Carbendazim formulations for the eradication of Dutch elm disease

Formulations containing carbendazim (40 or 80 mM) in hydrochloric acid (180 or 320 mM) were pressure-injected into elms previously inoculated with the fungus Ceratocystis ulmi (the cause of Dutch elm disease) and their performance as eradicants assessed. All formulations caused some damage to foliage but leaves regenerated. Treatment with carbendazim (80 mM) in hydrochloric acid (180 mM) resulted in four out of five trees remaining free from disease, not only immediately after treatment, but also throughout the following season. Injection of acid alone resulted in rapid death of the trees.     

Anatomical factors in resistance to Dutch elm disease

The localizing of pathogen (Ceratocystis ulmi) establishment in Dutch elm disease-resistant hosts is hypothesized as the major mechanism of resistance to this disease. Four factors are proposed that, singly or in all possible combinations, could regulate this general mechanism. We tested one of these factors, vessel size and number of contiguous vessels in the functional xylem at the point of natural inoculation. Using 23 selections from the Ulmaceae, we examined a constant area of second-year xylem of 2-year-old twigs. These anatomical data indicate that a correlation exists between increasing disease susceptibility and increasing vessel group size (the product of average vessel diameter and average number of contiguous vessels). Other evidence suggests that lateral pathogen movement is at first confined to the vessel group or groups of initial inoculation. Therefore, in a given limited time period, tylosis production could more effectively block vertical pathogen movement in vessel groups of small size. Relationships between vessel group size and the extent of sapwood discoloration are discussed. Vessel size and arrangement also is discussed in relationship to the resistance reported for young, greenhouse-grown trees. The use of vessel group size is suggested in screening programs for disease resistance. Recent research on oak suggests chemical modification of xylem tissue to lessen elm susceptibility.Samenvatting Als hypothese wordt gesteld, dat resistentie tegen de iepeziekte in de eerste plaats berust op het vermogen van resistente gastheren om de uitbreiding van de ziekteverwekker (Ceratocystis ulmi) te beperken. Er worden vier factoren genoemd die (alleen of in combinatie) dit vermogen zouden bepalen. Een van de vier werd getoetst, en wel afmeting van vaten en aantal aaneengrenzende vaten in de buitenste jaarring op de plaats waar natuurlijke infecties plaatsvinden. Er werden 22 iepeselecties en één andere Ulmacee gebruikt, waarin de vaten gemeten en geteld werden in een constant oppervlak van de dwarsdoorsnee van het tweede-jaars-hout van twee jaar oude twijgen. Deze anatomische gegevens tonen een correlatie tussen toenemende vatbaarheid voor de ziekte en toenemende vaatgroepgrootte, die hier gedefinieerd is als het produkt van de gemiddelde vatdiameter en het gemiddelde aantal aaneengrenzende vaten (zie Tabel 4). Uitbreiding van de schimmel in dwarsrichting van de boom is om te beginnen beperkt tot die vaatgroepen die oorspronkelijk geïnfecteerd waren. Daarom zal de uitbreiding van de schimmel in de lengterichting met meer effekt door thyllen geblokkeerd kunnen worden in vaatgroepen van geringere grootte.De verhouding tussen vaatgroepgrootte en mate van houtverkleuring na infectie wordt besproken. Grootte en rangschikking van vaten wordt ook genoemd in verband met een zekere mate van resistentie van jonge, in de kas opgekweekte bomen. Het gebruik van vaatgroepgrootte wordt voorgesteld als een maatstaf bij het selecteren van resistente individuen uit grote populaties. Recent onderzoek over het effect van de stof TCPA op de anatomie van eiken suggereert dat het mogelijk is met chemicaliën de opbouw van het houtweefsel van iep te wijzigen en zodoende zijn vatbaarheid voor de iepeziekte te verkleinen.Journal Paper No. J-6392 of the Iowa Agricultural and Home Economics Experiment Station, Ames, Iowa. Project No. 1706. Appears also as Mededeling 106 of the Forest Research Station De Dorschkamp.     

