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    Author(s): Alberto Santini; Francesco Pecori; Luisa Ghelardini
    Date: 2012
    Source: In: Sniezko, Richard A.; Yanchuk, Alvin D.; Kliejunas, John T.; Palmieri, Katharine M.; Alexander, Janice M.; Frankel, Susan J., tech. coords. Proceedings of the fourth international workshop on the genetics of host-parasite interactions in forestry: Disease and insect resistance in forest trees. Gen. Tech. Rep. PSW-GTR-240. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department of Agriculture. pp. 326-335
    Publication Series: General Technical Report (GTR)
    Station: Pacific Southwest Research Station
    PDF: View PDF  (960.81 KB)

    Description

    In the 20th century, elms across Europe and North America were devastated by two pandemics of Dutch elm disease (DED), caused by the introduction of two fungal pathogens: Ophiostoma ulmi, followed by O. novo-ulmi. At the end of 1920s, research into a resistance to DED began in Europe and then in the United States. No worthwhile resistance was ever found within the native European or American elms. The Dutch team resorted to hybridizing European elms, from which the first cultivars exhibiting a resistance were obtained during the 1930s, but these clones did not have sufficient resistance to the second pandemic. It was the use of Asian species, with their higher resistance to DED, which accelerated progress on both sides of the Atlantic. Eventually a number of second-generation resistant clones derived from hybrids of native and Asian species were released to commerce.

    Many efforts were dedicated to control the disease, such as the elm breeding program started in Italy in 1975 by the Institute of Plant Protection (IPP). This program was born of a conviction that the Mediterranean environment would demand its own selections. In Italy, the favorable adaptation of species such as the Siberian elm (U. pumila L.), and the unsuitability of the Dutch selections to the more arid regions, encouraged the wider assessment of the Asian elms. The purpose was twofold: to examine more fully adaptability to the climate and to broaden the genetic base of the native species.

    Selection of superior genotypes ostensibly reduces genetic variation in cultivated species. However, when breeding is designed for obtaining plants adapted to different environmental conditions and for different uses, the outcome can actually result in increased variation. The case of elm breeding for resistance to DED is paradigmatic. The uses of elm are in fact manifold. For this reason, breeding for resistance is not enough. Many other features are required, including fast growth, and aesthetic factors such as attractive shape and foliage. To satisfy all these needs, whilst maintaining enough genetic variability to buffer the effects of climate change and possible arrival of new strains of DED or other diseases, it was decided to undertake a fundamental broadening of genetic resources, or, as it will be called later, "incorporation." A base of native elms with enough good characters to act as parents was hybridized with those disease-resistant Asian species able to acclimatize.

    This program has produced DED-resistant elm varieties able to adapt to arid conditions, yet endowed with some remarkable ornamental characteristics. Five of these clones have already been patented and released to commerce: 'San Zanobi,' 'Plinio,' 'Arno,' 'Fiorente,' and, more recently, 'Morfeo.' 'Morfeo' is a robust, attractive tree that is extremely resistant to DED. It is also fast-growing and tolerant of both summer drought and winter floods, thus proving as well adapted to the climate of northwestern Europe as that of the Mediterranean. Indeed, following trials in England, 'Morfeo' is now considered potentially the most important cultivar in the conservation of several invertebrates there endangered by the consequences of DED.

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    Citation

    Santini, Alberto; Pecori, Francesco; Ghelardini, Luisa. 2012. The Italian elm breeding program for Dutch elm disease resistance. In: Sniezko, Richard A.; Yanchuk, Alvin D.; Kliejunas, John T.; Palmieri, Katharine M.; Alexander, Janice M.; Frankel, Susan J., tech. coords. Proceedings of the fourth international workshop on the genetics of host-parasite interactions in forestry: Disease and insect resistance in forest trees. Gen. Tech. Rep. PSW-GTR-240. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department of Agriculture. pp. 326-335.

    Keywords

    Dutch elm disease, Ophiostoma, Italian elm breeding program

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