Ulmus 'Sapporo Autumn Gold' | |
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Genus | Ulmus |
Hybrid parentage | U. davidiana var. japonica × U. pumila |
Cultivar | 'Sapporo Autumn Gold' |
Origin | seeds: Sapporo, Japan; cultivated: United States |
Ulmus 'Sapporo Autumn Gold' is one of the most commercially successful hybrid elm cultivars ever marketed, widely planted across North America and western Europe, although it has now been largely supplanted by more recent introductions. [1] Arising from a chance crossing of the Japanese elm (female parent) and Siberian elm, seed was sent in 1958 by Prof. Nobuku Takahashi and his colleagues at the Sapporo Botanical Garden of Hokkaido University, Sapporo, [2] to Eugene Smalley at the University of Wisconsin–Madison. [3] [4] The patent issued in 1975 has expired, and there are now no propagation restrictions. However, the tree has proven weak-wooded on maturity, and its popularity has waned in Europe as a consequence of susceptibility to wind damage. [5]
The tree usually forks at 1.5–2 m from the ground to produce a broad, rounded, densely foliated crown, though immature plants produce vigorous side shoots requiring assiduous pruning to maintain shape. The bark is pale grey, and longitudinally fissured to form a random lattice pattern. The leaves are narrowly elliptical, < 9 cm long by < 4.5 cm wide, with 8 mm petioles. As the name implies, the leaves turn pale yellow in autumn. [6] The perfect, apetalous wind-pollinated flowers appear in early March, followed by the seeds in April; flowering usually begins when the tree is aged six years.
'Sapporo Autumn Gold' possesses a very high resistance to Dutch elm disease; [7] [8] in trials in Italy, it sustained only 2.8% defoliation and 1.2% dieback when inoculated with unnaturally high concentrations of the fungal pathogen. [9] The cultivar also has a tolerance of Verticillium wilt. [10] The tree's foliage was adjudged 'resistant' to black spot by the Plant Diagnostic Clinic of the University of Missouri, [11] however it can be severely damaged by the elm leaf beetle ( Xanthogaleruca luteola ) in the United States [12] Several mature specimens near the Hampshire coast in England have become (2014) afflicted by Dryad's saddle fungus ( Polyporus squamosus ). [13]
In favorable conditions; notably a moist, well-drained soil, the tree can grow at a rate of almost one meter per year. Trials by the Northern Arizona University [14] found that it is not very tolerant of a hot, arid climate although its leaves sustained comparatively little scorch damage. In trials in southern England conducted by Butterfly Conservation , the tree was found to be intolerant of ponding overwinter. [13] 'Sapporo Autumn Gold' was first introduced to the UK by technology company Pitney Bowes as part of its 'Elms Across Europe' campaign. The company supplied the cultivar to schools, parks and gardens throughout the UK and Europe. [15] The tree remains popular in continental Europe but does not assimilate well in the countryside. In trials in France by Cemagref at Nogent-sur-Vernisson, Loiret, it was found to grow too vigorously in hedgerow conditions, eclipsing neighbouring shrubs and consequently creating gaps. In rich soils in the Netherlands the tree grows too fast and has poor wind resistance, whereas in poor, dry conditions growth is slower and more robust.
The hybrid was included in trials [16] in Canberra, Australia started in 1988, but has not performed well there.
In the UK, 'Sapporo Autumn Gold' has been found to host the endangered white-letter hairstreak butterfly (Satyrium w-album), whose larvae feed exclusively on elm. [17]
The very first tree planted in the UK in 1979 at the Pitney Bowes technology company by Denis Thatcher (where he was a director), survived in perfect health as of 2012; [18] however Poundland now occupy the site and the land was flattened in 2013/2014. Of five trees planted in 1980 on the green in Clifton, one survives (2016), the others having suffered "catastrophic branch collapse" in storms. [19] Other notable plantings were as street trees across Bexhill-on-Sea, East Sussex in late 1980s, and as riverside trees along the Ouse in York (from Lendal Bridge to Clifton Ings). The largest specimen in Europe known to Dutch elm expert Hans M. Heybroek grows at the Istituto per la Protezione delle Piante's Monna Giovanella nursery at Antella, near Florence (see Infobox photo), but this too was badly damaged by a storm in 2020. [13]
Ulmus pumila, the Siberian elm, is a tree native to Asia. It is also known as the Asiatic elm and dwarf elm, but sometimes miscalled the 'Chinese elm'. U. pumila has been widely cultivated throughout Asia, North America, Argentina, and southern Europe, becoming naturalized in many places, notably across much of the United States.
