Occurrence of horse chestnut bleeding canker caused by Pseudomonas syringae pv. aesculi in the Czech Republic

Between 2008 and 2010, horse chestnut (Aesculus hippocastanum) trees growing at 216 locations in the Czech Republic were surveyed for bleeding canker disease. Typical symptoms of bleeding canker were found at 16 locations, and samples were collected from five of these locations. The bacterium Pseudomonas syringae was isolated from five locations, and Pseudomonas syringae pathovar aesculi, which is the causal agent of bleeding canker disease, was isolated at one location. This is the first report of P. syringae pv. aesculi in the Czech Republic.     

Fast molecular detection of Pseudomonas syringae pv. aesculi in diseased horse chestnut trees

A molecular technique was used to detect the bacterium Pseudomonas syringae pv. aesculi in horse chestnut trees (Aesculus hippocastanum), affected by the recently recognized European ‘Pseudomonas horse chestnut bark disease’. The technique helped identify the pathogen within 6 h of sample preparation including DNA extraction, polymerase chain reaction (PCR) and electrophoresis until gel documentation. PCR primer pairs derived from the gyrase B gene sequence were used. Because of the great similarity in the gyrase B gene sequences of the numerous closely related P. syringae pathovars, the primers were not only totally specific to the pathovar aesculi, but also detected a few other pathovars. The assumption that other bacteria should not occur at least near to a necrotic lesion of a horse chestnut tree was corroborated by sequence identity of the PCR products obtained with the gyrase B gene sequence of P. syringae pv. aesculi. Koch’s postulates were fulfilled for an isolate of P. syringae pv. aesculi obtained from a diseased horse chestnut tree sampled in Hamburg in 2007.     

Pseudomonas syringae pv. aesculi: foliar infection of Aesculus species and temperature–growth relationships

Since 2001, the incidence of bleeding canker of horse chestnut (Aesculus hippocastanum) has increased markedly in western Europe. The causal agent, the bacterium Pseudomonas syringae pv. aesculi, originally isolated from foliar lesions on Indian horse chestnut (Aesculus indica) in India, is a bark killing pathogen on A. hippocastanum. In this study, P. syringae pv. aesculi was found as a foliar epiphyte on both A. hippocastanum and A. indica trees growing in the UK. When Aesculus leaves were challenged with cell suspensions (10⁹ CFU ml^?1) of Pseudomonas syringae pv. aesculi, a high level of asymptomatic infection occurred in all the species tested. The degree of re‐isolation of the bacterium after surface sterilization of leaves ranged from 33% (A. pavia) to 84 and 97% for A. hippocastanum and A. chinensis, respectively. The studies suggest both epiphytic and intrafoliar populations of P. syringae pv. aesculi could play a role in the incidence and spread of bleeding canker of horse chestnut. Growth–temperature responses of P. syringae pv. aesculi indicated a minimum of approximately ?4°C and a maximum of approximately 35°C, with an optimum of approximately 25°C. These findings show that P. syringae pv. aesculi is not restricted to bark lesions but is likely to be widespread in the environment. It is also capable of causing foliar infection of several Aesculus species and could persist under extremes of weather in the UK.     

Leaf necrosis and sucker and twig dieback of Alnus glutinosa incited by Pseudomonas syringae pv. syringae.

In central Italy, Pseudomonas syringae pv. syringae was isolated from Alnus glutinosa that showed, in spring, leaf necrosis and also sucker and twig dieback. The trees were located near a lake and a stream. Biochemical tests were consistent with those characterizing the pathovar. Pathogenicity tests yielded necrotic lesions on A. glutinosa and Syringa vulgaris leaves and also on lemon and orange fruits. In addition, whole-cell protein profiles of the isolates and P. s. pv. syringae reference strains were identical. Some isolates showed positive ice-nucleation activity. This is the first record of this pathogen on black alder.     

Bacterial canker of Maackia amurensis var. buergeri caused by a putative Pseudomonas syringae

A new disease of Maackia amurensis var. buergeri was recently found on the northern island of Hokkaido, Japan. Affected trees were heavily damaged and had cankers on both trunks and branches. After natural infection, a series of swellings on the bark surface developed longitudinally. These swellings burst and coalesced to become long cankers. It is proposed that the disease be designated ‘bacterial canker of Maackia’. The causal pathogen was isolated and characterized tentatively as Pseudomonas syringae on the basis of laboratory tests. Pathogenicity of the bacterium was confirmed by inoculation into the host.     

