Rootstock, Vine Vigor, and Light Mediate Methoxypyrazine Concentrations in the Grape Bunch Rachis ofVitis viniferaL. cv. Cabernet Sauvignon

Abstract

Ramsey rootstock has previously been implicated in an approximate 8-fold increase of 3-isobutyl-2-methoxypyrazine (IBMP) levels in the rachis (grape bunch stem) of Vitis vinifera L. cv. Shiraz scions over own-rooted Shiraz vines at harvest. IBMP extracted from rachis during red wine fermentation can contribute potent “green” flavors. Methoxypyrazines (MPs) are normally present in Cabernet Sauvignon grapes, rachis, and wines, but it is unknown whether rootstocks can influence the MP concentration in the rachis. This study considered the effect of eight rootstocks including Ramsey and own roots on the concentrations of IBMP, 3-isopropyl-2-methoxypyrazine (IPMP), and 3-sec-butyl-2-methoxypyrazine (SBMP) in the rachis and grapes of Cabernet Sauvignon over two seasons. IBMP predominated, and its concentration in rachis and berries at harvest was significantly affected by rootstock and growing season. In the 2020 vintage, light exclusion, vine vigor, and spatial variation in vine vigor were shown to significantly affect MP concentrations in rachis.

Grape Heterogeneity Index: Assessment of Overall Grape Heterogeneity Using an Aggregation of Multiple Indicators

“…The analysis of IBMP variability at bunch and vine levels has seemingly not been reported before but has been shown to be a dynamic feature of a vineyard at the block level [ 32 ]. Furthermore, vine vigour differences were deemed to result in spatial variability in IBMP across a vineyard [ 21 ].…”

“…Vine canopy architecture parameters (leaf area index, LAI and normalised difference vegetation index, NDVI), vine size (vegetative growth and yield), and soil EC a have been shown to correlate to grape maturity measures [ 19 , 20 , 21 , 37 ], and Figure 1 and Figure 2 demonstrate the change in grape heterogeneity relative to maturity. As such, this investigation considered whether overall grape heterogeneity might have an inverse relationship with these vine attributes and soil EC a .…”

“…Methoxypyrazines were extracted according to Dunlevy et al [ 45 ] and analysed by stable isotope dilution assay with headspace SPME-GC-MS following the previously reported procedure [ 14 ], with the inclusion of deuterated internal standards d 3 -IPMP and d 3 -SBMP for quantification of IPMP and SBMP, respectively [ 21 ].…”

“…Therefore, there has been growing interest in managing grape heterogeneity to achieve high-quality wine, with recent work focussing on the use of remote sensing and precision viticulture to address variability across a vineyard [ 18 , 19 , 20 ]. Differences in vineyard soil type and depth are considered significant driving forces for grape maturity variability as these geophysical parameters correlate to vine vigour and yield, which in turn alter berry composition [ 20 , 21 ].…”

Insights into the Uptake, Distribution, and Metabolism of 3-Isobutyl-2-hydroxypyrazine in Grapevine Using a Stable Isotope Tracer

“…7 In contrast, while VvOMT1 and 2 are capable of converting HPs to MPs, they have more than 200fold greater specific activity for compounds other than IBHP (such as quercetin, a flavonol) and the timing of expression is unrelated to changes in IBHP and IBMP concentrations. 10,11 The VvOMT4 expression profile closely resembles VvOMT3, but its copy number is 100 to 4000 times lower, 6 and VvOMT4 shows low levels of activity against HP substrates. 7 Curiously, V. vinifera varieties such as Shiraz and Pinot Noir 8,12 that are unable to produce MPs in the berry due to epigenetic differences in the regulation of VvOMT3 expression 13 have high concentrations of IBMP in the rachis 12 and tendrils 8 despite negligible levels of VvOMT3 expression and highly variable IBHP concentrations.…”