Phylogenomic incongruence in Ceratocystis: a clue to speciation?

Comparative analysis of mitochondrial genomes in Ceratocystis fimbriata complex across diverse hosts

The decline ofAcacia mangiumWilld. in Malaysia, especially in Sabah since 2010, is primarily due to Ceratocystiswilt and canker disease (CWCD) caused by theCeratocystis fimbriataEllis & Halst. complex. This study was aimed to investigate the mitochondrial genome architecture of two differentC. fimbriatacomplex isolates from Malaysia: one fromA. mangiumin Pahang (FRIM1162) and another fromEucalyptus pellitain Sarawak (FRIM1441). This research employed Next-Generation Sequencing (NGS) to contrast genomes from diverse hosts with nine additional mitochondrial sequences, identifying significant genetic diversity and mutational hotspots in the mitochondrial genome alignment. The mitochondrial genome-based phylogenetic analysis revealed a significant genetic relationship between the studied isolates and theC. fimbriatacomplex in the South American Subclade, indicating that theC. fimbriatacomplex discovered in Malaysia isC. manginecans. The comparative mitochondrial genome demonstrates the adaptability of the complex due to mobile genetic components and genomic rearrangements in the studiedfungal isolates. This research enhances our knowledge of the genetic diversity and evolutionary patterns within theC. fimbriatacomplex, aiding in a deeper understanding of fungal disease development and host adaption processes. The acquired insights are crucial for creating specific management strategies for CWCD, improving the overall understanding of fungal disease evolution and control.

Cross-Inoculation of Commercial Forestry, Amenity, and Horticulture Tree Species with Ceratocystis Isolates Collected from Different Host Species

Ceratocystis manginecans has caused significant losses in forestry productivity in Indonesia and neighboring nations. It also infects horticultural trees, but the host range of individual isolates of C. manginecans is poorly studied. So, this study aimed to better understand the potential host range and evaluate aggressiveness against forestry and fruit tree species of C. manginecans isolated from various tree species in Indonesia. Five C. manginecans isolates, four from different tree species and one from the shot-hole borer Euwallacea perbrevis, were used to inoculate seven fruit and six forest tree species, including E. pellita and Acacia mangium. Many of the inoculated trees produced typical canker disease symptoms, such as rough, swollen, and cracked lesions on the bark, but some trees did not have any external symptoms. Mortality in the most susceptible clone of A. mangium was 40% within 8 weeks. Forest tree species were more susceptible than fruit trees, with the length of xylem discoloration ranging from 0.4 to 101 cm. In fruit trees, the average extent of xylem discoloration was lower, ranging from 0.4 to 20.5 cm; however, mortalities were recorded in two fruit tree species, Citrus microcarpa and Durio zibethinus. Host-isolate interaction was evident; isolate Ep106C from Eucalyptus pellita caused the greatest xylem discoloration in Citrus sp., whereas Hy163C from Hymenaea courbaril was the most damaging in D. zibethinus, Artocarpus heterophyllus, and Mangifera indica. Increasingly globalized food and fiber systems increase risk of disease spread, and the serious threat of C. manginecans incursions into countries where it is not present must be evaluated more thoroughly.

Common Methods for Phylogenetic Tree Construction and Their Implementation in R

A phylogenetic tree can reflect the evolutionary relationships between species or gene families, and they play a critical role in modern biological research. In this review, we summarize common methods for constructing phylogenetic trees, including distance methods, maximum parsimony, maximum likelihood, Bayesian inference, and tree-integration methods (supermatrix and supertree). Here we discuss the advantages, shortcomings, and applications of each method and offer relevant codes to construct phylogenetic trees from molecular data using packages and algorithms in R. This review aims to provide comprehensive guidance and reference for researchers seeking to construct phylogenetic trees while also promoting further development and innovation in this field. By offering a clear and concise overview of the different methods available, we hope to enable researchers to select the most appropriate approach for their specific research questions and datasets.

