Fatty acids triggering coremia formation by Ceratocystis ulmi their occurrence and distribution in elm wood

This paper reports the identification of fatty acids in elm wood and its active extractives triggering coremia formation, their distribution between bark, sapwood and heartwood of elms, and their occurrence in the mycelium of the pathogen.     

Terpenes and unsaturated fatty acids trigger coremia formation by Ceratocystis ulmi

Coremia formation by Ceratocystis ulmi (Buis.) ist triggered by certain terpenes and unsaturated fatty acids, of which linoleic acid and its esters are the most active.     

Compatibility in Ceratocystis ulmi

Fourteen strains of Ceratocystis ulmi were crossed on semi-synthetic and synthetic media in vitro. Perithecia formed after 8 weeks of incubation. Some strains were found to be more fertile than others. The strains were classified into type A, type B and bisexual.     

Ultrastructure of Ceratocystis ulmi

Transmission electron microscopic observations of C. ulmi show that there are three distinct types of the hyphae and three distinct layers forming the nscocarp peridium. The cellular organelles of the hyphae and ascocarp peridial layers are described.     

Further studies on pathogenicity in Ceratocystis ulmi1

Inoculation experiments on Ulmus procera, U. glabra and U. pumila with isolates of Ceratocystis ulmi from Canada, the United States, England, France, the Netherlands and Iran confirmed earlier work on the correlation between cultural characters and pathogenicity. Inocula-     

Factor in Abies balsamea Responsible for Coremia Formation of Ceratocystis piceae

Compounds are present in sapwood of Abies balsamea (L.) Mill., triggering the formation of coremia by Ceratocystis piceae (Münch) Bakshi. From several unsaturated fatty acids, linoleic acid is the most active coremia inducer.     

Evaluation of Dutch elm disease susceptibility and pathogenicity of Ophiostoma ulmi using micropropagated elm shoots

Elm (Ulmus sp.) shoots from in vitro micropropagated plants were tested with Ophiostoma ulmi culture filtrates, at different dilutions to determine the susceptibility of different host clones to Dutch elm disease (DED). ‘Commelin’, a susceptible Dutch hybrid, showed a high wilting index but that of American elm was higher. Although U. pumila × japonica (Sapporo gold 2) was the most tolerant to spore inoculation, its wilting index was as high as that of ‘Commelin’. The absorption capacity and wilting index of the elm shoots showed consistent correlation to isolate effectiveness (as determined by inoculation experiments), to production of toxin (cerato-ulmin) and to filtrate dilution. This method could be used to assess the effectiveness of the different O. ulmi isolates and for the detection of elm genotypes that are highly susceptible to Dutch elm disease.     

The aggressive and non-aggressive strains of Ceratocystis ulmi in Iran

Two hundred and seventy-eight sample isolates of Ceratocystis ulmi were obtained from the Caspian Forest area. Without exception, they fell into either the aggressive or non-aggressive strains of C. ulmi on the basis of growth rate and colony morphology. These characters were again correlated with pathogenicity.     

Factors influencing mansonone induction in elm callus by culture filtrate elicitors of Qphiostoma ulmi

Mansonone F (phytoalexin) production in elm callus induced by elicitors of Ophiostoma ulmi is affLited by cultural and experimental conditions. These factors include different fun gal isolates, fungal culture age, elicitor concentration, the time of elicitor treatment, the callus cu Ytured with or without light and the callus subculturing frequency.     

Effects of Ophiostoma ulmi and Ophiostoma novo-ulmi culture filtrates on elm cultures from genotypes with different susceptibility to Dutch elm disease

Cell cultures of callus tissue cultures obtained from four elm genotypes (Ulmus minor; Ulmus minor×Ulmus pumila; [Ulmus carpinifolia×Ulmus glabra] × [Ulmus wallichiana×Ulmus glabra]; and Ulmus pumila), either susceptible or resistant to Dutch elm disease (DED) were exposed to culture filtrates of Ophiostoma ulmi and Ophiostoma novo-ulmi. Elm cells were largely affected by crude culture filtrate incorporated into the media. However, the correlation between ‘in vivo’ cell resistance and growth in the presence of culture filtrate was poor: the effects of fungal media components were greater than that exerted by fungal exotoxins. Therefore, it is concluded that these ‘in vitro’ assays cannot be used to evaluate resistance sources to DED in elms, or to assess specific pathogenicity of fungal isolates.     