Ulmus davidiana var. japonica, the Japanese elm, is one of the larger and more graceful Asiatic elms, endemic to much of continental northeast Asia and Japan, where it grows in swamp forest on young alluvial soils, although much of this habitat has now been lost to intensive rice cultivation.
Ulmus 'Nanguen' is a complex fourth generation Dutch hybrid cultivar raised at the Dorschkamp Research Institute for Forestry & Landscape Planning, Wageningen. Lutèce was derived from the cross 'Plantyn' ×, an ancestry comprising four field elms, a wych elm, the curious Exeter Elm ('Exoniensis'), and a frost-resistant selection of the Himalayan elm.
Ulmus 'New Horizon' is an American hybrid cultivar raised by the Wisconsin Alumni Research Foundation (WARF), from a crossing of the Japanese Elm clone W43-8 = 'Reseda' with Siberian Elm clone W426 grown from seed collected from a street tree at Yankton, South Dakota. As selection 'W917' it is a sibling of 'Rebona'. Tested in the US National Elm Trial coordinated by Colorado State University, 'New Horizon' averaged a survival rate of 74% after 10 years. 'New Horizon' was patented in the US in 1994, while in Europe, it is marketed as one of the 'Resista' elms protected under EU breeders' rights.
Ulmus 'Frontier' is an American hybrid cultivar, a United States National Arboretum introduction derived from a crossing of the European Field Elm Ulmus minor with the Chinese Elm Ulmus parvifolia in 1971. Released in 1990, the tree is a rare example of the hybridization of spring- and autumn-flowering elms. Tested in the US National Elm Trial coordinated by Colorado State University, 'Frontier' averaged a survival rate of 74% after 10 years.
The hybrid elm cultivar Ulmus × hollandica 'Pioneer' is an American clone arising from the crossing of two European species, Wych Elm U. glabra and Field Elm U. minor. Raised by the USDA station at Delaware, Ohio, in 1971, 'Pioneer' was released to commerce in 1983.
Ulmus 'Regal' is an American hybrid elm cultivar developed by the University of Wisconsin–Madison and released in 1983. 'Regal' was derived from seeds arising from the crossing of the Dutch hybrid clones 'Commelin' and '215' sent in 1960 by Hans M. Heybroek of the Dorschkamp Research Institute for Forestry & Landscape Planning, Wageningen, Netherlands.
Ulmus 'Urban' is an American hybrid elm cultivar selected from the progeny of a controlled crossing of the Siberian Elm Ulmus pumila with the Dutch clone '148' in 1958 by Toru Arisumi of the USDA at Columbus, Ohio. Clone '148' had been sent to the US from the Netherlands in 1952 by Johanna Went, leader of the elm research team at the Willie Commelin Scholten Phytopathology Laboratory in Baarn.
Ulmus 'Wanoux' is a Dutch hybrid cultivar raised at the Dorschkamp Research Institute for Forestry & Landscape Planning, Wageningen, from an open pollination of 'Plantyn'. Originally identified as clone No. 762, it was selected for assessment by the French Institut National de la Recherche Agronomique (INRA), which patented it as 'Wanoux' in 2006.
Ulmus 'Morton' is an elm cultivar cloned from a putative intraspecific hybrid planted at the Morton Arboretum in 1924, which itself originated as seed collected from a tree at the Arnold Arboretum in Massachusetts. Although this tree was originally identified as Ulmus crassifolia, it is now believed to have been a hybrid of the Japanese elm and Wilson's elm. Accolade has proven to be the most successful cultivar tested in the US National Elm Trial, averaging a survival rate of 92.5% overall.
Ulmus 'Morton Red Tip' is a hybrid cultivar raised by the Morton Arboretum from an open pollination of Ulmus 'Morton'. The tree has occasionally been reported as a hybrid of Accolade with the Siberian Elm Ulmus pumila, an error probably owing to the commercial propagation of the tree by grafting onto U. pumila rootstocks. Tested in the US National Elm Trial coordinated by Colorado State University, Danada Charm averaged a survival rate of 77.5% after 10 years.
