Ulmus 'Christine Buisman'

Ulmus minor
'Christine Buisman' Amsteldijk, Amsterdam.
Species	Ulmus minor
Cultivar	'Christine Buisman'
Origin	Netherlands

The Field Elm cultivar Ulmus minor 'Christine Buisman' was the first cultivar released by the Dutch elm breeding programme, initiated in response to the less virulent form of Dutch elm disease (DED), Ophiostoma ulmi, which afflicted Europe's elms after the First World War. 'Christine Buisman' was selected from a batch of 390 seedlings grown from seed collected in the Parque de la Quinta de la Fuente del Berro, Madrid, by Mrs Van Eeghen, a friend of elm researcher Johanna Westerdijk, in 1929 and named for the elm disease researcher Christine Buisman. Originally identified as Ulmus foliacea (syn. U. minor), it was later treated as Ulmus × hollandica by Melville. However, more recent research in Belgium using DNA markers has reaffirmed 'Christine Buisman' as a clone of U. minor.

Originally identified as clone No. '24', it showed no symptoms of DED after several artificial inoculations. In later years, minor symptoms were detected on both the motherplant and grafted descendants, but these were considered too insignificant to delay its release to commerce as Ulmus 'Christine Buisman' in 1937.

The tree was deemed to have 'no outstanding ornamental characteristics', being 'broadly pyramidal, but 'irregular' in shape, notably the habit of one or two of the main branches initially growing out almost horizontally for about 1 m before curving upwards to the vertical, while outer branches can be long and pendulous. Other authorities have been more generous, noting its straight trunk and relatively short and slender branches forming a small crown. The twigs are dark brown, strigose pubescent at first, becoming smooth. The alternate buds are ovoid, covered with a grey pubescence. The leaves are 7.0 cm long by 4.5 cm wide, very oblique at the base, with doubly serrate margins, smooth and dark green above, lighter below, and with prominent parallel veins covered with coarse white hair. The petiole is 10 mm long.

'Christine Buisman' was found to be highly resistant to DED, but prone to some strains of Coral Spot fungus Nectria cinnabarina as it lacked resistance mechanisms. In the USA, the clone also proved highly resistant to elm yellows, but very susceptible to Japanese beetles.