121-455: Dutch elm disease ( DED ) is caused by a member of the sac fungi (Ascomycota) affecting elm trees, and is spread by elm bark beetles . Believed to be originally native to Asia , the disease was accidentally introduced into America , Europe , and New Zealand . In these regions it has devastated native populations of elms that did not have resistance to the disease. The name "Dutch elm disease" refers to its identification in 1921 and later in
242-531: A gynaecological operation. Although the surgery initially appeared successful, she succumbed to an infection on March 27, just five days after her 36th birthday. Buisman was buried three days later at the hilltop cemetery 'Westerveld' at Driehuis , set in the dunes of the North Sea west of Amsterdam. When the Dutch Elm Committee decided to release clone No. 24 in 1937, the clone was named for
363-1196: A thallus usually referred to as the mycelium , which—when visible to the naked eye (macroscopic)—is commonly called mold . During sexual reproduction, many Ascomycota typically produce large numbers of asci . The ascus is often contained in a multicellular, occasionally readily visible fruiting structure, the ascocarp (also called an ascoma ). Ascocarps come in a very large variety of shapes: cup-shaped, club-shaped, potato-like, spongy, seed-like, oozing and pimple-like, coral-like, nit-like, golf-ball-shaped, perforated tennis ball-like, cushion-shaped, plated and feathered in miniature ( Laboulbeniales ), microscopic classic Greek shield-shaped, stalked or sessile. They can appear solitary or clustered. Their texture can likewise be very variable, including fleshy, like charcoal (carbonaceous), leathery, rubbery, gelatinous, slimy, powdery, or cob-web-like. Ascocarps come in multiple colors such as red, orange, yellow, brown, black, or, more rarely, green or blue. Some ascomyceous fungi, such as Saccharomyces cerevisiae , grow as single-celled yeasts, which—during sexual reproduction—develop into an ascus, and do not form fruiting bodies. In lichenized species,
484-515: A vector for infection, it is much less effective than the large elm bark beetle, S. scolytus . H. rufipes can be a vector for the disease, but is inefficient compared to the other vectors. S. schevyrewi was found in 2003 in Colorado and Utah . Other reported DED vectors include Scolytus sulcifrons , S. pygmaeus , S. laevis , Pteleobius vittatus and Р. kraatzi . Other elm bark beetle species are also likely vectors. 'Field resistance'
605-481: A DED-ridden area. These have been tested and some have a very high level of resistance. At Noordplant Nursery new hybrids have been tested since 2013. Ten resistant American elm cultivars are now in commerce in North America. No cultivar is immune to DED; even highly resistant cultivars can become infected, particularly if already stressed by drought or other environmental conditions where the disease prevalence
726-472: A bottle shaped cell called a phialide , from which the spores are produced. Not all of these asexual structures are a single hypha. In some groups, the conidiophores (the structures that bear the conidia) are aggregated to form a thick structure. E.g. In the order Moniliales, all of them are single hyphae with the exception of the aggregations, termed as coremia or synnema. These produce structures rather like corn-stokes, with many conidia being produced in
847-506: A double-dividing wall with a central lamella (layer) forms between the cells; the central layer then breaks down thereby releasing the spores. In rhexolytic dehiscence, the cell wall that joins the spores on the outside degenerates and releases the conidia. Several Ascomycota species are not known to have a sexual cycle. Such asexual species may be able to undergo genetic recombination between individuals by processes involving heterokaryosis and parasexual events. Parasexuality refers to
968-528: A few branches, and had largely died out by 1940 owing to its susceptibility to viruses. In around 1967, a new, far more virulent , strain arrived in Britain, apparently via east coast ports on shipments of rock elm U. thomasii logs from Canada destined for the small-boat industry, confirmed in 1973 when another consignment was examined at Southampton Docks. This strain proved both highly contagious and lethal to European elms; more than 25 million trees died in
1089-433: A form of pneumonia . Asci of Ascosphaera fill honey bee larvae and pupae causing mummification with a chalk-like appearance, hence the name "chalkbrood". Yeasts for small colonies in vitro and in vivo , and excessive growth of Candida species in the mouth or vagina causes "thrush", a form of candidiasis . The cell walls of the ascomycetes almost always contain chitin and β-glucans , and divisions within
1210-476: A further mitotic division that results in eight nuclei in each ascus. The nuclei along with some cytoplasma become enclosed within membranes and a cell wall to give rise to ascospores that are aligned inside the ascus like peas in a pod. Upon opening of the ascus, ascospores may be dispersed by the wind, while in some cases the spores are forcibly ejected form the ascus; certain species have evolved spore cannons, which can eject ascospores up to 30 cm. away. When
1331-743: A hypha. Vegetative hyphae of most ascomycetes contain only one nucleus per cell ( uninucleate hyphae), but multinucleate cells—especially in the apical regions of growing hyphae—can also be present. In common with other fungal phyla, the Ascomycota are heterotrophic organisms that require organic compounds as energy sources. These are obtained by feeding on a variety of organic substrates including dead matter, foodstuffs, or as symbionts in or on other living organisms. To obtain these nutrients from their surroundings, ascomycetous fungi secrete powerful digestive enzymes that break down organic substances into smaller molecules, which are then taken up into
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#17327943963281452-529: A large-scale specialized structure that helps to spread them. These two basic types can be further classified as follows: Sometimes the conidia are produced in structures visible to the naked eye, which help to distribute the spores. These structures are called "conidiomata" (singular: conidioma ), and may take the form of pycnidia (which are flask-shaped and arise in the fungal tissue) or acervuli (which are cushion-shaped and arise in host tissue). Dehiscence happens in two ways. In schizolytic dehiscence,
1573-433: A mass from the aggregated conidiophores. The diverse conidia and conidiophores sometimes develop in asexual sporocarps with different characteristics (e.g. acervulus, pycnidium, sporodochium). Some species of ascomycetes form their structures within plant tissue, either as parasite or saprophytes. These fungi have evolved more complex asexual sporing structures, probably influenced by the cultural conditions of plant tissue as
1694-430: A number of methods to control the epidemic, including sanitation , pruning , injecting trees with fungicide and replanting with DED-resistant American elm cultivars (see Ulmus americana cultivars ). The NPS combated the disease's local insect vector , the smaller European elm bark beetle ( Scolytus multistriatus ), by trapping and by spraying with insecticides . As a result, the population of American elms planted on
