The effect of different rootstocks on the occurrence of black root rot (Macrophoma castaneicola and Didymosporium radicicola) of chestnut (Castanea crenata Sieb. et Zucc.) trees.

摘要

To establish methods for controlling black root rot (caused by Macrophoma castaneicola [Sphaeropsis sp.] and Didymosporium radicicola) of Japanese chestnut (Castanea crenata) trees, resistant rootstocks were sought among seedlings of Shibaguri (wildC. crenata) and C. crenata cultivars. A survey of 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 sowing in the field was conducted. None of the open-pollinated Shibaguri seedlings found in 5 prefectures was resistant to black root rot; neither were the 9 cultivars tested. Fewer field-grafted cultivars on Shibaguri seedlings were infected with black root rot than clonally grafted nursery plants which were transplanted. Trees of cv. Tsukuba on 2-year-old seedlings derived from direct sowing in the field were attacked by black root rot more frequently than were transplanted nursery plants of the same cultivar. The lower incidence of 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 tended succumb to the disease because the fungi seem to spread from one tree to the next in the orchard.