41 B ROOTSTOCK, or 41 B Millardet et de Grasset (41 B MGt) to give it its full name, is a rootstock bred by Professor Alexis Millardet and Charles de Grasset in Bordeaux in 1882. It is a hybrid between the Vitis vinifera variety Chasselas and V. berlandieri. (See 333 EM for another example of a V. vinifera x V. berlandieri hybrid rootstock.) Dr Richard Smart (2015) says that as 41 B is ‘highly tolerant to lime it is widely used in [the] Cognac and Champagne [regions]. Its tolerance of phylloxera is sufficient but not absolute [due to its partial vinifera parentage]. This rootstock is moderately tolerant of drought.’ 41 B can have problems in the driest soils in Sherry, for example.
41 B has poor resistance to nematodes and is said to be a poor rooter, being slow to grow in the early years. 41 B encourages a short vegetative cycle, and thus promotes early ripening. Mature vines on 41 B are said to show good fruit set and yields.
In the Bordeaux region 41B is found on the most calcareous parts of the right bank where Merlot is the desirable scion. In addition, 41B regulates vigour in the scion to induce rapid flowering, providing both high yields and evenly ripened fruit. In Bordeaux, 41 B is being superceded by Fercal.
Dr Richard Smart, Oxford Companion to Wine 4th edition ed. Jancis Robinson MW and Julia Harding MW (Oxford University Press, 2015, p592.