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

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) ofVitis viniferaL. cv. Shiraz scions over own-rooted Shiraz vines at harvest. IBMPextracted from rachis during red wine fermentation can contribute potent"green"flavors. Methoxypyrazines (MPs) are normallypresent in Cabernet Sauvignon grapes, rachis, and wines, but it is unknown whether rootstocks can influence the MP concentrationin 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 Sauvignonover two seasons. IBMP predominated, and its concentration in rachis and berries at harvest was significantly affected by rootstockand growing season. In the 2020 vintage, light exclusion, vine vigor, and spatial variation in vine vigor were shown to significantlyaffect MP concentrations in rachis.