Understanding the onset of systemic infection of red blotch virus and phenotypic studies of grapevines expressing a red blotch virus infectious clone

Abstract

Context and purpose of the study. Red Blotch disease, an affliction caused by the Grapevine red blotch-associated virus (GRBaV), represents a formidable challenge for grape growers and winemakers in prominent viticultural regions around the world. A critical aspect of understanding this disease lies in examining how viruses, including GRBaV, interact intimately with cellular components and produce distinctive, often anomalous structures following infection. This study embarked on a detailed investigation of symptom expression, vine physiology, fruit quality, and the ultrastructural characteristics of various tissues in Pinot Noir and Merlot, employing advanced microscopy techniques to unveil the intricate relationship between cytopathological changes and GRBaV infection.

Materials and methods. During the growing season, vine samples were collected from vineyards with a history of Red Blotch (Pinot Noir and Merlot). Shoots were sampled for microscopy analysis to determine the structure of xylem and phloem. At harvest, fruits were sampled to compare primary and secondary metabolites between healthy and infected vines.

Results. The infected vines displayed typical red blotches on their leaves, characterized by pinkish-red veins, without the leaf margins curling at the onset of ripening. These vines developed clusters of “hens and chickens” and showed changes in seed morphology. In contrast, healthy seeds were pyriform in shape with a distinct beak. The infection significantly affected both the primary and secondary metabolites essential for wine production. Since the development and ripening of berries post-veraison depend on phloem influx, the altered metabolism suggests a disruption in the phloem pathway. Additionally, the browning process associated with periderm formation was disrupted in the infected canes. However, during the cold acclimation process, the infected green stems turned brown as expected. Although the infected vines retained their primary leaf anatomical organization, the chloroplasts underwent considerable ultrastructural changes. These changes ranged from complete disassembly of the chloroplasts to a significant accumulation of starch, development of plastoglobuli, and the presence of tannins within the cytoplasm. These findings highlight the importance of structural integrity in maintaining the normal metabolism of grapevines, offering new insights for developing innovative management strategies for Red Blotch disease.