FERCAL, a rootstock whose extremely high tolerance to active limestone sees it referred to as a ‘super 41 B‘. It was bred at INRA Bordeaux in 1959. It is a crossing of V. berlandieri-Colombard 2 (itself a V. berlandieri x Ugni Blanc hybrid) with 31 Richter, says Dr Richard Smart (2015, p627). It is resistant to phylloxera, grafts readily, is of moderate vigour [some Bordeaux growers feel Fercal can tempt scions like Cabernet Sauvignon into excess vigour], and more tolerant of chlorosis and drought than 41 B, Dr Richard Smart adds (2015, p627). See 333 EM for another rootstock with a V. vinifera x V. berlandieri bloodline.
Dr Richard Smart in the Oxford Companion to Wine 4th edition ed. Jancis Robinson MW and Julia Harding MW (Oxford University Press, 2015, p627.