Establishment of mono-cultivar cultivation in the pear through inactivating stylar RNase by heavy metal-salt application

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The stylar RNase activity was lowered to less than 1/3 of control by adding 1 mM CuSO_4, and enough fruit set was accomplished when 2 mM CuSO_4 was applied to the ‘Kosui’ flower buds. Bordeaux mixture application, a fungicide containing copper ions, also induced fruit set, and thus, the labor time necessary for pollination and fruit thinning was greatly reduced. The gibberellin paste treatment a month after anthesis promoted not only fruit growth but fruit maturation, resulted in enough fruit production. It was suggested that the copper ion does not overcome self-incompatibility of the pear but induce parthenocarpic fruit setting. Although the treatment of an inhibitor for ethylene biosynthesis accelerated fruit set, detectable inhibition of ethylene evolution, ACC synthase and ACC oxidase activities was not found in CuSO_4-treated flower cluster.