First report on the Dutch elm disease pathogen Ophiostoma novo‐ulmi from Latvia

During 2017, Dutch elm disease was investigated on 67 Ulmus glabra and 29 Ulmus laevis samples from 28 sites in Latvia. The presence of Ophiostoma novo‐ulmi was detected in 61.2% of the samples from U. glabra and in 34.5% of the samples from U. laevis. In 11% of cases, hybrids between subsp. novo‐ulmi and subsp. americana were identified, particularly in the sites in the southern part of Latvia. This study presents the first verified record of Ophiostoma novo‐ulmi and its subspecies in Latvia.     

American elm cultivars: Variation in compartmentalization of infection by Ophiostoma novo‐ulmi and its effects on hydraulic conductivity

Five cultivars and two populations of wild‐type seedlings of American elm (Ulmus americana), 3 and 4 years old, were examined for differences in their abilities to compartmentalize and resist infection by artificially inoculating with Ophiostoma novo‐ulmi. Morphological characteristics of tree defence, often referred to as the compartmentalization of decay in trees model, were used as a conceptual framework, with particular emphasis on the limiting of tangential spread of infection within the xylem and barriers that limit spread outwards to cells formed after infection. To investigate the change in functional xylem over time, 3‐year‐old trees were assessed at multiple time points following inoculation for hydraulic conductivity. Three and four‐year‐old cut trees were placed in 0.1% w/v safranin O for 18 to 24 hr to indicate functional xylem. Transverse sections of the stained stems were used to calculate per cent of sap‐conducting xylem area and the per cent of circumference conducting of first formed cells and later formed cells. At each collection time, trees were assessed for disease severity on a 1–12 scale, based on the percentage of permanent wilt in the crown. There was considerable variation between cultivars in disease severity and their capacity to localize and resist infection. “Prairie Expedition,” which had the lowest disease severity rating in 2015 and the second lowest in 2016, consistently limited the spread of infection into newly formed xylem and had functional xylem around the entire circumference of the stem at 90 days post‐inoculation. “Valley Forge” in 2016 had the lowest overall disease severity rating and was the only cultivar to consistently limit the tangential spread of infection within extant xylem. This research identifies key characteristics that some cultivars have to resist and limit infection and provides new information that can be used in disease screening programmes to evaluate other cultivars and older plant material.     

Ophiostoma ulmi metabolites and elm cell membrane permeability. Possible use in early tests of resistance

Electrolyte leakage from leaf discs of three Ulmus species when challenged with cultural filtrate of an NAN aggressive isolate of Ophiostoma ulmi paralleled their susceptibility to the disease in the field. But the correlation was not working with some hybrids derived from the common field elm showing intermediate resistance. The possible explanation will be checked in further tests which are in progress to assess the possibility of using this technique in early screening for resistance.     

A scanning electron microscope study of cell wall degradation in elm wood by aggressive and non-aggressive isolates of Ophiostoma ulmi

Degradation of cell walls in elm wood tissue (Ulmus americand) by aggressive and non-aggressive isolates of Ophiostoma ulmi was studied by scanning electron microscopy. Xylem vessel walls were much more affected after infection with the aggressive isolate than after infection with the non-aggressive one.     

