Length and diameter of xylem vessels as factors in resistance of elms to Ceratocystis ulmi

Abstract

Conductivity of the vascular system of 2-year-old shoots as regards air and water was higher in susceptible than in resistant elms. The xylem vessels of resistant elms were relatively shorter and the percentage of short vessels was greater than in susceptible elms. The percentage of vessels with a large diameter was smaller in resistant elms than in susceptible ones. These results might explain the limited spreading of the spores in the new annual ring of resistant elms.Data of resistance mechanisms of elms to Ceratoeystis ulmi (Buisman) C. Moreau are scarce. Pope (1943) found some anatomical differences between the susceptible Ulmus americana L. and the resistant U. pumila. In the latter the vessels of the springwood were smaller than in the former. Frequently in U. pumila only one row of these vessels was found. In this elm species formation of summerwood took place earlier in the growing season than in U. americana. In the latter the amount of branching between different vessel bundles, both radially and tangentially appeared to be more frequent than in U_ pumila, which might result in a more extensive spreading of the spores of C. ulmi after infection in U. americana than in U. pumila. In both species, however, the summerwood was characterized by a lack of interconnections between vessels, limiting the distribution of the spores.More recently Elgersma (1967) reported that the resistance in U. hollandica cl. 390 was due to a limited spreading of the fungus in the vascular system. As rate of multiplication of spores in the vessels of susceptible and resistant elms appeared to be similar during the first 3 days after inoculation, anti-fungal substances did not seem to be a factor in resistance. It was suggested that gum and tylose formation might occlude the infected vessels faster in resistant elms than in susceptible ones. By this occlusion transport of spores is hampered. No difference in rate of blockage of vessels, however, could be traced between susceptible and resistant elms during the first 3 days after inoculation examining fixed plant material (Elgersma, 1969). So a faster blockade of vessels as resistance mechanism appears not to be evident.Another possibility may be, as was supposed at the First International Symposium on Dutch elm disease in 1968 (Elgersma, in press), that differences in anatomical structure such as vessel length and diameter might be important in limiting the transport of the spores in resistant elms. In clones with relatively short vessels the fungus has to penetrate more mechanical barriers than in clones with relatively long vessels, thus giving the plants the opportunity to produce an effective barrier of gums and 179

Anatomical factors in resistance to Dutch elm disease

“…The average size of a vessel group is defined as the product of the average vessel diameter and the average number of contiguous vessels. As evidence indicates that lateral distribution of the pathogen is from one vessel element to another, we think that the vessel group constitutes a more significant unit than the single vessel (Elgersma 1970b, in this issue). Lateral movement would at first be confined to the vessel group or groups initially inoculated.…”

Etude comparée de l'infection par leFusarium oxysporum f. sp. albedinis, de trois variétés de palmier-dattier, l'une sensible (Deglet-Nour), les deux autres résistantes (Takerboucht et Tantabouchet)

“…• II n'y a pas de difference de longueur des groupes de vaisseaux entre les varietes sensibles et resistantes, ce qui aurait pu expliquer Ia resistance a Ia propagation des spores, comme dans le cas des spores de Ceratocystis ulmi (Elgersma, 1970). Par contre, chez les arbres adultes, il a ete etabli que le diametre des vaisseaux racinaires est un pcu plus grand chez le cultivar DcglctNour que chez le cultivar Tantabouchet.…”

Avoidance by early flushing: a new perspective on Dutch elm disease research

“…Thus, the CODIT model brings together different evidence about factors related to DED resistance. Anatomical characters, such as low vessel diameter and length (Elgersma 1970, Sinclair et al 1975, Solla & Gil 2002 or small size of vessel groups (Pope 1943, McNabb et al 1970),…”