Heredity 74 (1995) 39—47 Received 10 February 1994 Genetical Society of Great Britain and the implications for the conservation of its biodiver- SOKAL, R. R. AND ODEN, N. L. 1978a. Spatial autocorrelation in biology. 1. Methodology. Biol. J. Linn. Soc., 10, 199—228. lsoenzymes as an aid to clarify the taxonomy SOKAL, R. R. AND ODEN, N. L. 1978b. Spatial autocorrelation in biology. 2. Some biological implications and four applica- of French elms LEGENDRE, P. AND FORTIN,tions M. of evolutionary i. 1989. and Spatial ecological interest. pattern Biol. J.and Linn. SOKAL R. R. AND WARTENBERG. D. n. 1983. A test of spatial auto- N. MACHON*, M. LEFRANC, I. BILGERI AND J.-P. HENRY correlation analysis using an isolation-by-distance model. *Laboratofre d'Evo/ution et de Systématique des Végétaux, Bet. 362, Université Paris-Sud-CNRS (UR.A. 1492), F-91405 Orsay Cedex and tCEMAGREF (French Institute of Agricultural and Environmental Engineering Research), Domaine des Barres, F-45290 Nogent-sur-Vernisson, France MAYR, E. 1970. Populations, Species,zygosity and patchand structure Evolution. in plant populations Harvard as a Isoenzymeswere used to assess the genetic variability of the three French species of elms: Ulmus Tasmanian NRCP Technical Report No.6. Department of laevis Pall, from section Blepharocarpus, Ulmus minor Mill. and Ulmus glabra Huds. from section Parks Wildlife and Heritage,Spatial Tasmania patterns of chloroplast and Department DNA and cone morpho- of Ulmus. Three main results were obtained. The first was that these species are segmental tetraploids, within populations of a Pinus i.e. they behave as tetraploids for part of the genome and as diploids for the rest of it. Secondly, we ODEN, N. L. 1984. Assessingbanksiana—Pinus the significance contorta sympatric of region. a spatial Am. Nat., found that there exists a large amount of polymorphism in the French species of elm. Thirdly, WASER, N. M. 1987. Spatial genetic heterogeneity in a popula- Ulmus laevis produces isozyme patterns which differentiate it from species in section Ulmus. These PERRY, D. J. AND KNOWLES,tion P. of 1991. the montane Spatial perennial genetic plant Delphinium structure nelsonii. results contribute to a clarification of the taxonomy of elms. READ, 1. AND HILL, R. s. 1988.WRIGHT, The S.dynamics 1965. The interpretation of some of population rainforest structure Keywords:genetic diversity,isoenzymes, polymorphism, taxonomy of elms, tetraploidy, Ulmus sp. WRIGHT, 5. 1978. Evolution and the Genetics of Populations Vol. 4, Variability Within and Among Natural Populations. (U. x hollandica Mill. sensu lato), have been extensively species, Maclura pomifera (Moraceae) and Gleditsia Introduction propagated by humans since prehistoric times XIE, C. Y. AND KNOWLES, i'. 1991. Spatial genetic substructure triacanthos (Leguminosae). Heredity, 67, 357—364. Thetaxonomy of European elms is notoriously diffi- (Richens, 1983). Cuttings were sometimes transported LATFA, R. CL 1989.within Spatial natural populations autocorrelation of jack pines (Pinus banksiana). of cult. There are many reasons for this situation. Firstly, over large distances resulting in an intricate geographi- genotypes in populations of impatiens pallida and cal pattern of many distinctive interlocked clones of ZALUCKI, M. P., HUGHES, J. M. AND CARTER, P. A. 1987. Genetic there are very few floral characters which discriminate sHAPcorr, A. 1994. The populationvariation in geneticsDanau.s plexippus and L.: Habitatecology selection of or between taxa. The fruits provide some useful traits to varying size (see Richens, 1983 for a review of English the temperate rainforest treedifferences Atherosperma in activity times? Heredity, moschatum 59, 213—221. discriminate between major groups but they are not populations). sufficient for more detailed discrimination. Also they Finally, botanists have burdened themselves with the are available for a short time only on mature trees and rules of botanical nomenclature and the problems in they are not found in many herbarium collections. applying them to recalcitrant material such as elm. Therefore, vegetative characters such as leaf shape, More than 70 binomial names have been used for bark and cork features, and tree habit, are the main European elms, and there are many more intraspecific characters used to discriminate between the taxa (e.g. combinations. The same binomial is often used with a Jobling & Mitchell, 1974). These traits are very plastic; different meaning from one author to another. they vary even on a single tree during an individual life- In modern times, European botanists have used time depending on age and environmental conditions. various taxonomic systems which lie between two Herbarium samples do not supply information on the extremes based on studies of English populations. One shape of the tree. Moreover, these traits can only be extreme position assumes the existence of many used with mature and nonpollarded trees (which, with species and interspecific hybrids as described by Dutch Elm disease, are becoming scarce). Juvenile Melville (1975, 1978). For British elms of the section trees, which are in the majority in many populations, Ulmus, he assumed the existence of six species, some are very difficult to classify. 