Submitted to: Genome
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/12/2008
Publication Date: 7/1/2008
Citation: Zalapa, J.E., Brunet, J., Guries, R.P. 2008. Genetic diversity and relationships among Dutch elm disease tolerant Ulmus pumila L. accessions from China. Genome. 51(7):492-500. Interpretive Summary: Elms are widely distributed in the north temperate regions of the world and have been extensively used in urban and suburban landscapes because of their natural beauty and their ability to withstand numerous environmental stresses. However, in the 20th century, two Dutch elm disease (DED) pandemics decimated European and North American elm species. These pandemics triggered the search for sources of DED-resistance in susceptible elm species. No European or North American native species exist that exhibit sufficiently high levels of DED-tolerance to be immediately useful in breeding programs. However, most breeding programs have been successful in increasing DED-tolerance through hybridization with Asian elms such as Siberian elm, Ulmus pumila. The objective of this research was to determine the extent of genetic diversity and to assess the degree of genetic relatedness (using microsatellite loci) among 53 U. pumila accessions from the People’s Republic of China maintained at the University of Wisconsin-Madison (UW) Elm Arboretum. We found significant genetic variation at 15 microsatellite loci, and these 15 loci could easily identify each of our 53 accessions. In addition, despite the wind-dispersal of seeds and pollen for this plant species, we detected some geographic differentiation among regions of China which suggests that it is important to sample over diverse geographical areas in order to to capture the entire range of genetic diversity in U. pumila germplasm. This research provides useful information needed for DNA-based fingerprinting, breeding, ecological studies, and diversity assessment of elm germplasm.
Technical Abstract: Elm breeding programs worldwide have relied heavily on Asian elm germplasm, particularly U. pumila, for the breeding of Dutch elm disease tolerant cultivars. However, the extent and patterning of genetic variation in Asian elm species is unknown. Therefore, the objective of this research was to determine the extent of genetic diversity among 53 U. pumila accessions collected throughout the People’s Republic of China. Using 23 microsatellite loci recently developed in the genus Ulmus, a total of 94 alleles were identified in 15 polymorphic and four monomorphic loci. The average number of alleles per locus was 4.9 with a range of 2 -11 alleles. Gene diversity estimates per locus ranged from 0.08 to 0.87, and the non-exclusionary probability for the 15 polymorphic loci combined was 0.7 x 10 -9. Nineteen region-specific alleles were identified, and regional gene diversity estimates were moderately high (0.48 - 0.57). The genetic relationships among accessions and regions were estimated by the unweighted pair-group method with arithmetic averaging and principal coordinate analysis. Both techniques clearly discriminated all accessions and regions, and provided some evidence of genetic differentiation among regions, mainly consistent with the accession’s geographical origin. Two microsatellite markers (UR175 + UR123 or Ulm-3) were sufficient to discriminate up to 99.7% of the accessions studied. Accessions from Xinjiang, Shanxi, and Henan-2 were genetically the most distinct among all accessions in the collection. This research provides useful information needed for DNA-based fingerprinting, breeding, ecological studies, and diversity assessment of elm germplasm.