Thesis Title

Agronomic Performance of Leafroll Virus-Infected French-American Hybrid Grapevines

Date of Graduation

Fall 1999

Degree

Master of Science in Plant Science

Department

Biology

Committee Chair

Laszlo Kovacs

Subject Categories

Plant Sciences

Abstract

Infection of French-American hybrid grape cultivars by grapevine leafroll-associated virus 3 (GLARaV-3) is latent, and information about the impact of the virus on the performance of these cultivars is scarce. This study compares performance indices between plants that are naturally infected by GLRaV-3 and those that are free of the virus. The infection status of Vidal blanc and St. Vincent vines was determined by DAS-ELISA. No reduction in vigor and yield components was associated with GLRaV-3 infection in neither of these cultivars. There was a slight but significant reduction in soluble solids associated with GLRaV-3 infection both in Vidal blanc (0.4 degree Balling, P<0.001) and St. Vincent (0.7 degree Balling, P<0.02) three to seven days before commercial harvest. Average berry weight in both cultivars was 4 to 5% lower in plants that were infected with the virus (P<0.001). Also included in the study were a set of Vidal blanc plants that were naturally infected by both GLRaV-3 and grapevine fleck virus (GFkV). Plants that harbored both of these viruses had a 7% reduction in average berry weight and their fruit was 1.1 °Balling lower in soluble solids than their GLRaV-3/GFkV-free counterparts (P<0.001). Graft-transmission of the viral agents into Vitis vinifera cv. Cabernet franc and Vitis rupestris cv. St. George indicator plants resulted in typical leafroll and GFkV symptoms, respectively. This suggests that the absence of symptoms and the mild impact of GLRaV-3 on these cultivars is not due to the low virulence of the viral strain, but is the result of the resistance of the plants.

Copyright

© Hideaki Hanami

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