Showing papers by "Michael J. Wingfield published in 2022"

Calonectria in the age of genes and genomes: Towards understanding an important but relatively unknown group of pathogens

Abstract: Abstract The genus Calonectria includes many aggressive plant pathogens causing diseases on various agricultural crops as well as forestry and ornamental tree species. Some species have been accidentally introduced into new environments via international trade of putatively asymptomatic plant germplasm or contaminated soil, resulting in significant economic losses. This review provides an overview of the taxonomy, population biology, and pathology of Calonectria species, specifically emerging from contemporary studies that have relied on DNA‐based technologies. The growing importance of genomics in future research is highlighted. A life cycle is proposed for Calonectria species, aimed at improving our ability to manage diseases caused by these pathogens.

Diversity and Distribution of Calonectria Species from Plantation and Forest Soils in Fujian Province, China

Abstract: To meet the growing demand for wood and pulp products, Eucalyptus plantations have expanded rapidly during the past two decades, becoming an integral part of the southern China landscape. Leaf blight caused by various Calonectria spp., is a serious threat to these plantations. In order to explore the diversity and distribution of Calonectria spp. in Fujian Province soils, samples were collected in Eucalyptus plantations and adjacent plantings of Cunninghamia lanceolata, Phyllostachys heterocycle and Pinus massoniana as well as in natural forests. Three hundred and fifty-three Calonectria isolates were recovered from soil samples and they were identified based on a comparison of multilocus DNA sequence data for the act (actin), cmdA (calmodulin), his3 (histone H3), rpb2 (the second largest subunit of RNA polymerase), tef1 (translation elongation factor 1-alpha) and tub2 (β-tubulin) gene regions, as well as morphological characteristics. Six known taxa including Calonectria aconidialis, Ca. hongkongensis, Ca. ilicicola, Ca. kyotensis, Ca. pacifica, Ca. pseudoreteaudii and one novel species described here as Ca. minensis sp. nov. were identified. Of these, Ca. aconidialis and Ca. kyotensis were the most prevalent species, and found in eight and seven sites, and four and five forest types, respectively. Calonectria spp. were most abundant in soils from Eucalyptus stands, followed by P. heterocycle and natural forests. Relatively few species were found in the soils associated with Cunninghamia lanceolata and Pinus massoniana. The abundance of known Calonectria spp. suggests that these fungi have been relatively well sampled in Fujian. The results are also consistent with the fact that most Calonectria diseases are found on Angiosperm as opposed to Gymnosperm plants.

Calonectria queenslandica: Causal agent of Eucalyptus leaf blight in Southern China.

Abstract: Calonectria leaf blight caused by Calonectria spp. is amongst the most serious diseases affecting the health and sustainability of Eucalyptus plantations in Southern China. Recent outbreaks of this disease in GuangDong Province prompted a need to identify the species involved. Typical symptoms of Calonectria leaf blight were observed on 2-year-old E. urophylla × E. grandis trees in a plantation in the ZhaoQing region. Thirty-eight Calonectria isolates were collected from 32 diseased trees. All isolates were identified using DNA sequence analyses of the translation elongation factor 1-alpha (tef1), β-tubulin (tub2), calmodulin (cmdA) and histone H3 (his3) gene regions. Phylogenetic analyses revealed that C. queenslandica was the dominant species, accounting for 81.6% of the isolates collected. Other species isolated included C. pseudoreteaudii (10.5%), C. reteaudii (5.3%) and C. aconidialis (2.6%). This is the first report of C. queenslandica in China and all isolates had identical sequences in all four gene regions. PCR amplification using primers targeting the MAT1-1-1 and MAT1-2-1 genes in all C. queenslandica isolates revealed that only MAT1-2 idiomorph was present. The results suggest that C. queenslandica was introduced into the sampled area with very limited genetic diversity. Pathogenicity tests were conducted on two Eucalyptus genotypes widely planted in the GuangDong Province using isolates representing all species collected. The results showed that these species could all cause disease but the predominance of C. queenslandica on infected trees suggests that it is the major driver of the disease problem studied. Different Eucalyptus genotypes used in the pathogenicity tests differed in susceptibility to infection by the Calonectria spp. tested, providing opportunities to avoid leaf blight by deploying disease-tolerant planting stock.

