Effect of Colletotrichum acutatum ripe rot on the composition and sensory attributes of Cabernet Sauvignon grapes and wine

Background and Aim:  The impacts of the fungal bunch rot pathogen Colletotrichum acutatum (ripe rot) on grape growing are documented; however, little is known about how the disease affects the resulting wine. This work aimed to investigate how ripe rot affects wine composition and sensory properties.
Methods and Results:  Wine was made using Cabernet Sauvignon grapes grown in the Hastings Valley (NSW). Berries with ripe rot tended to shrivel and acquired a distinctive off flavour and bitterness, described as hessian sack and musty. Wine made from the infected fruit had a higher pH and a higher level of residual sugar, but lower titratable acidity. Volatile acidity in wine made from uninfected fruit was 0.57 g/L, but increased to 0.83 and 1.06 g/L with 1.5 and 3% infection, respectively. Wine made from infected fruit had higher levels of both glycerol and gluconic acid indicative of fungal contamination. Alcohol concentration was also higher in wine made from infected fruit. Sensory analysis indicated that wine made from as low as 3% infected fruit had a similar colour density to control fruit, but a distinctive off-flavour, and browner colour hue.
Conclusions:  As far as we are aware of, this is the first report of a correlation between the level of grape infection by C. acutatum and wine composition in Australia.
Significance of the Study:  These results underline the problems of red grapes infected with C. acutatum . It provides viticulturists and winemakers with information to be considered when assessing grape quality and winemaking process for red wines.     

Ripe rot of south‐eastern Australian wine grapes is caused by two species of Colletotrichum: C. acutatum and C. gloeosporioides with differences in infection and fungicide sensitivity

Background and Aims: Ripe rot of grapes is widespread in subtropical vineyards of south‐eastern Australia. We aimed to re‐evaluate the causative agent(s), berry susceptibility, fungicide sensitivity and differences in histopathology. Methods and Results: Both Colletotrichum acutatum and C. gloeosporioides were shown to be responsible for ripe rot in three vineyards surveyed in the Hastings Valley, NSW in 2007 and 2009. Observation on detached berries of Vitis vinifera (cv. Cabernet Sauvignon and Chardonnay) revealed that C. acutatum had a faster infection rate than C. gloeosporioides. C. acutatum also formed appressoria and penetrated grape tissue faster than C. gloeosporioides, which produced longer hyphae on the berry surface before penetration. Both C. acutatum and C. gloeosporioides produced acervuli 48 h after inoculation. In contrast, spore germination rates and growth rates on potato dextrose agar were greater for C. gloeosporioides. The two species differed in their sensitivity to the fungicides benomyl, captan and triadimenol. C. acutatum was significantly more sensitive to captan and triadimenol, whereas C. gloeosporioides was more sensitive to benomyl. Conclusions: Both C. acutatum and C. gloeosporioides cause ripe rot of wine grapes in Australia. Subtle differences in the infection process may explain the relative prevalence of the two species. Significance of the Study: This study confirms the involvement of C. acutatum and C. gloeosporioides in ripe rot of grapes in Australia. Knowledge of growth characteristics and fungicide sensitivity of ripe rot pathogens should aid disease management strategies.     

Advancement of grapevine maturity in Australia between 1993 and 2006: putative causes, magnitude of trends and viticultural consequences

