| Ulmus hybrid | |
|---|---|
Ulmus 'Patriot' at the USDA Plant Introduction Station, Glenn Dale, MD. |
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| Details | |
| Hybrid parentage | 'Urban' × 'Prospector' |
| Cultivar | 'Patriot' |
| Origin | USA |
The hybrid elm cultivar 'Patriot' [2] is a United States National Arboretum introduction derived in 1980 from a crossing of the American hybrid 'Urban' with the Wilson's Elm (now treated as Japanese Elm U. davidiana var. japonica) cultivar 'Prospector' and released to commerce, free of patent restrictions, in 1993. [3]
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The tree develops an upsweeping crown, ultimately adopting a narrow vase-shape. The leaves are slightly obovate, with doubly serrate margins and typically acuminate apices; they are of an average size for the genus, < 10 cm long by 7.5 cm broad, glossy dark green turning yellow in autumn.[1] The perfect, apetalous wind-pollinated flowers appear in March. Flowering usually begins when the tree is aged six years.
Growth is vigorous, specimens in the USDA trials reaching a height of over 13 m (43 ft) and a spread of nearly 8 m (25 ft) after only 13 years. In an assessment at U C Davis as part of the National Elm Trial, 'Patriot' increased in height by almost 1.5 m and d.b.h. by 2.5 cm per annum.[2] [4]
'Patriot' has a very high resistance to Dutch elm disease (DED), exhibiting 100% survival seven years after DED inoculation. Tolerance of the elm leaf beetle Xanthogaleruca luteola is generally regarded as only moderate, although specimens grown at the aforementioned trials at U C Davis were among those cultivars least affected;[2] resistance to Japanese Beetle is poor.[3] When grown for 11 years among hundreds of infected American Elms in Delaware, Ohio, the clone showed no signs of susceptibility to Elm Yellows.[5].[4]
The tree performs best in moist but well-drained soils, but will tolerate alkaline ground and salts [6]. In trials by Northern Arizona University in the hot and arid climate of Holbrook, eastern Arizona [7], it did not perform as well as the likes of 'Frontier' and 'Regal', but not as badly as others such as 'New Horizon' and 'Sapporo Autumn Gold'. In the cooler climes of Minnesota, it was recommended for every forester's 'Top Ten' list of urban trees.[5] 'Patriot' is extremely cold hardy; in artificial freezing tests at the Morton Arboretum [6] the LT50 (temp. at which 50% of tissues die) was found to be - 38 °C. In trials in southern England, 'Patriot' also proved resistant to ponding, surviving several months' inundation to a depth of 20 cm overwinter at a low-lying coastal site.
Propagation from softwood cuttings is reputedly easy; taken in mid-May, treated with a 3000 ppm IBA rooting hormone and placed under mist, < 95 % should root in less than four weeks. However, commercial propagation is commonly by grafting onto a Siberian Elm Ulmus pumila rootstock. As height increase can rapidly outstrip stem width, lopping the stem above a leaf node and vertically training the new leader is recommended to make a more stable structure.
The tree is currently being evaluated in the National Elm Trial [8] coordinated by Colorado State University. 'Patriot' was introduced to the UK [7] and the Netherlands in 2008, but will not be in commerce until 2012. Several small specimens were also introduced to Italy in 2011 by the Istituto per la Protezione delle Piante, Florence.