Control of Dutch elm disease by the sterol biosynthesis inhibitors fenpropimorph and fenpropidin

Sterol biosynthesis inhibitors that inhibit the yeast-hyphae conversion inOphiostoma ulmi suppressed Dutch elm disease development in two elm clones. After curative treatment with fenpropimorph-sulphate of 27 Vegeta elms which had previously been inoculated withO. ulmi, 25 trees did not show disease symptoms by the end of the second season. All 41 control trees, inoculated withO. ulmi only, were clearly diseased. In an experiment with Commelin elms three fenpropimorph salts and thiabendazole were compared. Injection of the trees three weeks after inoculation withO. ulmi gave by the end of the second season no symptoms of Dutch elm disease in any of the trees injected with fenpropimorph-phosphate or thiabendazole, and in most trees injected with fenpropimorph-acetate or-sulphate. Similar treatments with the free base of fenpropimorph and fenpropidin-sulphate were less effective due to insufficient uptake of the fenpropimorph emulsion and phytotoxicity of fenpropidin-sulphate, respectively. Injection of fenpropimorph-sulphate or thiabendazole six weeks after inoculation withO. ulmi did not result in significant differences from the control group inoculated withO. ulmi only.Fenpropimorph-phosphate and-sulphate completely suppressed Dutch elm disease upon injection of only 7.5 or 10 g per tree (average tree diameter 28 cm). Residue analyses showed only a slow decrease in concentration of the fungicide over two growing seasons and an apparent transport into the new annual ring, other prerequisites for a possible future use for control of Dutch elm disease.Samenvatting De iepeziekte kan onderdrukt worden door sterolbiosyntheseremmers die de overgang vanOphiostoma ulmi van de gistvorm in de hyfevorm remmen. Aan het eind van het tweede seizoen na een curatieve behandeling van 27 Vegeta iepen met fenpropimorfsulfaat bleken 25 bomen geen symptomen van iepeziekte te vertonen. Alle controlebomen, die alleen metO. ulmi geïnoculeerd waren, waren duidelijk ziek. In een proef met Commelin iepen werden drie fenpropimorfzouten en thiabendazool vergeleken. De zouten werden drie weken na de inoculatie metO. ulmi geïnjecteerd. Aan het eind van het tweede seizoen vertoonden geen van de bomen die met fenpropimorffosfaat of thiabendazool geïnjecteerd waren en slechts enkele bomen die met fenpropimorfacetaat of-sulfaat geïnjecteerd waren iepeziektesymptomen. Behandelingen met fenpropimorf (vrije base) en fenpropidinsulfaat werkten minder goed door de slechte opname van de fenpropimorfemulsie en de fytotoxiciteit van fenpropidin. Injectie met fenpropimorfsulfaat of thiabendazool zes weken na inoculatie leidde niet tot significante verschillen met de controlegroep die alleen metO. ulmi geïnoculeerd was.Een dosis fenpropimorffosfaat of-sulfaat van 7.5 of 10 g per boom met een gemiddelde boomdiameter van 26 cm bleek de iepeziekte volledig te kunnen onderdrukken. Uit residue-onderzoek bleek dat de concentratie van het fungicide gedurende de twee groeiseizoenen slechts langzaam afnam en dat het middel naar de nieuwe jaarring werd getransporteerd, twee voorwaarden voor een toepassing op praktijkschaal van fenpropimorf voor de bestrijding van de iepeziekte.     

