Dutch Elm Committee
U. “Christine Buisman” began life as Clone 24, one of a batch of several hundred seedlings grown in Holland from U. minor seed collected in 1929 in Madrid. The tree was regarded for many years as an U. x hollandica, following Melville, but genetic testing in Belgium subsequently confirmed it to be U. minor. The tree was released in 1937, named in memory of the Dutch phytopathologist Christine Buisman, who had first proved the connection between Graphium ulmi (now Ophiostoma ulmi) and elm disease before her very early death in 1936.
“Christine Buisman” was selected for resistance to the relatively non-aggressive strain of Ophiostoma responsible for the first major European outbreak of elm disease. The view later developed, perhaps as a not unreasonable hunch, that it was not satisfactorily resistant to the highly aggressive O. novo-ulmi which tore through Europe’s elms from the 1960s onwards.
This view is now being re-evaluated. There are indications that Christine Buisman is in fact highly resistant. Tests carried out by Green, Guries and Smalley (1982) in Wisconsin for volume of discoloured wood (VOD) after the inoculation of very young trees in vitro gave figures of 2.2 for the benchmark-resistant Sapporo Autumn Gold, and only 0.6 for Christine Buisman. Some have doubts about the validity of this technique, but the following year’s testing, in which Christine Buisman was not included, gave VOD of 87.2 for English Elm. That figure is very much in line with what would be expected from effective inoculation by the traditional method using a highly aggressive isolate. Meanwhile, Eric Collin reports that Christine Buisman performed better than any other cultivar of U. minor in French testing, and outperformed at least one modern Spanish clone in its ability to recover in the years subsequent to inoculation.
Unfortunately, concerns remain about Christine Buisman’s susceptibility to Nectria cinnabarina (Coral Spot fungus). Although there are reports from some that this is not in fact a problem, at least in mature trees in the Netherlands, there is no smoke without fire. It has been suggested that the cause of the vulnerability is the tendency of wounds to bleed sap for longer than is usual, so that they more readily become infected.
The distinguishing features of Christine Buisman are deeply furrowed bark and a light, open and disordered crown typically formed by three or four major branches departing at upright angles from comparatively low down the trunk. Some low branches leave the trunk at far more obtuse angles, but often change direction abruptly after about a metre’s growth. Branch breakage is frequent, whether because of poor resistance to wind or perhaps girdling by Coral Spot. Leaves are strongly basally asymmetric, broadly oval, mid-green and leathery. Well-grown trees have something of hornbeam or small-leaved lime about them. Trees in less favoured spots seem more like rather compromised birches, recalling Plot Elm but sadly not much of its charm. Maximum height appears to be about 25 metres.
Notwithstanding the renewal of interest in Christine Buisman and the re-examination of its actual disease resistance, the tree seems of limited landscape use. It can develop well when open grown with shelter, but a good many other species would ultimately be more impressive. It may be more suited in aesthetic terms to closer spacing, where repetition might give the eye the key to its rather wayward form which is difficult to assimilate when seen in isolation. Dead wood and breakage in reality would confine it to rustic or woodland settings where those problems would not matter too much.
The gradual rehabilitation of Christine Buisman is welcome, as is any addition to the diversity of resistant elms. However, as matters currently appear, there are better elms available.