Effects of Shade Treatments on Vine Growth and Production of Tubers and Propagules of Japanese Yam (Dioscorea Japonica) in Tea Gardens

Tea gardens have specific light and shade conditions because the tea trees are densely planted, with only a narrow space between rows. Therefore, in practice, the variety of weeds that grow in tea gardens is limited. Japanese yam (Dioscorea japonica) is a serious weed that grows under shade conditions in tea gardens. This study investigated the effects of shade conditions on the growth of Japanese yam vines and the production of tubers and propagules. We observed that shading did not limit the growth of Japanese yam vines that emerged from the tubers, and even under strong shading conditions of 0% relative irradiance, vines of Japanese yam were able to growth more than 2 m. Furthermore, although the formation of new tubers and production of propagules were limited under strong shading conditions, they were not limited under 50% relative irradiance. Since the relative irradiance at 10 cm below the canopy after harvesting in this study was 65 %, there is concern that Japanese yam produces propagules even under the canopy of tea plants. On the other hand, the plants from tubers emerged and reached the canopy of tea trees earlier than those from propagules. This suggests that differences in emergence time and growth speed of vines between plants from tubers and propagules may be a factor in prolonging the duration of weeding Japanese yams.