Dutch elm disease in New Zealand: impacts from eradication and management programmes

Ophiostoma novo‐ulmi, the cause of the current pandemic of Dutch elm disease, is considered one of the 20 worst pests to have been introduced to New Zealand. An attempt to eradicate the pathogen came close to success, but was eventually stopped and replaced by management programmes. These programmes are slowing the spread of the pathogen. If left uncontrolled it is likely that New Zealand will lose 90% of its elm trees. Although elms are exotic trees in New Zealand, the loss of such a large number of popular amenity trees is likely to have numerous social, cultural, environmental and economic effects. It is estimated that this disease could cost public and councils over NZD $350 million in tree removal and replacement costs. Control of O. novo‐ulmi is limited, but biological control using d‐factor viruses has been proposed. Although O. novo‐ulmi was not eradicated from New Zealand, the eradication programme had many successes; in particular, the effective interaction of good management and science in the early years of the campaign. Also highlighted in this review are several tactics and steps that could be applied to eradication attempts for other species.     

Dutch elm disease revisited: past,present and future management in Great Britain

The arrival of a new species of the fungus which causes Dutch elm disease into Great Britain in the 1960s caused widespread elm death and continues to be problematic following elm regeneration. Attempts at managing the disease have been largely unsuccessful. Forty years after the outbreak, however, researchers continue to be interested in both the underlying biology of such a severe and dramatic disease event and in the policy lessons that can be drawn from it. We develop a spatial model at a 1 km² resolution. Following parameterization to replay the historical epidemic, the model is used to explore previously proposed counterfactual management strategies. A new introduction date of late 1962 is estimated. We show that, even had there been high intervention at a national level in terms of disease management early in the epidemic, there would have been little long‐term effect on elm numbers. In Brighton, a local pocket of elm which survived the peak of the initial epidemic has been successfully managed. However, Brighton and similar locations are subject to repeated waves of the disease at a 15‐ to 20‐year intervals following regeneration and reinfection of the surrounding areas, during which much more intensive management is required.     

Monoclonal antibodies to specific components of the Dutch elm disease pathogen Ophiostoma ulmi

The potential of polyclonal antisera and monoclonal antibodies to differentiate the EAN and NAN aggressive subgroups of Ophiostoma ulmi was explored. Polyclonal antisera, when tested by ELISA, cross-reacted widely with unrelated species and failed to distinguish between the two aggressive subgroups but small quantitative differences were found, particularly between antigens secreted overnight, by EAN and NAN germlings. Monoclonal antibodies were raised in mice against mycelial homogenates. From two fusions, 33 cell lines were raised that secreted antibodies positive for O. ulmi. Approximately one third were non-specific; 11 were specific either to species or subspecies. Two cell lines differentiated mycelial antigens of the aggressive isolates of O. ulmi from those of the non-aggressive subgroup, but not antigens from surface washings. Only quantitative differences were detected between the EAN and NAN aggressive subgroups. Almost all the monoclonal antibodies and antiserum recognized antigens present in surface washings of cultures on solid medium, in cell-free extracts of mycelial homogenates, in cell-free culture fluids, and in substances secreted overnight by germinating spores. Specific detection of such molecules promises to provide a highly sensitive mechanism for studying early pathogen/host plant interactions. Most of the monoclonal antibodies appeared to have potential diagnostic value; they gave readings twofold to tenfold higher with extracts from diseased than from healthy tissue. However, one cell line that secreted antibodies specific to O. ulmi cross-reacted strongly with extracts of healthy tissue.     

Assessment of Phaeotheca dimorphospora for biological control of the Dutch elm disease pathogens, Ophiostoma ulmi and O. novo-ulmi

The antagonistic fungus Phaeotheca dimorphospora was tested as a biocontrol agent against the Dutch elm disease pathogens, Ophiostoma ulmi and O. novo-ulmi , on Ulmus americana seedlings in the glasshouse. Curative inoculation of seedlings with P. dimorphospora had no significant effect on disease development. Conditioning inoculation of seedlings with the antagonist protected them against O. ulmi but not against the more aggressive O. novo-ulmi . In seedlings challenged with both the antagonist and either one of the pathogens, P. dimorphospora only spread locally around the inoculation point; however, the pathogens spread systemically throughout the whole plant. O. novo-ulmi survived in the region colonized by P. dimorphospora , whereas O. ulmi did not.     

