Resistance to Dutch Elm Disease Reduces Presence of Xylem Endophytic Fungi in Elms (Ulmus spp.)

Abstract

Efforts to introduce pathogen resistance into landscape tree species by breeding may have unintended consequences for fungal diversity. To address this issue, we compared the frequency and diversity of endophytic fungi and defensive phenolic metabolites in elm (Ulmus spp.) trees with genotypes known to differ in resistance to Dutch elm disease. Our results indicate that resistant U. minor and U. pumila genotypes exhibit a lower frequency and diversity of fungal endophytes in the xylem than susceptible U. minor genotypes. However, resistant and susceptible genotypes showed a similar frequency and diversity of endophytes in the leaves and bark. The resistant and susceptible genotypes could be discriminated on the basis of the phenolic profile of the xylem, but not on basis of phenolics in the leaves or bark. As the Dutch elm disease pathogen develops within xylem tissues, the defensive chemistry of resistant elm genotypes thus appears to be one of the factors that may limit colonization by both the pathogen and endophytes. We discuss a potential trade-off between the benefits of breeding resistance into tree species, versus concomitant losses of fungal endophytes and the ecosystem services they provide.

Strong in vitro antagonism by elm xylem endophytes is not accompanied by temporally stable in planta protection against a vascular pathogen under field conditions

“…In an earlier paper, we investigated the frequency and diversity of elm endophytes in elm trees showing low or high susceptibility to DED (Martín et al 2013). The present work aims to gain a deeper insight into the potential role of elm endophytes in host defence against O. novo-ulmi.…”

Breeding and scientific advances in the fight against Dutch elm disease: Will they allow the use of elms in forest restoration?

“…Several works are in progress to explore the diversity and functions of elm endophytes. The diversity of xylem endophytic fungi isolated in artificial media was found to be higher in susceptible elm genotypes to DED than in tolerant genotypes, probably as a consequence of the different chemical profile of the two tree groups in xylem tissues (Martín et al 2013). The ability of certain elm endophytes to metabolize carbon sources was comparable to that of O. novo-ulmi, showing an extensive niche overlap between endophytes and the pathogen and suggesting that some endophyte strains may protect elms against DED pathogen through competition for substrates (Blumenstein et al 2015).…”

“…4). High constitutive or rapidly inducible production of antifungal and occlusive chemical compounds (phenolic compounds, pectin, suberin, lignin, mansonones…) contributes to localize the pathogen near its entry point at the cost of proportionally few blocked vessels (Ouellette and Rioux 1992;Duchesne 1993;Martín et al 2008Martín et al , 2013. The differences in numerous xylem characteristics between tolerant individuals and susceptible ones are probably related to slower propagation of the pathogen in the former.…”

The Natural Evolutionary Potential of Tree Populations to Cope with Newly Introduced Pests and Pathogens—Lessons Learned From Forest Health Catastrophes in Recent Decades

“…Tubakia dryina was found more often on diseased trees while Monochaetia monochaeta was more abundant on healthy trees. In contrast, Martin et al [118] found that U. minor genotypes with resistance against O. novo-ulmi (DED) had lower frequency and diversity of fungal endophytes in the xylem than susceptible U. minor genotypes. However, in laboratory conditions, Díaz et al [119] demonstrated that an isolate of Trichoderma atroviride extracted from elm trees inhibits growth of O. novo-ulmi and was, therefore, proposed to confer resistance to DED.…”