First report of Sydowia polyspora causing disease on Pinus pinea shoots

The fungus Sydowia polyspora is frequently isolated from conifers worldwide and is considered a pathogen on several hosts. Stone pine (Pinus pinea) is one of the most important forestry species throughout the Mediterranean basin due to the value of the edible pine nut. Stone pines showing tip dieback, needles with tan‐ to yellow‐coloured lesions and shoot death, observed in stands in Portugal, were sampled for analysis. Fungal colonies covered with cream‐coloured spore masses, were consistently obtained. Morphological and phylogenetic analyses of the ITS rDNA region enabled identification of these isolates as S. polyspora. Inoculation tests showed that the fungus caused lesions on excised P. pinea shoots. The symptoms observed might have a negative effect on pine nut production, and thus, evaluation of the impact of this disease is of relevance to future research. This paper is the first to report S. polyspora causing disease on P. pinea.     

The first record of Botryodiplodia canker in Poland

This study describes the first observation of Botryodiplodia canker in the Western Carpathians in south‐eastern Poland caused by Botryodiplodia hypodermia (Sacc.) Petr. (syn. Sphaeropsis hypodermia, S. ulmicola). The canker occurred on an approximately 17‐year‐old Ulmus glabra sapling in a mixed conifer/deciduous stand with elm trees severely damaged by Dutch elm disease. This paper describes disease symptoms and provides information on the macro‐ and micromorphology of the fungus isolated from the cankered tissues. The results of BLAST search using DNA sequences obtained for our cultures and subsequent phylogenetic positioning of the fungus among closely related Botryosphaeriaceae indicate that the species is much more closely related to Phaeobotryon than to the other Botryodiplodia or Sphaeropsis species. Moreover, a total of 16 polymorphisms within the ITS region were detected between S. ulmicola associated with Botryodiplodia canker in North America and B. hypodermia associated with the canker observed in Poland. Thus, the “European” variant of “Sphaeropsis” ulmicola can now be easily identified with our barcode sequences. The Botryodiplodia canker is much less prevalent in Europe than in North America. Differences in virulence of “American” and “European” linages and differences in susceptibility of various elm species may be the reason for the higher prevalence of the disease in North America.     

Identification and pathogenicity of Alternaria alternata causing leaf spot and blight disease of Ailanthus excelsa in India

Alternaria leaf spot of Ailanthus excelsa is generally considered as minor disease in India. Recently, severe disease outbreaks were recorded in the nursery of the Forest Research Institute, Dehradun, progeny trial at Jhumpa, Haryana, and in a nearby farm field. Leaf symptoms included small circular, brown, necrotic spots with a chlorotic halo. With severe infections, leaf spots coalesced and resulted in leaf blight. A small‐spored Alternaria with concatenated conidia was isolated consistently from the leaf samples with spot symptoms. Sequence analyses of the internal transcribed spacer (ITS) region of ribosomal DNA (rDNA) and the translation elongation factor 1‐alpha (tef‐1α) gene region of two fungal isolates confirmed the species as A. alternata. In detached leaf assays, both isolates produced symptoms similar to those observed on the nursery/field‐grown plants. To validate the detached leaf assay result, pathogenicity was also demonstrated on whole plants in a glasshouse. Koch's postulates were fulfilled by re‐isolating A. alternata from the inoculated leaves. This work is the first to confirm that A. alternata is associated with leaf spot and blight disease of A. excelsa in India.     

First report of Exobasidium gracile causing hypertrophied leaves of Camellia sasanqua in South Korea

This study presents the first report of Exobasidium gracile in South Korea. In 2012, a Camellia sasanqua tree with typical Exobasidium disease symptoms was observed for the first time in South Korea. The causal fungus was determined as E. gracile. The identification was based on host range, symptomatology, morphology and two‐gene sequence analyses.     

Genetic diversity and population structure of Raffaelea quercus‐mongolicae,a fungus associated with oak mortality in South Korea

Raffaelea quercus‐mongolicae is a fungus associated with oak wilt and deemed to cause extensive oak mortality in South Korea. Since the discovery of this fungus on a dead Mongolian oak (Quercus mongolica) in 2004, the mortality continued to spread southwards in South Korea. Despite continued expansion of the disease and associated significant impacts on forest ecosystems, information is lacking about the origin and genetic diversity of R. quercus‐mongolicae. Restriction‐site‐associated DNA (RAD) sequencing was used to assess genetic diversity and population structure among five populations (provinces) of R. quercus‐mongolicae in South Korea. In total, 179 single nucleotide polymorphisms (SNPs) were identified among 2,639 RAD loci across the nuclear genome of the 54 R. quercus‐mongolicae isolates (0.0012 SNPs per bp), which displayed an overall low expected heterozygosity and no apparent population structure. The low genetic diversity and no apparent population structure among South Korean populations of this ambrosia beetle‐vectored fungus support the hypothesis that this fungus was introduced to South Korea.     

