Fungus Ophiostoma Ulmi Research Articles

ECONOMIC AND SOCIAL CONSEQUENCES OF INVASIONS OF PESTS AND PATHOGENS OF TREES IN ST. PETERSBURG

An economic assessment of the damage caused by invasive tree insect pests and pathogens in urban plantings of St. Petersburg is given. Between 2001 and 2020, the invasion of elm bark beetles Scolytus multistriatus (Marsham), S. scolytus (Fabricius) and S. pygmaeus (Fabricius) and the concomitant spread of Dutch elm disease caused by the fungi Ophiostoma ulmi (Buisman) Nannfeldt and O. novo-ulmi (Brasier) (Ascomycota: Ophiostomataceae) resulted in the death of at least 37 000 elms in the city. The total damage exceeded 50 billion rubles. Compulsory sanitary cutting of the infected elms raised significant public concern. Plantations of common use, especially historical parks and gardens, lost most important landscape compositions, in which exactly elm trees had a key role. In two years, 2022-2022, the economic losses associated with the invasion and spread of Emerald ash borer Agrilus planipennis , reached 270 million rubles. Detection of infested ash trees and their timely felling was effective. However, not all infested trees were spotted and removed and the pest reproduction continued. Urgent measures are needed to prevent further spread of Emerald ash borer and other invasive pests and pathogens in St. Petersburg and adjacent territories.

Feeding by Scolytus bark beetles to test for differently susceptible elm varieties

AbstractDutch elm disease (DED), caused by the fungi Ophiostoma ulmi and O. novo‐ulmi, has reduced elm populations severely in Europe and North America. Breeding programmes are in action to find less susceptible elm varieties suitable for re‐establishing elm stands. Bark beetles, mainly Scolytus spp., are the only known natural vectors of DED. During twig feeding, beetles transfer Ophiostoma spores to healthy elms. Thus, less palatable elms should run a lower risk of DED infections. In feeding preference bioassays, we offered twigs from elms exhibiting different degree of susceptibility to O. novo‐ulmi, together with non‐host trees to Scolytus beetles. Scolytus multistriatus preferred wych elm, Ulmus glabra, to 100% in two‐choice tests, whereas S. laevis did not discriminate between a tolerant and a susceptible variety of field elm, U. minor. We suggest that the feeding assay is useful as a low‐tech method in breeding programmes for evaluating the suitability of promising elm genotypes to vector insects.

Diversity in yeast-mycelium dimorphism response of the Dutch elm disease pathogens: the inoculum size effect.

Dutch elm disease (DED) is caused by the dimorphic fungi Ophiostoma ulmi, Ophiostoma novo-ulmi, and Ophiostoma himal-ulmi. A cell population density-dependent phenomenon related to quorum sensing was previously shown to affect the reversible transition from yeast-like to mycelial growth in liquid shake cultures of O. novo-ulmi NRRL 6404. Since the response to external stimuli often varies among DED fungal strains, we evaluated the effect of inoculum size on 8 strains of the 3 species of DED agents by determining the proportion of yeast and mycelium produced at different spore inoculum concentrations in defined liquid shake medium. The results show that not all DED fungi strains respond similarly to inoculum size effect, since variations were observed among strains. It is thus possible that the different strains belonging to phylogenetically close species use different signalling molecules or molecular signalling pathways to regulate their growth mode via quorum-sensing mechanisms.

Dutch elm Disease and the Habitat of Endangered Rosalia LongicornRosalia alpina(L.): A Conservation Paradox?

ABSTRACT In central Europe, the endangered Rosalia longicorn Rosalia alpina (L.) has rarely been observed to develop in the wood of elms Ulmus sp.; however, this beetle has recently expanded into habitats formed by elms. The factors driving these changes are unknown in detail, but a potential one is the increasing amount of breeding material, namely, dead elm wood. Dutch elm disease, caused by the fungi Ophiostoma ulmi and O. novo-ulmi, by killing off elm trees, has created a supply of dead wood. The aim of this work was to assess the potential role of Dutch elm disease in the formation of habitats suitable for the endangered Rosalia longicorn. The health of four elm stands (Carpathians, SE Poland) was analysed and the pathogen responsible for elm death were determined by DNA sequence comparison. O. novo-ulmi — the causative agent of Dutch elm disease — was isolated from weakened and dying trees at all studied localities. In total, 30% of the elm trees were dead, 34% showed signs of dieback or were moribu...

