New branch disease of Styphnolobium japonicum caused by Fusarium solani in Xinjiang of China

Styphnolobium japonicum (L.) Schott is a deciduous tree belonging to family Fabaceae and has been widely planted as garden greenery in China. In May 2021, a serious branch canker disease was observed in Alaer City. In order to identify the pathogen, five fungi were isolated from the diseased branches and the pathogenicity was evaluated by inoculating the branches outdoors. The pathogen was re-isolated from all the inoculated branches, therefore fulfilling Koch's postulates. Based on the morphological characteristic and polygenetic analysis using the internal transcribed spacer region, β-tubulin and the translation elongation factor 1-alpha, the pathogen was identified as Fusarium solani. This is the first report of F. solani as the causal agent of a branch canker of S. japonicum in Xinjiang of China.     

Infection approach of Diplodia sapinea,the causal agent of tip blight of Pinus tabulaeformis in China

To clarify the infection approach of Diplodia sapinea, a pathogen that causes tip blight of Pinus tabulaeformis, the infection process of the pathogen in needles was observed using scanning electron microscopy (SEM). In addition, the disease incidence on branches damaged by Aphrophora flavipes (Hemiptera: Cercopidae) and Dioryctria splendidella (Lepidoptera: Pyralidae) in the forest was also investigated. Then, branches and needles of P. tabulaeformis were inoculated using the D. sapinea spore suspension under indoor and field conditions. The results showed that the damage caused by A. flavipes could aggravate the occurrence of tip blight of P. tabulaeformis to some extent. Moreover, the pathogen could also penetrate 1‐, 2‐ and 3‐year‐old pine needles through stomata in the field. The pathogen infected the 1‐year‐old branches first and then gradually spread to 2‐ and 3‐year‐old branches.     

Outbreak of shoot blight and dieback of Eucalyptus spp., caused by Pseudoplagiostoma eucalypti in Brazil

An outbreak of a new and severe disease was observed in Eucalyptus plantations of Bahia state, Brazil. An Ascomycota fungus has been frequently associated with the main symptoms of the disease namely leaf spot, branch cankers, shoot blight, defoliation, and dieback. Based on morphological characteristics, phylogenetic analysis (ITS and TEF-1α genes), and pathogenicity test on Eucalyptus plants, Pseudoplagiostoma eucalypti was identified as the causal agent of the disease. Although P. eucalytpi has been known from in Brazil since 1998, this is the first report of it causing severe disease and die-back on Eucalyptus spp. and we also record new symptoms associated with the pathogen.     

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.     

Bacterial shoot blight of sweet crab apple caused by Pseudomonas viridiflava

Sweet crab apple (Malus coronaria) is a popular ornamental tree planted in gardens and urban forests in South Korea. In 2018, severe symptoms were observed on street plantings of sweet crab apple in Jinju, South Korea including shoot blight: shoot tips, twigs and foliage of infected trees turned brown, and dried completely. The causal agent isolated from the disease lesions was identified as Pseudomonas viridiflava based on biochemical tests, pathogenicity, and 16S rRNA and rpoD gene sequencing. On artificial inoculation, this pathogen not only caused shoot blight on sweet crab apple, but also bulb rot and leaf blight on onion. Here, we report the occurrence of bacterial shoot blight caused by P. viridiflava in sweet crab apple for the first time in the world.     

Variation in pathogenicity among the three subspecies of Phytophthora alni on detached leaves,twigs and branches of Alnus glutinosa

Pathogenicity tests were carried out on leaves, twigs and branches of Alnus glutinosa using several isolates of Phytophthora alni ssp. alni, P. alni ssp. multiformis and P. alni ssp. uniformis in vitro. Healthy fresh leaves were collected from disease‐free areas and inoculated with mycelium on agar discs or by dipping in zoospore suspensions. In addition, twigs and branches were collected from both disease‐free and disease‐affected areas, inoculated with mycelium on agar discs and incubated at four temperatures (15, 20, 25, 30°C). All subspecies tested were pathogenic but with varied level of virulence. In inoculation tests on foliage, wounding was a key factor in causing infections: lesions on inoculated wounded leaves were larger than on non‐wounded leaves. In the twig and branch inoculation tests, no differences in virulence were observed among the P. alni subspecies in terms of sampling locations, but lesions differed in size according to incubation temperature, with the largest lesions occurring on tissues incubated at 25°C. The work is the first to report foliar necrosis caused by P. alni on A. glutinosa. P. alni ssp. uniformis was the least virulent of the subspecies in branch inoculations. These findings demonstrate that various tissues of A. glutinosa could act as sources of pathogen inoculum and may disseminate alder Phytophthora in natural ecosystems.     

