The Relation of Endogenous Abscisic Acid to the Dwarfing Capability of East Malling Apple Rootstocks1

Abstract

Roots, shoots, and leaves of 1- and 2-year-old ungrafted plants of EM IX, VII, and I, and roots of EM XVIa, were extracted to detect an inhibitor that appears identical with abscisic acid (ABA). The extracts were coned, partially purified chromatographically, and bioassayed using the wheat coleoptile straight growth and Lepidium seed germination tests. A strongly inhibitory substance was found in both bioassays at or close to the Rf values reported for maximum ABA activity or determined with the synthetic form. Extracts of EM IX tissue contained the highest levels of this inhibitor, presumed to be ABA. Progressively lower levels were found in extracts of EM VII, I, and XVIa, which is the same as the order of these clones in increasing vigor of grafted scions. This same order was indicated in nearly all bioassays of the 3 types of tissue extracts. Extracts of roots collected in early spring after overwintering either in storage or out-of-doors, in midsummer, and in the fall after cessation of growth all placed the clones in the same order. Levels in root and leaf extracts were generally higher than in those of shoots. The Lepidium seed bioassay appears to offer a convenient method for identification of strongly or semi-dwarfing individuals or clones. Leaves offer an obvious advantage over shoots or roots.

Gibberellic and Abscisic Acid-like Substances and the Regulation of Apple Shoot Extension1

“…There is less growth promoting activity and more growth inhibiting activity in the bark of a dwarf than vigorous rootstock (10). Progressively lower levels of an ABA-like inhibitor occurred in extracts of scions on mailing (M) 9, M 7, M 1, and M 16 (29). Single stem trees on dwarfing, intermediate, and vigorous rootstocks all stopped elongating and set terminal buds characteristic of summer dormancy when injected with 100 mg/liter of ABA (23).…”