Micro-meteorological, compositional and transcriptional study of corvina grape color during ripening

Abstract

Grape anthocyanin content and composition could affect the quality and the production strategies of red wines. Differences in the pigment composition modify the color properties in terms of hue, extractability and stability. Thus, for the production of a highly qualitative wine such as “Amarone”, variations in the pigment composition are not negligible. The aim of this work was the investigation of the anthocyanin profile changes during ripening in Corvina grapes, the main cultivar for the “Amarone” production. The experiment took place in 2015, in two vineyards located in Valpollicella (Italy). Micro-meteorological survey, carpological characterization, chemical analysis and transcriptional studies were carried out to clarify the anthocyanin biosynthesis regulation. Air and grape temperatures and global solar radiation inside the canopy where measured during the season. Grape samples were collected at seven stages of berry development from pre-véraison until harvest. Berry growth was followed by both weight and volume increases. At veraison, anthocyanin quantification, by spectroscopy, and profile composition analysis, by HPLC, started (5 developmental stages were analyzed). The expression level of structural and regulatory genes of anthocyanin pathway was studied via real time polymerase chain reaction during all the seven development stages considered. Even if the vineyards are close each other the different training systems (“Guyot” and “Pergola”) created different microclimates for grape ripening. As an example, in “Pergola” the grape temperatures rarely exceeded 40°C. On the opposite, in “Guyot” the temperatures rise over 59°C in hottest days, and often overpassed 50°C. Despite these differences, the anthocyanin profile similarly changed during ripening among the two vineyards. At color appearance (average anthocyanin content: 80 mg kg-1 of grapes), the di-substituted anthocyanins prevailed. During ripening, it was possible to observe a progressive increase of tri-substituted, methoxylated, and acylated pigments. The transcriptional levels of “Guyot” and “Pergola” confirmed to be similar. A clear correlation among expression of anthocyanin biosynthetic gene UDPglucose:flavonoid 3-O-glucosyltransferase (UFGT), transcription factors, MYBA1 and MYBA2, and total anthocyanin content during berry development has been identified. Chalcone synthase, flavonoid 3ʹ-hydroxylase (F3ʹH) and flavonoid 3ʹ,5ʹ-hydroxylase (F3ʹ5ʹH) genes of the flavonoid pathway showed high correlation as well. The proportion changes between tri- and di-substituted anthocyaninswas associated with an increasing ratio of F3ʹ5ʹH/F3ʹH gene transcription during ripening. The AOMT genes were expressed with a maximum at the onset of ripening, coherently with the rapid increase of methoxylated anthocyanin proportion in this stage. Detailed knowledges of grape color variations during ripening could support the vineyard management techniques including harvesting time.