Abscisic Acid and Gibberellin‐in Three Ungrafted Apple (Malus sylvestris) Rootstock Clones

ABA and gibberellin‐like substances were extracted from roots, shoots, and leaves of most dwarfing M9, semi‐dwarfing MM 106, and least dwarfing MM111 apple rootstock plants. Among tissues, the roots contained the largest and the shoots the smallest amounts of all the phytohormones studied. Plants of M9 contained the highest and MM111 the lowest ABA‐like substances in all tissues tested. Gibberellin4+7‐like compounds were at the highest levels in the roots of MM111 and lowest in the roots of M9, whereas GA3‐like substance was in the reverse order. All three gibberellin‐like compounds were highest in the shoots and leaves of MM111 and lowest in the respective tissues of M9 clone. Role of these phytohormones in the dwarfing mechanism is discussed.