Ulmus 'Cathedral' is a hybrid cultivar raised at University of Wisconsin–Madison patented in 1994. Arising from a chance crossing of the Japanese elm and Siberian elm, seed was sent in 1958 by Prof. Nobuku Takahashi and his colleagues at the Sapporo Botanical Garden of Hokkaido University, Sapporo, to Eugene Smalley at Wisconsin–Madison; 'Cathedral' is thus a sibling of 'Sapporo Autumn Gold'.
The American Elm cultivar Ulmus americana 'Valley Forge' was raised by the Agricultural Research Service in Maryland. The tree was released to wholesale nurseries without patent restrictions by the U. S. National Arboretum in 1995 after proving to have a high resistance to Dutch elm disease. 'Valley Forge' proved only moderately successful in the US National Elm Trial, averaging a survival rate of 66.7% overall, owing largely to environmental factors rather than susceptibility to disease.
The Japanese Elm cultivar Ulmus davidianavar.japonica 'Jacan' is a cold-resistant selection from Canada. The tree was one of a group of second-generation japonica seedlings raised in the 1970s, originally for use in the prairie regions, by the Morden Research Station, Morden, Manitoba. It was first distributed in 1977, and was later among the Asiatic elms, some sourced from Canada, donated to the UK in 1980 by the London branch of Mitsui & Co.
The Japanese elm cultivar Ulmus davidianavar.japonica 'Prospector' was originally treated as a cultivar of Wilson's elm U. wilsonianaSchneid., a species sunk as Ulmus davidiana var. japonica by Fu. A U.S. National Arboretum introduction, it was selected in 1975 from a batch of 1965 seedlings in Delaware, Ohio, and released without patent restrictions in 1990. 'Prospector' proved moderately successful in the US National Elm Trial, averaging a survival rate of 76% overall.
Ulmus 'Patriot' is a hybrid cultivar raised by the United States National Arboretum in 1980. Derived from a crossing of the American hybrid 'Urban' with the Wilson's Elm cultivar 'Prospector', 'Patriot' was released to commerce, free of patent restrictions, in 1993. Tested in the US National Elm Trial coordinated by Colorado State University, 'Patriot' averaged a survival rate of 85% after 10 years.
The field elm cultivar Ulmus minor 'Ademuz' was cloned by root cuttings from a tree assumed to be growing in or near the eponymous town 100 km north-west of Valencia, Spain. The tree was discovered in 1996 by Margarita Burón of the Escuela Técnica Superior de Ingenieros de Montes, Universidad Politėcnica de Madrid (UPM). 'Ademuz' is one of a number of U. minor clones found to have a very high resistance to Dutch Elm Disease, on a par with, if not greater than, the hybrid cultivar 'Sapporo Autumn Gold' grown as a control. In the Madrid study, the appearance of the tree was rated 4.5 / 5, the most attractive of the seven selected cultivars.
The field elm cultivar Ulmus minor 'Dehesa de Amaniel' was raised from seed collected in 1999 from a tree growing in the Dehesa de la Villa park, within the Moncloa-Aravaca district of north-west Madrid by researchers at the Escuela Técnica Superior de Ingenieros de Montes, Universidad Politėcnica de Madrid. 'Dehesa de Amaniel' is one of a number of Spanish Ulmus minor found to have a very high resistance to Dutch Elm Disease, on a par with, if not greater than, the hybrid cultivar 'Sapporo Autumn Gold'.
The Field Elm cultivar Ulmus minor 'Dehesa de la Villa' was cloned by root cuttings from a tree growing in the eponymous park within the Moncloa-Aravaca district of north-west Madrid, by researchers at the Escuela Técnica Superior de Ingenieros de Montes, Universidad Politėcnica de Madrid in 1990.
The Field Elm cultivar Ulmus minor 'Retiro' was raised from seed collected in 2002 from a tree growing in the El Retiro park, in the centre of Madrid by researchers at the Escuela Técnica Superior de Ingenieros de Montes, Universidad Politėcnica de Madrid.