The study of the role of xylem vessels in resistance to Dutch elm disease

The role of xylem vessel dimensions and some anatomical attributes in relation with it for occurrence of various rates of resistance to Dutch elm disease in elm trees is probable. The present research was carried to compare the xylem vessel diameter and some anatomic traits related to it in Ulmus glabra, U. carpinifolia var. umbraculifera and U. parvifolia as the important factors of host-resistance to Dutch elm disease. In this experiment, in addition to estimate the diameter of vessels, indexes of percentage of vessel transactional area, percentage of vessels greater than 100 micrometer and rate of relative theoretical hydraulic conductance were calculated in the second and third-year-rings for the elm species. The results showed that significant difference at probability level 1% was among the calculated indexes of the elms, so that U. glabra had the vessels with more diameters than U. parvifolia and Ulmus carpinifolia var. umbraculifera. The percentage of vessel transactional areas and vessels greater than 100 micrometer were calculated for U. glabra more than U. parvifolia Ulmus carpinifolia var. umbraculifera. The relative theoretical hydraulic conductance index was also received significantly for U. glabra the highest rate of the rest. The U. parvifolia showed the least rates of measured indexes in this experiment. Totally, being of the significant differences among cited anatomical indexes for U. glabra and U. carpinifolia var. umbraculifera, susceptible to Dutch elm disease, and U. parvifolia, resistant to Dutch elm disease, Ophiostoma novo-ulmi, could be affected to indicate agent or agents of host-resistance with respect to Dutch elm disease that were discussed in this paper.