Barrier Zone Formation as a Resistance Mechanism of Elms to Dutch Elm Disease

Host responses of elms susceptible and resistant to Dutch elm disease were histologically examined. In a time course study the susceptible elm clone Ulmus × hollandica 'Belgica' and U. × hollandica '390', a clone which shows a high degree of resistance to non-aggressive isolates and a moderate degree of resistance to aggressive isolates of Ophiostoma ulmi, were inoculated in twig or trunk with either an aggressive or a non-aggressive isolate of O. ulmi. For purposes of comparison, the susceptible elm U. americana and the more resistant clones U. × hollandica 'Groeneveld', U. 'Lobel' and U. 'Sapporo Autumn Gold' were included. Depending on clone-isolate compatibility, infected twigs reacted by a walling off process, by barrier zone formation, or failed to resist the infection and died. Trees inoculated into the trunk reacted comparably but in the case of a compatible combination they always formed a barrier zone and the cambium never died in the year of inoculation.

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Barrier zone formation in host and nonhost trees inoculated with Ophiostoma ulmi. I. Anatomy and histochemistry

Canadian Journal of Botany ◽

10.1139/b91-258 ◽

1991 ◽

Vol 69 (9) ◽

pp. 2055-2073 ◽

Cited By ~ 42

Author(s):

Danny Rioux ◽

G. B. Ouellette

Keyword(s):

Principal Component ◽

Dutch Elm Disease ◽

Populus Balsamifera ◽

Ulmus Americana ◽

Zone Formation ◽

Ophiostoma Ulmi ◽

Parenchyma Cells ◽

Zone Cell ◽

Histochemical Tests ◽

Barrier Zone

Barrier zone formation was studied in small branches of Ulmus americana L., Prunus pensylvanica L.f., and Populus balsamifera L. following inoculation with Ophiostoma ulmi (Buism.) Nannf. (the Dutch elm disease pathogen). Barrier zones were continuous in the nonhosts whereas they were generally discontinuous in U. americana; barrier zone formation also occurred at a later stage of infection in the latter than in the former. Barrier zones were formed of parenchyma cells and fibers in U. americana, mainly of parenchyma cells in Prunus pensylvanica, and of fibers in Populus balsamifera. Fibers as a principal component of barrier zones are described for the first time. Histochemical tests revealed that the proportion of lignin was higher in barrier zone cell walls than in elements of the noninvaded xylem. Barrier zones contained suberized cells, the number of which was progressively greater in the order U. americana, Prunus pensylvanica, and Populus balsamifera. However, many fibers of U. americana occasionally formed a continuous barrier zone and had an internal layer that was slightly suberized. In addition, phenolic compounds were usually detected within barrier zone cells of these species. Key words: Dutch elm disease, nonhost plants, Ophiostoma ulmi, Ulmus americana, anatomy, histochemistry.

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Light microscope observations of histological changes induced by Ophiostoma ulmi in various nonhost trees and shrubs

Canadian Journal of Botany ◽

10.1139/b89-299 ◽

1989 ◽

Vol 67 (8) ◽

pp. 2335-2351 ◽

Cited By ~ 26

Author(s):

Danny Rioux ◽

G. B. Ouellette

Keyword(s):

Dutch Elm Disease ◽

Populus Balsamifera ◽

Class Iii ◽

Shrub Species ◽

Histological Changes ◽

Zone Formation ◽

Ophiostoma Ulmi ◽

Parenchyma Cells ◽

Barrier Zone ◽

Trees And Shrubs

Ophiostoma ulmi (the Dutch elm disease pathogen) was inoculated into 13 nonhost tree and shrub species. Four classes were recognized based on their susceptibility to this pathogen. In Prunus pensylvanica (class I), bubbles formed in vessel members within 3 days after inoculation, and gels formed 5 days later. At day 5, the vascular cambium covering the colonized zone became altered. A barrier zone was formed in 60% of the inoculated twigs. When twigs wilted, the vessels around the twig were occluded, and barrier zone formation was partial. In Populus balsamifera (class II), tyloses formed in vessels of invaded xylem within 8 days after inoculation followed by accumulation of compounds suspected to be phenolics in parenchyma cells. Barrier zone formation occurred in 66% of the inoculated twigs. In Sorbus americana (class III), a pronounced dark discoloration developed rapidly in the invaded xylem. Sparse gels and O. ulmi cells were present in vessel members. Gel formation was limited to vessels that were adjacent to parenchyma cells. Pit membranes of bordered and half-bordered pit pairs became thicker and more darkly stained than in controls. These observations suggest that the first steps of pathogenesis are induced by the action of harmful metabolites of O. ulmi. Few noticeable changes occurred in the species of class IV.