Lecanosticta pharomachri and its newly discovered sexual state causing a serious needle disease of Pinus spp. in Colombia.

Abstract: Brown spot needle blight (BSNB), caused by the fungal pathogen Lecanosticta acicola, is a well-known disease of Pinus species in several Northern Hemisphere countries. In the Southern Hemisphere, this disease has been reported only in Colombia and, apart from a single report of severe defoliation of Pinus radiata plantations in the early 1980s, has not caused serious damage in this country. A recent outbreak of a disease resembling BSNB on Mesoamerican Pinus species grown in Colombia has raised concern that L. acicola may have re-emerged as a pathogen. DNA sequence-based analyses for the ITS, TEF1 and RPB2 regions showed that the outbreaks were caused by Lecanosticta pharomachri, a recently described species distinct from, but closely related to L. acicola. The discovery of L. pharomachri in Colombia is the first incidence of the pathogen causing a serious disease problem and the first occurrence on the hosts Pinus patula and Pinus maximinoi. A sexual state for L. pharomachri was discovered for the first time and the description of the species has thus been amended.

Cypress Canker: An important disease discovered for the first time on a native South African tree

Abstract: Cypress canker is a branch and stem canker disease of Cupressaceae trees, particularly those in the genera Cupressus and Hesperocyparis. These trees have been planted in many parts of the world as ornamentals and the Seiridium species that cause the disease, consequently, also have an almost global distribution. The taxonomy of Seiridium species causing cypress canker has recently been revised and numerous species are now believed to cause the disease. This study describes, for the first time, cypress canker on the native South African Cupressaceae tree, Widdringtonia nodiflora. The aim was to identify the causal agent and confirm its pathogenicity. Phylogenetic analyses of sequence data for four regions identified the fungus as Seiridium neocupressi, a species previously known only from Australia, New Zealand and Italy. Field inoculations of W. nodiflora branches resulted in distinct cankers within 6 weeks and the fungus could be reisolated from the treated trees. Cypress canker has been known in South Africa for many decades, where it causes a serious disease on nonnative species of Cupressus, but it has never been found on native Cupressaceae. The newly discovered disease caused by a probable alien pathogen is of particular concern because only three species of Widdringtonia occur in South Africa and are important components of the native flora. The two other species, W. wallichii and W. schwartzii, occur in small endemic and threatened populations. The origin of S. neocupressi in South Africa and the relative susceptibility of the three Widdringtonia species, consequently, requires urgent attention.

Botryosphaeriaceae diversity on Eucalyptus clones in different climate zones of Indonesia

Abstract: The Botryosphaeriaceae is an important and diverse family of latent fungal pathogens of woody plants, including Eucalyptus. These fungi live within infected plant tissues for extended periods without causing symptoms, but emerge to cause severe disease when their hosts are subjected to stress. In this study, we compared the diversity of the Botryosphaeriaceae in samples from nine different Eucalyptus clones growing in North and Central Sumatra, Indonesia, having distinct climates. Samples were taken from asymptomatic trees as well as those damaged by a sucking insect (Helopeltis sp.: Miridae), a stem boring moth (Polyphagozerra coffeae: Cossidae) and a Eucalyptus scab and shoot malformation fungal disease caused by Elsinoe necatrix. In total, 215 Botryosphaeriaceae isolates were obtained from which 13 species were identified based on rDNA-ITS, TEF-1α, β-tubulin and rpb2 sequence data. These species included seven Lasiodiplodia species, four Neofusicoccum species as well as Endomelanconiopsis endophytica and Cophinforma atrovirens. A new species of Lasiodiplodia arose from collections and for which the name L. riauensis is provided. Two species, L. theobromae and L. brasiliensis, were found in both climatic zones, whereas other species were specific to the areas from which they were collected. No correlation was found between the Botryosphaeriaceae species diversity and damage to trees caused by insects or E. necatrix disease.

Comparison of Hyphal Fragments and Spores to Evaluate the Pathogenicity of the Eucalyptus Leaf and Shoot Pathogen Calonectria pseudoreteaudii.

