For this treason it is solely imported from Israel, where it has adaptedTreason indeed! They sold the entire crop of Israeli sweet potatoes to the UK. And the sweet-potato and goat's cheese casserole I wanted to prepare for Shavuot had to make do with just plain potatoes.
well to growing conditions and can be exported quickly to the UK, reducing
quality issues such as rots.
As Jim Davila pointed out, Second Temple sectarians would have observed Shavuot today. The source for this piece of information, which is cited in the Babylonian Talmud, Menahot 65a, is the scholion of Megillat Ta'anit. All the Scroll itself says is:
מן תמניה ביה ועד סוף מועדא איתקין חגא דלא למספד
"From the 8th of Nissan until the end of the Moed is a festival, and eulogizing is forbidden". But the scholia (two versions, and one hybrid) give a long description of the debate between Rabban Yohanan ben Zakkai and one of the Baitusians. The crux of the debate was that the sectarians understood "Mi'mohorat ha-Shabbat" to mean the morrow of the Sabbath, i.e. Sunday. The Hachamim, on the other hand, read Shabbat here to mean the festival. And Shavuot is celebrated on the day in the week which follows that on which the first day of Passover was celebrated.
One segment of the dialogue is worth quoting. The sectarian says to Rabban Yohanan that Moses loved the people of Israel, and therefore he gave them Shavuot, so that they would have a long weekend, because he knew Shavuot is only one day long.
Rabban Yohanan answers: If Moses really loved them so much, how come he made them run around in circles for forty years?
On all of this, see Vered Noam's acclaimed edition of the Scroll of Fasts and its scholia, pp. 59-63, 135-140, 174-179.