of Philosophy (Ph.D.)
Department Plant Pathology & Crop Physiology
Advisory Committee
Advisor Name Title
Christopher A. Clark Committee Chair
Ding S. Shih Committee Member
Raymond W. Schneider Committee Member
Rodrigo A. Valverde Committee Member
Eric P. Webster Dean's Representative
  • taqman fluorescent probes
  • quantitative PCR
  • virus titer quantification
  • viral synergism
Date of Defense 2006-02-22
Availability unrestricted
Viral diseases, especially those caused by mixed infections, are among the economically most important diseases of sweetpotato. Real-time PCR assays were developed for the detection and quantification of the potyviruses Sweet potato feathery mottle virus (SPFMV), Sweet potato virus G (SPVG), Ipomoea vein mosaic virus (IVMV); the crinivirus Sweet potato chlorotic stunt virus (SPCSV), and the begomovirus Sweet potato leaf curl virus (SPLCV) directly from infected sweetpotato plants. Titers of SPFMV, IVMV, and SPVG were lower in singly-infected sweetpotato plants compared to singly-infected plants of the standard indicator host Brazilian morning-glory (Ipomoea setosa) and the standard propagation host I. nil cv. ‘Scarlet O’ Hara’ plants. The effect of SPSCV on titers of potyviruses infecting sweetpotato in the U.S. was investigated in a separate study. Titers of all potyviruses evaluated were enhanced in the presence of SPCSV suggesting that a conserved mechanism may underlie the enhancement of different potyviruses. Although titers of the common strain of SPFMV (SPFMV-C) were enhanced similarly to the russet crack strain (SPFMV-RC), SPFMV-C did not cause typical sweet potato virus disease (SPVD) symptoms when co-infecting with SPCSV, whereas SPFMV-RC with SPCSV caused severe SPVD symptoms. Titers of SPCSV were lower when coinfecting with potyviruses compared to plants infected with SPCSV alone. Expression analysis using cDNA microarrays revealed that the number of differentially expressed genes in plants infected with either SPFMV or SPCSV alone compared to virus-tested plants was 3 and 14, respectively. These findings were in stark contrast with SPVD-affected plants where over 200 genes were differentially expressed. SPVD-responsive genes are involved in various cellular processes including several that were identified as pathogenesis- or stress-induced. Even though titers of the U.S. isolate of SPLCV (SPLCV-US) were greater in the presence of potyviruses compared to titers of SPLCV in single infections, they were statistically different only when co-infecting SPFMV-RC and IVMV. Quantification of SPLCV in sweetpotato cultivars revealed that titers were significantly lower in cultivars known to be tolerant of the effects of SPLCV on yield. Real-time PCR was a more sensitive and specific detection method for the viruses evaluated compared to conventional PCR or ELISA assays.
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