1815-879: A paper published in the Journal of the Arnold Arboretum , Vol. XII (1931): "Three Species of Botryodiplodia Sacc. on Elm Trees in the United States". During Buisman's stay in the US, the threat posed by DED in the Netherlands was taken more seriously and, in February 1930, a second attempt led to the founding of the Committee for Study and Control of the Elm Disease . Westerdijk invited Buisman to accept
1936-560: A prevention program initiated in 1981. Alberta and British Columbia are the only provinces that are currently free of Dutch elm disease, although, in an isolated case, an elm tree in Wainwright, Alberta , was found diseased in June 1998 and was immediately destroyed. The presence of DED was monitored in this area during subsequent years but was not seen again. Today, Alberta has the largest number of elms unaffected by Dutch elm disease in
2057-666: A progressive manner throughout the tree, with further dieback of branches. Eventually, the roots die, starved of nutrients from the leaves. Often, not all the roots die: the roots of some species, especially the English elm (formerly Ulmus procera ), can repeatedly put up suckers, which flourish for approximately 15 years before dying off. Dutch elm disease was first noticed in continental Europe in 1910, and spread slowly and eventually extended to all other countries except Greece and Finland. Barendina Gerarda Spierenburg compiled records of trees displaying symptoms from 1900 - 1905 onwards in
2178-552: A separate artificial phylum , the Deuteromycota (or "Fungi Imperfecti"). Where recent molecular analyses have identified close relationships with ascus-bearing taxa, anamorphic species have been grouped into the Ascomycota, despite the absence of the defining ascus. Sexual and asexual isolates of the same species commonly carry different binomial species names, as, for example, Aspergillus nidulans and Emericella nidulans , for asexual and sexual isolates, respectively, of
2299-486: A shipment of logs from the Netherlands destined for use as veneer in the Ohio furniture industry. Quarantine and sanitation procedures held most cases within 150 mi (240 km) of metropolitan New York City until 1941 when war demands began to curtail them. The disease spread from New England westward and southward, almost completely destroying the famous elms in the "Elm City" of New Haven, Connecticut , reaching
2420-545: A small number of wych elms U. glabra surviving in areas of high infectivity, prompting the Royal Botanic Garden Edinburgh to begin a programme of selecting trees, with a view to determining innate resistance (2009). The Garden is raising and distributing in Scotland seedlings derived from controlled crosses of rare survivors in these areas (2023). In 2001–2004, English elm U. minor 'Atinia'
2541-652: A source of antifungal genes. Early efforts in the USA involved the hybridization of the Siberian elm U. pumila with American red elm U. rubra to produce resistant trees. Resulting cultivars lacked the traditional shape and landscape value of the American elm; few were planted. In 2005, the National Elm Trial (USA) began a 10-year evaluation of 19 cultivars in plantings across the United States. The trees in
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#17327943963282662-408: A substrate. These structures are called the sporodochium . This is a cushion of conidiophores created from a pseudoparenchymatous stroma in plant tissue. The pycnidium is a globose to flask-shaped parenchymatous structure, lined on its inner wall with conidiophores. The acervulus is a flat saucer shaped bed of conidiophores produced under a plant cuticle, which eventually erupt through
2783-469: A syringe, a method which would be used in successive decades. In 1927, she succeeded in producing both vascular discolouration and leaf wilt, simply by inoculating her trial plants earlier in summer than Bea Schwarz had done in 1921, confirming the results achieved by Wollenweber and Stapp in Berlin, providing the definitive proof that Graphium ulmi caused Dutch elm disease (DED). In 1929, Buisman left
2904-551: A tetraploid nucleus which divided into four diploid nuclei by meiosis and then into eight haploid nuclei by a supposed process called brachymeiosis , but this hypothesis was disproven in the 1950s. From the fertilized ascogonium, dinucleate hyphae emerge in which each cell contains two nuclei. These hyphae are called ascogenous or fertile hyphae. They are supported by the vegetative mycelium containing uni– (or mono–) nucleate hyphae, which are sterile. The mycelium containing both sterile and fertile hyphae may grow into fruiting body,
3025-485: A tree has unusual symbolic value or occupies a particularly important place in the landscape. Research to select resistant cultivars and varieties began in the Netherlands in 1928, followed by the United States in 1937 (see Ulmus americana cultivars ). Initial efforts in the Netherlands involved crossing varieties of U. minor and U. glabra , but later included the Himalayan or Kashmir elm U. wallichiana as
3146-511: A trend aided by fungicides . Lignasan BLP ( carbendazim phosphate ), introduced in the 1970s, was the first fungicide used to control Dutch elm disease. This had to be injected into the base of the tree using specialized equipment, and was never especially effective. It is still sold under the name "Elm Fungicide". Arbotect ( thiabendazole hypophosphite ) became available some years later, and it has been proven effective. Arbotect must be injected every two to three years to provide ongoing control;
3267-423: A variety of stresses such as nutrient limitation. The sexual part of the life cycle commences when two hyphal structures mate . In the case of homothallic species, mating is enabled between hyphae of the same fungal clone , whereas in heterothallic species, the two hyphae must originate from fungal clones that differ genetically, i.e., those that are of a different mating type . Mating types are typical of
3388-476: A wind speed of less than five metres per second. The largest concentration of mature elms in Scotland is in Edinburgh , where over 5,000 remained in 2009 from some 35,000 in 1976. The city council gives the overall number of elms as 15,000 (2016). Edinburgh's Leith Links and Meadows have some of the highest concentrations of mature elms among U.K. parks (2014). A policy of sanitary felling has kept losses in
3509-417: Is a dictyospore . In staurospores ray-like arms radiate from a central body; in others ( helicospores ) the entire spore is wound up in a spiral like a spring. Very long worm-like spores with a length-to-diameter ratio of more than 15:1, are called scolecospores . Important characteristics of the anamorphs of the Ascomycota are conidiogenesis , which includes spore formation and dehiscence (separation from
3630-484: Is a tube-shaped vessel, a meiosporangium , which contains the sexual spores produced by meiosis and which are called ascospores . Apart from a few exceptions, such as Candida albicans , most ascomycetes are haploid , i.e., they contain one set of chromosomes per nucleus. During sexual reproduction there is a diploid phase, which commonly is very short, and meiosis restores the haploid state. The sexual cycle of one well-studied representative species of Ascomycota
