Date of Award

1995

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Plant Pathology and Crop Physiology

First Advisor

Rodrigo A. Valverde

Abstract

Tobacco etch virus (TEV) causes an important viral disease of pepper (Capsicum spp.) in the Western Hemisphere. In this study, 36 isolates of TEV from the United States, Mexico, the Caribbean, Central America, and South America were mechanically inoculated in the greenhouse to selected pepper lines reported to have resistance to one or more TEV isolates. Goals of the research were to evaluate reactions of the resistant pepper lines to the TEV isolates, and to determine if the TEV isolates could be grouped into pathotypes based on their reactions in pepper lines chosen as differentials during the course of the study. Additional goals were to determine if dsRNA analysis and light microscopic evaluations of nuclear inclusions could be used to group and distinguish TEV isolates. Definite trends were evident with respect to virulence of isolates and resistance of pepper lines through the course of the study. Certain TEV isolates infected most of the resistant lines while others infected very few. There were isolates representing many gradations between the extremes. Reactions of specific pepper lines to specific TEV isolates sometimes varied in the different experiments of the study, possibly due to temperature and/or light intensity effects on resistance during the different times of the year in which experiments were carried out. Therefore it was not possible to distinguish clear virus pathotypes, nor to choose pepper line differentials to separate the isolates into pathotypes. However, using eight pepper lines: Yolo Wonder as susceptible control, VR2, Magda, Jaloro, VR4, Delray Bell, PI 159236, and PI 152225, most TEV isolates could be grouped into general categories of high and low virulence, and certain unusual isolates could be well defined. Regarding variability in resistance among pepper lines, Agronomico 10C-5, Delray Bell, VR4, Jaloro, and PI 152225 were resistant to many TEV isolates tested, and appear to be good sources of resistance for use in breeding programs. Additional traits studied did not distinguish TEV isolates. All virus isolates reacted similarly in dsRNA analysis. Three of 10 virus isolates tested induced distinctive nuclear inclusion types, whereas the remaining seven isolates shared a single inclusion type.

Pages

82

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