Progress Report: This is an ongoing project for the Washington Grape & Wine Research Program
Date: April 2013-October 2013
Project Title: Structural and compositional characterization towards unlocking the unknowns of sour shrivel to sustain optimum fruit composition and wine quality
Principal Investigator(s): Bhaskar Bondada
Collaborator(s): Markus Keller
Commercial vineyards were monitored before veraison for the incidence of SOUR shrivel disorder in red and white cultivars. In addition to Cabernet sauvignon, SOUR shrivel was observed in Barbera and Riesling, which showed great losses in both yield and quality. Fruit organoleptic attributes coupled with morphology and structure, and tissue organization in various organs of healthy and afflicted grapevines were examined using a range of microscopy techniques. Regardless of grape types, the SOUR shrivel symptoms were identical in all cultivars. As opposed to healthy berries, SOUR shrivel berries were flaccid due to a collapsed nonviable mesocarp, which seriously compromised its fruit quality attributes such as hexoses, nutrients, and various phenolic compounds including anthocyanins. Despite such extreme quality losses, the spatial architecture and integrity of various tissues in organs such as canes, inflorescence framework of afflicted vines were remarkably similar to healthy grapevines with notable exceptions. The cluster framework that assembled SOUR shrivel berries developed red coloration but showed no relation with the flaccidity of the berries as healthy vines that bore entirely SOUR shrivel free clusters, too had the same feature. Furthermore, although the phloem sieve tubes in both grapevines were plugged with callose, a carbohydrate generally implicated in impeding translocation in the phloem, the afflicted grapevines exhibited relatively more plugged sieve tubes. The study revealed that the spatio-temporal pattern of various tissues determining the structure-function relationship in afflicted vines remains intact throughout the growing season; however, the functionality, especially of flows in vascular tissues (sieve tubes) started to slow down and eventually ceased during the course of ripening as evident from dramatic reductions in fruit quality attributes. Hence, in future studies a broader analysis of phloem sieve tubes entailing its flows and ultrastructure is needed. More specifically, grapevines that have been phloem- girdled to simulate the development of SOUR shrivel berries would provide clues about what perturbs the normal progression of ripening process succumbing the clusters to such disorder.
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