Abstract: The genus Calonectria includes many aggressive plant pathogenic species with a worldwide distribution. Calonectria leaf blight is one of the most prominent diseases of Eucalyptus trees in Southeast Asian and South American plantations. Inoculation trials to evaluate pathogenicity of Calonectria species typically use conidial suspensions but this is not possible for species that do not sporulate sufficiently in culture. Calonectria pseudoreteaudii is one of the most aggressive species to Eucalyptus in China, but most isolates fail to produce conidia in culture, requiring an alternative procedure for artificial inoculation. This study compared inoculations utilizing conidial and hyphal fragment suspensions. Two Eucalyptus genotypes were used, and these were inoculated with different concentrations of hyphal fragments or conidia of three C. pseudoreteaudii isolates. Three days after inoculation, the treated Eucalyptus plants displayed similar disease symptoms, irrespective of whether they had been inoculated with conidia or hyphal fragments. This was consistent for all of C. pseudoreteaudii isolates and also the different Eucalyptus genotypes. The results demonstrate that hyphal fragment suspensions can be used to provide a reliable indication of C. pseudoreteaudii isolate pathogenicity when conidia are not available for inoculation studies.

A serious shoot and leaf disease caused by Colletotrichum theobromicola discovered on eucalypts in South Africa

Abstract: Eucalypt plantations in South Africa make up an important part of the local forestry industry. Recently, one-year-old nursery plants of a Eucalyptus grandis × Eucalyptus urophylla variety displayed symptoms of leaf and shoot anthracnose disease. Samples were collected from these plants and isolations were made from the disease symptoms. Isolates were identified based on their morphological characteristics and DNA sequence data for eight gene regions. Phylogenetic analyses led to the isolates being identified as Colletotrichum theobromicola and the reduction of Colletotrichum pseudotheobromicola to synonymy with the former species. Pathogenicity trials with isolates of C. theobromicola were conducted on clones of E. grandis and hybrids of E. grandis × E. urophylla and E. grandis × Eucalyptus camaldulensis. Resulting symptoms were similar to those found on naturally infected plants and the fungus was re-isolated from the infections. Colletotrichum theobromicola is known to cause anthracnose on various plants including eucalypts in Brazil, but this is the first record of the pathogen in South Africa.

Soil-borne Calonectria (Hypocreales, Nectriaceae) associated with Eucalyptus plantations in Colombia

Abstract: Abstract Eucalyptus spp. are widely planted in Colombia as an important component of a growing paper and pulp industry. Leaf and shoot blight caused by Calonectria spp. was one of the first disease problems to emerge in these plantations. A survey of Eucalyptus plantations in four forestry regions of Colombia during 2016 resulted in a large number of Calonectria isolates from soil samples collected in the understories of trees having symptoms of Calonectria leaf and shoot blight. The aim of this study was to identify and resolve the phylogenetic relationships for these isolates using DNA sequence comparisons of six gene regions as well as morphological characters. From a collection of 107 isolates, seven Calonectria species residing in three species complexes were identified. Two of these represented undescribed species, namely C.exiguisporasp. nov. and C.guahibosp. nov.Calonectriaparvispora and C.spathulata were the most commonly isolated species, each of which accounted for approximately 30% of the isolates. The results suggest that Colombia has a wide diversity of Calonectria spp. and that these could challenge Eucalyptus plantation forestry in the future.

High diversity and clonality are hallmarks of Fusarium circinatum in South Africa

Abstract: Pitch canker on plantation-grown Pinus species, caused by the fungal pathogen Fusarium circinatum, first appeared in the western and southern Cape regions of South Africa. However, outbreaks have subsequently been reported from the major plantation growing regions of KwaZulu-Natal and Limpopo in the eastern, summer rainfall regions of the country. It is more than 10 years since the last detailed population genetics studies on F. circinatum in the region were conducted. To shed light on the population biology of F. circinatum in this region of South Africa, we used microsatellite markers and mating-type assays to study a collection of 296 isolates from different nurseries and plantation sites. Our results showed that populations in the region are highly diverse, but strongly interconnected, with various genotypes shared across nursery and plantation collection sites. In contrast to nursery populations, those associated with pitch canker outbreaks were characterized by the presence of relatively small numbers of dominant genotypes that were generally widespread across the region. Opposite mating-type individuals occurred in most of the isolate collections, but multilocus linkage disequilibrium analyses pointed towards clonality being the main reproductive mode of F. circinatum in the region. Most of the pathogen's genetic variation could probably have resulted from multiple different introductions into the country and more specifically, into the summer rainfall region. Because the spread and establishment of invasive pathogens are typically driven by aggressive clones, the results of this study provide important considerations for current and future Pinus disease management strategies.

