First report of Teratosphaeria gauchensis causing stem canker of Eucalyptus in Kenya

Teratosphaeria stem canker is an important disease of Eucalyptus species in many parts of the world where these trees are intensively propagated in plantations. Symptoms similar to those of Teratosphaeria stem canker were observed on Eucalyptus grandis and a E. grandis × E. camaldulensis hybrid clone in the Central Highlands of Kenya. Symptomatic bark samples were collected from two sites and the associated fungus isolated and identified using DNA sequence analyses of multiple gene regions. The pathogen was identified as Teratosphaeria gauchensis. This represents the first report of the disease and the pathogen in Kenya.     

Involvement of Cylindrocarpon destructans in root death of Pinus sylvestris seedlings: Pathogenic behaviour and predisposing factors

The common rhizospheric fungus Cylindrocarpon destructans was investigated in relation to its role in root death of Pinus sylvestris in Nordic nurseries and plantations. Laboratory methods were developed for studying similar root problems as well as the early effects of phytotoxicity and fungal infection. Seedlings grown under standardized optimal conditions were exposed to controlled stress (known to occur in nurseries), with or without C. destructans in the rhizosphere. Low light conditions, anaerobic root environment, and fungicide treatment were each found to predispose pine seedlings to invasion by the pathogen. The pathogen was very sensitive to competition as well as antagonism on the root, and fungicide‐induced inhibition of antagonists such as Trichoderma spp. also increased the severity of attack by the pathogen. To compete successfully, the pathogen would have to invade and dominate weakened roots prior to the arrival of saprophytes. Toxic metabolites produced by the pathogen weakened or killed nearby root tissues, and pathogen metabolites seemed to prevent saprophytes from taking hold in the infected roots. Such heavily infected, dead roots may act as inoculum sources allowing the pathogen to invade adjacent living roots, even healthy ones. Dead roots left in nursery soil after earlier harvests may act as reservoirs of inoculum for long periods and pose a threat to new plants.     

Growth and spore germination of Cylindrocarpon destructans in associative cultures with bacteria and actinomycetes1

Studies were made on the effect of bacteria and actinomycetes on growth and spore germination of Cylindrocarpon destructans. The effect of bacteria on growth of this fungus as well as on spore germination was statistically not significant. The actinomycetes in general inhibited or had no influence on growth and germination of conidia of C. destructans.     

Teratosphaeria gauchensis associated with trunk,stem and foliar lesions of Eucalyptus globulus in Portugal

Teratosphaeria gauchensis and T. zuluensis both cause a stem canker of eucalypts that leads to serious damage in various parts of the world. Until recently, this disease was unknown in Portugal. Nevertheless, severe damage to Eucalyptus globulus has been observed in Portugal since 2006 when symptoms appeared as necrotic spots on young green stems and leaves, twig lesions, and dark oval‐shaped lesions on stems and trunks. The isolates from affected E. globulus tree plantations were identified using sequence data of the ITS1‐5.8S‐ITS2 and EF‐1α clusters, together with morphological characteristics. Based on these results, the causal organism was identified as T. gauchensis, which represents the first report of this pathogen from Portugal.     

Phylogenetic and pathogenicity evaluation of the marasmioid fungus Marasmius palmivorus causing fruit bunch rot disease of oil palm

Marasmius palmivorus is a marasmioid fungal species that exhibits parasitic behaviour, although most marasmioids are rarely parasitic. The fungus has been reported to cause fruit bunch rot disease of oil palm and coconut, but only a few studies on its pathogenic behaviour are available, particularly on oil palm. Hence, there is a need to assess the ability of the fungus to act as a pathogen and to study its molecular evolution and taxonomy. Nine isolates of M. palmivorus were successfully isolated from basidiocarps and diseased fruitlets of oil palm collected from oil palm plantations and were morphologically characterized on potato dextrose agar (PDA) followed by molecular identification based on nucleotide sequence alignments of internal transcribed spacer (ITS) regions of ribosomal RNA (rRNA) gene clusters with sequences from GenBank. Koch's Postulates confirmed that M. palmivorus could infect oil palm fruitlets with symptoms similar to those observed for bunch rot disease. Molecular phylogenetic studies using nucleotide sequences of ITS and the nuclear ribosomal large subunit (nLSU) showed that isolates sharing the same phenotypic characteristics of Marasmius palmivorus and Marasmiellus palmivorus are monophyletic and share a common ancestor. The fungus has also been shown to be more closely related to the genus Marasmius than Marasmiellus; therefore, we support retention of the taxon name of the pathogen causing bunch rot disease of oil palm as Marasmius palmivorus.     