Effector Repertoire of the Sweetpotato Black Rot Fungal Pathogen Ceratocystis fimbriata

In 2015, sweetpotato producers in the United States experienced one of the worst outbreaks of black rot recorded in history, with up to 60% losses reported in the field and packing houses and at shipping ports. Host resistance remains the ideal management tool to decrease crop losses. Lack of knowledge of Ceratocystis fimbriata biology represents a critical barrier for the deployment of resistance to black rot in sweetpotato. In this study, we scanned the recent near chromosomal-level assembly for putative secreted effectors in the sweetpotato C. fimbriata isolate AS236 using a custom fungal effector annotation pipeline. We identified a set of 188 putative effectors on the basis of secretion signal and in silico prediction in EffectorP. We conducted a deep RNA time-course sequencing experiment to determine whether C. fimbriata modulates effectors in planta and to define a candidate list of effectors expressed during infection. We examined the expression profile of two C. fimbriata isolates, a pre-epidemic (1990s) isolate and a post-epidemic (2015) isolate. Our in planta expression profiling revealed clusters of co-expressed secreted effector candidates. Based on fold-change differences of putative effectors in both isolates and over the course of infection, we suggested prioritization of 31 effectors for functional characterization. Among this set, we identified several effectors that provide evidence for a marked biotrophic phase in C. fimbriata during infection of sweetpotato storage roots. Our study revealed a catalog of effector proteins that provide insight into C. fimbriata infection mechanisms and represent a core catalog to implement effector-assisted breeding in sweetpotato. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

An expanded concept of Ceratocystis manginecans and five new species in the Latin American clade of Ceratocystis

The genus Ceratocystis contains a number of emerging plant pathogens, mostly members of the Latin American Clade (LAC), in which there are several unresolved taxonomic controversies. Among the most important are Brazilian pathogens in the C. fimbriata complex, C. manginecans and C. eucalypticola. Representatives of C. manginecans and C. eucalypticola from India and China, respectively, were shown to be fully interfertile in laboratory matings, and hybrids between the putative species were identified on Punica in India. An Indian tester strain was sexually compatible with representatives of what has been considered C. fimbriata on numerous hosts across Brazil. In this revision of the LAC, the name C. fimbriata is restricted to the widely dispersed Ipomoea strain, and C. manginecans is recognized as a Brazilian species that is important on Mangifera, Eucalyptus, and many other crops. C. mangivora and C. mangicola are also considered synonyms of C. manginecans. Based on phylogenetics and mating studies, two other Brazilian species are recognized: C. atlantica, sp. nov., and C. alfenasii, sp. nov., each with wide host ranges. Three new Caribbean species are recognized based on phylogenetics and earlier inoculation studies: C. costaricensis, sp. nov., on Coffea, C. cubensis, sp. nov., on Spathodea, and C. xanthosomatis, sp. nov., on the vegetatively propagated aroids Xanthosoma and Syngonium. Some of the other Ceratocystis species were based primarily on unique internal transcribed spacer (ITS) rDNA sequences, but the unreliability of rDNA sequences was demonstrated when intraspecific crossing of isolates with differing ITS sequences generated single-ascospore progeny with intragenomic variation in ITS sequences and others with new ITS sequences. Species recognition in Ceratocystis should use phenotype, including intersterility tests, to help identify which lineages are species. Although some species remain under-studied, we recognize 16 species in the LAC, all believed to be native to Latin America, the Caribbean region, or eastern USA.

A repertoire of candidate effector proteins of the fungus Ceratocystis cacaofunesta

The genus Ceratocystis includes many phytopathogenic fungi that affect different plant species. One of these is Ceratocystis cacaofunesta, which is pathogenic to the cocoa tree and causes Ceratocystis wilt, a lethal disease for the crop. However, little is known about how this pathogen interacts with its host. The knowledge and identification of possible genes encoding effector proteins are essential to understanding this pathosystem. The present work aimed to predict genes that code effector proteins of C. cacaofunesta from a comparative analysis of the genomes of five Ceratocystis species available in databases. We performed a new genome annotation through an in-silico analysis. We analyzed the secretome and effectorome of C. cacaofunesta using the characteristics of the peptides, such as the presence of signal peptide for secretion, absence of transmembrane domain, and richness of cysteine residues. We identified 160 candidate effector proteins in the C. cacaofunesta proteome that could be classified as cytoplasmic (102) or apoplastic (58). Of the total number of candidate effector proteins, 146 were expressed, presenting an average of 206.56 transcripts per million. Our database was created using a robust bioinformatics strategy, followed by manual curation, generating information on pathogenicity-related genes involved in plant interactions, including CAZymes, hydrolases, lyases, and oxidoreductases. Comparing proteins already characterized as effectors in Sordariomycetes species revealed five groups of protein sequences homologous to C. cacaofunesta. These data provide a valuable resource for studying the infection mechanisms of these pathogens in their hosts.