Characterization,pathogenicity and host range studies of Paecilomyces formosus associated with dieback of Christ's thorn trees (Paliurus spina-christi Mill.) in Iran

Christ's thorn (Paliurus spina-christi Mill.) tree is an important and valuable forestry species and has significant potential in afforestation and reforestation systems. In recent years, dieback symptoms were observed on Paliurus spina-christi trees in Gilan-e Gharb region of Kermanshah province, west Iran. During 2020 to 2021, Christ's thorn trees that exhibit branch dieback symptoms were sampled for fungal isolations. The pathogenicity tests, biochemical assay of growth, acid production on creatine sucrose agar (CREA) medium and morphological and molecular investigations (ITS and β-tubulin regions) identified Paecilomyces formosus as a dieback causal agent. This is the first report of P. formosus pathogenicity on Paliurus spina-christi trees. Furthermore, disease severity was assayed on 11 tree species under three different temperatures 15, 25 and 35°C. Disease severity caused by all isolates on detached branches was greater at 35°C than at 15 and 25°C. This study presents the host range of this pathogen and showed that these potential hosts are prone to this pathogen under high temperatures, which forest trees experienced in recent decades.     

Mechanisms and metabolomics of the host–pathogen interactions between Chestnut (Castanea species) and Chestnut blight (Cryphonectria parasitica)

Chestnut blight is a stem‐girdling disease of Castanea caused by the fungal pathogen Cryphonectria parasitica. Chestnut blight affects all Castanea species to some degree. In Asian species, chestnut blight is a commercially relevant disease which primarily affects nut production. In American and European species, chestnut blight has caused significant declines in wild populations and continues to negatively affect nut production in the European chestnut (C. sativa). Despite the profound effect of this disease in the Castanea genus, very little is known concerning the factors involved in the host–pathogen interaction between C. parasitica and its Castanea hosts. This review summarizes information on known mechanisms and metabolites involved in the host–pathogen interaction and contributes original information on the pathogen in relation to susceptible and putatively resistant genotypes with a view to furthering research that will promote a better understanding of this devastating disease and enable its control.     

Quambalaria eucalypti found on Eucalyptus in Indonesia

The Eucalyptus plantation industry in Indonesia has expanded rapidly during the last few decades. During routine nursery disease surveys, symptoms of a leaf and shoot blight disease were detected on Eucalyptus mother plants. Isolates were obtained from symptomatic tissues and identified using DNA sequence analyses. Phylogenetic analyses showed that the isolates were those of Quambalaria eucalypti. Pathogenicity tests were conducted with isolates of Q. eucalypti on clones of E. pellita and E. grandis × E. pellita hybrids. These resulted in symptoms similar to those observed on naturally infected plants. Eucalyptus genotypes tested showed variation in their susceptibility, highlighting the potential to select and breed for resistance and thus to manage future outbreaks of the disease. This is the first report of the pathogen in Indonesia as well as in Southeast Asia.     

Morphological and molecular characterization of Fusarium oxysporum and Fusarium avenaceum causing a novel needle blight of Picea asperata in China

Picea asperata is a unique tree species in China. It has important economic and ecological values. In this study, the disease symptoms resembling needle blight, a new disease of P. asperata (10- to 15-year-old), were detected in a forest area in Tianshui City, Gansu Province, China, in August 2020. Affected needles turned yellow, the colour became darker at the junction of infected and healthy areas, the needles wilted and even fell off the tree. Through pathogenicity tests, the two pure fungi strains isolated from diseased needles caused distinct needle blight symptoms on P. asperata, with symptoms similar to those observed in the forest. It was observed that they had sickle-shaped conidia. Subsequently, multilocus phylogenetic analysis of partial sequences of the internal transcribed spacer region (ITS), translation elongation factor 1-α (TEF-1α) and RNA polymerase II second major subunit (RPB2) genes was performed. They were found closely clustered with Fusarium oxysporum and F. avenaceum, respectively. Based on morphological and molecular biological determinations, the two pathogens were identified as F. oxysporum and F. avenaceum. To our knowledge, this is the first report of needle blight caused by F. oxysporum and F. avenaceum on P. asperata in China.     