Pseudomonas for biological control of Dutch elm disease. III. Field trials at various locations in the Netherlands

The prophylactic effect in elm of one treatment with aPseudomonas isolate was monitored in two types of field trials. In one type only natural Dutch elm disease infections were monitored and hence large numbers of trees were necessary due to the low incidence of natural occurring infections. In the other type trees were artificially infected.The large-scale field trials in which only natural infections were monitored, were based on expected annual losses due to Dutch elm disease of approximately 2%. As a result of the Dutch sanitation program, which was based on the prompt removal of every weakened or diseased elm, the actual losses were generally threefold lower. Dutch elm disease incidence was 22–45% lower in the trees treated with aPseudomonas isolate in the year of treatment and the year after. The results of the biocontrol treatment were negatively influenced because on several locations trees were felled that showed initial signs of Dutch elm disease, which probably would have disappeared during the season.The advantage of artificial infections withOphiostoma ulmi was a reproducable development of symptoms and the possibility to maintain diseased trees, at least till the first signs of elm bark beetle breeding. For Commelin elms an increase in symptoms was observed with increasingO. ulmi dose till 3000 conidia per tree; the standard 500 000 conidia used for most experiments was well above this critical value. No decrease in effectiveness of the bacterial pre-treatment was observed with increasingO. ulmi inoculum. Different bacterial treatments suggested that injections at a smaller interval (i.e. more injections per tree) may result in a better prophylactic effect, but the significance of the correlation remained doubtful. A comparison of several elm species and clones showed the importance of the host tree. Prophylaxis as a result of one bacterial treatment was shown repeatedly in Commelin elms; the numbers of trees showing symptoms by the end of the second year were 10 to 85% lower in the bacteria-treated groups in comparison with the controls. Also in one experiment with Belgica elms prophylaxis was observed, resulting in a 84% decrease in the number of trees showing symptoms by the end of the second year after the prophylactic treatment followed by inoculation withO. ulmi. In Vegeta symptom development was only less severe and in field elms (Ulmus carpinifolia) some prophylactic effect was observed in one experiment, but no effect in two others.Samenvatting De mogelijke bescherming tegen de iepeziekte, verkregen door injectie van de boom met bacteriën van het geslachtPseudomonas, werd gemeten in twee soorten experimenten. In het ene soort werden natuurlijke infecties gemeten, waardoor grote proefgroepen nodig waren. In het andere soort werden de iepen kunstmatig geinfecteerd.De grootschalige veldexperimenten waarbij natuurlijke iepeziekte-infecties werden gemeten, waren gebaseerd op een verwachte jaarlijkse uitval van 2%. Als gevolg van de landelijke bestrijdingscampagne bleken de verliezen slechts ongeveer een derde hiervan te zijn. Er kwam minder iepeziekte voor in de metPseudomonas geïnjecteerde bomen in het jaar van injectie en in het jaar daarna. Een storende invloed op de resultaten had het effect dat ook met bacteriën geïnjecteerde bomen soms beginnende symptomen vertonen na infectie metOphiostoma ulmi, symptomen die in de loop van het seizoen soms weer verdwijnen. Als gevolg van de bestrijdingscampagne werden zulke bomen toch geveld.Het voordeel van kunstmatige infecties metO. ulmi was een voorspelbaar verloop van de symptoomontwikkeling en de mogelijkheid om zieke bomen te laten staan tot er iepespintkevers in kwamen. In Commelin iepen bleken de symptomen toe te nemen met een tot 3000 conidiën per boom toenemende dosisO. ulmi. De gebruikelijke 500000 conidiën die in de meeste experimenten werden gebruikt lagen ver boven deze kritische waarde. Er werd geen effect van een toenemende dosisO. ulmi op de effectiviteit van een bacteriebehandeling waargenomen.Uit variaties in de diverse bacteriebehandelingen kwam naar voren dat injecties met een kleinere tussenruimte (dus meer injecties per boom) mogelijk het effect verbeterden, maar de significantie van deze correlatie bleef twijfelachtig.Vergelijken van diverse iepen toont dat soort en kloon type een belangrijke rol speelt bij deze bestrijdingsmethode. Bescherming tegen de iepeziekte als gevolg van een bacteriebehandeling werd diverse malen aangetoond in Commelin iepen; het aantal bomen met iepeziekte-symptomen was aan het eind van het tweede seizoen in de met bacteriën behandelde groepen 10 tot 85 % lager dan in de controlegroepen. Ook in een experiment met Belgica iepen werd een goede bescherming gemeten. In Vegeta werd slechts een verminderde symptoomontwikkeling gemeten en in veldiepen (U. carpinifolia) werd enige bescherming gevonden in één experiment, maar geen effect in twee andere.     