3751-491: Is an umbrella term covering the various factors by which some elms avoid infection in the first place, rather than survive it. A clear example would be the European White Elm ( Ulmus laevis ) which, while having little or no genetic resistance to DED, synthesizes a triterpene , Alnulin, rendering the bark distasteful to the vector beetles, obliging them to look further afield for more suitable elms. Another would be
Dutch elm disease - Misplaced Pages Continue
3872-600: Is believed to be in the city of Winnipeg , where close to 200,000 elms remain. The city spends $ 3 million annually to aggressively combat the disease using Dursban Turf and the Dutch Trig vaccine. Dutch elm disease has reached New Zealand . It was found in Napier where it was eradicated and was also found in the Auckland Region in 1989. The Ministry of Agriculture funded a national management programme but it
3993-457: Is described in greater detail in Neurospora crassa . Also, the adaptive basis for the maintenance of sexual reproduction in the Ascomycota fungi was reviewed by Wallen and Perlin. They concluded that the most plausible reason for the maintenance of this capability is the benefit of repairing DNA damage by using recombination that occurs during meiosis . DNA damage can be caused by
4114-703: Is high. With the exception of 'Princeton', no trees have yet been grown to maturity; trees cannot be said to be mature until they have reached an age of 60 years. Notable cultivars include: In 2007, the Elm Recovery Project of the University of Guelph Arboretum in Ontario, Canada, reported that cuttings from healthy surviving old elms surveyed across Ontario had been grown to produce a bank of resistant trees, isolated for selective breeding of highly resistant cultivars. The University of Minnesota USA
4235-413: Is injected. Alamo is primarily recommended for treatment of oak wilt . Multistriatin is a pheromone produced by female elm bark beetles, which can be produced synthetically. It has potential in being used to trap male beetles, which carry the fungus. Because of the ban on the use of chemicals on street and park trees in the Netherlands, the University of Amsterdam developed a biological vaccine by
4356-600: Is now hoped that the controlled crossing of the best seven of these (genetically and aesthetically) will produce Ulmus minor hybrids with effective 'field resistance' and market appeal. Similar results are beginning to emerge in trials on surviving field elms in Greece. Much of the work in the United Kingdom is by the Forestry Commission's research arm, which has had Dutch elm disease on its agenda since
4477-531: Is only found on Nothofagus (Southern Beech) in the Southern Hemisphere . Asexual reproduction is the dominant form of propagation in the Ascomycota, and is responsible for the rapid spread of these fungi into new areas. It occurs through vegetative reproductive spores, the conidia . The conidiospores commonly contain one nucleus and are products of mitotic cell divisions and thus are sometimes called mitospores, which are genetically identical to
4598-434: Is standard in both continents, its composition reflects the different Ophiostoma species, subspecies and hybrids endemic to the two continents. In Italy for example, two subspecies, americana and novo-ulmi , are present together with their hybrid, whereas in North America, ssp. novo-ulmi is unknown. The differences in method and inocula possibly explain why the American cultivar 'Princeton' , displaying high resistance in
4719-526: Is testing various elms, including a huge now-patented century-old survivor known as "The St. Croix Elm" , which is located in a Minneapolis-St. Paul, MN suburb (Afton) in the St. Croix River valley—a designated National Scenic Riverway. The slippery or red elm U. rubra is marginally less susceptible to Dutch elm disease than the other American species, but this quality seems to have been largely ignored in American research. No cultivars were ever selected, although
4840-527: Is the elm most favoured by the Scolytus beetles. Thirty years after the outbreak of the epidemic , nearly all these trees, which often grew to more than 45 m high, are gone. The species still survives in hedgerows , as the roots are not killed and send up root sprouts ( "suckers" ). These suckers rarely reach more than 5 m tall before dying off from a new attack. However, established hedges kept low by clipping have remained apparently healthy throughout
4961-461: Is the unique example of the European white elm U. laevis , which has little innate resistance to DED, but is eschewed by the vector bark beetles and only rarely becomes infected. Recent research has indicated it is the presence of certain organic compounds, such as triterpenes and sterols , which serves to make the tree bark unattractive to the beetle species that spread the disease. In Europe
Dutch elm disease - Misplaced Pages Continue
5082-463: Is usually inconspicuous because it is commonly embedded in the substrate, such as soil, or grows on or inside a living host, and only the ascoma may be seen when fruiting. Pigmentation , such as melanin in hyphal walls, along with prolific growth on surfaces can result in visible mold colonies; examples include Cladosporium species, which form black spots on bathroom caulking and other moist areas. Many ascomycetes cause food spoilage, and, therefore,
5203-416: The ascocarp , which may contain millions of fertile hyphae. An ascocarp is the fruiting body of the sexual phase in Ascomycota. There are five morphologically different types of ascocarp, namely: The sexual structures are formed in the fruiting layer of the ascocarp, the hymenium . At one end of ascogenous hyphae, characteristic U-shaped hooks develop, which curve back opposite to the growth direction of
5324-402: The ascogonium , and merges with a gametangium (the antheridium ) of the other fungal isolate. The nuclei in the antheridium then migrate into the ascogonium, and plasmogamy —the mixing of the cytoplasm —occurs. Unlike in animals and plants, plasmogamy is not immediately followed by the merging of the nuclei (called karyogamy ). Instead, the nuclei from the two hyphae form pairs, initiating
5445-729: The Basidiomycota , forms the subkingdom Dikarya . Its members are commonly known as the sac fungi or ascomycetes . It is the largest phylum of Fungi, with over 64,000 species . The defining feature of this fungal group is the " ascus " (from Ancient Greek ἀσκός ( askós ) 'sac, wineskin'), a microscopic sexual structure in which nonmotile spores , called ascospores , are formed. However, some species of Ascomycota are asexual and thus do not form asci or ascospores. Familiar examples of sac fungi include morels , truffles , brewers' and bakers' yeast , dead man's fingers , and cup fungi . The fungal symbionts in
5566-643: The Detroit area in 1950, the Chicago area by 1960, and Minneapolis by 1970. Of the estimated 77 million elms in North America in 1930, over 75% had been lost by 1989. The disease first appeared on the planted rows of American elm trees ( Ulmus americana ) on the National Mall in Washington, D.C. , during the 1950s and reached a peak in the 1970s. The United States National Park Service (NPS) used