Background and Aims: Recent warming has accelerated phenological development of many crops. We quantified the rate of change in date of designated maturity (21.8°Brix), date of harvest, and sugar concentration of berries at harvest in Chardonnay, Cabernet Sauvignon and Shiraz between 1993 and 2006. Methods and Results: Data from 18 Australian regions indicated that: (i) the date of designated maturity advanced at rates between ?0.5 and ?3.1 days/year; (ii) trends in the date of designated maturity were unrelated to trends in yield; (iii) trends of monthly temperature ranged from negligible up to 0.19°C/year; (iv) the rate of change in date of designated maturity was correlated with rate of change of temperature for Chardonnay and Cabernet Sauvignon, but not for Shiraz; (v) harvest was accelerated at a rate between ?0.4 and ?2.4 days/year; (vi) the rate of change in harvest date for Chardonnay was commensurate with the rate of change in maturity, hence berry sugar concentration at harvest remained stable with time; and (vii) the advancement of harvest for Cabernet Sauvignon and Shiraz only partially offset the advancements in maturity, hence the increase in the concentration of berry sugar at harvest, up to ~0.3°Brix/year. Conclusions: Maturity advanced at rates between half and 3 days per year. On a temperature basis, these rates are comparable to long‐term rates reported for the northern hemisphere. Significance of the Study: This is the first report of time trends in phenology of grapevine in Australia and provides a benchmark for the industry.     

Methoxypyrazine Analysis and Influence of Viticultural and Enological Procedures on their Levels in Grapes,Musts, and Wines

This review discusses the factors that affect the concentrations of methoxypyrazines (MPs) and the techniques used to analyze MPs in grapes, musts, and wines. MPs are commonly studied pyrazines in food science due to their contribution of aroma and flavor to numerous vegetables such as peas and asparagus. They are described as highly odorous compounds with a very low olfactory threshold. The grape varietals that exhibit green or herbaceous aromas that are characteristic of MPs are predominantly Vitis vinifera cv. Cabernet Sauvignon and Sauvignon Blanc, but include others. The most extensively studied MPs include 3-isobutyl-2-methoxypyrazine, 3-isopropyl-2-methoxypyrazine, and 3-sec-butyl-2-methoxypyrazine. It outlines the significance of methoxypyrazines in grapes, musts, and wines in terms of the concentrations that are capable of contributing their sensory characteristics to wines. This review discusses methods for analyzing MPs including gas chromatography-mass spectroscopy (one or two dimension) and high-performance liquid chromatography, the appropriate extraction techniques, and the efficacy of these methods. Additionally, this review explores factors that affect pyrazine content of grapes, must, and wines, such as the effects of different viticultural practices, effects of light exposure and grape maturation, climate, soil, the multi-colored Asian lady beetle and the effects of different vinification processes.     

The aroma of Muscat of Frontignan grapes: effect of the light environment of vine or bunch on volatiles and glycoconjugates

Effects of the modification of whole vine or individual cluster light environment by shade cloth from berry set to maturity were studied on the volatiles and glycoconjugates in Muscat (Muscat of Frontignan; Vitis vinifera L) berries over 2 years. Whole vines were shaded with 50 and 70% shade cloth, while bunches were shaded with 90% shade cloth. The sun‐exposed berries were chosen as control berries, and the berries naturally shaded under foliage were also studied. The natural shading of bunches under foliage did not decrease the levels of free and bound compounds in Muscat berries compared to sun‐exposed berries. The artificially shaded bunches showed lower levels of monoterpenols and C13 norisoprenoids than sun‐exposed berries and berries from naturally shaded bunches. Moreover, the effect of vine shading on the aroma composition of Muscat berries was lower compared to artificial bunch shading. In 1996 the leaf area/fruit yield ratio was modified by decreasing the bunch number per vine. This change did not influence the total amounts of glycosidically bound compounds, except for monoterpenic glycoconjugates. However, the higher monoterpenic glycoconjugate levels in these berries were likely related to their early maturity. Under our experimental conditions, berry aroma composition did not appear to be affected by foliage shade. © 2000 Society of Chemical Industry     

Quantifying the onset,rate and duration of sugar accumulation in berries from commercial vineyards in contrasting climates of Australia