Dutch elm disease and elm bark beetles: a century of association

Bark beetles of the genus Scolytus Geoffroy are the main vectors of the fungus Ophiostoma ulmi s.l., which causes the Dutch elm disease. The large and small elm bark beetles - S. scolytus (F.) and S. multistriatus (Marsham), respectively - are the most common and important species spreading the pathogen worldwide. The success of the pathogen-insect interactions is mainly due to the characteristic reproductive behavior of the elm bark beetles, which, however, largely depends on the occurrence of infected trees. During feeding activity on elm twigs, callow adults carrying pathogen conidia on their bodies contaminate healthy trees and facilitate pathogen development and movement within the wood vessels. Infected trees become then suitable for insect breeding in the stem bark. This well-known mutualistic association has devastating consequences for elm survival. Although much is known about insect-pathogen interactions and transmission mechanisms, many topics still deserve additional attention, as, for example, beetle systematic based on new molecular tools and morphological characters; selection of European elm clones based on disease avoidance; consequences of global warming on life-history of the three organisms (fungus-insect-tree) involved in the pathosystem; new problems resulting from the rapid increase of international trade among continents, leading to the accidental introduction of new vector species or new pathogen species or races, or to the introduction of new highly susceptible elm species in gardens and public parks. A holistic approach to tackle the problem is highly recommended, taking into account how these organisms interact with each other and the environment, and how their interactions could be modified in order to face one of the most destructive diseases ever known in plant pathology.

Sequencing and annotation of the Ophiostoma ulmigenome

BackgroundThe ascomycete fungus Ophiostoma ulmi was responsible for the initial pandemic of the massively destructive Dutch elm disease in Europe and North America in early 1910. Dutch elm disease has ravaged the elm tree population globally and is a major threat to the remaining elm population. O. ulmi is also associated with valuable biomaterials applications. It was recently discovered that proteins from O. ulmi can be used for efficient transformation of amylose in the production of bioplastics.ResultsWe have sequenced the 31.5 Mb genome of O.ulmi using Illumina next generation sequencing. Applying both de novo and comparative genome annotation methods, we predict a total of 8639 gene models. The quality of the predicted genes was validated using a variety of data sources consisting of EST data, mRNA-seq data and orthologs from related fungal species. Sequence-based computational methods were used to identify candidate virulence-related genes. Metabolic pathways were reconstructed and highlight specific enzymes that may play a role in virulence.ConclusionsThis genome sequence will be a useful resource for further research aimed at understanding the molecular mechanisms of pathogenicity by O. ulmi. It will also facilitate the identification of enzymes necessary for industrial biotransformation applications.

Antifungal effect and reduction of Ulmus minor symptoms to Ophiostoma novo-ulmi by carvacrol and salicylic acid

There are still no effective means to control Dutch elm disease (DED), caused by the vascular fungi Ophiostoma ulmi and O. novo-ulmi. Plant phenolics may provide a new strategy for DED control, given their known antifungal activity against pathogens and their involvement in plant defence mechanisms. The in vitro antifungal activity of salicylic acid, carvacrol, thymol, phenol, o-cresol, m-cresol, p-cresol, and 2,5-xylenol against the DED pathogens was tested. Also, the protective effect of watering Ulmus minor seedlings with these compounds was tested against O. novo-ulmi. Salicylic acid, carvacrol, and thymol showed the strongest antifungal in vitro activity, while carvacrol and salicylic acid provided the strongest in vivo protection against O. novo-ulmi (63 and 46% reduction of leaf wilting symptoms with respect to controls, respectively). The effect of the treatments on tree phenology was low, and a significant negative relation was observed between the number of days to bud burst and the leaf wilting symptoms after inoculation, probably determined by genetic differences among the elm tree progenies used. The treatments with salicylic acid, carvacrol and thymol induced the highest shift in phenolic metabolite profile with respect to control trees. The protective effect of carvacrol and salicylic acid is discussed in terms of their combined activity as antifungal compounds and as inductors of tree defence responses.