The Unique Homothallic Mating-Type Loci of the Fungal Tree Pathogens Chrysoporthe syzygiicola and Chrysoporthe zambiensis from Africa

Chrysoporthe syzygiicola and C. zambiensis are ascomycete tree pathogens first described from Zambia, causing stem canker on Syzygium guineense and Eucalyptus grandis, respectively. The taxonomic descriptions of these two species were based on their anamorphic states, as no sexual states are known. The main purpose of this work was to use whole genome sequences to identify and define the mating-type (MAT1) loci of these two species. The unique MAT1 loci for C. zambiensis and C. syzygiicola consist of the MAT1-1-1, MAT1-1-2, and MAT1-2-1 genes, but the MAT1-1-3 gene is absent. Genes canonically associated with opposite mating types were present at the single mating-type locus, suggesting that C. zambiensis and C. syzygiicola have homothallic mating systems.

Chromosomal polymorphism of the Ceratocystis fimbriata species complex in Brazil

Ceratocystis fimbriata is an important pathogen that causes wilt in several plant species. Despite the importance of this pathogen, knowledge about its karyotypic polymorphism and genomic architecture is limited. The main objective of this study was to investigate the karyotype of isolates of the C. fimbriata species complex from different host plants and geographical origins in Brazil. First, the identity of the isolates was confirmed conducting multilocus sequence analysis (MLSA) phylogeny using β-tubulin (TUBB), translation elongation factor 1α (TEF-1α) and mating-type (MAT1 and MAT2) gene sequences. To investigate the chromosomal polymorphism, two conditions of pulsed-field gel electrophoresis (PFGE) were used and the karyotypes of the isolates obtained. The retrotransposon-microsatellite amplified polymorphism (REMAP) molecular marker was utilized to assess the genetic variability among isolates. In the MLSA utilizing the concatenated gene sequences, Ceratocystis cacaofunesta and C. fimbriata formed separate clades, but considerable variation among C. fimbriata isolates was observed. Polymorphism in chromosome number and size was found, indicating the existence of genomic differences among isolates and occurrence of chromosomal rearrangements in the species complex. The number of chromosomes varied from seven to nine and the estimated minimum chromosome sizes were estimated to be between 2.7 to 6.0 Mbp. Small polymorphic chromosomes ranging from 1.2 to 1.8 Mbp were observed in all isolates, raising the hypothesis that they could be supernumerary chromosomes. REMAP analysis revealed a high genetic variability and that isolates from the same host tend to group together in a same cluster. Our results bring new insights into the chromosomal diversity and genome organization of the C. fimbriata complex.

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

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.

A New Real-Time PCR Assay for Detecting Fungi in Genus Ceratocystis

The genus Ceratocystis contains several significant plant pathogens, causing wilt and canker disease on a wide range of plant species. There are >40 known species of Ceratocystis, some of which are becoming increasingly important in agricultural or natural ecosystems. The diagnostic procedures for most Ceratocystis species rely on time-consuming and labor-intensive culturing approaches. To provide more time-efficient and sensitive molecular diagnostic tools for Ceratocystis, a generic TaqMan real-time PCR assay was developed using the ITS gene. This novel two-probe TaqMan assay amplified DNA from all tested Ceratocystis species. Some nonspecific amplification of a few species from closely related genera was observed under certain conditions; however, these false-positive detections could be ruled out using the additional PCR primers developed for further sequence-based identification of the detected species. The assay was found to be highly sensitive, as it detected 0.2 pg/μl of Ceratocystis DNA in water as well as in host DNA matrix. Further validation with artificially inoculated fig stem tissue demonstrated that the assay was also able to effectively detect the pathogen in infected asymptomatic stem tissue. This newly developed real-time PCR assay has practical applications in biosecurity, conservation, and agriculture; it will enable the detection of Ceratocystis species directly from plant material to facilitate more sensitive screening of imported plant germplasm, and allow rapid tracking of pathogens in the case of disease outbreaks.

