Resistance to Ophiostoma novo-ulmi in Ulmus carpinifolia var. umbraculifera, U. glabra and U. parvifolia

Dutch elm disease is one of the most important vascular diseases, causing severe epidemics. With regard to occurrence of aggressive species and races of the disease, nowadays applying resistant species and varieties of elm is the best method to manage practices against this disease. In this research, resistance rate of Ulmus carpinifolia var. umbraculifera Rehd., U. glabra Huds. and U. parvifolia Jacq. -inoculated by three isolates of Ophiostoma novo-ulmi in vivo- was evaluated. Estimating the wilt and defoliation percent of saplings of U. carpinifolia var. umbraculifera and U. glabra showed very high susceptibility rate and almost die-off after eight weeks, but saplings of U. parvifolia showed a few wilt percent following the same time laps. The results indicated which saplings of U. parvifolia with 1-11% have, significantly (P<%5), very low susceptibility in comparison with U. carpinifolia var. umbraculifera and U. glabra to the isolates of Ophiostoma novo-ulmi. In this survey, On3 isolate also showed more severity pathogenesis than other isolates. In this survey, has indicated isolates of O. n vo-ulmi have very high pathogenesis ability, in spite of the fact that Chinese elm indicated high relative resistance.Using of this elm, as resistant species against Dutch elm disease in country, to replace highsusceptible species such as U. glabra and U. carpinifolia var. umbraculifera, and using in elmbreeding programs for to obtain hybrid elms with favorite resistances is discussed in this paper.