Comparison of growth, yield efficiency and fruit quality between 'Fuji' on M.9Nagano rootstock and 'Fuji' on M.9Nagano (interstock)/Marubakaido (Malus prunifolia bork. var. ringo asami) under high density planting

M.9 is the most commonly planted rootstock in high density apple orchards in the world, However, M.9 rootstock has not been used in Japan because of infection with apple chlorotic leaf spot virus (ACLSV). M.9Nagano, an ACLSV-free clone and called M.9 minus was developed at the Nagano Fruit Tree Experiment Station. The growth, yield efficiency and fruit quality of the graft combinations, 'Fuji'/M.9Nagano and 'Fuji'/M.9Nagano (interstock) / Marubakaido were compared for 8 years at the Nagano Fruit Tree Experiment Station. Trees of 'Fuji'/M.9Nagano with rootstock half-buried developed into small trees, whereas those of 'Fuji' on M.9Nagano/Marubakaido with 30 cm of interstem half-buried grew vigorously. Limbs of the latter crossed severely so that every second tree was removed after the 6th year, resulting in a 4 X 4 m planting, No significant difference in fruit quality was noticeable between trees on M.9Nagano and M.9Nagano/Marubakaido. In conclusion, 8-year-old 'Fuji' trees on M.9Nagano are thought to be well adapted for 2 X 4 m or higher planting density under 40 to 50 cm layer of gravelly brown lowland soil condition.