Rootstock effects on the reaction of cypress to Seiridium cardinale bark canker disease.

Reciprocal grafting was carried out on Cupressus sempervirens resistant or susceptible clones previously grown from self-rooting. When the scions were 10 mm in diameter, they were inoculated and then infection by Seiridium cardinale was observed over 2 years. The rootstock had no noticeable effect on the basic behaviour of scions. The susceptible clones died while resistant clones survived However, the reactions of resistant clones to disease and scarring varied according to the rootstock clone. Resistance was correlated with tree growth, namely to the vigour conferred to scions by the rootstock. Resistance and growth, both induced by meristematic activity show a good linear regression. It would be interesting to select vigorous rootstock clones, in order to increase resistance or tolerance as a consequence of an earlier compartmentalization and decrease the heterogeneity resulting from grafting on seedlings at random. Such a progress would require a good knowledge of self-rooting techniques.