Genotypic Difference in Resistance to Internal Bark Necrosis in Apple Trees Is Related to Manganese Uptake, the Distribution of Manganese, and Antioxidant Activity

摘要

Field investigations and pot culture experiments were performed to elucidate the genotypic differences of two apple cultivars that vary in resistance to internal bark necrosis (IBN). Factors examined were manganese (Mn) uptake, antioxidant activity, as well as the accumulation and distribution of Mn in apple branches. Lesser Mn concentrations were found in the bark and branches of an IBN-tolerant cultivar ('Jonagold') than in those of the sensitive cultivar ('Fuji') from both field investigations and pot culture, which is correlated with a reduction in Mn uptake from soil. Histochemical tests and x-ray microanalyses indicated that Mn is localized in the bark and coincided with the occurrence of necrosis in 'Fuji,' whereas a more homogenous distribution of Mn was found in 'Jonagold,' possibly resulting in an alleviation of Mn toxicity. Physiological parameters indicated that the occurrence of IBN in apple was related to oxidative stress. Under field conditions, ascorbic acid concentration in the bark or leaves of 'Fuji,' which were severely affected by IBN, was less than that of 'Jonagold.' Because of greater Mn uptake from soil, an uneven distribution of Mn among tissues, and less reduction activity in the sensitive apple tree, oxidized Mn precipitation occurred in the bark, which ultimately exhibited IBN.