Plant Propogation and Nursery Management

Introduction

The inability of two different plant parts grafted or budded together, to produce a successful union and to develop into a composite plant is termed as ‘graft incompatibility’ (Fig.10.1). Graft failure can be caused by anatomical mismatching, poor craftsmanship, adverse environmental conditions, diseases and graft incompatibility. Graft incompatibility occurs because of following reasons:

• Adverse physiological responses between the grafting partners
• Virus or phytoplasma transmission
• Anatomical abnormalities of vascular tissue in the callus bridge.



Figure 10.1 Graft incompatibility

External symptoms of graft incompatibility
Graft union malformation resulting from incompatibility can usually be correlated with certain external symptoms. The following symptoms have been associated with incompatible graft combination:

I. Failure to form a successful graft or bud union in a high percentage of cases.
II. Yellowing of foliage in the latter part of the growing season, followed by an early defoliation, decline in vegetative growth, appearance of shoot die-back, and general ill health of the tree
III. Premature death of the trees, which may live for only a year or two in the nursery
IV. Marked difference in growth rate of the scion and rootstock
V. Over growth at, above or below the graft union
VI. Suckering of rootstock
VII. Breakdown of graft union cleanly