Plant Propogation and Nursery Management

Stages of Bud/Graft Union Formation

There are four stages viz; pre-callus, callus formation of cambial bridge and healing of the bud union.

Pre-callus stage: It lasts for 5 to 8 days, after budding or grafting operation. During this stage, there is no sign of callus formation and scion falls if the wrapping material is removed.
Callus formation: After 5th to 8th day, the callus formation may take place in the bud/graft union. The process of callus formation is fast in firmly attached stock and scion. The initiation of callus formation takes place either from stock, scion or both. Usually, living cells of recently formed xylem and phloem play active role in the callus formation.
Formation of cambial bridges: The paranchymatous cells of the callus form a cambial bridge within 12 to15 days after budding. After the formation of cambial bridge, de-differentiation of secondary xylem and phloem takes place after 36-48 days of budding. Afterwards, the partial movement of stock to scion takes place. The bud union is completed within 6-7 weeks, if conditions are favourable.
Healing of the bud/graft union: After de-differentiation of secondary xylem and phloem of both stock and scion, there is formation of many new xylem and phloem cells after 6-8 months of budding or grafting. The callus unites completely with the scion pith and the union heals completely. In general, better contact and alignment of the cambial cells of stock and scion helps in development and proliferation of callus.