5687-639: The Netherlands by Dutch phytopathologists Bea Schwarz and Christine Buisman , who both worked with professor Johanna Westerdijk . The disease affects species in the genera Ulmus and Zelkova , therefore it is not specific to the Dutch elm hybrid . Dutch elm disease (DED) is caused by ascomycete microfungi . Three species are now recognized: DED is spread in North America by three species of bark beetles (Family: Curculionidae , Subfamily: Scolytinae): In Europe, while S. multistriatus still acts as
5808-456: The conidia . The asexual, non-motile haploid spores of a fungus, which are named after the Greek word for dust (conia), are hence also known as conidiospores . The conidiospores commonly contain one nucleus and are products of mitotic cell divisions and thus are sometimes called mitospores , which are genetically identical to the mycelium from which they originate. They are typically formed at
5929-627: The detritivores (animals that feed on decomposing material) to obtain their nutrients. Ascomycetes, along with other fungi, can break down large molecules such as cellulose or lignin , and thus have important roles in nutrient cycling such as the carbon cycle . The fruiting bodies of the Ascomycota provide food for many animals ranging from insects and slugs and snails ( Gastropoda ) to rodents and larger mammals such as deer and wild boars . Many ascomycetes also form symbiotic relationships with other organisms, including plants and animals. Probably since early in their evolutionary history,
6050-401: The dikaryophase of the sexual cycle, during which time the pairs of nuclei synchronously divide. Fusion of the paired nuclei leads to mixing of the genetic material and recombination and is followed by meiosis . A similar sexual cycle is present in the red algae (Rhodophyta). A discarded hypothesis held that a second karyogamy event occurred in the ascogonium prior to ascogeny, resulting in
6171-685: The ergot fungi, black knot , and the powdery mildews . The members of the genus Cordyceps are entomopathogenic fungi , meaning that they parasitise and kill insects. Other entomopathogenic ascomycetes have been used successfully in biological pest control , such as Beauveria . Several species of ascomycetes are biological model organisms in laboratory research. Most famously, Neurospora crassa , several species of yeasts , and Aspergillus species are used in many genetics and cell biology studies. Ascomycetes are 'spore shooters'. They are fungi which produce microscopic spores inside special, elongated cells or sacs, known as 'asci', which give
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#17327943963286292-479: The photoautotrophic algal partner generates metabolic energy through photosynthesis, the fungus offers a stable, supportive matrix and protects cells from radiation and dehydration. Around 42% of the Ascomycota (about 18,000 species) form lichens, and almost all the fungal partners of lichens belong to the Ascomycota. Christine Buisman Christine Johanna Buisman ( Dutch pronunciation: [krɪsˈtinə joːˈɦɑnaː ˈbœysmɑn] ; 22 March 1900 – 27 March 1936)
6413-446: The vascular cambium , the other being the phloem ) delivers water and nutrients to the rest of the plant, these plugs prevent them from travelling up the trunk of the tree , starving the tree of water and nutrients, which eventually kills it. The first symptom of infection is usually an upper branch of the tree with leaves starting to wither and yellow in summer, months before the normal autumnal leaf shedding. This morbidity spreads in
6534-399: The 1920s. In 1994 a Research Information Note (no 252) was published, written by John Gibbs, Clive Brasier and Joan Webber, and in 2010 a Pathology Advisory Note, as well as throughout the period a stream of more academic papers: notable results have been the observation that the progress of the disease through Scotland has been quite slow, and that genetic engineering has been tried to improve
6655-472: The 1940s and 50s; the species last featured in hybridization as the female parent of 'Repura' and 'Revera' , both patented in 1993, although neither has yet appeared in commerce. In Italy , research was initiated at the Istituto per la Protezione delle Piante, Florence, to produce a range of disease-resistant trees adapted to the warmer Mediterranean climate, using a variety of Asiatic species crossed with
6776-571: The 1990s, a programme of antifungal injections of the most prominent 10,000 elms, and of sanitation felling, has reduced annual elm losses in The Hague from 7% to less than 1% (see below: Preventive treatment ). The losses are made up by the planting of disease-resistant cultivars . The largest concentration of mature elm trees remaining in England is in Brighton and Hove , East Sussex , where of
6897-669: The 30,000 elms in 1983 15,000 still stand (2005 figures), several of which are estimated to be over 400 years old. Their survival is owing to the isolation of the area, between the English Channel and the South Downs , and the assiduous efforts of local authorities to identify and remove infected sections of trees immediately when they show symptoms of the disease. Empowered by the Dutch Elm Disease (Local Authorities) (Amendment) Order 1988, local authorities may order
7018-456: The American elm have been successful; in a six-year experiment with the American elm in Denver, CO, annual Dutch elm disease losses declined significantly after the first year from 7 percent to between 0.4 and 0.6 percent; a greater and more rapid reduction in disease incidence than the accompanying tree sanitation and plant health care programs. Preventive treatment is usually justified only when
7139-542: The Ascomycota have formed symbiotic associations with green algae ( Chlorophyta ), and other types of algae and cyanobacteria . These mutualistic associations are commonly known as lichens , and can grow and persist in terrestrial regions of the earth that are inhospitable to other organisms and characterized by extremes in temperature and humidity, including the Arctic , the Antarctic , deserts , and mountaintops. While
7260-410: The Ascomycota. The most frequent types are the single-celled spores, which are designated amerospores . If the spore is divided into two by a cross-wall ( septum ), it is called a didymospore . When there are two or more cross-walls, the classification depends on spore shape. If the septae are transversal , like the rungs of a ladder, it is a phragmospore , and if they possess a net-like structure it
7381-649: The Ascomycota. These include the following sexual ( teleomorphic ) groups, defined by the structures of their sexual fruiting bodies : the Discomycetes , which included all species forming apothecia ; the Pyrenomycetes , which included all sac fungi that formed perithecia or pseudothecia , or any structure resembling these morphological structures; and the Plectomycetes, which included those species that form cleistothecia . Hemiascomycetes included
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#17327943963287502-649: The British countryside: parent trees are monitored for disease, while saplings were offered free to schools and community groups, who are asked to monitor their trees' progress on the Foundation's online elm map; in London, places with 'elm' in their name were offered a sapling – in an attempt to find out why some elms have survived while others succumbed to Dutch elm disease. Both these projects have been discontinued. The spread of DED to Scotland has focussed attention on
