Influence of deficit irrigation and kaolin particle film on grape composition and volatile compounds in Merlot grape (Vitis vinifera L.)

Abstract

The effect of deficit irrigation and a kaolin-based, foliar reflectant particle film (PF) on grape composition and volatile compounds in Merlot grapes was investigated over two growing seasons in semi-arid, south-western Idaho. Vines were provided with differential amounts of water based on their estimated crop evapotranspiration (ET_c) throughout berry development, and particle film was applied to half of the vines in each irrigation main plot. Free and bound volatile compounds in grapes were analyzed using stir bar sorptive extraction–gas chromatography–mass spectrometry (SBSE–GC–MS). The concentrations of free C₆ compounds (hexanal, trans-2-hexenal, and 1-hexanol) decreased, and bound terpene alcohols (nerol and geraniol) and C₁₃-norisoprenoids (β-damascenone, 3-hydroxy-β-damascenone, 1,1,6-trimethyl-1,2-dihydronaphthalene, and 3-oxo-α-ionol) increased in berries each year in response to severity of vine water stress. Concentrations of C₁₃-norisoprenoids and bound forms of nerol and geraniol were positively correlated with their concentrations in the corresponding wines. Particle film application had minimum effect on free and bound volatile composition in the grapes, and there was no interactive effect between particle film and deficit irrigation. However, particle film application enhanced the total amount of berry anthocyanins.

Introduction

Grape-derived volatile compounds are the secondary metabolites of grape vine, and are considered to be the most important factor for grape and wine quality. These secondary metabolites are found in a wide range of concentrations and chemical classes (Ribéreau-Gayon et al., 2000, Sefton, 1998). Grape volatiles can exist as free form, but a large percentage exists in the grape as nonvolatile precursors, binding to sugars or amino acids (Ribéreau-Gayon et al., 2000). Bound volatiles are potential aromas, they can be converted to the free volatiles through enzyme or chemical hydrolysis during the vinification and ageing process, and contribute to wine aroma (Ibarz, Ferreira, Hernandez-Orte, Loscos, & Cacho, 2006).

The concentrations of volatile compounds and precursors in grape berries are highly influenced by viticultural practices, such as vine training (Jackson & Lombard, 1993), cluster thinning (Reynolds et al., 2007), leaf removal (Kwasniewski et al., 2010, Reynolds et al., 2007), and water management (Bindon et al., 2007, Deluc et al., 2009, Jackson and Lombard, 1993). Among these cultural practices, deficit irrigation, aimed at improving water use efficiency and reducing canopy vigour (Shellie & Glenn, 2008), is an important practice for sustainable agriculture, especially in arid and semi-arid areas (Chaves et al., 2007, Koundouras et al., 2006).

Imposing a water deficit to the vine during berry development is an important vineyard management strategy to alter grape and wine quality. Previous studies have shown that water deficit influenced physiological parameters of the vine (Iacono, Buccella, & Peterlunger, 1998), changed berry composition (Bindon et al., 2008, Esteban et al., 1999), and improved the sensory attribute of wines by increasing fruity aroma and decreasing vegetal aromas (Chapman, Roby, Ebeler, Guinard, & Matthews, 2005). Although many literatures have reported the effect of vine water status on grape derived volatiles and their precursors (Bindon et al., 2007, Koundouras et al., 2006, Koundouras et al., 2009, Peyrot des Gachons et al., 2005), the results are still inconclusive due to the variations in irrigation regimes, cultivars and other agronomical conditions. In general, water deficit increases C₁₃-norisoprenoids (Bindon et al., 2007, Koundouras et al., 2009) and glycosylated volatile compounds. Although it is possible that water deficit induced volatile increase is merely due to reduction in berry size (Koundouras et al., 2009), it has been demonstrated that increases in the concentration of C₁₃-norisoprenoids were independent of berry size (Bindon et al., 2007). Furthermore, it has been shown that water deficit significantly affected the transcripts and pathways associated with the production of volatile compounds (Deluc et al., 2009).

Water deficit reduces canopy size, which subsequently alters the canopy microclimate and increases cluster exposure to sunlight (Intrigliolo & Castel, 2010). Severe water deficit can result in excessive cluster exposure, and lead to supra-optimal berry temperature and sunburn, especially in warm, semi-arid production regions with high solar radiation (Shellie, 2006, Spayd et al., 2002), and have a negative effect on grape quality (Peyrot des Gachons et al., 2005).

Kaolin, a white, inert clay mineral, was used as a base to develop a particle film for foliar application to inhibit insect damage in tree fruit and has since been found to reduce heat stress in plants by reflecting infrared (IR) radiation (Glenn & Puterka, 2005). Kaolin particle film (PF) has been reported to reduce leaf and fruit tissue temperature of vines under water deficit (Glenn et al., 2010, Shellie and Glenn, 2008). While PF application did not eliminate heat stress under the most extreme environmental conditions, berry composition data at harvest suggested that the film increased vine capacity (Cooley et al., 2006, Shellie and Glenn, 2008). In addition, water deficit altered the volatile composition and sensory properties of the wine (Ou, Du, Shellie, Ross, & Qian, 2010). However, it will be advantageous to directly study the volatile and the precursor compositions in the grapes to eliminate the volatile profile modification during vinification. The objective of this study was to investigate effects of vine water deficit and PF on grape quality, so the results can be used to develop a vineyard irrigation guide to conserve water usage in a semi-arid climate.