Variation among Italian and French elm clones in their response to Ophiostoma novo‐ulmi inoculation

In 1995 a clone bank of elms from across Italy was created at Antella (Florence, I) under a European Union project. In 1998 an experimental planting of some clones from this source was established in Antella together with material from a similar clone bank in France and two reference clones: Commelin (relatively susceptible) and Lobel (relatively resistant). In May 2001, the elms were inoculated with Ophiostoma novo‐ulmi and disease development was assessed throughout that summer and the next. Significant differences in susceptibility were found between taxonomic groups, with putative natural hybrids between Ulmus minor and Ulmus pumila being the most resistant and Ulmus glabra the most susceptible. Significant differences were also found within U. minor, some clones being as resistant as Lobel. For U. minor, a statistically significant relation was found with latitude, southerly clones showing less disease than more northerly ones. Relationships were also found between disease severity and times to bud burst, these relationships applying both to the different taxonomic groups and within U. minor. Relationships between growth increment and disease severity were inconsistent. These results are discussed in relation to the intrinsic genetically‐controlled differences that exist between elms and to differences in susceptibility that occur as the growing season proceeds and as a consequence of environmental influences.     

Inhibition of Ceratocystis ulmi by mansonones A,C, D,E, F,and G isolated from Ulmus americana

Six mansonoes, previously isolated from Ulmus americana L. infected by Ceratocystis ulmi (Buis.) C. Moreau, were assayed for their inhibitory activity against several strains of the fungus. Mansonone A was most effective in inhibiting the linear growth of six strains of C. ulmi tested. A mixture of the pure mansonones, recombined at their original concentrations, was less inhibitory to the three aggressive strains of C. ulmi than the non-aggressive ones. The total mansonone fraction accounted for all the inhibition of the three non-aggressive strains.     

Presence and accumulation of fungitoxic substances against Ceratocystis ulmi in Ulmus americana: possible relation to induced resistance1

This paper reports the differential accumulation of inhibitory compounds in American elm seedlings after inoculation with a non-aggressive and an aggressive strain of C, ulmi.     

Dutch elm disease pathogen transmission by the banded elm bark beetle Scolytus schevyrewi

Dutch Elm Disease (DED) is a vascular wilt disease of Ulmus species (elms) incited in North America primarily by the exotic fungus Ophiostoma novo‐ulmi. The pathogen is transmitted via root grafts and elm bark beetle vectors, including the native North American elm bark beetle, Hylurgopinus rufipes and the exotic smaller European elm bark beetle, Scolytus multistriatus. The banded elm bark beetle, Scolytus schevyrewi, is an exotic Asian bark beetle that is now apparently the dominant elm bark beetle in the Rocky Mountain region of the USA. It is not known if S. schevyrewi will have an equivalent vector competence or if management recommendations need to be updated. Thus the study objectives were to: (i) determine the type and size of wounds made by adult S. schevyrewi on branches of Ulmus americana and (ii) determine if adult S. schevyrewi can transfer the pathogen to American elms during maturation feeding. To determine the DED vectoring capability of S. schevyrewi, newly emerged adults were infested with spores of Ophiostoma novo‐ulmi and then placed with either in‐vivo or in‐vitro branches of American elm trees. The inoculation of trees via feeding wounds was successful 30% of the time for in‐vivo trials and 33% for in‐vitro trials. Although the infection rate of DED has declined in Colorado over the past 10 years, the disease is still present in urban elms. While it appears that S. schevyrewi is another vector of the DED pathogens, it appears that S. schevyrewi is no more efficient than S. multistriatus. Thus, management programs that remove elm bark beetle breeding sites, rapidly remove DED‐infected elms and include the planting of DED‐resistant elms should continue to be effective management tactics.     

长喙壳Ceratocystis sensu lato真菌引起的杨树病害

该文着重阐述长喙壳属Ceratocystis sensu lato中引起杨树溃疡病最重要的病原菌甘薯长喙壳C.fimbriata Ell.et Halst.引起的杨树病害的症状、形态学、寄主范围、传播媒介、致病性、寄主的抗病性和病理变化等。     

The fatty acid composition and its alterations due to different incubation temperature in the lipids of aggressive and non-aggressive strains of Ceratocystis ulmi

Lipids and their fatty acids from the mycelia of aggressive and non-aggressive strains of Ceratocystis ulmi were examined at different incubation temperature. The quantity and degree of fatty acid unsaturation were correlated with the pathogenicity of the fungus.