7623-773: The CBS for further study in Dahlem Berlin. In August that year, she attended a congress of the International Federation of University Women in Geneva, where she met Bernice Cronkhite , dean of Harvard University ’s Radcliffe College in Boston , US. Buisman seized the opportunity to apply for a fellowship to study the elms and elm diseases in the US, and by the next month she began her one year’s study in Boston, with
7744-740: The French Institut National de la Recherche Agronomique (INRA), which subjected the trees to 20 years of field trials in the Bois de Vincennes , Paris , before releasing them to commerce—-in 2002 and 2006, respectively. Asian species featured in the American DED research programs were the Siberian elm U. pumila , Japanese elm U. davidiana var. japonica , and the Chinese elm U. parvifolia , which gave rise to several dozen hybrid cultivars resistant not just to DED, but also to
7865-527: The Mall and its surrounding areas has remained intact for more than 80 years. DED reached eastern Canada during World War II, and spread to Ontario in 1967, Manitoba in 1975 and Saskatchewan in 1981. In Toronto , 80% of the elm trees have been lost to Dutch elm disease; many more fell victim in Ottawa , Montreal and other cities during the 1970s and 1980s. Quebec City still has about 21,000 elms, thanks to
7986-468: The Netherlands and USA, identified the sexual stage of the fungal pathogen and also developed methods for experimental infections of elm seedlings that led to selection of resistant trees. In Britain, the disease was first identified in 1927 by T R Peace on English elm in Hertfordshire. This first strain was a relatively mild one, which killed only a small proportion of elms, more often just killing
8107-492: The Netherlands and her publication of this information in 1921 was one part of the start of extensive research and practical measures to try to halt the disease. In addition the fungus that caused the disease was isolated in 1921 in The Netherlands by Bea Schwarz , a pioneering Dutch phytopathologist , and this discovery would lend the disease its name. Following this, in the 1920s and 30s Christine Buisman , working in
8228-588: The US, has often succumbed to Dutch elm disease in Europe. Many attempts to breed disease-resistant cultivar hybrids have involved a genetic contribution from Asian elm species that are demonstrably resistant to this fungal disease. Much of the early work was undertaken in the Netherlands. The Dutch research programme began in 1928, and ended in 1992. During those 64 years, well over 1000 cultivars were raised and evaluated. Still in use are cultivars such as 'Groeneveld', 'Lobel', 'Dodoens', 'Clusius' and 'Plantijn', although
8349-464: The US, when Dutch elm disease spread away from the Atlantic coast, control focused on controlling the bark beetle by using insecticides such as DDT and dieldrin , which were sprayed heavily across all parts of elm trees, usually twice a year in the spring and again at a lower concentration in the summer. In its early years, it was generally thought by observers that pesticides did slow the spread of
8470-538: The United Kingdom alone, while France lost 97% of its elms. The disease spread rapidly northwards, reaching Scotland within 10 years. By 1990, very few mature elms were left in Britain or much of continental Europe. One of the most distinctive English countryside trees (See John Constable 's painting Salisbury Cathedral from the South-West ), the English elm U. minor 'Atinia' , is particularly susceptible as it
8591-453: The atmosphere and freshwater environments, as well as ocean beaches and tidal zones. The distribution of species is variable; while some are found on all continents, others, as for example the white truffle Tuber magnatum , only occur in isolated locations in Italy and Eastern Europe. The distribution of plant-parasitic species is often restricted by host distributions; for example, Cyttaria
8712-755: The cell. Many species live on dead plant material such as leaves, twigs, or logs. Several species colonize plants, animals, or other fungi as parasites or mutualistic symbionts and derive all their metabolic energy in form of nutrients from the tissues of their hosts. Owing to their long evolutionary history, the Ascomycota have evolved the capacity to break down almost every organic substance. Unlike most organisms, they are able to use their own enzymes to digest plant biopolymers such as cellulose or lignin . Collagen , an abundant structural protein in animals, and keratin —a protein that forms hair and nails—, can also serve as food sources. Unusual examples include Aureobasidium pullulans , which feeds on wall paint, and
8833-498: The city to an average of 1,000 a year (2009). Between 2013 and 2020 losses were below 1,000 a year. Elm was the most common tree in Paris from the 17th century; before the 1970s there were some 30,000 ormes parisiens . Today, only 1,000 mature elms survive in the city, including examples in the large avenues (Avenue d'Italie, Avenue de Choisy, Boulevard Lefebvre, Boulevard de Grenelle, Boulevard Garibaldi) and two very old specimens, one in
8954-417: The cuticle for dispersal. Asexual reproduction process in ascomycetes also involves the budding which we clearly observe in yeast. This is termed a "blastic process". It involves the blowing out or blebbing of the hyphal tip wall. The blastic process can involve all wall layers, or there can be a new cell wall synthesized which is extruded from within the old wall. The initial events of budding can be seen as
9075-570: The dedicated elm researcher. Although the 'Christine Buisman' elm didn't meet expectations concerning its growth habit, and appeared to be susceptible to Coral Spot fungus, Nectria cinnabarina , many mature specimens still survive in the Netherlands, England and the US as living proof of her achievement. The Dutch resistant-elm breeding project continued until 1992, followed in due course by similar projects in North America, Italy, and Spain, releasing to commerce many more DED-resistant elm cultivars. Soon after her death, Buisman's parents inaugurated
9196-449: The destruction of any infected trees or timber, although in practice they usually do it themselves, successfully reducing the numbers of elm bark beetle Scolytus spp. Sanitary felling has also, to date, preserved most of the 250,000 elms on the Isle of Man , where average temperature and wind speed inhibit the activity of the beetles, which need a temperature of at least 20 degrees to fly and
9317-605: The development of a ring of chitin around the point where the bud is about to appear. This reinforces and stabilizes the cell wall. Enzymatic activity and turgor pressure act to weaken and extrude the cell wall. New cell wall material is incorporated during this phase. Cell contents are forced into the progeny cell, and as the final phase of mitosis ends a cell plate, the point at which a new cell wall will grow inwards from, forms. There are three subphyla that are described and accepted: Several outdated taxon names—based on morphological features—are still occasionally used for species of