First report of Teratosphaeria zuluensis causing stem canker of Eucalyptus grandis in Uganda

Teratosphaeria stem canker is one of the most important diseases to have emerged on non‐native plantation‐grown Eucalyptus trees globally. In 2012, Eucalyptus grandis trees with typical Teratosphaeria stem canker symptoms were observed in Uganda. Multigene sequence analyses of isolates from these cankers led to the identification of T. gauchensis, previously recorded in Uganda, and T. zuluensis. This study represents the first report of T. zuluensis in Uganda. Furthermore, this is the first report of the co‐occurrence of T. zuluensis and T. gauchensis in a single area.     

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.     

Mycosphaerellaceae and Teratosphaeriaceae associated with Eucalyptus leaf diseases and stem cankers in Uruguay

Mycosphaerella leaf diseases represent one of the most important impediments to Eucalyptus plantation forestry. Yet they have been afforded little attention in Uruguay where these trees are an important resource for a growing pulp industry. The objective of this study was to identify species of Mycosphaerellaceae and Teratosphaeriaceae resulting from surveys in all major Eucalyptus growing areas of the country. Species identification was based on morphological characteristics and DNA sequence comparisons for the Internal Transcribed Spacer (ITS) region of the rDNA operon. A total of ten Mycosphaerellaceae and Teratosphaeriaceae were found associated with leaf spots and stem cankers on Eucalyptus. Of these, Mycosphaerella aurantia, M. heimii, M. lateralis, M. scytalidii, Pseudocercospora norchiensis, Teratosphaeria ohnowa and T. pluritubularis are newly recorded in Uruguay. This is also the first report of M. aurantia occurring outside of Australia, and the first record of P. norchiensis and T. pluritubularis in South America. New hosts were identified for Kirramyces gauchensis, M. aurantia, M. marksii, M. lateralis, M. scytalidii, P. norchiensis, T. molleriana, T. ohnowa and T. pluritubularis. Interestingly K. gauchensis, which has been known only as a stem pathogen, was isolated from leaf spots on E. maidenii and E. tereticornis. The large number of Mycosphaerellaceae and Teratosphaeriaceae occurring in Uruguay is disturbing and raises concerns regarding the introduction of new pathogens that could threaten not only Eucalyptus plantations but also native forests.     

Interaction between Epicoccum purpurascens and xylophagous basidiomycetes on wood blocks

Epicoccum purpurascens, a component of the bark micromycota, was evaluated as a potential biocontrol agent for three decay‐causing hymenomycetes frequently found in Buenos Aires city trees, Ganoderma platense, Inonotus rickii and Rigidoporus ulmarius. Treatments consisted of dual cultures of E. purpurascens and xylophagous fungi on box elder (Acer negundo) wood blocks. Two inoculation sequences were tested: (i) the biocontrol agent as the first microorganism inoculated followed by the pathogen; and (ii) the xylophagous fungus as the first microorganism inoculated followed by the biocontrol agent. After 3 months of incubation, percentage dry weight loss was calculated. When E. purpurascens was allowed to colonize wood blocks before the introduction of the xylophagous fungus, dry weight loss was significantly reduced in all instances. However, as a secondary colonizer, E. purpurascens mildly reduced the weight loss caused by G. platense, had no effect on degradation by I. rickii and increased wood weight loss by R. ulmarius.     

Toxin production by Rosellinia desmazieresii (Berk. & Br.) Sacc.

