5 C TELEKI is a rootstock, a V. Berlandieri x V. riparia hybrid selected in 1896 by Alexandre Teleki, says Dr Richard Smart (2015, p627-8). The rootstock is similar to SO 4 in aptitude, and is mostly used in Germany, Dr Smart (ibid) adds. 5 C Teleki matures early, and is therefore suited to northerly wine regions, hence its popularity in Germany. 5 C Teleki is said to be susceptible to the bacterial vine disease crown gall, which is common in cold regions.
Dr Richard Smart in the Oxford Companion to Wine 4th edition ed. Jancis Robinson MW and Julia Harding MW (Oxford University Press, 2015, p627-8.