Abstract
The natural or induced development of noble rot caused by the fungus Botrytis cinerea during the late stages of grapevine (Vitis vinifera L.) berry ripening is used in some traditional viticulture areas to produce high-quality wines such as Sauternes and Tokaji. In this research, we wanted to verify if by changing the environmental conditions during post-harvest withering we could induce the noble rot development on harvested berries in order to positively change the wine produced from withered Garganega berries. Therefore, we exposed the berries to postharvest withering under normal or artificially humid conditions, the latter to induce noble rot. The presence of noble rot symptoms was associated with the development of B. cinerea in the berries maintained under humid conditions. The composition of infected and non-infected berries was investigated by untargeted metabolomics using liquid chromatography/mass spectrometry. We also explored the effects of the two withering methods on the abundance of volatile organic compounds in wine by yeast-inoculated micro-fermentation followed by targeted gas chromatography/mass spectrometry. These experiments revealed significant metabolic differences between berries withered under normal and humid conditions, indicating that noble rot affects berry metabolism and composition. As well as well-known botrytization markers, we detected two novel lipids that have not been observed before in berries infected with noble rot. Unraveling the specific metabolic profile of berries infected with noble rot may help to determine the compounds responsible for the organoleptic quality traits of botrytized Garganega wines.
Highlights
The necrotrophic ascomycete Botrytis cinerea has been described as a ‘Jekyll and Hyde’ fungus because it causes devastating gray mold disease in grapevine plants but is responsible for noble rot in ripe and overripe berries, which allows the production of high-quality sweet wines such as Sauternes and Tokaji (Fournier et al, 2013)
At the end of the withering process, only the covered berries showed the typical symptoms of noble rot, with roughly 70% of the berries visually appearing as chocolate-brown colored, more shriveled and dehydrated compared to control berries (Figures 2C,D)
This was associated with a higher prevalence of B. cinerea colonization as determined by counting the number of colony forming units (CFUs) on selective medium, confirming that the conditions used for induction supported B. cinerea growth in its latent form (p < 0.05, Figure 2F)
Summary
The necrotrophic ascomycete Botrytis cinerea has been described as a ‘Jekyll and Hyde’ fungus because it causes devastating gray mold disease in grapevine plants but is responsible for noble rot in ripe and overripe berries, which allows the production of high-quality sweet wines such as Sauternes and Tokaji (Fournier et al, 2013). The development of B. cinerea as noble rot (botrytization) is a favorable process lasting 10–20 days and is typical of particular wine productions. In addition to directly producing potent odorants such as phenylacetaldehyde, lactones and vanillin (Lopez Pinar et al, 2016), noble rot infection can stimulate production, in the berry, of cysteine and glutathione conjugates which can be transformed by the yeast into the powerful aroma compound 3-mercaptohexanol (Thibon et al, 2009, 2011). Foggy mornings and dry, sunny days promote the slow infection that results in noble rot, whereas strong rainfall and high humidity facilitate the more aggressive gray mold (Ribéreau-Gayon et al, 1980; Gubler et al, 2013)
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