Influence of the d2 factor on survival and infection by the Dutch elm disease pathogen Ophiostoma ulmi

A particular form of mycovirus, the d² factor, which attacks the elm pathogen Ophiostoma ulmi, was found to be extremely deleterious to this fungus both in vitro and in vivo. Most significantly, d²-infected conidia were poor at persisting in feeding grooves, the usual infection court of the pathogen, and also showed a 50-fold reduction in successful xylem infection compared with their healthy counterparts. In addition, transmission of the d² factor from diseased to healthy isolates of O. ulmi was found to take place in feeding grooves, indicating that the fungus exists in a mycelial phase prior to invading xylem vessels.     

Formulations for the control of dutch elm disease

Solutions of methyl benzimidazol-2-ylcarbamate (carbendazim, formerly MBC) in dilute hydrochloric, orthophosphoric or hypophosphorous acid and in dilute hydrochloric acid containing methanol (“Lignasan”) and aqueous solutions of 2-(thiazol-4-yl) benzimidazole (thiabendazole) hypophosphite, 8-hydroxyquinoline (oxine)hydro-chloride and dodecylguanidine acetate (dodine), were tested in the field for their efficacy in controlling Dutch elm disease caused by Ceratocystis ulmi. All gave some degree of control although some were phytotoxic, the benzimidazoles being the most active compounds tested. The anion and the concentration of acid present in the formulation may have some effect on retention of active material within the crown of the tree.     

The influence of temperature and light on defoliation levels of elm by dutch elm disease

ABSTRACT The amount of defoliation of elm (Ulmus procera) caused by three Ophiostoma novoulmi Eurasian race isolates over 14 seasons of field trials was found to be strongly correlated with mean air temperature and mean number of sunshine hours over the 12-week period from inoculation to assessment, and with tree age. The coefficient of determination for the regression of percent defoliation on the environmental and tree factors was 0.76, P < 0.001 (33 df). Levels of defoliation were greatest when mean air temperatures exceeded 17 degrees C with moderate light (5 to 7 h of sunshine), and lowest under conditions of either high light (>7.5 h of sunshine) at all air temperatures or low light (<4.5 h of sunshine) and air temperatures of less than 15.5 degrees C. The model varied in its intercept for the three isolates, reflecting their different levels of aggressiveness. The role of environmental factors in the development of Dutch elm disease symptoms and the implications for elm resistance breeding are discussed.     

Production in vitro of phytotoxic compounds by non-aggressive and aggressive isolates of Ophiostoma ulmi, the Dutch elm disease pathogen

Development in shake culture of two non-aggressive and two aggressive isolates of the Dutch elm disease fungus, Ophiostoma ulmi, was monitored in a time course study. The time sequences for the production of total biomass, spores, polysaccharides and phytotoxic compounds were followed, but none of them showed a clear correlation with aggressiveness. The same parameters were examined for nine non-aggressive and 11 aggressive isolates after 10 days growth. Of two phytotoxic compounds, a glycopeptide and the protein cerato-ulmin, only the latter was generally produced in larger quantities by aggressive isolates. However, variability in production and a number of exceptions to the trend made cerato-ulmin production an uncertain criterion for assessing the aggressiveness of an individual isolate.Immunofluorescence of sections of infected elms treated with an anti-glycopeptide serum showed intense fluorescence only in the cell walls of the fungus. Apparently the glycopeptide is abundantly present in or on fungal cell walls.The roles of the different compounds in relation to Dutch elm disease symptom development are discussed.     