Background and Aim: To predict the trajectory of sugar accumulation in berries for planning of harvest and post‐harvest operations, we derived a simple model that is consistent with the known biological and viticultural drivers of berry ripening and requires inputs that are readily available to industry. Methods and Results: We used data from three vintages in climatically contrasting regions of Australia to derive a relationship between total soluble solids (TSS) and thermal time. A linear‐plateau function was fitted to the 90th percentile data, hence providing a boundary function representing the potential for each variety‐environment combination. Biologically relevant parameters were derived including the rate of change in TSS, maximum TSS (TSS_max), the threshold thermal time when berries reached TSS_max, the onset and the duration of the period of linear increase in TSS. Gaps, calculated as the difference between actual TSS and the boundary function, correlated positively with vapour pressure. A model with the observed onset of ripening as an input and a variety and site specific rate as parameter accounted for 81–92% of the variation in TSS for independent data sets. Conclusion: The trajectory of TSS in berries can be modelled ‘as if’ the main environmental and management sources of variation affect the onset rather than the rate of sugar accumulation. Significance of the Study: Our onset‐rate model can be coupled with: (i) short‐term temperature forecasts to predict the trajectory of TSS for management purposes; and (ii) long‐term records of temperature to produce probabilistic profiles of maturity date.     

Environmental effects on cv Cabernet Sauvignon (Vitis vinifera L.) grown in Hawke's Bay, New Zealand.: 1. Phenology and characterisation of viticultural environments

Six Cabernet Sauvignon vineyard sites in Hawke's Bay (New Zealand), selected out of 28 sites observed in 1996/97, were studied over three consecutive seasons in order to characterise viticultural environments of this region for this cultivar. Indices of precocity of vine phenology were used to analyse the relationship between phenology at the selected sites and vegetative growth, productivity, fruit ripening and wine sensory characteristics. Marked differences in indices of precocity existed between sites. These differences were mostly correlated with vine vegetative growth and canopy indices. There was no relationship between yield and vine phenology. Indices of precocity were correlated with certain juice constituents measured on a common date, as well as the sensory scores of wines produced by microvinification from grapes harvested on different dates and maturity levels. Vineyard sites that differed in indices of precocity also differed in their environmental characteristics, particularly in soil physical properties and water balance.     

Environmental effects on cv Cabernet Sauvignon (Vitis vinifera L.) grown in Hawke's Bay, New Zealand.: 2. Development of a site index

Based on observations of Cabernet Sauvignon phenology, cropping and fruit characteristics at six vineyard sites in Hawke's Bay (New Zealand) studied over three seasons, a numerical model is proposed to characterise environmental conditions of a vineyard site. The proposed model is based on air temperature in October and January, seasonal rainfall, rooting depth, gravel percentage and clay-to-silt ratio in topsoil. The 'Site Index' (SI) calculated from these variables was significantly correlated with soil temperature and volumetric soil moisture content, themselves closely linked with clay-to-silt ratio, air temperature and rainfall. Vegetative growth, canopy characteristics, precocity of veraison, total anthocyanins, TSS and malic acid concentration in grapes, as well as wine sensory score, were all significantly correlated with the SI values at six sites and over two seasons. Over the same period, correlation of SI with several viticultural variables was generally stronger than five existing climatic indices for viticulture calculated for these sites. The proposed SI index appears to have potential use for vineyard zoning and site selection and evaluation.     

Identification,distribution and current taxonomy of Botryosphaeriaceae species associated with grapevine decline in New South Wales and South Australia

Background and Aims: Botryosphaeriaceae species are recognised as important pathogens of grapevines both in Australia and overseas. The identity, prevalence and distribution of Botryosphaeriaceae species in vineyards throughout the major winegrowing regions of New South Wales (NSW) and South Australia (SA) was determined to provide a foundation for improved disease prevention and management. Methods and Results: Field surveys from 91 vineyards across NSW and SA resulted in the collection of 2239 diseased wood samples and subsequent isolation of 1258 Botryosphaeriaceae isolates. Morphological identification along with phylogenetic analysis of ribosomal DNA internal transcribed spacer regions (ITS1-5.8S-ITS2) and partial sequences of the translation elongation factor 1-α gene (EF1-α) showed that eight Botryosphaeriaceae species from four phylogenetic lineages occur on grapevines in eastern Australia, including Diplodia seriata, Diplodia mutila, Lasiodiplodia theobromae, Neofusicoccum parvum, Neofusicoccum australe, Botryosphaeria dothidea, Dothiorella viticola and Dothiorella iberica. Conclusions: The prevalence of individual species varied according to geography and climate. Species of Diplodia and Dothiorella, characterised by thick-walled, pigmented conidia were the most prevalent and were distributed widely throughout both NSW and SA. Species with hyaline conidia, such as Neofusicoccum and Fusicoccum, were isolated less frequently and displayed more limited geographic ranges, whilst only a single isolate of Lasiodiplodia was recovered, this being from the northern most region of NSW. Significance of the Study: The identification of eight taxa within the Botryosphaeriaceae, and their distributions throughout south-eastern Australia was established and discussed in context with climate, reported optimum growth temperatures, and more recent taxonomic and nomenclatural revisions. We established a sound base for control strategies based on the prevailing species in Australian viticultural regions.     