Analysis of Spanish populations of Ophiostoma ulmi and O. novo‐ulmi using phenotypic characteristics and RAPD markers

One hundred and six isolates of the Dutch elm disease (DED) fungi Ophiostoma ulmi and Ophiostoma novo‐ulmi were collected from elm trees with symptoms in 15 regions of Spain. Isolates were compared with eight reference strains belonging to O. ulmi and the two subspecies of O. novo‐ulmi. The purpose of this study was to assign Spanish isolates to species and subspecies of the DED fungi and to analyse the genetic variability within the Spanish populations of these pathogens. Isolates were examined for their growth rates, colony morphologies and fertility responses and by using random amplified polymorphic DNA (RAPD) markers. Six isolates were identified as O. ulmi, 16 as O. novo‐ulmi ssp. novo‐ulmi and 78 as O. novo‐ulmi ssp. americana. Nei's and Shannon's diversity indices and the upgma dendrogram from RAPD profiles indicated a high level of variation among isolates, probably reflecting post‐epidemic status of DED in Spain. Although most isolates were separated into three major clusters representing the three taxa of DED fungi in the RAPD analysis, two isolates from central Spain clustered between O. novo‐ulmi ssp. americana and O. novo‐ulmi ssp. novo‐ulmi, and four isolates from Mallorca clustered between O. ulmi and the group representing O. novo‐ulmi ssp. novo‐ulmi. Mating tests conducted with these isolates revealed a variety of fertility responses. The novel combinations between molecular profile and fertility reaction suggest that three isolates from Mallorca may be interspecific hybrids of the DED fungi.

Molecular and cellular aspects of Dutch elm disease

The folio wing review gives an overview of current research in the area of molecular and cellular interactions in Dutch elm disease. This vascular wilt disease is caused by the fungus Ophiostoma ulmi and is transmitted from diseased to healthy trees by the elm bark beetles. Fungal toxins are described which are associated with pathogenesis, one of which, ceratoulmin, is under investigation at the molecular level, particularly regarding its mode of action and localization. The fungus has also been examined at the molecular level to differentiate between aggressive and non-aggressive isolates on the basis of protein and nucleic acid profiles. Genetic linkage maps are being developed to correlate disruption of certain genes with the loss of pathogenicity. Viral and bacterial antagonists of the fungus, which may serve as biological control mechanisms for Dutch elm disease, have been characterized, as have several of the active molecules responsible for control. Host responses are also discussed at the molecular and biochemical level, including phytoalexins and defense mechanism elicitors. Several Unes of investigation are discussed to provide an overview of molecular approaches to understanding and manipulating the organisms involved with the ultimate goal of controlling Dutch elm disease.

The American elm and Dutch elm disease

Shortly after World War I, a new disease previously unknown among elms emerged in Holland. It spread rapidly from Europe to Great Britain (1927), United States (1930), and Canada (1945), killing millions of elms. The disease known, as Dutch elm disease (DED) is a wilt disease, caused by the fungus Ophiostoma ulmi. It is transmitted from tree to tree by elm bark beetles (scolytid) vectors. Numerous attempts to control the disease have concentrated on the reduction of insect vector populations, exploitation of natural host resistance, extensive application of fungicides and integrated pest management. In spite of these efforts in Canada, the disease continues to migrate westwards threatening the elm populations in Saskatchewan and Alberta. Today there are approximately 700 000 elm shade trees in cities and towns across Canada and their value exceeds $2.5 billion dollars.With the advance of molecular biology new, powerful tools are now available to study, in greater detail, the molecular and biochemical mechanisms of the DED pathogen, with particular reference to the mechanisms that induce host defenses. A glycoprotein has been isolated and identified such that when injected either in liquid or pellet form into the elm tree, significantly reduced the wilting symptoms of both five-year old elm seedlings and 10 cm diameter trees. The elicitor induces a chain of defensive reactions that prevent the rapid spread of the fungus within the vascular system of the host. Key words: Ophiostoma ulmi, elm bark beetle vectors, induced resistance, chemical control, RFLP, mitochondrial DNA, ribosomal DNA, virus-like DNA, resistance breeding

Refinement of physiological roles for cerato-ulmin by analogy with other hydrophobins

Cerato-ulmin, a hydrophobic protein produced by the Dutch elm disease fungus Ophiostoma ulmi, is toxic to susceptible elms. The physiological role of this protein may be related to its location on hyphal surfaces. Cerato-ulmin is a member of the hydrophobins, proteins used in the formation of structures involved in asexual reproduction (sporulation and conidiation).

