The vintage effect overcomes the terroir effect : a three years survey on the wine yeast biodiversity in Franciacorta and Oltrepò Pavese, two Northern Italian vine-growing areas

A three-years survey on the dominant yeast populations in samples of air, must and wine in different vineyards and cellars of two Northern Italian vine-growing territories (6 sites in Franciacorta and 8 sites in Oltrepò Pavese areas) was carried out. A total of 505 isolates were ascribed to 31 different species by RFLP analysis of ITS1- 5.8SrRNA - ITS2 region and partial sequence analysis of 26S rRNA gene. The most found species were Saccharomyces cerevisiae (Frequency, F'= 58.7%, Incidence, I' = 53.5%), Hanseniaspora uvarum (F '= 14.3%, I' = 5.3%), Metschnikowia fructicola (F '= 11.1%, I' = 5.0%) and Torulaspora delbrueckii (F '= 10.3%, I' = 3.8%). From 270 S. cerevisiae new isolates, 156 (57.8%) revealed a different genetic pattern through the polymorphism analysis of the interdelta regions by capillary electrophoresis, while 47 isolates (17.4%) resulted clones of starter cultures. By considering the Shannon-Wiener index and results of PCA analyses, the year of isolation (vintage) proved to be a factor that significantly affected the biodiversity of the yeast species, whereas the geographic site (terroir) was not. The 75% of S. cerevisiae isolates gathered in unique cluster at a similarity level of 82%, while the remaining 25% were separated in minor groups without any evident relationship between δ-PCR profile and territory, year or source of isolation. However, in six cases a same strain appeared at the harvesting time both in Franciacorta and in Oltrepò Pavese areas, whereas, surprisingly, no strain was reisolated in a same vineyard or cellar for consecutive years.