Search

Resistance breeding of the native elms against Dutch elm disease, caused by the fungus Ophiostoma novo-ulmi Brasier, is a major objective in Europe for the conservation of this tree species. More than 2,500 cuttings of 324 elm clones (Ulmus minor Miller, U. glabra Huds., U. laevis Pall., U. pumila L., U. minor x U. glabra, and U. minor x U. pumila) from eight European countries, planted in several randomized two-block designed plots were inoculated with various O. novo-ulmi strains. Crown wilting and dieback were recorded during the first year after inoculation. The wilting of the control trees varied among the plots, making the results difficult to compare, but analysis of variance (ANOVA) within each plot showed significant differences in disease severity among the clones tested, allowing study of the variation of the response among elm taxa. Results showed that 19 European inoculated clones recovered from O. novo-ulmi attack, giving hope for the reestablishment of native elms in countryside hedges and forests.

The bud-burst dates of clones of Ulmus minor, Ulmus glabra, and Ulmus laevis were recorded in the field during the spring of 2000, 2001 and 2002 at six locations in five European countries. Meteorological data were obtained from stations close to the plots. Thermal time to bud-burst (T) and chilling (C) were calculated. A relationship on the form T = a + b erC was fitted for each species. In the three species, winter rest release seems to be controlled by two opposite quantitative effects of the temperature, which interrelate according to an inverse exponential relation. Besides, the bud-burst date was found to be stable between years characterised by different winter thermal trends. These three Elm species have small chilling requirements. U. minor has chilling requirements lower than those of the other two species, in agreement with the more southern distribution. Durante las primaveras de los años 2000, 2001 y 2002 se registró en campo, en seis localidades de cinco países europeos, la fecha de apertura de yemas en un número de clones pertenecientes a Ulmus minor, Ulmus glabra y Ulmus laevis. Simultáneamente se obtuvieron datos meteorológicos en estaciones próximas a las parcelas. Se calculó los grados día (T) y el requerimiento de frío (C). Para cada especie se estableció una relación de la forma T = a + b erC. En las tres especies, la interrupción de la quiescencia parece estar controlada por dos efectos termales cuantitativos opuestos, relacionados por una exponencial inversa. Se ha encontrados que la fecha de apertura de yemas ha sido estable incluso en años con características térmicas invernales considerablemente diferentes. Los requerimientos de frío son pequeños en las tres especies de olmo. U. minor requiere fríos menores que las otras dos especies, lo que es consistente con su distribución más meridional.

International audience; The progress made in the conservation of European elm genetic resources since the 1st International Elm Conference is reviewed, and the complementarity of in situ and ex situ methods is discussed. The financial support of the European Union to RESGEN project CT96-78 has permitted to co-ordinate and rationalize the ex situ conservation of elms. The project, which involved 17 partner institutes in nine west European countries, aimed at a better evaluation, conservation and utilisation of the existing collections of native elm clones. Main achievements are: establishing a common database of about 2000 clones; characterizing over 500 clones through RAPDs and chloroplast DNA PCR-RFLPs molecular markers; completing and rationalizing the existing collections; establishing a long-term core collection of 850 clones; cryo-preserving a subset of 444 clones; and identifying clones of interest for breeding and prudent use in the reconstruction of countryside hedges. The 'Noble Hardwoods' network of the pan-European program EUFORGEN groups members representative of 31 countries, and promotes the dynamic conservation of the genetic resources of several genera of broadleaf forest trees, including Ulmus spp. Strategies for the conservation of the adaptive potential of elm resources were defined and will be disseminated among foresters and conservationists through "Guidelines" leaflets. Some countries have already started implementing conservation measures for U. laevis, associating in situ preservation and the establishment of seed orchards. Others are undertaking inventories, or acquiring genetic knowledge on target populations. At a broader scale, the 'Noble Hardwoods' network facilitates the rationalisation of the conservation populations network in a range-wide perspective.