Comparison of xylem vessels diameter and some attributes relation With it at Ulmus parvifolia and U. minor as factors of Resistance to Dutch elm disease

The present research was carried out for comparison of xylem vessels diameter and some anatomical attributes relation with it at Ulmus minor and U. parvifolia as the important factors of host-resistance to Dutch elm disease. In this experiment, in addition to estimate of vessels diameter, 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 these two elm species. The results showed that significant difference at probability level 1% was among the calculated indexes of these elms, so that U. minor had the less vessels but with more diameters than U. parvifolia. The percentage of vessel transactional areas and vessels greater than 100 micrometer were calculated for U. minor more than U. parvifolia. The relative theoretical hydraulic conductance index was also received significantly for U. minor higher than U. parvifolia. Totally, being of these significant differences among cited anatomical indexes for U. minor, susceptible to Dutch elm disease, and U. parvifolia, resistant to Dutch elm disease, could be affected to indicate agent or agents of host-resistance with respect to Dutch elm disease, that were discussed in this paper.