The mitochondrial genome of Ophiostoma himal-ulmi and comparison with other Dutch elm disease causing fungi.

The mitochondrial genome of Ophiostoma himal-ulmi, a species endemic to the Western Himalayas and a member of the Dutch elm disease-causing fungi, has been sequenced and characterized. The mitochondrial genome was compared with other available genomes for members of the Ophiostomatales, including other agents of Dutch elm disease (Ophiostoma ulmi, Ophiostoma novo-ulmi subspecies novo-ulmi and Ophiostoma novo-ulmi subspecies americana) and it was noted that gene synteny is highly conserved and variability among members of the Dutch-elm disease-causing fungi is primarily due to the number of intron insertions. Among the Dutch elm disease-causing fungi examined, O. himal-ulmi has the largest mitochondrial genomes ranging from 94 934 bp to 111 712 bp due to the expansion of the number of introns.

Nature of the Dutch elm disease: new aspects of diagnostics, pathogenesis, and etiology

Расхождения по установлению первопричины голландской болезни вязов (ГБВ) возникли сразу после её обнаружения в 1918 г. В разные годы указывали фитопатогенные бактерии (Васillus amylovorus, Miсrососсus ulmi, Рseudomonas lignicola) и гриб Ophiostoma (Ceratostomella) ulmi (Graphium ulmi). В 1937 г. в Краснодарском крае наряду с закупоркой сосудов на вязах описано ядро бактериальной водянки, т. е. уже 80 100 лет назад отмечали смешанную этиологию ГБВ, но бактериозы посчитали недостоверной причиной, возобладала теория грибной моноинфекции. Позже открыли агрессивный патоген Ophiostoma novoulmi, близкие виды O. himalulmi, O. novoulmi subsp. novoulmi, O. novoulmi subsp. americana. Параллельно на вязах выявлены бактериальная водянка (Pectobacterium carotovorum), бактериальный ожог (Erwinia группы Amylovora), Pseudomonas amygdali pv. ulmi, связанная с поражением коры, Xylella fastidiosa, вызывающая ожог листвы. К симптоматике ГБВ причастны виды фитопатогенных бактерий. Анализ факторов патогенности гриба показывает неоднозначность их проявления в симптоматике ГБВ. Агрессивность O. novoulmi проявилась не в патогенезе, а в вытеснении O. ulmi. Продукты метаболизма бактерий (кислота, газ, ферменты) разрушают целлюлозу, лигнин клеточных стенок, срединную пластинку и крахмал, вызывая камедь, мокроту, экссудат, закупорку сосудов, некрозы, мацерацию, растрескивание коры и древесины. Graphium ulmi развивается на подготовленных тканях совместно с бактериями как факультативный паразит, не проявляя антагонизма. Предполагается, что ГБВ имеет либо полифункциональную этиологию смешанного бактериальногрибного происхождения, либо самостоятельную бактериальную. Ареалы ильмовых пород, таксонов комплекса Ophiostoma ulmi и бактериозов имеют зоны перекрытия, что предполагает смешанный или сопряженный патогенез. В проблеме ГБВ на смену теории грибной моноинфекции должна прийти парадигма фитопатологической диагностики с использованием метагеномного анализа. Discordance on establishing the prime cause of the Dutch elm disease (DED) arose soon after its discovery in 1918. Through the years different causes were specified in literature: phytopathogenic bacteria (Bacillus amylovorus, Micrococcus ulmi, Pseudomonas lignicola) and fungi Ophiostoma (Ceratostomella) ulmi (Graphium ulmi). The bacterial dropsy together with obstruction of vessels was described in 1937. Hence, even 80 100 years ago the mixed etiology was noted. However, bacterioses were considered as a doubtful reason. Later on, an aggressive pathogen Ophiostoma novoulmi and close species O. himalulmi, O. novoulmi subsp. novoulmi, O. novoulmi subsp. americana were found. At the same time, bacterial dropsy (Pectobacterium carotovorum), fire blight (Erwinia of group Amylovora), Pseudomonas amygdali pv. ulmi connected to the injuries of bark, and Xylella fastidiosa causing foliage burn, were revealed on elms. Some species of phytopathogenic bacteria are also involved in symptoms of DED. The analysis of factors of pathogenesis of G. ulmi shows ambiguity of their manifestation in DED symptoms. The aggressivity of O. novoulmi was not in pathogenesis, these fungi force another species O. ulmi out. Products of bacteria metabolism (acid, gas, and enzymes) destroy cellulose, lignin cell walls, middle plate, and starch, causing gum, sputum, exudate, blockage of vessels, necrosis, maceration, cracks of bark and wood. Graphiosis settles on the prepared tissues where G. ulmi grows as a facultative parasite together with bacteria without showing any antagonism. It is suggested that DED has polyfunctional etiology of the mixed bacterial and fungi origin or independent bacterial origin. Distribution areas of elms, taxa of the Ophiostoma ulmi complex and the main bacterioses of elms have overlapping zones, that suggests mixed or associated pathogenesis. The theory of fungal monoinfection in a problem of DED requires a change of the paradigm of phytopathological diagnostics and use of metagenomic analysis in the diagnostics.

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.

The occurrence of endophytic fungus Phomopsis oblonga on elms in the area of southern Bohemia

The health condition of the population of elms in the region of southern Bohemiawas studied from the viewpoint of their decline, the occurrence of Dutch Elm Disease (DED) and the presence of other diseases. Of the total number of 105 elms in total 33 of them were without any symptoms of the disease or other damage. Elms regenerated quite spontaneously in the neighbourhood of mother trees and their increasing population in mixed forests is hopeful. According to macroscopic symptoms, DED was identified in 10 trees but the presence of pathogens Ophiostoma ulmi and Ophiostoma novo-ulmi was not identified in isolations. A possible reason of this observation is overgrowing the colonies by the Phomopsis oblonga mycelium. This fungus was identified in most isolations. Thus, its role requires further research.

Contribution to identify the causal gents of Dutch elm disease in the Czech Republic

This study provides new data on Dutch elm disease in the Czech Republic. <I>Ophiostoma novo-ulmi</I> is reported for the first time in the area of the Czech Republic, as well as both subspecies ssp. <I>novo-ulmi</I> (indigenous in the area of the Ukraine and Moldavia), and ssp. <I>Americana</I> indigenous in North America. The majority of the recorded strains belonged to <I>O. n.-u.</I> ssp. <I>novo-ulmi</I>, while <I>O. n.-u.</I> ssp. <I>Americana</I> and hybrids of these two subspecies were found less frequently. On the other hand, <I>Ophiostoma ulmi</I> was not found at all in the investigated samples. Identification on the subspecies level was performed by methods of molecular biology, i.e. PCR and RFLP of gene regions<I> cu</I> and <I>col1</I>.