Temperature effects on the biosynthesis of aroma compounds in glera grapes

This paper describes the first year results of a study that investigated the effects of altitude and related temperature parameters on the biosynthesis of aromas in the Italian cultivar Glera. 

The trial was carried out in a commercial vineyard planted on a steep slope in the Valdobbiadene area (North-East of Italy). Three sites were selected at three different altitudes, ranging from 200 m a.s.l. to 380 m a.s.l. In each site air and berry temperature were constantly monitored during the ripening period. Starting from veraisón, grape samples were collected from each site approximately every 10 days, and then analyzed to determine the ripening level (soluble solids, acidity, pH), the amount of aroma volatile compounds and the expression of some key genes involved in the terpenoid biosynthesis. 

Preliminary data collected in 2012 highlighted the strong influence that altitude exerts on both air temperature and fruit temperature during the ripening period. The lowest site recorded the lowest minimum night temperatures, about 2°C lower than the medium and high sites, and consequently the grape ripening in this site was notably delayed compared to the medium and high sites. A similar delay was not observed in the synthesis of aroma compounds. At harvesting, the three principal classes of compounds (terpenes, norisoprenoids and benzenoids) showed lower levels in the low site. However, comparing grape samples from the three sites at the same level of ripeness, the low one displayed significantly higher amounts for all the classes of aromas. 

Preliminary results from gene expression analysis showed that the linalool synthase VvPNLinNer1 was more expressed in samples collected from the medium site. This result correlated with the higher accumulation of linalool plus its derivatives in this site.