A robust disease scoring method to screen Eucalyptus for resistance against the aggressive leaf blight pathogen, Teratosphaeria destructans.

Abstract: Shoot and leaf blight caused by Teratosphaeria destructans is one of the most devastating foliar diseases of Eucalyptus. Therefore, breeding for resistance to this disease is considered urgent. Differences in susceptibility to T. destructans have been observed in the field, but a robust inoculation protocol has, until recently, been unavailable and a disease scoring method for precise phenotyping has not been established. A first objective of this study was to determine the optimal conidial concentration for T. destructans inoculations on a susceptible Eucalyptus host. This concentration was then used to determine differences in susceptibility of six genotypes of Eucalyptus grandis x Eucalyptus urophylla to the pathogen by assessing the percentage of infected stomata using electron microscopy and the percentage of leaf area covered by lesions (PLACL) using image processing. In addition, we developed a disease susceptibility index (SI) of six categories ranging from highly resistant (SI= 0), to highly susceptible (SI= 1.5-2). The more resistant genotypes were moderately resistant with an SI value of 0.49 - 0.54 and a PLACL of 6.5 - 9%. In contrast, the more susceptible genotype scored an SI of 1.52 and PLACL of 48%. Host susceptibility was also assessed relative to the sporulation of the pathogen. This showed that the percentage of sporulation did significantly correlate with host resistance. Overall, the results provide the basis for rigorous screening and selection of resistant genotypes to the disease caused by T. destructans using artificial inoculation.

Epidemic spread of smut fungi (Quambalaria) by sexual reproduction in a native pathosystem

Abstract: Abstract Quambalaria are fungal pathogens of Corymbia , Eucalyptus and related genera of Myrtaceae. They are smut fungi (Ustilaginomycota) described from structures that resemble conidia and conidiophores. Whether these spore forms have asexual or sexual roles in life cycles of Quambalaria is unknown. An epidemic of Q. pitereka destroyed plantations of Corymbia in New South Wales and Queensland (Australia) in 2008. We sampled 177 individuals from three plantations of C. variegata and used AFLPs to test hypotheses that the epidemic was spread by asexual reproduction and dominated by a single genotype. There was high genotypic diversity across ≥600 AFLP loci in the pathogen populations at each plantation, and evidence of sexual reproduction based on neighbour-net analyses and rejection of linkage disequilibrium. The populations were not structured by host or location. Our data did not support a hypothesis of asexual reproduction but instead that Q. pitereka spreads exclusively by sexual reproduction, similar to life cycles of other smut fungi. Epidemics were exacerbated by monocultures of Corymbia established from seed collected from a single provenance. This study showcases an example of an endemic pathogen, Q. pitereka , with a strictly outbreeding life cycle that has caused epidemics when susceptible hosts were planted in large monoculture plantations.

First Report of Dutch Elm Disease Caused by Ophiostoma novo-ulmi in South Korea

Abstract: During a routine survey conducted in July 2021, several dead and dying Ulmus macrocarpa trees were observed in an urban forest located in the Gyeonggi Province of South Korea. The trees had symptoms of wilt with yellowing and browning of leaves, and, in most cases, the trunks of dying trees were infested by bark beetles. Isolations were made from small pieces of wood taken from dying trees, and beetles were collected from the infested stems. Fungal isolates and the beetles were identified using DNA sequence-based phylogenies and morphology, respectively. The results revealed that the fungus was Ophiostoma novo-ulmi, the causal agent of Dutch elm disease, and the associated bark beetle was Scolytus jacobsoni. This study provides the first record of Dutch elm disease in South Korea and suggests that a nationwide survey for the disease should be undertaken.