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Abstract
Officially, 1972 marks the 100th anniversary of the modern apple industry in Japan. Although a small, crab-type apple was grown there for several centuries, the modern cultivated apple was virtually unknown in Japan prior to the Meiji Restoration which reopened the country to foreign trade in 1868. Since their introduction in 1872 apples have become the second leading fruit crop with 149,000 acres currently producing some 90 million boxes (40 lb.) annually.
Abstract
Apple topworking disease is one of the most important problems in apple culture in Japan. This disease which affects all apple cultivars is caused by an extreme sensitivity of the rootstock cultivars commonly used in Japan to latent viruses that are present in many of the scion cultivars. Recent work indicates that apple chlorotic leaf spot virus causes decline of trees grown on Malus prunifolia Borkh.var. ringo Asami rootstocks and that stem pitting virus causes decline of trees grown on M. sieboldii Rehd. andM sieboldii Rehd. var. arborescens Rehd. rootstocks. The need for a virus-free certification program is recognized. However, the general practice of topworking old orchard trees, most of which are on virus-sensitive rootstocks, with new apple cultivars makes implementation of such a program difficult. This report was written because little is known outside of Japan about the disease or about the cultural practices that have contributed to its importance. Nearly all published reports on this disorder were presented in Japanese; many without English summaries.