There are two different grape varieties with this name:
The white grape variety is a new variety between Riesling x unknown variety according to DNA analyses published in 2012. The parenthood stated in the breeding list(Rieslaner x Grüner Silvaner) x Müller-Thurgau turned out to be wrong. Synonyms are Gloriosa and Würzburg B 55-8-53. The cross was made in 1955 by Dr. Hans Breider (1908-2000) at the State Institute for Viticulture in Würzburg. Plant variety protection was granted in 1980 and no stocks were recorded in 2016 (statistics Kym Anderson).
The glossary is a monumental achievement and one of the most important contributions to wine knowledge. Of all the encyclopaedias I use on the subject of wine, it is by far the most important. That was the case ten years ago and it hasn't changed since.Andreas Essl