A new bacterial disease observed on Quercus myrsinifolia

This is the first report of a new bacterial disease occurring on Quercus myrsinifolia in the nurseries of the Kyushu district in Japan. The main symptoms are shoot and twig blight, which begins with black necrotic lesions. In addition, unclear blackish discolorations, bacterial ooze and water‐soaked lesions were observed as early symptoms, and spindle‐shaped cankers and stem cankers with irregular surface were observed as secondary symptoms. The blight symptoms observed on the current‐year shoots were first observed during the rainy season and continued until autumn (June–October). In summer, the symptoms were pronounced. A yellowish bacterium was consistently isolated from the affected shoots of Q. myrsinifolia, and on inoculation into healthy trees, it caused the same symptoms, which were more severe after wound inoculation than after non‐wound inoculation. Wound inoculation also caused the disease symptoms on Quercus spp., Fagus crenata and Lithocarpus glaber, but not on several other species of Fagaceae. The causal bacterium was identified as Xanthomonas arboricola based on its morphological, cultural and biochemical characteristics and genetic sequence analysis of 16S rDNA, 16S‐23S spacer regions and gyrB. To our knowledge, there are no previous records of xanthomonads causing shoot blight on fagaceous plants like Q. myrsinifolia. Therefore, we postulate that the shoot blight of Q. myrsinifolia is a new bacterial disease. We propose the name of the disease to be ‘bacterial shoot blight’ based on its main symptoms.     

Estimating the equilibrium position by measuring growth stress in weeping branches ofPrunus spachiana Kitamura f.spachiana cv.Plenarosea

The equilibrium position of a current-year branch of the weeping Japanese cherry,Prunus spachiana Kitamura f.spachiana cv.Plenarosea, was estimated by measuring the released strains of growth stresses. In current-year branches that were supported with wires to prevent weeping as soon as the branches first budded, tensile growth stresses on the upper side were smaller than those of the control branches. Gelatinous fibers were rarely found on the upper part of the cross section of the supported branches, whereas the control branches had many gelatinous fibers on the upper part. The upright orientation of the supported branches was closer to the equilibrium position than the weeping orientation of the control branches. The equilibrium position of the branches was thought to be in the initial bud direction, above the horizontal plane; and the weeping style of branch was not the preferred angular orientation forP. spachiana.     

Risk from Sirococcus conigenus to understory red pine seedlings in northern Wisconsin

Interest in development of multicohort stands of red pine (Pinus resinosa) in the Great Lakes region of North America prompted an investigation of the potential impact of the shoot blight pathogen Sirococcus conigenus (syn. S. strobilinus) on understory red pine seedlings. In May 2002 and 2003 healthy, 1‐year‐old red pine seedlings were planted in the understory of a maturing red pine plantation in northern Wisconsin in an area with a history of presence of this pathogen. Occurrence of shoot blight symptoms was recorded periodically during the summer, and in each year seedlings were harvested in fall and examined for signs of shoot blight pathogens. By fall 2002 and 2003, respectively, shoot blight incidence was 89% and 98% and most seedlings were dying. Pycnidia with conidia of S. conigenus were present on almost all of the symptomatic seedlings. The conifer shoot blight and canker pathogen Diplodia pinea (syn. Sphaeropsis sapinea) was also detected, though less frequently. Pycnidia of S. conigenus tended to be found more frequently on symptomatic current year's shoots than symptomatic previous year's shoots; the opposite was true for pycnidia of D. pinea. Risk from S. conigenus to understory red pine seedlings should be considered in any plans for development of multicohort red pine stands in areas where the pathogen is present.     

