Light and Temperature Independently Influence Methoxypyrazine Content of Vitis vinifera (cv. Cabernet Sauvignon) Berries

Abstract

Methoxypyrazines (MPs) are fruit-derived extractable compounds that contribute to cultivar-specific aroma traits in wine, and greater concentrations can contribute to unpleasant vegetative aromas. Both light exposure and temperature have been reported to influence MP content in developing wine grapes, but individual effects of light and temperature are confounded. A novel method of manipulating light exposure with light-emitting diodes (LEDs) was used to impose light treatments with little or no effect on cluster temperature. Three treatments were imposed on developing fruit of Vitis vinifera (cv. Cabernet Sauvignon): 1) clusters exposed to direct sunlight, 2) clusters shaded by the grapevine canopy, and 3) clusters shaded by the canopy and exposed to supplemental LED light. Experiments were conducted over 3 years across pre-and postveraison periods of fruit development. A second experiment imposed the same light exposure treatments to ripening clusters on vines experiencing continual shoot growth during the postveraison period. Light exposure reduced 3-isobutyl-2-methoxypyrazine (IBMP) concentration of developing grape berries in the preveraison period independently of berry heating from solar radiation. Berry IBMP responded less to postveraison light levels, except on vines with active shoot growth, suggesting IBMP synthesis was continued during active vine growth but was suppressed by light. An inverse relationship of growing degree days (GDDs) with berry IBMP was observed, indicating high temperatures also reduce berry IBMP concentration. Response to temperature could result from either radiant heating of light-exposed clusters or from high ambient air temperature. Canopy management should consider the impact of both light and temperature on IBMP, and vine management practices should be adjusted appropriately to regional growing conditions and grape cultivars.

Grape Berry Secondary Metabolites and Their Modulation by Abiotic Factors in a Climate Change Scenario–A Review

“…Similarly, Šuklje et al (2014) found increased concentration of thiols in clusters exposed to sunlight, and it is generally known that light exposure during ripening reduces MP content in berries (Roujou de Boubee et al, 2000;Sala et al, 2004;Stummer et al, 2005;Darriet et al, 2012;Sidhu et al, 2015;Martin et al, 2016;Cassandra et al, 2019;Torres et al, 2020a). Interestingly, according to Koch et al (2012), higher light intensity before and not during ripening has a greater impact of methoxypyrazine concentration at harvest.…”

Figure 1 from: Montague T, Graff E, Kar S (2020) Secondary Bud Gas Exchange, Growth, and Fruitfulness of Vitis vinifera L. cultivars, ‘Grenache’ and ‘Cabernet Sauvignon’ Grown on the Texas High Plains. Viticulture Data Journal 2: e60430. https://doi.org/10.3897/vdj.2.e60430

“…Vines were bilateral cordon trained (cordons established 0.9 m above the soil), and spur-pruned to four spurs for each cordon, with two buds for each spur. Canopies were managed in a sprawl configuration, with single foliage catch wires at ≈ 15.0 cm, and ≈ 37.0 cm above each cordon (Plank et al 2019).…”

“…Therefore, there were 36 total vines, and 18 vines for each cultivar and shoot treatment combination. Prior to, and during experiment years, vines were irrigated through a drip irrigation system (Plank et al 2019). In addition, during each growing season, all vines were managed according to viticultural practices common for the Texas High Plains AVA (Kamas 2017, Townsend and Hellman 2014).…”

Climate Change Effects on Grapevine Physiology and Biochemistry: Benefits and Challenges of High Altitude as an Adaptation Strategy

“…The chemical component responsible for bell pepper aroma, 2-methoxy-3-isobutylpyrazine (MIBP), was positively associated by regression to vineyard altitude and lower seasonal temperature ( Falcão et al, 2007 ). Pyrazine’s accumulation is known to be lower with cooler climates ( Romero et al, 2006 ; Plank et al, 2019 ), and their degradation has been linked to sunlight exposure ( Koch et al, 2012 ; Sivilotti et al, 2016 ). Furthermore, after a sensory evaluation of Merlot and Cabernet Sauvignon wines from 2,282, 2,435 and 2,608 m a.s.l., the trained panelists scored higher those wines coming from higher altitudes, highlighting an improvement in characteristics such as taste quality and aroma intensity ( Jin et al, 2017 ).…”