Abstract
The relation between the swelling of graft union and trunk girth or shear strength at graft union was investigated. The trunk girth of trees grafted onto JM7 was largest and the coefficient of variance among scion cultivars and among tested trees was small. Meanwhile, the trunk girth of trees grafted onto JM5 was the smallest and varied greatly. All graft combinations showed overgrowth of rootstock, and the combinations on JM2 tended to show less overgrowth of rootstock than that on other rootstock cultivars. Swelling was small in JM2 and JM7 and the coefficient of variance among scion cultivars was also small. Although the degree of swelling of trees grafted onto JM1, JM5 and JM8 varied greatly among graft combinations, the degree of swelling did not necessarily affect the trunk girth. The shear strength at graft union was highest in trees grafted onto JM2 and low in that grafted onto JM1 and JM5. These results clarified that graft combinations having larger swelling of graft union had lower shear strength, which made it easy for the tree to break at the graft union, although swelling of graft union did not always make the tree weak.