PF7-5对烟草角斑病的室内及大田防治效果

为验证荧光假单胞杆菌PF7-5对烟草角斑病的生物防治效果,设计了荧光假单胞杆菌PF7-5对烟草角斑病菌的室内和大田抑菌试验。结果表明,室内试验中荧光假单胞杆菌PF7-5代谢产物对烟草角斑病的抑菌效果达到71%,大田试验中PF7-5活菌的50倍稀释液田间防治效果达87.34%,说明荧光假单胞杆菌PF7-5对烟草角斑病有一定的防治效果。     

Relationship between canker size and wood starch in American chestnut

Chestnut trees (Castanca dentata) were wounded in May and inoculated with Cryphonectria parasitica. In August, canker area was measured and the surfaces of longitudinal dissections of stem wood were stained with I₂KI to reveal the presence of starch. Sections with the most starch had smaller cankers than sections with no starch. Results show that starch reserves were related to canker size and therefore may play a role in the tree's ability to respond to infection.     

Botryosphaeriaceae associated with Eucalyptus canker diseases in Colombia

The identities of Botryosphaeriaceae causing cankers on Eucalyptus in Colombia were investigated using morphological and DNA sequence comparisons. The pathogenicity of the species was also assessed on 42 Eucalyptus grandis clones planted at four different sites. Two species of the Botryosphaeriaceae were found to occur on E. grandis in Colombia. Neofusicoccum ribis was the more common species, and also the most pathogenic. Botryosphaeria dothidea was found only in one zone of Colombia, and was also less pathogenic than N. ribis. These two species could be distinguished easily based on DNA sequences of the ITS1/ITS2 rDNA region and EF1‐α, in addition to conidial sizes. Significant differences in resistance of clones to these pathogens were also evident from the various trials.     

The bacterial disease of ash (Fraxinus excelsior), caused by Pseudomonas syringae subsp. savastanoi pv. Fraxini II. Etiology and taxonomic considerations

The results of studies of various bacteria isolated from characteristic excrescences of the so-called bacterial canker of common ash are reported. A fungus (formerly known as Plenodomus rabenhorstii Preuss) associated with this disease, is described and renamed as Phoma riggenbachii Boerema et Janse. Based on biochemical, serological and pathological work the name Pseudomonas syringae subsp. savastanoi (ex Smith) subsp. nov., nom. rev. pv. fraxini is proposed for the ash bacterium. The closely related causal organisms of olive and oleander have been compared and named pv. oleae and pv. nerii.     

Neofusicoccum parvum associated with pomegranate branch canker in Iran

Pomegranate (Punica granatum) is native to Iran and neighbouring countries and is negatively affected by a wide range of diseases. Canker and dieback diseases caused by Cytospora punicae and members of the family Botryosphaeriaceae are the main trunk diseases on pomegranate. In summer 2017, progressive dieback of branches on some young pomegranate trees was observed in orchards of the Gorgan Region (Golestan province, Northeast Iran). Fungal colonies with similar colony colour were isolated from symptomatic tissues. The identity of the causal agent was determined as Neofusicoccum parvum, based on a polyphasic taxonomic approach including morphological features of conidiomata and phylogenetic inference based on the ITS‐rDNA region and translation elongation factor 1 alpha (tef1‐α) gene. Koch's postulates were fulfilled using an excised shoot method. This study provides the first report on the occurrence of N. parvum as a cause of branch canker on pomegranate in Iran.     

Triazole induced drought tolerance in horse chestnut (Aesculus hippocastanum)

