Effects of tape covering and vine vigor on development of surface callus in girdle of grapevine
The effects of vine vigor (shoot growth) and covering the girdle surface with plastic tape on the development of a surface callus (SC) in the girdle of grapevine were studied by histological observation. The SC was formed in a tape-covering treatment but was not formed unless the girdle surface was covered with plastic tape (exposing treatment). Histological observation revealed that in the tape-covering treatment, callus cells developed mainly from the ray parenchyma cells on the girdle surface 2 days after girdling (DAG), leading to the formation of the SC, which grew and filled the girdle portion by 7 DAG. When 16 vines were divided into three categories based on scaffold branch length, vines with 7.5 m scaffold branches developed shorter shoots with smaller internode diameters than did vines with 4.5 and 6.0 m scaffold branches. In vines with 7.5 m scaffold branches, the SC covered a smaller area of the girdle surface than in vines with 4.5 and 6.0 m scaffold branches. The length and diameter of the shoot were significantly correlated (r2 = 0.75** and 0.70**, respectively) with the ratio of the girdle area covered by the SC to the whole girdle area (SC covering ratio). These results show that the SC originates mainly from the ray parenchyma cells and that SC development is strongly affected by vine vigor. Consequently, to ensure SC development, girdling should be done by tape covering in vines with shoot diameters larger than 8 mm.
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