Masters Theses

Date of Award

5-2009

Degree Type

Thesis

Degree Name

Master of Science

Major

Entomology and Plant Pathology

Major Professor

Reza Hajimorad

Abstract

RNA viruses have high potential for genetic variation. This intrinsic variability is due to lack of proof-reading activity of RNA-dependant RNA-polymerase; hence replication of RNA viruses leads to the generation of individuals that differ genetically from their parental viruses. These individuals are referred to as variants or mutants. The dynamic distribution of mutants that compose replicating RNA viruses is termed quasi-species. Through quasi-species, RNA viruses refine their genetic structure and adapt to changing environment especially when moved from one host to the next. Genetic variability of RNA viruses may influence viral diagnosis and the durability of plant resistance to viral infection. Genetic variation leads to emergence of new viruses as well. New human, animal and plant viruses emerge through mutation, recombination and reassortment. Heterogeneity of plant RNA viruses is being studied to establish their evolutionary history and most importantly to design strategies for effective diagnosis and control of viral diseases. This research was aimed at studying the genetic variability of Hosta virus X (HVX) isolates using the coat protein (CP) gene and triple gene block 1 (TGB1). Thirty HVX isolates from naturally infected hosta cultivars were obtained from different geographical regions of Tennessee. These isolates, along with previously reported HVX isolates, and representative species of Flexiviridae family were used to infer phylogenetic relationships. The widespread presence of HVX in the State of Tennessee was established. Based on comparison of sequences of CP and TGB1, it was demonstrated that all HVX isolates sequenced to date are closely related, and that the CP gene is more conserved than TGB1 among the isolates of the virus. Based on these findings, a reverse transcription--polymerase chain reaction combined with restriction fragment length polymorphism assay (RTLP) assay was developed for sensitive detection of HVX in hosta.

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