ROOTSTOCK EFFECTS ON GROWTH AND FLOWERING IN YOUNG APPLE-TREES GROWN WITH AMMONIUM AND NITRATE NITROGEN

Ungrafted trees of seven apple rootstock cultivars, M.4, M.7, M.11, M.26, M.27, MM.106, and Marubakaidou (Malus prunifolia Borkh. var. ringo Asami; weeping type), and 'Fuji' (Malus domestica Borkh.) trees grafted on these seven plus M.9 and M.16 rootstocks were grown in sand. They were regularly supplied with nutrient solutions of N as ammonium alone (A), nitrate alone (T), and both (AT). With both ungrafted and grafted trees, the shoot growth of six rootstocks (M.11, M.4, M.7, MM.106, M.26, and M.27) was significantly less with A than with T. With 'Fuji' trees grafted on the above six rootstocks, the number of flowering buds and the ratios of flowering buds to total emerged buds were significantly enhanced by treatments A and AT, especially in the formation of axillary flowering buds. Flowering and shoot growth of 'Fuji' trees grafted on M. prunifolia and M.16 were slightly affected by the form of supplied N. In the xylem sap, cytokinin-like activity was detected in a single zone in paper chromatography in all rootstocks and 'Fuji' trees. The activity in six ungrafted rootstocks (M.4, M.7, M.11, M.26, M.27, and MM.106) and 'Fuji' trees grafted on these plus M.9 rootstocks were higher with A than with T. Gibberellin-like activity in the same sap was detected in two zones, Rfs 0.3 to 0.4 and Rfs 0.7 to 0.8 in paper chromatography. In the six ungrafted rootstocks and in 'Fuji' trees grafted on these plus M.9, A led to higher activity at Rfs 0.7 to 0.8, but T led to higher activity at Rfs 0.3 to 0.4. Cytokinin-like and gibberellin-like activities in ungrafted M. prunifolia and 'Fuji' trees grafted on M. prunifolia or M.16 were not affected by the form of N.