Genetic investigation of grapevine varieties ‘Ribolla Gialla’ (Italy), ‘Rebula’ (Slovenia) and ‘Robola’ (Ionian Islands)

'Ribolla Gialla' is a very old grape variety cultivated today in the Friuli Venezia Giulia region in northeastern Italy. The historical reputation of this variety in central Eastern Europe was strongly related to the vast distribution of the Venetian Republic markets. In the 1960s, the interest of Italian winegrowers in 'Ribolla Gialla' decreased and it was replaced by international varieties. Despite historical documents reporting the longstanding tradition of 'Ribolla Gialla' cultivation and winemaking in Friuli Venezia Giulia, the origin of this variety is still questionable. The aims of this work were to study the genetic identity of `Ribolla Gialla' and to investigate the possible genetic relationships with 'Rebula' and 'Robola' that have been traditionally cultivated in other European Countries (Goriska brda in Slovenia and Kefalonia Island in Greece). For this purpose, 35 SSR loci were analyzed to fingerprint 19 accessions with denominations or morphologies that are similar to `Ribolla Gialla'. The Italian `Ribolla Gialla' accessions (#5) and the Slovenian 'Rebula' accessions (#2) revealed identical genotypes in all 35 analyzed SSR markers, and can therefore be confirmed as synonyms. The group of Greek 'Robola' accessions resulted as the most heterogeneous, showing several distinct allelic profiles. By phylogenetic analysis, two 'Robola' accessions were clustered with 'Ribolla Gialla' (or 'Rebula'), and parentage analysis strongly suggested a full-siblings relationship between 'Ribolla Gialla' and 'Robola'.