Genetic evidence for natural hybridization between the Dutch elm disease pathogens Ophiostoma novo-ulmi ssp. novo-ulmi and O. novo-ulmi ssp. americana

The Dutch elm disease pathogen Ophiostoma novo-ulmi is separated into subspecies novo-ulmi , formerly known as the Eurasian (EAN) race, and subspecies americana , formerly known as the North American (NAN) race. Both subspecies occur in Europe, and hybrids between them are suspected to have emerged in parts of Europe where their ranges overlap. Authenticated isolates of both subspecies were examined in order to determine whether fixed mutations occur in the cerato-ulmin ( cu ) and in the colony type gene ( col1 ). One and six mutations were detected between subspp. novo-ulmi and americana in cu and col1 , respectively. The mutation in cu and one mutation in col1 proved to be located within restriction sites, and were used for PCR-RFLP. This method provides a quick and reliable diagnostic method to differentiate the two subspecies. Seven isolates of O. novo-ulmi from Austria were suspected to be hybrids between subspp. novo-ulmi and americana , and were tested by PCR-RFLP of their cu and col1 genes. Two of the suspected hybrids from Austria (isolates AT73 and AT146) had the cu PCR-RFLP profile of ssp. americana and the col1 PCR-RFLP profile of ssp. novo-ulmi . Furthermore, a ssp. novo-ulmi tester isolate from Poland (P150) showed a similar hybrid pattern. This is the first evidence revealing recombination between two genes and thus hybridization between the two subspecies of O. novo-ulmi in nature.     

Heritability of Ulmus minor resistance to Dutch elm disease and its relationship to vessel size,but not to xylem vulnerability to drought

Dutch elm disease (DED) is a vascular wilt disease that causes the occlusion and cavitation of xylem vessels. Therefore, it is hypothesized that those elms that are less vulnerable to cavitation by drought might be more resistant to DED. To test this hypothesis, the relationship between xylem vulnerability to cavitation and susceptibility to DED was examined in progenies of crosses between susceptible and resistant individuals of Ulmus minor. Hydraulic conductivity and xylem vulnerability curves were evaluated and anatomical features such as vessel size, length and grouping were measured. Next, elms were inoculated with Ophiostoma novo‐ulmi, the cause of DED, and pre‐dawn and midday water potentials, stomatal conductance and wilting percentages were assessed. Progenies of R × R crosses showed significantly lower mean wilting percentages (30–50%) than the progeny of S × S crosses (75%). Fifty percent conductivity loss was reached at c. ?1 MPa, pointing out a high vulnerability of this species to drought‐induced cavitation. Crown wilting percentage as a result of inoculation and xylem vulnerability to cavitation by water stress did not show any significant correlation. Nevertheless, significant differences in theoretical hydraulic conductivity and vessel size parameters (diameter, length and size distributions) were found among the tested progenies. Susceptible trees had significantly wider and longer vessels. Xylem structure of resistant elms seems to restrict pathogen spread rather than prevent cavitation.     

Tracking an invader to its origins: the invasion case history of Crupina vulgaris

