Volatile Metabolism of Wine Grape Trincadeira: Impact of Infection with Botrytis cinerea

Abstract

The aroma of grapes is cultivar dependent and is influenced by terroir, vineyard practices, and abiotic and biotic stresses. Trincadeira is a non-aromatic variety associated with low phenolic content and high sugar and organic acid levels. This cultivar, widely used in Portuguese wines, presents high susceptibility to Botrytis cinerea. This work aimed to characterise the volatile profile of Trincadeira grapes and how it changes under infection with B. cinerea. Thirty-six volatile organic compounds were identified, from different functional groups, namely alcohols, ester acetates, fatty acid esters, fatty acids, aldehydes, and products of the lipoxygenase pathway. Both free and glycosidic volatile organic compounds were analysed by Gas Chromatography and Gas Chromatography coupled to Mass Spectrometry for component quantification and identification, respectively. A multivariance analysis showed a clear discrimination between healthy and infected grapes with 2-trans-hexenal and isoamyl-acetate among the compounds identified as negative and positive markers of infection, respectively. Ester acetates such as 2-phenylethyl acetate, isoamyl acetate, and 2-methylbutyl acetate were present in higher contents in infected samples, whereas the contents of several fatty acid esters, such as ethyl decanoate and ethyl dodecanoate, decreased. These data were integrated with quantitative PCR data regarding genes involved in volatile metabolism and showed up-regulation of a gene coding for Hydroperoxide Lyase 2 in infected grapes. Altogether, these changes in volatile metabolism indicate an impact on the grape quality and may be related to defence against B. cinerea. The presence/absence of specific compounds might be used as infection biomarkers in the assessment of Trincadeira grapes’ quality.

Effect of Pathogenic Fungal Infestation on the Berry Quality and Volatile Organic Compounds of Cabernet Sauvignon and Petit Manseng Grapes

“…Shiojiri et al (2006) showed that overexpression of hydroperoxide lyase (HPL) in Arabidopsis led to higher resistance of transgenic plants to Botrytis cinerea, which may be due to the increasing contents of C6 VOCs emitted by plants after infection, reflecting the assumed role of VOCs metabolism in grape defense mechanism. However, our results are in agreement with those reported by Santos et al (2022), who found that hexanal and (E)-2-hexenal decreased greatly both in free or glycosylated after infection with Botrytis cinerea, suggesting that C6-VOCs can be used as a stress signal for plant biological stress. Schueuermann et al (2018) also confirmed the concentration of (E)-2-hexenal in V. vinifera cv.…”

“…Chardonnay grapes decreased after infection with Botrytis cinerea in two out of three vintages. We speculated that pathogenic fungal infestation could manipulate the level of C6-VOCs to reduce the defense effect of fruit, because low concentrations of (E)-2-hexenal may promote mycelium growth (Santos et al, 2022). Moreover, previous studies also showed that green aroma gradually decreased with fruit maturation, which was also a possibility for the decrease of hexanal and (E)-2-hexenal (Agudelo-Romero et al, 2013).…”

“…It is worth noting that the TP content in CS and PM presented the opposite effects after infection with gray mold, which showed that CS decreased by 5.02 mg GAE/g but PM increased by 2.02 mg GAE/g compared with CK. A study reported that total phenolic extracted in methanol had a visible downward tendency after infection, and total phenolic extracted in water, mainly hydrophilic compounds such as hydroxybenzoic acid, anthocyanin, flavonoids, or tannin, decreased after infection (Santos et al, 2022). However, wines made from powdery mildew-affected grapes generally have higher phenolic levels than wines made from unaffected grapes (Steel et al, 2013).…”

“…Volatile organic compounds (VOCs) play an indispensable role in the key metabolic pathways involved in plant growth, development, reproduction, and defense (Bouwmeester et al, 2019). Once the fruit was infected by pathogenic fungal, VOCs can be used as toxins, defense compounds, energy sources, and infection enhancers (Santos et al, 2022). Understanding the alterations of fruit to pathogenic fungal infestation is essential for the improvement of grapes and for the sustainability of wine production.…”

“…In addition to such visible quality characteristics, the nutritional value and chemical constituents of grapes will be changed, including more microbial metabolites, sugar degradation, and acid production (Solairaj et al, 2021). Santos et al (2022) found that Trincadeira wine grapes showed serious symptoms after Botrytis cinerea infection, the content of total phenol and total anthocyanin was greatly lower than in healthy samples. An infection experiment conducted by Pons et al (2018) confirmed that, for Merlot wines, pH and total acidity were the parameters that were systematically influenced by P. viticola infection.…”