The Formation of Callus at the Graft Interface in Sitka Spruce

Abstract

The early stages of graft union formation in Sitka spruce [Picea sitchensis (Bong.) Carr] have been examined using light microscopy in order to determine the origin of callus between the scion and rootstock. All living, undamaged cells exposed to the environment by the process of stern preparation for grafting have been found to be capable of producing callus. The first cells to respond in this way, within two days of grafting, were the epithelial cells of severed resin canals and ray parenchyma exposed where the phloem and xylem of the seion and rootstock were cut through. Fusiform cambium cells near to the graft interface dedifferentiated into callus much later (12-15 days after grafting) by becoming rounded in transverse seetion, and by dividing horizontally to produce a large number of smaller callus cells. Most callus was produced by cells external to the cambium by dedifferentiation and proliferation of ray cells, and of parenchyma associated with severed needle traces.

Some Factors Involved in the Success of Side Veneer Grafting of Pinus engelmannii Carr.

“…The effect of cambium has been reported in different graft survival studies [26,36,52]. It has been reported that the meristematic activity of the cambium between the scion and the rootstock is an important factor in the successful establishment of the graft [16,17]. In the present study, the size of the surface area of the scions and the rootstock plants showed a similarity of 97%; however, the cambium of the scions is irregularly shaped, in contrast to the almost circular shape of the cambium of the rootstock plants (Figure 3).…”

“…Carr. [16], and in the genus Rhododendron L. [17]. Three important stages of graft development are recognized in this process: callus formation, cambial differentiation, and cambial continuity (vascular tissue formation) [18].…”