Summary Based on its Mediterranean origins and close relationship with other highly invasive Asteraceae species, Crupina vulgaris was declared a Federal Noxious Weed shortly after its discovery in Idaho in 1968. Twenty-two years later, surveys revealed over 25 500 ha infested with five separate populations in four states. Despite this expansion, no-one knew how this unlikely invader with its large seed was moving long distances or how it had escaped detection entering the country. The objectives of this study were to characterize the invasion history by estimating when, how, from where and how many times Crupina vulgaris was introduced in North America. Methods included molecular markers (random amplification of polymorphic DNA), distribution maps and historical sleuthing. Molecular markers linked all five North American populations with the Iberian Peninsula, with at least three colonization events. Distribution maps limited the area to northern Spain, where C. vulgaris occurs outside the range of Crupina crupinastrum . Site histories indicated four, perhaps five, successful introductions from northern Spain, associated with Basque sheepherders. Two remote sites (Lake Chelan, WA, and Modoc County, CA) had direct links with northern Spain from the 1950s into the 1970s. It appeared that the other introductions also occurred decades before the discovery dates. Detailed knowledge of individual invasion case histories is relevant for preventing future weed introductions and as a framework for future ecological investigations, such as effects of selection pressures during immigration or niche relationships in native and introduced habitats.     

榆树脐腹小蠹的识别与防治

描述了榆树上重要蛀干害虫脐腹小蠹（Scolytus schevyrewi Semenov）的鉴别特征, 附有识别特征图, 并依据生物学特性提出防治措施。     

A rapid virulence assay for the Dutch elm disease fungus Ophiostoma novo‐ulmi by inoculation of apple (Malus × domestica ‘Golden Delicious’) fruits

Large‐scale virulence tests using trees or saplings are expensive, time‐consuming and require a considerable amount of space. The suitability of using ‘Golden Delicious’ apples as a rapid screen for identifying Ophiostoma novo‐ulmi transformants with reduced virulence was thus evaluated. When a collection of O. novo‐ulmi field isolates belonging to subspecies novo‐ulmi or americana was inoculated to apples, members of subsp. novo‐ulmi induced, on average, larger necrotic lesions than subsp. americana isolates. The size of the lesions on apples was not correlated with mycelial growth rate of isolates on nutrient agar. Insertional mutants from O. novo‐ulmi subsp. novo‐ulmi isolate H327 were inoculated to ‘Golden Delicious’ apples and Ulmus parvifolia × U. americana saplings in parallel experiments. Results clearly indicated that the O. novo‐ulmi transformants included several exhibiting significantly altered levels of virulence. Variability among replicates within a treatment was reduced in apple inoculation data compared to elm sapling data. Overall, the ‘Golden Delicious’ apple assay was found to be an excellent means for rapidly assessing the virulence level of O. novo‐ulmi isolates.     

The relation of mansonones to resistance against dutch elm disease and their accumulation,as induced by several agents

No evidence was found that mansonones E and F, which accumulated in elms after infection withCeratocystis ulmi, were responsible for resistance against Dutch elm disease inUlmus hollandica cl. 390. Furthermore, production of mansonones inU. americana was only about one-fifteenth of that inU. hollandica cl. Belgica. Yet both are susceptible to Dutch elm disease.Induction of these compounds was not specific, for accumulation occurred not only after introduction of crude toxin ofC. ulmi, but also after inoculation withVerticillium albo-atrum and after introduction of H₂SO₄ or ethanol.The dark discolouration of the wood after toxin treatment was restricted to the lower part of the stem. No mansonones could be detected in the non-discoloured higher parts of the stem or from the necrotic or wilted leaves.Samenvatting Er werd geen aanwijzing gevonden dat mansononen E en F, die na infectie metC. ulmi gevormd worden, verantwoordelijk zijn voor de resistentie tegen de iepziekte inU. hollandica cl. 390 (Tabel 1). U. americana bevat ongeveer 15 maal zo weinig van deze stoffen alsU. hollandica cl. Belgica, terwijl beide vatbaar zijn.De inductie van de synthese van deze stoffen bleek niet specifiek te zijn, omdat bij chemische beschadiging met H₂SO₄ of ethanol ook mansononen gevormd werden.De donkere verkleuring van het hout bleek na toxine toediening beperkt tot het onderste gedeelte van de stam. Geen mansononen werden gevonden in hoger gelegen, niet verkleurde stamgedeelten of in de necrotische en verwelkte bladeren.