Damage symptoms, were expressed on detached shoots of Salix repens within 24 hours of exposure to toxin preparations from culture filtrates of Rosellina desmazieresii. Many of these symptoms, which resembled those observed on diseased plants, could also be obtained in the test system by exposure to cytochalasin E solutions. This toxic compound is produced by R. desmazieresii and may be important in symptom development, since culture filtrate preparations from isolates producing little cytochalasin E induced few symptoms. Toxin preparations from R. desmazieresii induced damage on detached shoots of several woody species, including both hosts and non-hosts of this fungus.     

Local epidemiology of the wood decay agent Laetiporus sulphureus in carob stands in Sicily

The basidiomycete Laetiporus sulphureus (Bull) Murrill is a forest pathogen causing brown cubical heart rot in a broad range of host trees. Despite its wide distribution and importance, studies aimed at understanding the epidemiology of the fungus in specific areas or hosts are lacking. In this study, an incidence of L. sulphureus as high as 34% was determined through molecular analysis of wood samples collected from 70 carob (Ceratonia siliqua L.) trees in the South‐west of Sicily, Italy. A phylogenetic analysis of Internal Transcribed Spacer (ITS) sequences indicated that all carob isolates belonged to the cluster E of Laetiporus taxonomy. Ten molecular markers based on Single Sequence Repeats (SSRs) designed on the L. sulphureus genome were developed, and isolates were genotyped through High‐resolution Melting (HRM) analysis. High gene diversity (0.581), no correlation between fungal genotype and host tree species and significant correlation between spatial and genetic distance were observed, suggesting an important role of basidiospores in the epidemiology of the fungus and a risk of transmission from a host tree species to the others. Finally, from a prognostic perspective, significant differences among isolates in terms of mycelial growth suggest that in addition to an accurate identification, a phenotypic characterization of isolates affecting trees may also be important.     

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.     

Discula quercina as a possible causal agent of dieback on oak trees in Iran

During spring and summer of 2016, dieback symptoms including blights of leaves, twigs, and acorns were observed on current year shoots of Quercus infectoria in the Zagros oak forests of Iran. The fungus isolated from damaged tissues was identified as Discula quercina based on both morphological characteristics and ITS sequencing. To fulfil the Koch's postulates, a representative isolate was inoculated onto shoots of Q. infectoria and Quercus libani in both laboratory and forest conditions. Responses of the two oak species to inoculation with D. quercina were examined under laboratory and forest conditions in a completely randomized experiment. Discula quercina was clearly involved in oak dieback, and Q. infectoria was more susceptible than Q. libani to damage by the pathogen. This is the first record of the occurrence and pathogenicity of the fungus Discula quercina on Quercus infectoria. The fungus is considered as an emerging pathogen on oak trees in Zagros forests in Iran. Furthermore, the pathogenicity of the Discula quercina on Q. libani under laboratory and forest conditions increases the potential importance of this pathogen in Zagros forests.     

Association of Eucalyptus globulus leaf anatomy with susceptibility to Teratosphaeria leaf disease

Resistance of Eucalyptus globulus juvenile foliage to Teratosphaeria leaf disease (TLD) damage has been shown to be under genetic control. Constitutive traits of juvenile leaves such as stomatal density (counted with wax on and with wax removed), total phenolics, total leaf wax, leaf mass per area (LMA) and leaf anatomical features were assessed to determine differences between pairs of resistant and susceptible families. Anatomic features assessed included cuticle, epidermis, palisade spongy mesophyll and total leaf thickness, as well as palisade cell size, shape and intercellular airspace. One interprovenance, one intraprovenance and two within‐family contrasts were used to compare resistant and susceptible pairs of families of Australian origin. The more resistant families had a significantly higher LMA and smaller percentage airspace compared with susceptible families. It is argued that one of the mechanisms by which E. globulus resists TLD involves the closely packed palisade mesophyll cells that increases LMA and reduces airspace, thereby restricting pathogen spread once infection has occurred.     