9438-701: The disease across the United States but as early as 1947, concern was raised that many bird species were killed in large numbers by ingesting poisoned invertebrates. In areas sprayed during the 1950s, local people observed birds such as the American woodcock , American robin , white-breasted nuthatch , brown creeper and various Poecile species dying. Biologist Rachel Carson consequently argued for improved sanitation and against spraying elms, which she saw as having been more effective in areas with earlier and greater experience countering Dutch elm disease. Spraying against elm bark beetles declined very rapidly after 1962,
9559-421: The disease generally cannot be eradicated once a tree is infected. Arbotect is not effective on root graft infections from adjacent elm trees. It is more than 99.5% effective for three years from beetle infections, which is the primary mode of tree infection. Alamo ( propiconazole ) has become available more recently, though several university studies show it to be effective only for the current season in which it
9680-400: The early Dutch hybrid 'Plantyn' as a safeguard against any future mutation of the disease. Two trees with very high levels of resistance, 'San Zanobi' and 'Plinio' , were released in 2003. 'Arno' and 'Fiorente' were patented in 2006 and entered commerce in 2012. All four have the Siberian elm U. pumila as a parent, the source of disease-resistance and drought-tolerance genes. 'Morfeo'
9801-407: The ends of specialized hyphae, the conidiophores. Depending on the species they may be dispersed by wind or water, or by animals. Conidiophores may simply branch off from the mycelia or they may be formed in fruiting bodies. The hypha that creates the sporing (conidiating) tip can be very similar to the normal hyphal tip, or it can be differentiated. The most common differentiation is the formation of
9922-415: The extreme cold of Asian winters. Among the most widely planted of these, both in North America and in Europe, are 'Sapporo Autumn Gold' , 'New Horizon' and 'Rebona' . Some hybrid cultivars, such as 'Regal' and 'Pioneer' are the product of both Dutch and American research. Hybridization experiments using the slippery (or red) elm U. rubra resulted in the release of 'Coolshade' and 'Rosehill' in
10043-474: The fungal pathogen in late May when the tree's growth is at its annual peak. Clones raised for testing are grown to an age of 3 or 4 years. In Europe, the inoculum is introduced into the cambium by a knife wound. However this method, developed in the Netherlands, was considered too severe in America, where the principal disease vector is the bark beetle Scolytus multistriatus , a far less effective vector than
10164-663: The fungal symbiont directly obtains products of photosynthesis . In common with many basidiomycetes and Glomeromycota , some ascomycetes form symbioses with plants by colonizing the roots to form mycorrhizal associations. The Ascomycota also represents several carnivorous fungi , which have developed hyphal traps to capture small protists such as amoebae , as well as roundworms ( Nematoda ), rotifers , tardigrades , and small arthropods such as springtails ( Collembola ). The Ascomycota are represented in all land ecosystems worldwide, occurring on all continents including Antarctica . Spores and hyphal fragments are dispersed through
10285-428: The fungi and correspond roughly to the sexes in plants and animals; however one species may have more than two mating types, resulting in sometimes complex vegetative incompatibility systems. The adaptive function of mating type is discussed in Neurospora crassa . Gametangia are sexual structures formed from hyphae, and are the generative cells. A very fine hypha, called trichogyne emerges from one gametangium,
10406-676: The garden of the Tuileries in front of the l'Orangerie and another in the Place Saint-Gervais in front of l'hôtel de ville de Paris . Losses are now being made up with disease-resistant cultivars, especially the Dutch-French research elm 'Nanguen' ( Lutèce ) , named for the ancient Roman name for the city: Lutetia. DED was first reported in the United States in 1928, with the beetles believed to have arrived in
10527-642: The generative form of the fungus, Ceratostomella ulmi . The first ever resistant elm clone released in the Netherlands was named for her in 1937, following her untimely death the previous year. Buisman was the eldest of four children raised in a liberal and socially conscious family in Leeuwarden . She completed her secondary education at the local gymnasium in 1919, after which she studied Biology in Amsterdam, her main interest at that time being marine flora. During 1923–24, Buisman joined practical courses at
10648-517: The group its name. Asexual reproduction is the dominant form of propagation in the Ascomycota, and is responsible for the rapid spread of these fungi into new areas. Asexual reproduction of ascomycetes is very diverse from both structural and functional points of view. The most important and general is production of conidia, but chlamydospores are also frequently produced. Furthermore, Ascomycota also reproduce asexually through budding. Asexual reproduction may occur through vegetative reproductive spores,
10769-523: The hook with one nucleus, one at the basal of the original hypha that contains one nucleus, and one that separates the U-shaped part, which contains the other two nuclei. Fusion of the nuclei (karyogamy) takes place in the U-shaped cells in the hymenium, and results in the formation of a diploid zygote . The zygote grows into the ascus , an elongated tube-shaped or cylinder-shaped capsule. Meiosis then gives rise to four haploid nuclei, usually followed by
10890-446: The hyphae, called " septa ", are the internal boundaries of individual cells (or compartments). The cell wall and septa give stability and rigidity to the hyphae and may prevent loss of cytoplasm in case of local damage to cell wall and cell membrane . The septa commonly have a small opening in the center, which functions as a cytoplasmic connection between adjacent cells, also sometimes allowing cell-to-cell movement of nuclei within
11011-416: The hyphae. The two nuclei contained in the apical part of each hypha divide in such a way that the threads of their mitotic spindles run parallel, creating two pairs of genetically different nuclei. One daughter nucleus migrates close to the hook, while the other daughter nucleus locates to the basal part of the hypha. The formation of two parallel cross-walls then divides the hypha into three sections: one at
11132-440: The inability of the beetles to see elms which did not break the silhouette. 'Weeping' elms are often spared infection owing to the beetles' aversion to hanging upside-down while feeding. In an attempt to block the fungus from spreading farther, the tree reacts by plugging its own xylem tissue with gum and tyloses , bladder-like extensions of the xylem cell wall . As the xylem (one of the two types of vascular tissue produced by
11253-612: The kerosene fungus Amorphotheca resinae , which feeds on aircraft fuel (causing occasional problems for the airline industry), and may sometimes block fuel pipes. Other species can resist high osmotic stress and grow, for example, on salted fish, and a few ascomycetes are aquatic. The Ascomycota is characterized by a high degree of specialization; for instance, certain species of Laboulbeniales attack only one particular leg of one particular insect species. Many Ascomycota engage in symbiotic relationships such as in lichens—symbiotic associations with green algae or cyanobacteria —in which