We determined the influence of the triazole derivatives paclobutrazol, penconazole, epixiconazole, propiconazole and myclobutanil on the drought tolerance and post drought recovery of container-grown horse chestnut (Aesculus hippocastanum L.) saplings. Myclobutanil neither conferred drought resistance, as assessed by its effects on a number of physiological and biochemical parameters, nor affected growth parameters measured after recovery from drought. Chlorophyll fluorescence (F(v)/F(m)), photosynthetic rates, total foliar chlorophyll and carotenoid concentrations, foliar proline concentration and superoxide dismutase and catalase activities were consistently higher and leaf necrosis and cellular electrolyte leakage was lower at the end of a 3-week drought in trees treated with paclobutrazol, penconazole, epixiconazole or propiconazole than in control trees. Twelve weeks after drought treatment, leaf area and shoot, root and total plant dry masses were greater in triazole-treated trees than in control trees with the exception of those treated with myclobutanil. In a separate study, trees were subjected to a 2-week drought and then sprayed with paclobutrazol, penconazole, epixiconazole, propiconazole or myclobutanil. Chlorophyll fluorescence, photosynthetic rate, foliar chlorophyll concentration and catalase activity over the following 12 weeks were 20 to 50% higher in triazole-treated trees than in control trees. At the end of the 12-week recovery period, leaf area and shoot, root and total plant dry masses were higher in triazole-treated trees than in control trees, with the exception of trees treated with myclobutanil. Application of triazole derivatives, with the exception of myclobutanil, enhanced tolerance to prolonged drought and, when applied after a 2-week drought, hastened recovery from drought. The magnitude of treatment effects was in the order epixiconazole approximately propiconazole > penconazole > paclobutrazol > myclobutanil.     

Microorganisms associated with canker rots and heart rot of oak

Pure cultures of the canker-rot fungi Inonotus hispidus, Phellinus andersonii and Spongipellis pachyodon, were isolated from non-compartmentalized decay and stain in cankers on Quercus phellos. Hericum erinaceum was isolated from compartmentalized decay columns in Q. phellos in consistent association with imperfect fungi.     

Phytophthora species associated with dieback of sweet chestnut in Western Turkey

Sweet chestnut (Castanea sativa) is an important tree species in the Marmara and Aegean regions of Turkey as these two regions produce the great majority of edible nuts, especially those used for marron glacé production. Chestnut forests and orchards in these regions showing severe dieback symptoms not associated with chestnut blight were investigated to determine the role of Phytophthora spp. in the decline syndrome. Soil samples were collected from around 108 symptomatic chestnut trees at 29 sites and Phytophthora spp. isolated using soil baiting technique and selective medium. Species isolated were identified by cultural characteristics and ITS sequencing. Phytophthora x cambivora was the dominant species detected in 13 sites, followed by P. cinnamomi (5 sites), P. plurivora (3 sites) and P. cryptogea (1 site). Phytophthora x cambivora was present in both regions, while P. cinnamomi was found only in the Marmara region in coastal areas around Istanbul. When inoculated at the stem bases of 3‐year‐old chestnut saplings, P. cinnamomi produced significantly longer necrotic lesions (7.8–12.0 cm) than P. x cambivora (2.6–6.3 cm) by 12 days after inoculation. Phytophthora plurivora was the least aggressive species causing only small lesions. Phytophthora cryptogea, which represents the first record on chestnut in Turkey, produced intermediate sized lesions in between P. x cambivora and P. plurivora. These results indicate that P. x cambivora and in some areas P. cinnamomi play major roles in the observed dieback of sweet chestnut in western Turkey.     

Phytophthora citrophthora,a new pathogen causing decline on horse chestnut in Turkey

Dieback symptoms were observed on horse chestnut trees planted approximately 40 years ago in Ankara, Turkey. Lesions at the stem bases of the affected trees were similar to those of ink disease on sweet chestnut. A Phytophthora sp. was isolated from the fine roots and soil samples collected around the stem bases by baiting using chestnut leaves. The pathogen was identified as Phytophthora citrophthora based on several morphological features and DNA sequences of the ITS region. Pathogenicity of P. citrophthora was tested by stem inoculation on 3‐year‐old horse chestnut saplings. P. citrophthora produced large cankers in 20 days and killed 40% of the saplings. This is the first report of P. citrophthora causing dieback on horse chestnut.     

Informative value of canker morphology on the presence or absence of virus infection in chestnut blight cankers

Chestnut blight destroyed the native chestnut forests in North America and also severely affected the European chestnut trees after its introduction in the 20th century. The ascomycete fungus Cryphonectria parasitica is responsible for this serious disease and causes lethal bark cankers on susceptible chestnut trees. In Europe, however, an infection of C. parasitica with Cryphonectria hypovirus 1 (CHV‐1) causes hypovirulence in C. parasitica and reduces the severity of the disease. Hypovirulence biologically controls chestnut blight in many regions to date. In this study, our goal was to determine morphological canker characteristics that are indicative of virus presence or absence in C. parasitica. We investigated 677 chestnut blight cankers from seven different geographic locations across Europe. For each canker, we assessed canker length, stem encircling, canker depth, presence of sporulation, canker activity and virus infection. We statistically analysed the informative value of these morphological characteristics for the presence or absence of CHV‐1. However, we did not find reliable indicators. Our logistic regression analysis revealed that virus infection of C. parasitica is not clearly related to canker morphology. This implies that fungal isolations from chestnut blight cankers and assessments in the laboratory are required to determine infection with CHV‐1 unequivocally.     