Dormouse injuries predispose beech to infection by Neonectria ditissima

After awaking from winter hibernation, the Edible dormouse begins to feed by stripping the bark and the outer part of the xylem from the branches of both broadleaves and conifers. Natural or artificial wounds are essential for the penetration and colonisation of the tissues by the fungal pathogen Neonectria ditissima. This pathogen creates open cankers on beech branches and other broadleaves, which are frequently later infected by wood‐decaying fungi. Because of the high frequencies of both dormouse injuries and branch cankers in a large monospecific beech forest in northern Italy, field and laboratory investigations were conducted to verify whether rodent‐inflicted injuries on beech were a preferred infection point for the pathogen. These studies also examined the susceptibility to infection of the dormouse‐inflicted wounds over time, and the relationships between dormouse damage, Neonectria infection, and wood decay. The results showed a significant direct correlation between the percentage of infections and their proximity to the wounds, indicating that the parasite localises to sites where there are receptive dormouse injuries. In addition, the susceptibility of the wound was found to diminish with increasing age, disappearing in 120–150 days. The association between dormouse injuries, Neonectria cankers and wood decay was also found to cause approximately half of the frequent beech branch breakages during intense weather events.     

Losses caused by the needle blight fungus Delphinella abietis in a greenery trial of Nobel fir in western Norway

In a greenery trial of Nobel fir (Abies procera) in western Norway, most branches had good quality until 1994 when 31% of the branches were discarded. Since then a high level of losses has been noted and 87% were discarded in 2000. A survey in 1998 revealed that the needle blight fungus Delphinella abietis was the main cause. It seems that frost did not initiate or maintain the disease in the stand, but generally low temperatures may have been important. Discarded branches with the fungus have been left on the ground and have probably been important in maintaining a high level of attack.     

First report on the association of Pestalotiopsis mangiferae with leaf blight disease of Canthium dicoccum in India

The multi‐use tree Canthium dicoccum (Rubiaceae) growing in shrub forests of Mysore, Mandya and Chamarajanagar (India) was severely affected by a leaf blight disease. The ascomycete Pestalotiopsis mangiferae was consistently isolated from symptomatic leaves and identified by micromorphology and ITS rDNA sequencing analysis. Pathogenicity test was performed and Koch's postulates were fulfilled. This is the first report of P. mangiferae causing leaf blight of C. dicoccum in India.     

Occurrence of leaf spot disease caused by Neopestalotiopsis clavispora on Taxus chinensis in China

Taxus chinensis is a valuable tree with uses for timber, medicinal, ornamental and landscape purposes. Most importantly, it is a source of the anti‐cancer drug paclitaxel. In 2016, needle spot disease was observed on T. chinensis in Fujian Province of China. Five isolates of similar morphology were isolated from diseased samples. The pathogen was identified as Neopestalotiopsis clavispora based on morphological and cultural characteristics and confirmed by sequence analysis of the internal transcribed spacer region (ITS) and the large subunit ribosomal RNA gene (LSU). The pathogenicity of the isolates was confirmed by fulfilling Koch's postulates. To the best of our knowledge, this is the first report to indicate that the causal agent of needle spot disease on Chinese yew in China is N. clavispora.     

First report of bacterial wilt caused by Ralstonia solanacearum on fig trees in China

This article presents the first report of bacterial wilt on fig (Ficus carica) trees in China. In 2014, fig trees with typical bacterial wilt symptoms were observed for the first time in China. The causal pathogen was determined to be Ralstonia solanacearum. Identification was based on symptomatology, morphology, BioLog carbohydrate utilization, 16S rDNA sequence analyses and phylotype‐specific multiplex‐PCR assays.     

Erysiphe australiana: the cause of powdery mildew on Lagerstroemia speciosa in Brazil

Powdery mildew symptoms and signs were observed on seedlings of Lagerstroemia speciosa within an ornamental plant nursery in Viçosa, State of Minas Gerais, Brazil. Signs were most prominent as intense mycelial growth and sporulation on the shoots, new branches and leaves, which led to tissue necrosis. Based on morphological characteristics and phylogenetic analyses of ITS and 28S rDNA sequences, the powdery mildew pathogen of L. speciosa was identified as Erysiphe australiana, a well‐known powdery mildew pathogen infecting Lagerstroemia spp. worldwide. To our knowledge, this is the first report of E. australiana causing powdery mildew on L. speciosa in Brazil.