Effects of root pruning radius and time on yield of tuberous roots and resource allocation in a crop of Helianthus tuberosus L.

The production of tuberous roots is usually reduced by vigorous vegetative growth because of the competition for resource between the vegetative parts and reproductive organs. In this study, we conducted root pruning to examine the vigorous vegetative growth by regulating root growth, subsequently limiting vegetative growth and improving tuber yield. Compared with the control, stem, tuber, and root biomasses were all improved, whereas both flower and leaf biomasses were increased. Tuber biomass was improved by 23.48% to 50.32%, with the largest tuber biomass obtained at root cutting radius 4/5 R. With delayed root cutting time, tuber and root biomasses increased first and then decreased. The largest tuber biomass was obtained at 65 seedling stage. With a delay in root cutting time, the trend line of aboveground, underground, and total biomasses changed gradually. However, whereas underground and total biomasses showed a gradually increasing, aboveground biomass showed a decreasing. The values of stem-leaf and shoot-root ratios under different root cutting were higher than those of the control. With a delay in root cutting time, stem-leaf ratio showed an initial increase and then decreased with largest value being obtained at 80 seedling stage, whereas the largest shoot-root ratio was obtained at 115 seedling stage.