Caveats of the internal transcribed spacer region as a barcode to resolve species boundaries in Diaporthe

Species in Diaporthe are largely reported as important plant pathogens. Identification of species in this genus has been complemented by morphological and molecular features. However, one important factor delaying this process is the struggle to formulate robust species concepts to create adequate international phytosanitary measures. Regardless of the wide use of the internal transcribed spacer (ITS) rDNA region, established as the primary DNA barcode for fungi, the tendency for intraspecific variation has been reported, misleading interpretation of phylogenetic analyses. Therefore, the present study aimed to illustrate, using specific examples, how the ITS region may be problematic for species delimitation. We showed that the ITS region is highly variable, with strains of Diaporthe malorum and Diaporthe novem falling into more than one clade, which if analyzed on their own, would be likely recognized as distinct taxa. Divergent ITS paralogs were also proven to coexist within the genome of D. novem. We also suggest that ITS may have escaped from concerted evolution or has undergone a duplication event. Furthermore, this study reports for the first time the existence of a putative hybrid in the genus Diaporthe. Our findings offer new clues towards the intraspecific and intragenomic variation in the ITS region, raising questions about its value for barcoding, i.e., identifying species in the genus Diaporthe. Therefore, we recommend that the ITS region be analyzed cautiously and always compared for congruence prior to description of novel taxa.

Phylogenetic incongruence in Cymbidium orchids

Cymbidium, which includes approximately 80 species, is one of the most ornamental and cultivated orchid genera. However, a lack of markers and sparse sampling have posed great challenges to resolving the phylogenetic relationships within the genus. In the present study, we reconstructed the phylogenetic relationships by utilizing one nuclear DNA (nrITS) and seven plastid genes (rbcL, trnS, trnG, matK, trnL, psbA, and atpI) from 70 species (varieties) in Cymbidium. We also examined the occurrence of phylogenetic conflict between nuclear (nrITS) and plastid loci and investigated how phylogenetic conflict bears on taxonomic classification within the genus. We found that phylogenetic conflict and low support values may be explained by hybridization and a lack of informative characteristics. Our results do not support previous classification of the subgenera and sections within Cymbidium. Discordance between gene trees and network analysis indicate that reticulate evolution occurred in the genus Cymbidium. Overall, our study indicates that Cymbidium has undergone a complex evolution.

Population Diversity and Genetic Structure Reveal Patterns of Host Association and Anthropogenic Impact for the Globally Important Fungal Tree Pathogen Ceratocystis manginecans

Species in the Ceratocystis manginecans complex are important fungal pathogens of plantation trees globally. The most important hosts include species of Eucalyptus, Acacia, Mangifera, and Punica. Despite their relevance and widespread occurrence, little is known regarding their population genetics and how this might relate to their host associations or geographic regions in which they occur. A global collection of 491 isolates representing the C. manginecans complex, from four different plant hosts and nine countries, were genotyped using microsatellite markers. Population genetic analyses using numerous tools were conducted to interrogate how their genetic diversity and structure might be affected by host or areas of occurrence. Results of genetic diversity studies showed that when grouping isolates into populations based on their host associations, the population on Eucalyptus was most diverse, and it also has a broad global distribution. When considering countries of origin as a basis for defining populations, the gene and genotypic diversity were highest in populations from China, Indonesia, and Brazil. In contrast, populations from Oman and Pakistan collected from Mangifera had the lowest genetic diversity and were clonal. Molecular variance, population differentiation, and network and structure analyses showed that the genetic structure of isolates in the C. manginecans complex is influenced by both host association as well as geographical isolation. Furthermore, the results reflected the movement of genotypes between plant hosts and geographic regions that have implications regarding the broad global distribution of this pathogen.