11374-474: The larger beetle endemic to Europe, Scolytus scolytus , which is unknown in America. In the method devised by the USDA , the inoculum is introduced to the cambium via a 2 mm-diameter hole drilled through the bark in the lower third of the tree. This method was further refined by the University of Wisconsin team, which drilled holes in the branches to simulate natural infection by the bark beetles feeding in
11495-431: The late 1980s. Dutch Trig is nontoxic, consisting of a suspension in distilled water of spores of a strain of the fungus Verticillium albo-atrum that has lost much of its pathogenic capabilities, injected in the elm in spring. The strain is believed to have enough pathogenicity left to induce an immune response in the elm, protecting it against DED during one growing season. This is called induced resistance . Trials with
11616-526: The main objective of determining whether Graphium ulmi was also present in the US. It was not until the last days before her return to Europe that she managed to isolate the fungus in samples from Cleveland , being the first to confirm the presence of the fungus on the North American continent. She also studied other elm diseases, helped by donations of Ulmus americana seedlings from the U.S. Department of Agriculture . She recorded this research in
11737-1159: The majority of lichens (loosely termed "ascolichens") such as Cladonia belong to the Ascomycota. Ascomycota is a monophyletic group (containing all of the descendants of a common ancestor). Previously placed in the Basidiomycota along with asexual species from other fungal taxa, asexual (or anamorphic ) ascomycetes are now identified and classified based on morphological or physiological similarities to ascus-bearing taxa , and by phylogenetic analyses of DNA sequences. Ascomycetes are of particular use to humans as sources of medicinally important compounds such as antibiotics , as well as for fermenting bread, alcoholic beverages, and cheese. Examples of ascomycetes include Penicillium species on cheeses and those producing antibiotics for treating bacterial infectious diseases . Many ascomycetes are pathogens , both of animals, including humans, and of plants. Examples of ascomycetes that can cause infections in humans include Candida albicans , Aspergillus niger and several tens of species that cause skin infections . The many plant-pathogenic ascomycetes include apple scab , rice blast ,
11858-402: The mycelium from which they originate. They are typically formed at the ends of specialized hyphae , the conidiophores . Depending on the species they may be dispersed by wind or water, or by animals. Different types of asexual spores can be identified by colour, shape, and how they are released as individual spores. Spore types can be used as taxonomic characters in the classification within
11979-610: The nearly 40 years since the onset of the disease in the United Kingdom. The largest concentrations of mature elms in Europe are now in Amsterdam and The Hague . In 2005, Amsterdam was declared the "Elm City of Europe": the city's streets and canals are lined with at least 75,000 elms, including several generations of research-elms (see below: Resistant trees ). Some 30,000 of the 100,000 mature trees in The Hague are elms, planted because of their tolerance of salty sea-winds. Since
12100-436: The original parent nuclei. Alternatively, nuclei may lose some chromosomes, resulting in aneuploid cells. Candida albicans (class Saccharomycetes) is an example of a fungus that has a parasexual cycle (see Candida albicans and Parasexual cycle ). Sexual reproduction in the Ascomycota leads to the formation of the ascus , the structure that defines this fungal group and distinguishes it from other fungal phyla. The ascus
12221-413: The parent structure). Conidiogenesis corresponds to Embryology in animals and plants and can be divided into two fundamental forms of development: blastic conidiogenesis, where the spore is already evident before it separates from the conidiogenic hypha, and thallic conidiogenesis, during which a cross-wall forms and the newly created cell develops into a spore. The spores may or may not be generated in
12342-472: The pellicles or moldy layers that develop on jams, juices, and other foods are the mycelia of these species or occasionally Mucoromycotina and almost never Basidiomycota . Sooty molds that develop on plants, especially in the tropics are the thalli of many species. Large masses of yeast cells, asci or ascus-like cells, or conidia can also form macroscopic structures. For example. Pneumocystis species can colonize lung cavities (visible in x-rays), causing
12463-598: The phytopathology laboratory “Willie Commelin Scholten” in Baarn , a small town near Amsterdam. The laboratory was accommodated in the leafy Villa Java alongside the Centraal Bureau voor Schimmelcultures ( fungiculture ) (CBS), where Buisman also worked as an assistant. Both institutions were led by Prof. Johanna Westerdijk (1883–1961), the first female professor in the Netherlands, appointed in 1917. In 1927, Buisman
12584-737: The position of researcher at Baarn on her return in October 1930. During her years at Baarn, Buisman wrote many publications on elm disease, delivering speeches in and beyond the Netherlands (she was multilingual), quickly establishing herself as the paramount elm specialist in Europe. From the thousands of seedlings under test, by 1935 Buisman had selected several promising elm clones with a significantly better resistance to DED, notably two from France (clone no. 1) and Spain (clone no. 24), which she prepared to use in hybridization experiments in The Hague , assisted by Simon Doorenbos , director of that city's parks department. In March 1936, Buisman underwent
12705-656: The process of heterokaryosis, caused by merging of two hyphae belonging to different individuals, by a process called anastomosis , followed by a series of events resulting in genetically different cell nuclei in the mycelium . The merging of nuclei is not followed by meiotic events , such as gamete formation and results in an increased number of chromosomes per nuclei. Mitotic crossover may enable recombination , i.e., an exchange of genetic material between homologous chromosomes . The chromosome number may then be restored to its haploid state by nuclear division , with each daughter nuclei being genetically different from
12826-548: The resistance levels in these trees aren't high enough to confer good protection. The programme had three major successes: 'Columella' , 'Nanguen' Lutèce , and 'Wanoux' Vada , all found to have an extremely high resistance to the disease when inoculated with unnaturally large doses of the fungus. Only 'Columella' was released during the Dutch programme's lifetime—-in 1987. Patents for the Lutèce and Vada clones were purchased by
12947-599: The resistance of the English elm . In England the Conservation Foundation had been propagating, distributing and planting clones of surviving indigenous elms, including field elms (but not the highly susceptible English elm ), as part of a scheme to return elms to city and countryside. The Foundation was running two elm programmes: the 'Great British Elm Experiment' and 'Ulmus londinium', an elm programme for London – these use saplings cultivated through micropropagation from mature parent elms found growing in
