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HYBRID ELMS (ULMUS SPP.): ADAPTABILITY IN PARIS AND BEHAVIOUR TOWARDS DUTCH ELM DISEASE (OPHIOSTOMA NOVO-ULMI)
When possible, the clones were propagated by cuttings.
Vegetative copies were submitted to several inoculations with fresh isolates of Ophiostoma novo-ulmi in INRA nurseries.
The rooting ability of the clones was variable.
Some rooted poorly and were then propagated by grafting with a high percentage of success.
Most of the clones exhibit good juvenile vigour.
A wide range of reaction to inoculation was found and several clones are tolerant to infection and better than the older Dutch clones (‘Dodoens’, ‘Lobel’ and ‘Plantyn’) used as standards.
In the plantation, mortality was observed in some clones.
It was mainly due to graft incompatibility and low resistance to drought with subsequent invasion by Nectria and bark beetles.
Some natural infections by O. novo-ulmi were detected.
According to the clones, recovery or mortality was observed.
Some clones fit the main requirements for amenity planting in France: rooting ability, good growth and shape and tolerance to the disease.
In addition to ‘Sapporo Gold’, already planted in France, it becomes realistic to foresee the culture of some new clones for amenity purposes.