ROOTSTOCK EFFECTS ON FRUIT-QUALITY OF FUJI APPLES GROWN WITH AMMONIUMOR NITRATE-NITROGEN IN SAND CULTURE

Fruit quality of 'Fuji' apples (Malus domestica Borkh,) grafted on thr ee rootstock cultivars (a weeping-type clone of 'Marubakaidou' (Malus prunifolia Borkh. var. ringo Asami), MM.106, and M.26) were investigat ed in sand culture. The trees were grown in a nutrient solution with n itrogen supplied as ammonium or nitrate. With MM.106 and M.26 rootstoc ks, fruit from the trees fed with nitrate nitrogen were larger, had be tter surface color, higher soluble solids, higher levels of sugars, an d higher acidity than those fed with ammonium nitrogen. Fruit from tre es grafted on MM.106 and M.26 treated with ammonium nitrogen had highe r N but lower calcium content than those treated with nitrate nitrogen . With M, prunifolia rootstocks, however, the form of nitrogen supplie d had no influence on the surface color, juice quality, and mineral co ntent of the fruit.