The analysis of grapevine response to smoke exposure

Abstract

Smoke taint is a fault found in wines made from grapes exposed to bushfire smoke. It is characterised by objectionable smoky and ashy aromas and flavours, which have been attributed to the presence of smoke derived volatile phenols, in free and glycoconjugate forms. Chapter 1 comprises a summary of the impact of bushfires on the wine industry and a review of previous smoke taint research, which includes many investigations into the composition of wine produced from smoke-affected fruit. Gaps of knowledge are identified in Chapter 1, and the issues addressed in this thesis are identified and summarised in the research aims. Chapter 2 describes a field trial that investigated the accumulation of smoke taint precursors in three Vitis vinifera cultivars, Sauvignon Blanc, Chardonnay and Merlot, at different time points, following grapevine exposure to smoke under experimental conditions. Varietal differences in volatile phenol glycoconjugate profiles were observed; interestingly, these profiles also differed between samples harvested 1 day after smoke exposure and samples harvested at maturity. An evaluation of the effect of an agrichemical applied to grapevine fruit and foliage as a physical barrier to prevent the uptake of smoke is also reported; together with the results of an investigation into the potential for reflectance spectroscopy, measured using a handheld spectrometer, to detect smoke-affected fruit. A subsequent field trial sought to further verify the use of a second agrichemical to mitigate the impacts of grapevine exposure to smoke; and reflectance spectroscopy to evaluate smoke exposure in the vineyard and is also included in Chapter 2. Whereas the glycosylation of smoke derived volatile phenols in grapevine fruit and leaves following exposure to smoke is reasonably well understood, the biochemical and molecular consequences of grapevine smoke exposure have received comparatively little consideration. The research described in Chapter 3 endeavours to address this knowledge gap through investigations into the expression of grapevine glycosyltransferases (GTs) following smoke exposure. Higher expression profiles of certain sets of genes (including heat shock proteins and putative GTs) were identified through RNA sequencing of two grape cultivars grown as potted grapevines in a growth room. Selected GT candidates were analysed in a subsequent field trial, in which Q-PCR expression analysis showed higher expression of two GT1 family genes at specific time points; with differential expression found to be highest in skin, rather than pulp, fractions following smoke exposure. To date, the occurrence of smoke taint has not been reported in crops other than grapes, despite the proximity of bushfires in regions comprising broader agricultural production. The final chapter of experimental work in this thesis, Chapter 4, describes analysis of a field trial involving the application of smoke to apple trees, to investigate whether or not apples can be similarly affected by smoke. Chapter 5 reflects on the experimental work described in this thesis, including a discussion towards challenges and future directions in the research of smoke taint.