U. minor “Ademuz”
Universidad Politecnica de Madrid
“Ademuz” is a Spanish field elm (U. minor var. minor) which is among the 0.5% of native Spanish elms found by the Spanish breeding programme to exhibit significant resistance to elm disease.
U. minor var. minor is the elm of the eastern counties of England, and is known as narrow-leaved elm, smooth-leaved elm, or simply field elm. This is the species of which English Elm is a distinct variety.
Ademuz is in the final group of seven Iberian clones whose resistance is such that the Spanish programme abandoned its original plans to hybridise with Siberian Elm (U. pumila), and instead concentrated on developing these trees in their own right.
This clone’s provenance is the small town of the same name in the hinterland of Valencia. “Ademuz” (Valencian “Ademus”) comes from the Arabic “Ad-damus”, which appears to mean “impregnable”, and would describe the fortress which looms over the town. The word’s earlier origin is probably Greek, and the words “diamond” and “adamant” derive from the same source.
In inoculation trials conducted in 2008, Ademuz sustained approximately 10% damage (assumed in the absence of further detail to be wilting rather than die-back) against a score of c. 45% for the benchmark-resistant clone Sapporo Autumn Gold. There are many variables involved in inoculation trialling, but these results taken at face value are remarkable. In 2009 Ademuz scored c. 18%, and Sapporo c. 21%. Ademuz therefore appears to show a level of resistance unprecedented in European field elm.
Ademuz is not the most resistant of the group of seven U. minor with which the Spanish programme is currently working. However, it shows the best balance between resistance and ornamental value out of the seven Spanish U. minor clones.
Pending the formal introduction of this tree into the United Kingdom and the time which will be needed to observe it closely, data on growth and appearance are inevitably sparse. The Spanish programme rates Ademuz 4.5/5 in terms of ornamental value; no clone achieves a higher mark, and since English Elm was a familiar tree across much of Spain the ultimate comparator was to hand. The clone is relatively late-leafing. That is something of a disadvantage if excessive, but is typical of U. minor. The stem appears to weave, as is often the case with U. minor in East Kent. Foliage is initially bright green, but rapidly takes on a much darker colour. The foliage has a degree of gloss which brings it close to Dutch Elm (x hollandica). Leaves on young plants have very short stalks. This is subjectively considered an advantage; short stalks, by no means common in U. minor, promote an angle of leafing shared by English Elm.
Ademuz seems to be among the most significant developments in elm breeding or selection for decades. Here is an elm which is quite as “native” as any English field elm. Its mature form is currently a matter of conjecture pending further information from Madrid, but there is every reason to assume that it will be within the range of U. minor in Britain (the same cannot be said of some of the other six Madrid clones).
As long as Sapporo remains the benchmark for disease resistance, the performance of Ademuz must be rated exemplary. The one caveat is that Madrid-developed clones have tended to show more susceptibility to elm yellows in Italy’s European elm collection than those of any other provenance. Whether Ademuz shares this susceptibility is not yet known.
After a period during 2013 in which the Spanish governmental authorities seemed to lack the will and the funding to take the development of its elite U. minor clones further, progress is now being made. Further information about timescales is awaited.