13068-766: The same species. Species of the Deuteromycota were classified as Coelomycetes if they produced their conidia in minute flask- or saucer-shaped conidiomata, known technically as pycnidia and acervuli . The Hyphomycetes were those species where the conidiophores ( i.e. , the hyphal structures that carry conidia-forming cells at the end) are free or loosely organized. They are mostly isolated but sometimes also appear as bundles of cells aligned in parallel (described as synnematal ) or as cushion-shaped masses (described as sporodochial ). Most species grow as filamentous, microscopic structures called hyphae or as budding single cells (yeasts). Many interconnected hyphae form
13189-514: The spores reach a suitable substrate, they germinate, form new hyphae, which restarts the fungal life cycle. The form of the ascus is important for classification and is divided into four basic types: unitunicate-operculate, unitunicate-inoperculate, bitunicate, or prototunicate. See the article on asci for further details. The Ascomycota fulfil a central role in most land-based ecosystems . They are important decomposers , breaking down organic materials, such as dead leaves and animals, and helping
13310-507: The testing of clones of surviving field elms for innate resistance has been carried out since the 1990s by national research institutes, with findings centrally assessed and published. The first results of this ongoing project suggest that in some countries a very small number of native field elm genotypes have comparatively high levels of tolerance to DED. In Spain, for example, of around 5,000 native elms evaluated to 2013, some 25 genotypes (0.5% of those tested) fall into this category; and it
13431-409: The thallus of the fungus defines the shape of the symbiotic colony. Some dimorphic species, such as Candida albicans , can switch between growth as single cells and as filamentous, multicellular hyphae. Other species are pleomorphic , exhibiting asexual (anamorphic) as well as a sexual (teleomorphic) growth forms. Except for lichens, the non-reproductive (vegetative) mycelium of most ascomycetes
13552-965: The tree was used in hybridization experiments (see above). In 1993, Mariam B. Sticklen and James L. Sherald reported the results of NPS-funded experiments conducted at Michigan State University in East Lansing that were designed to apply genetic engineering techniques to the development of DED-resistant strains of American elm trees. In 2007, AE Newhouse and F Schrodt of the State University of New York College of Environmental Science and Forestry in Syracuse reported that young transgenic American elm trees had shown reduced DED symptoms and normal mycorrhizal colonization. By 2013, researchers in both New York State and North Carolina were conducting field trials of genetically engineered DED-resistant American elms. Among European species, there
13673-656: The trial were exclusively American developments; no European cultivars were included. Based on the trial's final ratings, the preferred cultivars of the American elm ( Ulmus americana ) are ‘New Harmony’ and ‘Princeton’. The preferred cultivars of Asian elms are the Morton Arboretum introductions and ‘New Horizon’. Recent research in Sweden has established that early-flushing clones are less susceptible to DED owing to an asynchrony between DED susceptibility and infection. Elms are tested for resistance by inoculation with
13794-432: The twig crotches, but results from this method were found to exaggerate the genetic resistance of the host. Consequently, tests were conducted on specimens in a controlled environment, either in greenhouses or customized plant chambers, facilitating more accurate evaluation of both internal and external symptoms of disease. Another variable is the composition of the inoculum; while an inoculum strength of 10 spores / ml
13915-489: The world. The provinces of Alberta, Manitoba, and Saskatchewan all prohibit the pruning of elm trees during the middle of the year (taking effect in April, and lasting through the end of September, July, and August respectively), which they deem to be the most active time of year for bark beetles. It is also illegal to use, store, sell, or transport elm firewood. The largest surviving urban forest of elm trees in North America
14036-857: The yeasts and yeast-like fungi that have now been placed into the Saccharomycotina or Taphrinomycotina , while the Euascomycetes included the remaining species of the Ascomycota, which are now in the Pezizomycotina , and the Neolecta , which are in the Taphrinomycotina. Some ascomycetes do not reproduce sexually or are not known to produce asci and are therefore anamorphic species. Those anamorphs that produce conidia (mitospores) were previously described as mitosporic Ascomycota . Some taxonomists placed this group into
14157-493: Was a Dutch phytopathologist who dedicated her short career to the research of Dutch elm disease and the selection of resistant elm seedlings. In 1927, Buisman provided the final proof that Graphium ulmi (later named Ophiostoma ulmi ) was the causal agent of the disease, concluding the controversy which had raged among Dutch and German scientists since 1922. Buisman developed the inoculation method for screening large numbers of elm plants for resistance, and in 1932 discovered
14278-401: Was awarded a doctorate by Utrecht University for work on root-rotting Phycomycetes ( Phytophthora and Pythium ). At the end of 1926, funds were granted for further research into the cause of Dutch elm disease. Buisman was charged with this two-year project, and part of the villa garden was duly planted with elm seedlings. To infect so many plants, Buisman experimented with the use of
14399-700: Was cancelled to allow more funds to be available for pests of a higher priority. A major outbreak occurred in New Zealand in July 2013, particularly at the site of Kingseat Hospital , south of Auckland . Auckland has 20,000 elms. The first attempts to control Dutch elm disease consisted of pruning trees to remove and burn diseased timber . While this method was effective in New York State and adjacent areas, its cost made it uneconomical except in large cities where elms were considered valuable attractions. In
14520-404: Was genetically engineered to resist disease, in experiments at Abertay University , Dundee , Scotland , by transferring antifungal genes into the elm genome using minute DNA-coated ball bearings. However, owing to reservations to GM developments, there are no plans to release the trees into the countryside. Sac fungi Ascomycota is a phylum of the kingdom Fungi that, together with
14641-601: Was released in 2011; it arose from a crossing of the Dutch hybrid clone '405' (female parent) and the Chenmou Elm , the latter a small tree from the provinces of Anhui and Jiangsu in eastern China, The '405' clone is a crossing of an English U. × hollandica and a French U. minor . In the Netherlands a new program has been initiated. From the old proving grounds of the Dorschkamp Research Institute, 10 fourth-generation hybrids survive in
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