Abstract
Young, one-week-old seedlings of‘Shishiomaru (Notocactus submammulosus var. pampeanus) and rooted cuttings of‘Sankakuchu’(Hylocereus trigonus) were used as scions and stocks respectively.
The basal end of the scion and the top end of the stock were cut transversely, and the scion was placed onto the stock in such a manner that the cut ends of vascular bundles of both graft components were in close proximity (1), or they were stepped 1mm or 3mm apart sideways from each other (2).
(1) Graft union in case of the close proximity grafting method.
Callus cells were observed in the graft region 2 to 4 days after grafting. Callus cells derived from both graft components soon adhered and developed into callus. Procambial cells were first observed in the callus on the 8 to 10th day of grafting. The procambial cells continued to increase in number, and finally connected with the existing cambium of the graft components rectilineally.
By the 12th day of grafting, the procambial cells differentiated into vessel members, sieve tubes and cambial cells. The strands of these differentiated cells developed into new vascular bundles“Connecting vascular bundles”, and all of the grafts completed graft union.
(2) Graft union in the stepped case.
Even when both vascular bundles of scion and stock had not been placed in direct contact with each other, some of the grafts completed vascular connection after passing through the same process as in the former case. However, most of the grafts displayed no further development beyond either of the following stages. a) Cell adhesion was completed, but no cyto-differentiation was observed in the callus till the end of the experiment. b) Certain cells of callus which were oriented just under the vascular cut end of the scion differentiated into a meristematic cell nodule. The nodule did not develop further, so the vascular connection could not be completed.
In cases where vascular cut ends of graft components were stepped 1mm and 3mm transversely away from each other, the rates of vascular connected grafts to all survival grafts were no more than 30% and 10% respectively.
