Rheum palmatum L.の生育および収量と栽培環境の関係−北海道内6試験地で実施した5年間の栽培試験から−

抄録

Rheum palmatum L., one of the source plants of the crude drug Rhei Rhizoma, is native to mountainous regions of China. Since R. palmatum needs four to five years from sowing to harvest, and prefers a cool climate in summer, selecting suitable locations is crucial for large-scale domestic production in Japan. Hokkaido, an important agricultural region with relatively cool temperatures, has 83,424 km² of land area surrounded by different ocean currents, which generates a variety of climatic and soil conditions. To clarify the relationships between plant growth, harvest yield of R. palmatum, and environmental factors, we produced seedlings of R. palmatum, and cultivated them with uniform planting density and fertilization at six locations in Hokkaido. The dry weights of the harvested rhizome and root after a five-year cultivation were 389.9-1,406.2 g and 915.8-1,896.6 g per plant, respectively. Both the growing duration and the location had a significant （p<0.0001） effect on the dry weights of the harvested rhizome and root, and an interaction effect was also found between them （p<0.01）. A strong and positive correlation （r=0.9504） was found between the dry weight of the above-ground part and that of the harvested rhizome and root of the plants, which indicates that above-ground growth affects the underground harvest yield. Considering actual climatic and soil data, we conclude that the following factors are advantageous for growing R. palmatum: as few days as possible with a mean temperature over 25°C; moderate wind strength; no frozen ground in winter; high water retention but well-drained soil; and pH 6.0-7.0 humus-rich soil. In addition to searching for an optimal geographical location, using appropriate cultivation measures will also be beneficial for successful cultivation of R. palmatum.