Nonsporulation in the Dutch elm disease fungus Ophiostoma ulmi: evidence for control by a single nuclear gene

A single nuclear gene controls nonsporulation in a novel isolate of the Dutch elm disease fungus Ophiostoma ulmi (Buism.) Nannf. This has been clearly demonstrated through segregation of the nonsporulating phenotype-in meiotic products recovered from crosses between a mutant nonsporulating isolate (WRB2-1) and wild-type sporulating isolates, between F1 progeny and their parents, and between F1 progeny. All crosses between nonsporulating and sporulating isolates yielded a 1:1 ratio for these two phenotypes in the meiotic products, whereas all crossings between isolates of the same phenotype produced meiotic products of that phenotype. The genetic stability of the nonsporulating phenotype was clearly shown when no disease symptoms were observed following artificial inoculation of the nonsporulating progeny into white elm, Ulmus americana L. Exposure to trifluoperazine, a calmodulin inhibitor, did not shift the nonsporulating isolates to the yeast phase, which supports our findings that nonsporulation is under genetic control rather than metabolic control. Key words: nonsporulation, Ophiostoma ulmi, mutant, single nuclear gene, meiotic products.

Effect of polyamine biosynthesis inhibitors on mycelial growth and concentrations of polyamines in Ophiostoma ulmi (Buism.) Nannf.

Several inhibitors of polyamine biosynthesis reduced mycelial growth of the fungus Ophiostoma ulmi (Buism.) Nannf. cultured on malt extract-agar medium. Growth inhibition was particularly evident when expressed in terms of fresh weight rather than colony diameter. Of the different drugs tested, the most effective was difluoromethylarginine (DFMA), while difluoromethylornithine (DFMO) and methylglyoxal(bis)guanyl-hydrazone (MGBG) plus cyclohexylamine (CHA) reduced growth only by 75 and 62% respectively. The growth inhibition by DFMO + DFMA, measured as colony diameter, was apparently reversed by putrescine (PUT), but not when expressed in terms of fresh weight. Spermidine (SPD) was the most abundant polyamine in control cultures, followed by PUT and spermine (SPM). PUT was no longer detectable 8 d after inoculation. On day 10, DFMO and DFMA, alone and in combination, caused a significant reduction in cellular SPD concentrations, while exogenously supplied PUT restored the levels of this polyamine to control values. MGBG + CHA caused a conspicuous accumulation of PUT and an approximately 50% reduction in SPD titres. DFMA, alone or in combination with DFMO and with or without PUT, led to increased cellular levels of SPM. The latter polyamine, but not PUT or SPD, strongly retarded growth when added to the growth medium. As suggested by the effectiveness of DFMA in inhibiting growth, arginine decarboxylase activity was shown to be prevalent over ornithine decarboxylase activity in this fungus.

Effect of Elm Selection, Explant Source and Medium Composition on Growth of Ophiostoma ulmi on Callus Cultures

Abstract We examined the effects of elm selection, explant source and media composition on growth of the Dutch elm disease (DED) fungus Ophiostoma ulmi on callus cultures. Calluses were generated from leaf and stem tissue of an American elm (Ulmus Americana L.) seedling (A), susceptible to the disease; an American elm selection 8630, resistant to the disease; and a Siberian elm (U. pumila L.) seedling, also resistant to DED. Calluses were generated on modified Murashige-Skoog (MMS) medium, either with (MMSC) or without coconut milk. Explant source did not affect the fungal growth rate on the callus. Rate of O. ulmi growth on American elm A callus was similar on both media; on Siberian and 8630, fungal growth rate was more rapid on callus cultured on MMS than on MMSC. However, in the absence of callus tissue, O. ulmi growth on MMSC medium was more than five times as rapid as it was on MMS. We observed significant interactions between explant source and selection, and between medium and selection. Fungal growth was always more rapid on American A, and American 8630 then on Siberian. Scanning electron microscopy revealed heavy fungal sporulation on American A, slight on Siberian and none on American 8630. High performance liquid chromatography analysis showed that the secondary metabolic profiles were distinguishable for callus tissue versus explant tissue, but were similar for calli generated from different explant sources.