Volatile composition and aromatic attributes of wine made with Vitisvinifera L.cv Cabernet Sauvignon grapes in the Xinjiang region of China: effect of different commercial yeasts

The Xinjiang region is a major grape- and wine-production area in China, but the region’s notably high temperatures in the summer and year-round intense sun exposure play negative roles in the aroma, complexity, and elegance of Cabernet Sauvignon wine. In this study, Cabernet Sauvignon grapes harvested in this region were fermented on an industrial scale using four commercial yeast strains (L2323, D254, RVA, and CECA) and spontaneous yeast (NF). The results showed that a total of 123 volatile compounds were detected and 15 volatile compounds significantly contributed their flavor notes to the wine’s overall aroma. The use of RVA and CECA strains resulted in wine with higher concentrations of higher alcohols, terpenes and norisoprenoids. However, the D254-fermented wine showed high level of esters and carbonyl compounds. Wine fermented with the L2323 and D254 strain possessed a stronger fruity aroma, whereas the RVA strain enhanced the herbaceous, chemical, and fatty aromas in wine. Principal component analysis revealed that a significant aromatic feature difference was observed in these wines after alcoholic and malolactic fermentation. The use of different commercial yeast strains altered the aromatic profile of Cabernet Sauvignon wine.     

Influence of trellis system and shoot positioning on light interception and distribution in two grapevine cultivars with different architectures: an original approach based on 3D canopy modelling

Background and Aims: A 3D modelling approach simulating canopy structure was used in combination with a radiative transfer model to simulate light interception, distribution and microclimate in the fruiting zone. Methods and Results: This model was parameterised for four training systems (two vertical shoot‐positioned systems with one or two pairs of catch wires (VSP‐1W, VSP‐2W); two non‐shoot‐positioned systems, gobelet (GOB) and bilateral free cordon (BFC)) and two cultivars (Syrah and Grenache). Light interception and canopy microclimate depended on the interactions between the intrinsic architecture of the cultivars and canopy manipulations. Shoot vigour and leaf area were the main determinants of canopy radiative balance. However, differences in shoot architecture accounted for up to 25% of the difference in light interception between cultivar × trellis system pairs at a given leaf area index (LAI). Light interception efficiencies and the proportion of sunlit leaf area (SLA) were 25–30% lower for VSP‐2W than for BFC for intermediate LAI values. The genotypic differences in the ability to capture light were mostly induced by the ‘procumbent’ habit of the Syrah shoots. For this cultivar, shoot‐positioned systems resulted in lower levels of fruit illumination at midday than the BFC and GOB systems, whereas the use of a catch wire in VSP‐Grenache canopies made it possible to maintain light penetration in the fruit zone. Conclusions: These results highlight the problem of adapting the training system to both the architectural characteristics of the cultivar and climate. Free‐standing systems had greater light interception and SLA than shoot‐positioned systems. They may enhance fruit illumination for cultivars with ‘procumbent’ shoots. Significance of the Study: Non‐positioned shoot systems offer the possibility of combining a high level of light interception, favourable microclimate and reduced labour‐intensive practices for vineyards in conditions of moderate vigour.