Distribution of Pythium zingiberum causing rhizome rot in ginger-growing and its surrounding uncultivated soils.

Abstract

Pythium zingiberum causing rhizome rots of ginger (Zingibey officinale Rose. cv. Oshoga) and mioga (Zingiber mioga (Thunb.) Rose.) was easily isolated from soils in which they are cultivated1,2). Using semi-quantitative detection method of the fungus in the soil3), the pattern of incidence and development of the disease of ginger plant was then examined in continuous indoor cultivation for immature rhizome production4). Further studies have demonstrated that naturally infested soils near plastic houses may be involved in primary infection to ginger cultivation inside the houses5). This paper deals with the distribution of P. zingiberum in soils in and around the region of outdoor rotation cultivation for mature rhizome production in Miyazu city, Kyoto prefecture, Japan, and discusses a survival of this fungus in the ginger-growing area after a relatively shorter period of rotation cropping. A part of this work was presented at the meeting of the Kansai division, Phytopathological Society of Japan6). In Nakamura and Waki areas (See Fig. 1), ginger has been cultivated since late in 19th century. Ginger cultivation has increased in Shingu, Chishi and Yawara areas after the middle of 20th century by the promotion project for developing upland field cropping. Mixed cultivation of ginger and Yam (Dioscorea japonica Thunb.) is commonly seen in these regions although this system is rarely carried in Japan. The percentage of rhizome rot of ginger plant caused by the pathogen ranged from 5 to 30 during the survey in these areas. Field soil samples were collected by the method reported previously4) from the place where ginger seed pieces are expected to be planted. Mountainous districts around ginger-growing area where ginger has never been cultivated were also investigated. They have granitic dry brown forest soils7) and