A new leaf disease on Populus euphratica in south‐western Iran

During the winter of 2012, a leaf spot disease was observed on Euphrates poplar (Populus euphratica) in the forest areas of Khuzestan province, south‐western Iran, causing significant damage in the Karun's riverside forests. Symptoms consisted of necrotic dark brown, circular to oval, 5‐ to 10‐mm spots on both surfaces of the leaves. A fungus having distinct dictyospores similar to those produced by Alternaria spp. was observed. The morphological characteristics, as well as the phylogenetic analysis of the internal transcribed spacer (ITS1‐5,8S‐ITS2) region, confirmed the identity of the strains belonging to the species Alternaria alternata. Pathogenicity tests were conducted on the alive leaves of P. euphratica on the young branches, as well as on the detached leaves in Petri dishes, through inoculation with spore suspension. Target spot symptoms similar to those observed in naturally infected leaves were developed on the inoculated leaves seven to 10 days after inoculation in both the inoculation procedures. A. alternata was consistently re‐isolated from the spots. Interestingly, similar symptoms were observed 7 days after detached leaf treatment with droplets of 15‐day‐old fungal culture filtrate, suggesting the production of pathotoxic compounds by the fungus. To our knowledge, this is the first report of A. alternata causing leaf spot on Euphrates poplar in Iran.     

Biocontrol potential of Pseudomonas azotoformans,Serratia marcescens and Trichoderma virens against Fusarium wilt of Dalbergia sissoo

Wilt disease caused by Fusarium solani is a serious constraint to Dalbergia sissoo (shisham) plantations in northern India. In this study, the antagonistic potential of 40 bacterial isolates recovered from rhizophere soil of healthy shisham trees, and a well‐characterized Trichoderma species (Trichoderma virens) were tested for their possibility as biocontrol agents for F. solani. Two promising isolates (S1 and S15) were identified which inhibited pathogen growth, caused chitin degradation, produced siderophores and solubilized phosphate in vitro. Isolate S15 scored highest for hydrogen cyanide (HCN) production while isolate S1 was a non‐HCN producer. These two isolates were identified as Serratia marcescens (S1) and Pseudomonas azotoformans (S15) following sequence analysis of 16S rDNA. In dual culture assays, T. virens caused 80% inhibition of mycelial growth of the test fungus. The three selected antagonists when tested in planta in the glasshouse completely suppressed production of wilt symptoms on 12‐month‐old shisham plants. Further work is needed to ascertain the potential of these isolates to be used as biocontrol agents to manage shisham wilt under field conditions.     

Erysiphe alphitoides causes powdery mildew on Eucalyptus gunnii

In June 2016, pot‐grown Eucalyptus gunnii plants showing typical symptoms of powdery mildew disease were found in a greenhouse in Korea. Morphological characteristics of the anamorph and molecular sequence analyses of the ITS regions and 28S rDNA verified the fungus as Erysiphe alphitoides, which is known as common and widespread powdery mildew on Quercus spp. Although E. alphitoides has been reportedly associated with powdery mildew diseases of tropical trees and shrubs other than Quercus spp., this is the first finding of E. alphitoides on a Eucalyptus tree worldwide.     

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 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.     

Colletotrichum siamense: A novel leaf pathogen of Sterculia nobilis Smith detected in China

Sterculia nobilis is an important tropical woody plant with high ornamental and economic value. At present, there are few reports of diseases on this plant. In August 2018, an unknown leaf spot disease was observed on S. nobilis in Nanning, China, affecting the inner leaves of the canopy and causing considerable defoliation. The pathogen was isolated, and pathogenicity tests carried out on detached leaves to verify Koch's postulates. Based on morphological observations and polygenic analyses, the pathogen causing leaf spots on S. nobilis was identified as Colletotrichum siamense.     

Canker disease of willow and poplar caused by Cryptosphaeria pullmanensis recorded in China

A new canker disease of Salix alba and Populus alba has been observed in Xinjiang, China. Black circular spots on dead branches and stems are the symptoms of the disease. Sixty‐seven isolates recovered from Salix matsudana, S. alba and Populus alba were identified as Cryptosphaeria pullmanensis based on morphological features and multigene phylogeny. Pathogenicity tests were performed on S. alba and P. alba stems using the C. pullmanensis isolates. Cankers on and Cryptosphaeria pullmanensis of C. pullmanensis from the stems fulfilled Koch's postulates and confirmed C. pullmanensis as the causal agent of the canker disease. C. pullmanensis is characterized by its yellow stromatic tissue surrounded by a black conceptacle with regularly arranged multiple locules sharing common walls and hyaline, allantoid, aseptate conidia (mean size 7.42 × 1.72 μm). This is the first report of C. pullmanensis causing Cryptosphaeria canker in China, and S. alba and P. alba are new host records for C. pullmanensis.     