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Barrier zone formation in host and nonhost trees inoculated with Ophiostoma ulmi. II. Ultrastructure

Canadian Journal of Botany ◽

10.1139/b91-259 ◽

1991 ◽

Vol 69 (9) ◽

pp. 2074-2083 ◽

Cited By ~ 14

Author(s):

Danny Rioux ◽

G. B. Ouellette

Keyword(s):

Electron Microscopy ◽

Dutch Elm Disease ◽

Populus Balsamifera ◽

Ulmus Americana ◽

Light Microscope Level ◽

Zone Formation ◽

Ophiostoma Ulmi ◽

Transmission Electron ◽

Histochemical Tests ◽

Barrier Zone

Barrier zone formation was studied in annual shoots and small branches of Ulmus americana L., Prunus pensylvanica L.f., and Populus balsamifera L. following inoculation with Ophiostoma ulmi (Buism.) Nannf. Ultrastructural observations showed that electron-opaque compounds, which usually were identified as containing phenolics by previous histochemical tests, were often present within cells of this tissue. Many lipidic globules were also observed within some barrier zone cells of Populus balsamifera. Additional wall layers, suberized or not, were frequently observed in these barrier zone cells. When histochemical tests for suberin at the light microscope level were strongly positive, the lamellation typical of suberin was evident in transmission electron microscopy. Gum canal formation in Prunus pensylvanica was found to be initiated and the canals widened predominantly by a lysogenous process. Key words: Dutch elm disease, nonhost plants, Ophiostoma ulmi, Ulmus americana, ultrastructure, gum canals, suberized layers.

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Variation in Response of Selected American Elm Clones to Ophiostoma ulmi

Journal of Environmental Horticulture ◽

10.24266/0738-2898-13.3.126 ◽

1995 ◽

Vol 13 (3) ◽

pp. 126-128 ◽

Cited By ~ 3

Author(s):

A.M. Townsend ◽

S.E. Bentz ◽

G.R. Johnson

Keyword(s):

Dutch Elm Disease ◽

Main Trunk ◽

Ulmus Americana ◽

Disease Symptoms ◽

Ophiostoma Ulmi ◽

American Elm ◽

Causal Fungus ◽

One Year ◽

Crown Dieback ◽

High Degree

Abstract Ramets of nine American elm (Ulmus americana L.) clones or cultivars were planted with ramets of Ulmus ‘Frontier’, Ulmus ‘Prospector’, and American elm seedlings in a randomized block, split-plot design. When they were three years old, the trees were inoculated in the main trunk on either one of two selected dates in May with a spore suspension of Ophiostoma ulmi, the causal fungus for Dutch elm disease (DED). Analyses of variance showed significant variation among clones and between inoculation dates in disease symptoms four weeks and one year after inoculation. Inoculations made on May 18 generally created significantly more symptoms than inoculations made only nine days later. Four-week symptom expression was influenced also by a significant interaction between clonal or seedling group and inoculation date. When data from both inoculation dates were combined, six American elm clones (‘American Liberty’, ‘Princeton’, 680, R18–2, 180, and 3) showed significantly fewer foliar symptoms after four weeks than the American elm seedlings and three other American elm clones. Five of these same six more tolerant American clones averaged significantly less crown dieback after one year than the other American clones or seedlings tested. One of the American elm clones (clone 3) showed a level of disease tolerance equal statistically to ‘Frontier’ and ‘Prospector’, two cultivars which have shown a high degree of tolerance to DED in other studies.

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Two-dimensional mapping of mycelial polypeptides of Ophiostoma ulmi and Ophiostoma novo-ulmi, causal agents of Dutch elm disease

Canadian Journal of Botany ◽

10.1139/b94-050 ◽

1994 ◽

Vol 72 (3) ◽

pp. 370-377 ◽

Cited By ~ 7

Author(s):

Robert S. Jeng ◽

Clive M. Brasier

Keyword(s):

North American ◽

Nuclear Dna ◽

Dutch Elm Disease ◽

Dna Polymorphisms ◽

Two Dimensional ◽

Ophiostoma Ulmi ◽

Race Specificity ◽

High Degree ◽

Basic Polypeptide ◽

Intraspecific Relationships

Two-dimensional mycelial polypeptide maps were used to compare interspecific and intraspecific relationships among six isolates of Ophiostoma ulmi and four Eurasian and four North American race isolates of Ophiostoma novo-ulmi. The basic polypeptide pattern of O. ulmi differs markedly from that of O. novo-ulmi. A number of polypeptides were identified that could differentiate the two species and one was detected that may discriminate Eurasian from North American races. Overall, a high degree of correlation between species, race, and polypeptides was evident. However, two O. ulmi isolates (MAB and M273) and one O. novo-ulmi isolate (83) exhibited the same unique polypeptides. These isolates otherwise exhibit typical O. ulmi or O. novo-ulmi nuclear DNA polymorphisms. This suggests that they may share a common developmental pathway absent in other isolates examined. In view of this phenomenon, the greatest value of two-dimensional polypeptide gels may lie in the elucidation of proteins involved in species or race specificity, in pathogenesis, or in development rather than in routine species identification. Key words: Ophiostoma ulmi, Ophiostoma novo-ulmi, two-dimensional polypeptide mapping, introgression.

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