Graft formation in Kalanchoe blossfeldiana

Three phases of cohesion between the stock and scion are observable during the formation of compatible autografts in Kalanchoe blossfeldiana. The first phase of cohesion: (a) lasts four to five days, (b) is correlated with an accumulation of dictyosomes along the graft interface and with callus proliferation in the stock and scion, and (c) is characterized by a tensile strength of approximately 5 g breaking weight (BW) mm^-2 graft area (GA) by 5 d after grafting. The second phase of cohesion lasts from days 5-20 after grafting and is correlated with (a) an interdigitation of callus cells at the graft interface, (b) the differentiation of vascular tissue across the graft interface, and (c) a 20-fold increase in the tensile strength of the graft union to approximately 100 g BW mm^-2 GA by 20 d after grafting. This cohesive strength is comparable to that of an intact, non-grafted stem. The third phase of cohesion is characterized by a levelling off of the increase in tensile strength of the graft union with time at approximately 125 g BW mm^-2 GA. The results of this study are discussed relative to other structural studies of and proposed mechanisms for graft development.