Touchdown treatment of root trainer shortened the formation time of root mass of rubber tree seedlings

Root trainers are increasingly being used to avoid root coiling and distortion and lack of wind tolerance after field transplanting, when compared to the conventional polybag planting system. Root tips grew out of root trainer forming an intact root mass and then could be transplanted to the field with high survival rate. While the influence of spatial position on root tips growing out of budded stump root trainer was still unknown at nursery stage. Therefore, the bottoms of root trainer were placed in aboveground(20cm, current practice), touchdown(0cm) and underground(15cm) for budded stump nursery, respectively. Clone CATAS 7-20-59 budded stump was raised in root trainer and percentage of plants with root tips outgrowing, growth performance, leaf N content, leaf SPAD, leaf temperature and leaf surface humility were recorded, respectively. The results showed that root trainer touchdown of budded stump gave more percentage in root tips growing out of root trainer, more leaf N content(P <0.01), more leaf SPAD value (P <0.01)and higher leaf surface humility(P <0.01) when compared to underground and aboveground treatments. Thus, touchdown was the optimal choice for rubber budded stump root trainer nursery.