Disease biology and histopathology of bronze leaf disease: a threat to cultivated aspens,white poplars and their hybrids

Bronze leaf disease (BLD) of species and hybrids of aspens, grey and white poplars (Genus Populus, section Populus) is a systemic disease incited by the fungus Apioplagiostoma populi (E.K. Cash & A.M. Waterman) M.E. Barr that results in a characteristic bronze to dark brown pigmentation of infected leaves in late summer and early fall. Branches on affected trees die over a period of several years, disfiguring trees and eventually leading to mortality of susceptible trees planted in landscapes. In this study, we describe the histopathology of the disease and fungus development relative to external symptoms on affected trees. A. populi hyphae were observed in leaf vessels, lateral veins and xylem vessels of stems and roots of affected trees. Hyphae were also observed in veins and vessels of asymptomatic leaves. Xylem vessels of growth rings on dead branches were completely occluded with A. populi near the vascular cambium and together with the ray parenchyma were stained a bronze colour. Evidence of putative toxin damage to mesophyll cells, not colonized by hyphae, was observed and may contribute to the characteristic tissue staining observed. The development of the fungus was consistent with previous reports, but in this study, we report additional details including perithecial development and ascospore release from predominantly abaxial leaf surfaces. We also report for the first time the isolation and growth of the pathogen in pure culture and systemic infection of roots.     

A method for observing and manipulating roots and root associated fungi on plants growing in nonsterile substrates

Standard 14‐cm plastic‐petri dishes were used as root substrate chambers allowing controlled inoculation, regular inspection under the dissecting microscope, and manipulation of root infections with pathogens and mycorrhizal fungi under nonsterile conditions. Roots of young pine seedlings were placed on the root substrate and, especially those growing on the substrate surface under the lid, were very easy to manipulate. Mycorrhizal species and inoculation methods were compared and the infection process followed continuously under various conditions. The air pockets formed between the lid and the substrate favoured mycorrhiza formation. Brief, periodic flooding prevented formation of mycorrhizas in two mycorrhizal species having hydrophobic hyphae but did not prevent it in less hydrophobic species. IAA treatment of roots led to heavy production of mycorrhizas. Fruiting body formation in Lacearia laccata was induced and followed in the dish cultures. Pure mycorrhizal stock cultures were able to be revitalized in the dish cultures and reisolated in pure culture. The infection strategy of a weak root pathogen, Cylindrocarpon destructans, was studied with the same technique, which was also used for investigating treatments predisposing seedlings to pathogen infection.     

Shot hole disease on Prunus laurocerasus caused by Neofusicoccum parvum in Serbia

Between 2010 and 2014, symptoms of a shot hole disease were observed on cherry laurel (Prunus laurocerasus L.) trees and shrubs in parks and other public plantings in Belgrade, Serbia. Ten symptomatic leaves were collected from each of the diseased plants and the associated fungus isolated and identified using multigene phylogenetic analyses and asexual morphological characters. The pathogen was identified as Neofusicoccum parvum. The same symptoms were produced when the pathogen was inoculated on test plants. To the best of our knowledge, this is the first report of N. parvum causing shot hole disease on P. laurocerasus.     

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.     

PCR primers for identification of Sirococcus conigenus and S. tsugae,and detection of S. conigenus from symptomatic and asymptomatic red pine shoots

Regions of diversity in the internal transcribed spacer (ITS) sequences of Sirococcus species were exploited to design primer pairs used in a PCR-based method for the identification of the conifer shoot blight pathogen Sirococcus conigenus and the closely related fungus Sirococcus tsugae. The specificity of each primer pair for the respective fungus, detection limits and utility for detection from host material were confirmed. The S. conigenus primers were then used to detect this pathogen in tissues of symptomatic or apparently healthy red pine shoots collected at six locations in Wisconsin and Michigan and results compared with those obtained using a cultural assay. For needles, bark and wood of symptomatic shoots, the mean frequencies of detection of S. conigenus using the PCR-based methods were consistent (≥7.5 out of 10) and always greater than for the cultural assay. Detection from symptomatic shoots using the cultural assay was more frequent from needles than from bark or wood. Both the PCR-based method and the cultural assay detected S. conigenus in similar frequencies from asymptomatic shoots, although less frequently than from symptomatic shoots. The efficiency of the PCR-based method and its utility for direct testing of host material should make it particularly useful in areas where multiple shoot blight pathogens are found.