Graft Incompatibility

• The ability of two different plants when grafted together to produce a successful union and also to develop into new successful plant is termed as ‘Compatibility’
• The inability of two different plants to do so when grafted together as often defined as ‘incompatibility’ or graft

Incompatibility

• The distinction between a compatible and incompatible graft union is not clear cut
• On one hands, stocks and scions of closely related plats unite readily and grows as one plant
• On the other hands stocks and scions of unrelated plants grafted together are likely to fail completely in union
• Much graft combination lie between these extremes viz. compatible to incompatible and therefore the characterization of incompatibility is not distinct
• Incapability may be classified as ‘ Translocated Incompatibility’ and ‘Localized incompatibility ‘.
• The former type refers those cases in which the incompatible condition cannot be overcome by insertion of a mutually compatible inter stock
• This is due to apparently some label influence moving across it
• This type involves phloem degeneration and development of a brown line or necrotic area in the bark.

The second type vig. ‘Localized incompatibility’ includes that combination in which incompatibly reaction apparently depends upon actual contact between stock and scion

• Introduction of a mutually compatible inters pick will normally overcome the incompatibility weak with discontinuous in cambium and vascular tissues
• A typical example of this kind of incompatibility is that when bartlett pear is grafted directly on quince stocks, it is incompatible.
• When old home inter stock is introduces in between that combination, the three parts combination compatible and it grows satisfactory In some cases, the stock scion combination grows in an apparently normal fashion for varying periods of times perhaps for many years and then difficulties arises
• This is called as delayed incompatibility
• A good example of the above phenomenon is the Black lien of walnut, which occur in certain Persian walnut orchards in California and France
• When cultivars of Juglans regia are grafted on seeing rootstocks of J. hindsi or Paradox rootstocks. ( J. Hindsil and regia ) the trees grows satisfactorily for 15 to 20 years or even more years of age, thereafter the trouble starts.

A thin layer of cambium and phloem and the dead tissues develop at one point and gradually extend around the tree at the graft union until the tree becomes girdled

• The vertical width of the dead area may reach 30 cm
• Such girdling may kill the plants above the graft union but the stock remains alive and sprout
• Incompatibility is manifested by over growing of scion resulting in produced distortion at the bud joint and the graft dies prematurely.