The response of phenolic compounds in grapes of the variety ‘Chardonnay’ (Vitis vinifera L.) to the infection by phytoplasma Bois noir

The study was carried out on phytoplasma susceptible grapevine variety ‘Chardonnay’ (Vitis vinifera L.). The changes in total and individual phenolics, with a focus on hydroxycinnamic acids, flavanols and flavonol contents, were studied in phytoplasma-symptomatic and non-symptomatic berries of Bois noir (BN) infected and uninfected vines. Evident responses to BN infection at veraison have been monitored in a decreased accumulation of caftaric and coutaric acids, p-coumaroyl hexose, procyanidin B1, procyanidin trimer as well as of quercetin-3-O-glucoside, quercetin-3-O-glucuronide and quercetin-3-O-xyloside. At berry softening BN infection statistically increased the content of total phenolics, hydroxycinnamic acids and flavanols, but decreased the flavonol contents, especially at phytoplasma-symptomatic berry skins. Later, at harvest, the BN infection caused an additional significant decrease of coutaric acid and p-coumaroyl pentose contents, moreover of procyanidin B1 and procyanidin dimmers (1, 2, and 3), trimer, kaempferol-3-O-glucoside and of most identified quercetins, except of quercetin-3-O-xyloside. At harvest, non-symptomatic berries from infected plants showed similar dynamics in the total phenolic content compared to berry skins from uninfected plants, but in total flavanols and flavonols content similarity to those symptomatic was observed. The latter decreases grape quality and its antioxidant potential. The Bois noir disease showed specific, local and growth-phase-induced responses regarding the content of phenolics in berry skins, where in particular the differences between phytoplasma-symptomatic and non-symptomatic grapes have to be underlined.