Genetic and environmental factors associated with susceptibility of elms (Ulmus spp) to the elm leaf beetle (Coleoptera: Chrysomelidae).

摘要

In north eastern Arizona where dry and windy environmental conditions prevail, Siberian elms are among the very few tree species that can thrive in the urban landscape without supplemental irrigation. However, Siberian elms are highly susceptible to defoliation by the elm leaf beetle Pyrrhalta luteola Muller, which is an introduced pest from Europe. In order to provide alternatives to the planting of Siberian elms, I evaluated the susceptibility of 32 elm genotypes (species, cultivars and hybrids) in an experimental elm plantation established within the city of Holbrook, AZ. The following nine genotypes consistently sustained 15--46% mean overall defoliation: (1) Siberian elm (U. pumila L.); (2) Dropmore elm (U. pumila); (3) Camperdown elm (U. glabra Huds.); (4) Regal elm (U. glabra x U. carpinifolia Gledisch x U. pumila); (5) Sapporo Autumn Gold elm (U. pumila x U. japonica Sang.); (6) New Horizon elm (U. pumila x U. japonica); (7) Charisma elm [(U. japonica x U. wilsoniana Schneid.) x (U. japonica x U. pumila)]; (8) W2115-1 elm ( U. parvifolia Jacq. x U. procera Salisb); and (9) Homestead elm [(U. hollandica Mill. x U. carpinifolia) x (U. pumila-racemosa Dieck x U. carpinifolia)]. Four Chinese elm (U. parvifolia ) cultivars (Allee, Athena, Glory and Kings Choice) were less susceptible to the elm leaf beetle than Siberian elm. In addition, seven Asian elms (including U. chemnoui Cheng., U. bergmaniana Sneid, U. szechuanica Fang, and species of the U. davidiana Planch. complex [U. davidiana, U. japonica, U. wilsoniana, and U. propinqua Koidz.) and the American elm (U. americana L.) cultivar Valley Forge were also less susceptible than Siberian elm. An evaluation of host traits that may be associated with susceptibility indicated weak negative correlations between susceptibility and trichome density on the abaxial surface of leaves, foliar concentrations of iron, phosphorus, manganese, and soluble nitrogen. An evaluation of the impact of water stress on three elm species ( U. pumila, U. americana, and U. parvifolia) showed that trichome density, iron and magnesium concentrations increased in severely water-stressed Siberian elms. However, stress caused a reduction in trichome density in American elm, but had no effect on foliar mineral concentration. Also, the stress treatment had no influence on host traits in Chinese elm. Implications on how the results might explain elm resistance to elm leaf beetle are discussed.