Abstract
Size-controlling rootstocks have generally been selfrooted by grafting their scions on rootstocks cuttings of Malus prunifolia BORKHAUSEN var.ringo ASAMI in Japan. In Aomori Prefecture, the rootstocks have widely been used without removing a rooted portion of M. prunifolia ringo.Thus a rootstock is composed of two rooted portions;M. prunifolia and the size-controlling rootstock.If either a size-controlling rootstock or a cultiver scion carriesapple chlorotic leaf spot virus (ACLSV), the virus will cause innerbark necrosis andpittig on M. prunifolia ringo.
Effect of the ACLSV on the occurrence of white root rot caused by Rosellinia necatrix BERL.or violet root rot caused by Helicobasidium mompa TANAKA was evaluated in the field.Seedlings of M.scheidekeri Z.which is susceptible to the ACLSV were used as the rootstock.After planting apple trees in an orchard infested with high density of pathogenic fungi, half of them were inoculated with the ACLSV and others were left free from the virus.The trees inoculated with the ACLSV were more susceptible to the two fungi than ACLSV-free trees.According to the survey at an orchard where the violet root rot was predominant, trees showing necrosis symptoms induced by ACLSV on the part of M. prunifolia ringo were more affected by H. mompa than those without the symptoms.