'almost hybridized out of existence', and 11 inter- In addition to these technical difficulties, there has specific hybrids, involving up to four species. He been extensive hybridization between taxa, which carried out less investigation into continental Euro- followed a phase of differentiation in several presumed pean elms but recognized another species in the east- refugia during the last glacial period (Richens, 1983, ern Mediterranean region (U. canescens Melville). chap. 3). Moreover, some elms, especially field elms According to Richens (1983, p. 86), 'If the same (Ulmus minor Mill. sensu Richens) and hybrid elms approach were applied to the European elms as a whole, it would be difficult, without inconsistency of *Correspondence treatment, to get away with less than 20 species'. At the 39 40 N. MACHON ETAL. other extreme, Richens (1968) pooled all the European Materials and methods elms of the section Ulmus in two species: U glabra Huds. and U minor Mill. sensu latissimo, with one Inthe framework of the programme led by the interspecific hybrid (U x hollandicaMill. s. 1.). CEMAGREF (French Institute of Agricultural and Discussions concerning these two taxonomic treat- Environmental Engineering Research), aimed at pre- ments have been presented by Melville (1978) and serving the genetic diversity of French elms, a thorough Richens (1980). survey was carried out in five regions (Table 1) to list For 50 years, very few studies have been concerned every mature and healthy elm tree (diameter of the with the variability of French elm populations. Richens trunk more than 15 cm and height more than 1.3 m). & Jeffers (1975, 1978) made a biometrical survey of Most trees were cloned by cuttings which were planted elms of northern France. A taxonomic revision of elms in a conservatory plantation at Nogent-sur-Vernisson in Anjou was carried out by Corillion (1991), using (Loiret, France) comprising about 270 trees in 1993. classical taxonomic methods; with a narrow-species The plant material used for our study consisted of concept, he assumed five species in this region (inclu- samples taken from all the trees in the conservatory ding the U laevis Pallas species, which is quite different plantation and other samples taken from other trees in from the others and which belongs to the section their natural environment. Field determinations of Blepharocarpus Dumort.). In recent times, most French species were made by the persons who collected the Floras and catalogues (e.g. Guinochet & Vilmorin, samples. We worked on 298 trees: 151 U minor Mill., 1973; Grenier, 1992; Kerguelen, 1993) merely follow 48 U. glabra Huds., 74 U. laevis Pall. and 25 trees the taxonomic treatment of Tutin in Flora Europaea which have been recorded as putative hybrids between (1st edn, 1964), assuming four species in western U minor and U glabra, (U. X hollandica Mill. sensu Europe: U laevis Pall. from the section Blepharocar- lato). Additionally, seedlings of offspring of three U pus, and U glabra Huds., U minor Mill. and U procera Salisb. (=Uminor var. vulgaris (Aiton) Richens, see Richens, 1968) from the section Ulmus; but there is considerable disagreement and problems Table 1 Sample sizes (N) for each region and species of elm concerning the presence and frequency of this last species in France. Regions N Species N During the years 1970—80, the second epidemic of Dutch elm disease destroyed most mature trees in Nord-pas de Calais 26 U minor 20 France as in other countries. The French Ministry for U glabra 0 Agriculture has initiated a programme for the conser- U. laevis 6 U. X vation of genetic resources including the search for and hollandica 0 collection of healthy French elms and research. In the lie de France 30 U minor 18 framework of this programme, we studied the genetic U glabra 2 diversity of the elm collection. In this article, we U laevis 8 present results obtained on allozyme diversity and we U Xhollandica 2 discuss implications for the systematics of French elms. Normandie 65 U minor 43 Isoenzymatic data have been previously reported by Uglabra 2 Pearce & Richens (1977) and Richens & Pearce(1984) U laevis 0 for European elms, with only one system, and by U Xhollandica 20 Sherman-Broyles et a!. (1992) for the American Poitou 64 U minor 59 species U crassifolia Nutt. Wiegrefe (1992) and Uglabra 0 Wiegrefe eta!. (1993) used molecular tools to study the U laevis 5 genetic diversity of the genus Ulmus. In this paper, the U. Xhollandica 0 taxonomic treatment of Richens is adopted (assuming East of France 113 U minor 11 four taxa: U laevis, U glabra, U minor and the hybrids Uglabra 44 between U glabra and U minor U. X hollandica) U laevis 55 because our vegetative material, consisting mainly of U.