Hormonal Changes during the Rooting of Hardwood Cuttings of Grapevine Rootstocks

Abstract

Hardwood cuttings of grapevine rootstocks Kober 5 BB (easy to root) and 140 Ruggeri (hard to root) were bioassayed for some of their hormones. 140 R contained a low level of auxin and a very high amount of GA-like and ABA-like substances, which are inhibitors of root formation, whereas Kober 5 BB contained a very high amount of auxins, but a very low level of acid GA- and ABA-like substances. During root formation, IAA-like hormones increased slightly in both rootstocks until bud burst; they then decreased to a low level at root emergence. At the same time, GA-like compounds increased rapidly in 140 R, but decreased in Kober 5 BB. The ABA-like pattern also differed between the two rootstocks: in 140 R it reached a high level, whereas in Kober 5 BB it remained low. Soaking cuttings in water enhanced the rooting ability of 140 Ruggeri, and raised its IAA level. This growth regulator is generally considered to play the most important role in root initiation.