Eutypella canker of maple: first report from Germany and situation in Austria

Eutypella canker of maple, caused by Eutypella parasitica (which is native to North America), is reported for the first time from Germany. From 2013 to 2015, this perennial canker disease was recorded on 105 maple trees in Munich. Six maple species were affected: Acer pseudoplatanus, A. campestre, A. platanoides, A. cappadocicum, A. heldreichii ssp. trautvetteri and A. hyrcanum. Occurrence on the latter three species represents new host records for E. parasitica. In Austria, Eutypella canker was newly discovered on two trees at a second locality in 2011, and it is now known to occur on seven A. pseudoplatanus trees at two localities, which are separated nearly 150 km. A. pseudoplatanus was the most frequent host of E. parasitica in Munich and Austria, which is in agreement with previous studies in Europe. The identity of the causative pathogen as E. parasitica was verified by ITS rDNA sequencing of fungal cultures obtained from cankers in Munich and at both Austrian localities. The presence of large and old cankers in both countries suggests that introduction of E. parasitica dates back a long time, probably several decades. The new records of Eutypella canker in Germany and Austria show that the disease is more widely distributed in central Europe than previously recognized.     

First detection of Neoscytalidium dimidiatum associated with canker disease in Egyptian Ficus trees

In September 2013, a canker disease of Ficus nitida and F. benjamina was reported for the first time in Assiut governorate, Egypt. Infected samples were collected from various locations. Pure cultures of a fungus were isolated on potato dextrose agar at 25°C from diseased plants. Morphological investigation and DNA sequencing showed that the causal agent was Neoscytalidium dimidiatum. A pathogenicity test conducted using 2‐year‐old plants of each host gave 70%–80% infection, and the pathogen was reisolated from the inoculated plants. A pure culture of N. dimidiatum was deposited in the culture collection of the Assiut University Mycological Centre (AUMC) under the code AUMC 9293 and the ITS sequence was placed in NCBI under accession number KX985929 .     

Occurrence of the moth Cydia pactolana is associated with the spruce canker fungus Neonectria fuckeliana

Several young damaged Norway spruce stands in eastern and central Finland were observed from 2013 to 2016. The damage included trees with heavy resin flow, necrotic foliage, stem and branch cankers and dead trees. Pest identification resulted in the tortricid moth Cydia pactolana whose occurrence was always associated with the presence of the ascomycete pathogen Neonectria fuckeliana. Both the insect and the disease contributed to the extent of the damage, but it is not possible to say in which order they had attacked the trees. Apparently, changed climate has affected the increased occurrence of both the fungus and the moth. However, the characteristics of the insect–fungus interaction and the factors contributing to the coincidences are unknown. Emerging coexistence or potential symbiosis of the two damaging agents is a serious threat for Norway spruce cultivation. Understanding the biology of this fungus–insect interaction is important for controlling them.     

Parasitic Ichneumonoidea on the horse chestnut leaf miner, Cameraria ohridella (Lepidoptera: Gracillariidae) in Slovakia

Parasitic Hymenoptera from the suprafamily Ichneumonoidea attacking the horse chestnut leafminer Cameraria ohridella Deschka & Dimic (Lepidoptera: Gracillariidae) were studied in southwest Slovakia during 2000 and 2001. The search for such species resulted in the determination of eight ichneumonid species, Gelis agilis (Fabricius), Itoplectis alternans (Gravenhorst), I. clavicornis (Thompson), I. maculator (Fabricius), Scambus annulatus (Kiss), S. brevicornis (Gravenhorst), Zatypota percontatoria (Müller), Adelognathus sp. and a braconid Colastes braconius Haliday. The most abundant species was S. annulatus. All these species recorded are polyphagous and often facultative hyperparasitoids, except C. braconius, which departs from this norm in not being hyperparasitic. The presence of more diversified native parasitoids and hyperparasitoids from the Ichneumonoidea predicate a slow successive adaptation of the parasitoid fauna to the invasive host, Cameraria ohridella.