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.     

First molecular detection of Lecanosticta acicola from Poland on Pinus mugo

The presence of quarantine pathogen Lecanosticta acicola, the causal agent of brown spot needle blight, was confirmed using molecular methods for the first time in northern part of Poland on the coastal area adjacent to the Baltic Sea. This area includes sandy beaches, where Pinus mugo and P. sylvestris were planted. Symptomatic needles were collected in 2017 from 20 P. mugo trees growing in one stand in Ustka. Typical symptoms of brown spot needle blight infection, including dead needle tips and central zones with yellow or reddish brown, circular spots in green tissue, were observed on all samples. Only, the asexual stage of L. acicola was obtained during this work. The pathogen species identity was confirmed using classical morphological methods (microscopic examination of the infected needles), real‐time and species‐specific priming (SSPP) PCR, and ITS sequencing. Analysis of mating‐type (MAT) genes showed the presence of both mating types in northern Poland.     

Salix tetradenia Hand.‐Mazz: a new natural plant host of ‘Candidatus phytoplasma’

This article reports Salix tetradenia Hand.‐Mazz as a new host of Candidatus phytoplasma and demonstrates its association with witches' broom disease on S. tetradenia plants. Plants exhibited typical visual symptoms of phytoplasma with virescence, abnormality of flowers and witches' broom, and phytoplasma bodies were observed by transmission electron microscopy. Products of 1.2 kb were amplified by nested PCR using phytoplasma universal primer pairs R16F2n/R16R2, but no amplification products were obtained from symptomless plants. The sequence analysis of three 16S rDNA isolates showed 99.84%, 99.68% and 99.76% identify, respectively, with the homologous gene (nc_005303) of member of ‘Candidatus phytoplasma asteris’ (16SrI) group. Phylogenetic and virtual computer‐simulated restriction fragment length polymorphism analysis of the 16S rRNA, tuf and rp gene sequences confirmed that this phytoplasma clustered in the 16SrI‐B subgroup. These results indicated that the diseased S. tetradenia plants were infected by a phytoplasma of the 16SrI group. This is the first report on the occurrence of phytoplasma disease on S. tetradenia worldwide.     

Investigation of the mating‐type distribution of Raffaelea quercus‐mongolicae in South Korea

Raffaelea quercus‐mongolicae is a mycangial symbiont of a wood‐boring ambrosia beetle, Platypus koryoensis (Coleoptera: Curculionidae: Platypodidae), which is believed to be associated with oak mortality in South Korea. Since the first discovery of the disease in 2004, oak mortality has continued to spread across the country, and the pathogen has had a significant impact on forest ecosystems in the country; however, little is known regarding the biology of the fungus. The aim of this study was to develop markers to determine the mating types of individual isolates of R. quercus‐mongolicae collected across the country and then determine the mating‐type ratio in natural populations. To achieve this, partial sequences of MAT1‐1–3 and MAT1‐2–1 genes were amplified using degenerate primers and cloned. The new primer sets, which were specific to each mating‐type idiomorph, identified isolates as MAT1‐1 and MAT1‐2 mating types. The roughly equal frequencies of the two mating types suggest that sexual reproduction might have occurred in natural populations of R. quercus‐mongolicae in South Korea.     

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.     

Decline of Paulownia tomentosa caused by Trametes hirsuta in Serbia

During the monitoring of the health status of nurseries and plantations in Serbia, a decline in a 5‐year‐old Paulownia tomentosa plantation was recorded. Trees displayed symptoms of dieback, massive breaking at different positions, the appearance of decay and fungal fruitbodies at the stems. Using standard isolation methods, white colonies with cottony surfaces and regular growth were obtained from the decaying wood samples, and after the oxidation degree analysis, it was determined that these isolates belonged to Davidson's group 6, indicating white rot basidiomycetes. To identify the isolated fungus, the ITS region of one selected isolate was sequenced. Based on the morphological analysis of the obtained colonies, collected fruitbodies and ITS sequence analysis, this fungus was identified as Trametes hirsuta. This is the first report of T. hirsuta on Paulownia tomentosa in Serbia. Irregularly performed pruning as the possible infection route and the implications of these findings are discussed.