台木がクリ黒根立枯病の発生に及ぼす影響

Abstract

Black root rot disease of chestnut (Castanea crenata Sieb, et Zucc.) is caused by the fungi (Macrophoma castaneicola and Didymosporium radicicola). To establish methods for controlling black root rot of chestnut trees, resistant rootstocks were sought among seedlings of shibaguri (wild species of Castanea crenata Sieb. et Zucc.) and chestnut cultivars. A survey on the presence of the black root rot in chestnut cultivars that had been grafted on native shibaguri and those field-grafted onto open-pollinated seedlings of cultivars derived by direct seeding in the field was conducted. 1. No one of the open-pollinated shibaguri seedlings found in five prefectures was resistant to black root rot ; neither were the nine cultivars tested. 2. Fewer field-grafted cultivars on shibaguri seedlings were infected with black root rot than clonally grafted nursery plants which were transplanted. 3. Trees of 'Tsukuba' on 2-years-old seedlings derived from direct seeding in the field were attacked by black root rot more frequently than were the transplanted nursery plants of the same cultivar. 4. That less black root rot infection on chestnut cultivars grafted on native shibaguri rootstocks is attributed to the better development of their rootstocks. However, more older trees tend succumb to the disease because the fungi seem to spread from one trees to the next in the orchard.