Trunk Cankers Research Articles

Dilodia sapinea as the pathogen causing trunk canker on Pinus bungeana trees in China

Pinus bungeana belonging to the genus Pinus is a pine tree species endemic to China. It plays vital roles in afforestation, forest regeneration, landscaping, forest ecosystems, and environmental protection. However, P. bungeana has been listed as a rare and endangered species in recent years due to population fragmentation. The occurrence of lethal diseases on the trees has made the situation even worse. This study aimed to identify the pathogen causing the trunk canker on P. bungeana trees in Qingdao, China. The morphological identification of the pathogen relied primarily on the morphology of conidia. Molecular identification was performed using the combined sequences of ITS, Tef and Tub2 genes. The eight isolates were all identified as Diplodia sapinea. The pathogenicity of the eight isolates was examined both in vitro and in vivo. The results showed that all the fungal isolates caused severe canker symptoms on the inoculated P. bungeana branches. Moreover, D. sapinea was re-isolated from the inoculated branches. This study is novel in reporting D. sapinea causing trunk canker on P. bungeana trees in China.

New Data on Fungal Species Composition in Spruce Trunk Canker

New Data on Fungal Species Composition in Spruce Trunk Canker

Current status of pistachio diseases in countries of the Mediterranean Basin

AbstractIn the Mediterranean Basin, the pistachio crop is considered an emerging nut crop due to the dependence of the European nut markets on international imports. Consequently, the extension and intensification of pistachio production to nontraditional growing areas has promoted both classic and emerging diseases of this nut tree, which are limiting factors in crop production. Due to the limited interest in pistachio crops, the aetiology and epidemiology of the main pistachio diseases are poorly studied. Thus, this review summarizes the state of pistachio disease research, with particular attention given to the Mediterranean area. The information reported here is based not only on the literature, but also the advancement of our research on pistachio diseases conducted in both Italy and Spain. We describe the main fungal diseases of the tree canopy in Mediterranean countries, such as Botryosphaeria panicle and shoot blight, Septoria leaf spot, and stem, branch and trunk canker diseases, followed by the main soilborne diseases. In addition, we review minor and/or sporadic fungal diseases originating in not only the Mediterranean, but also other pistachio‐producing countries. Another section is dedicated to other diseases caused by bacteria, phytoplasmas, viruses and nematodes. Finally, we summarize the main control strategies adopted in Mediterranean Basin countries against pistachio diseases.

The Comparative Genomics of Botryosphaeriaceae Suggests Gene Families of Botryosphaeria dothidea Related to Pathogenicity on Chinese Hickory Tree.

Trunk canker poses a major threat to the production of Chinese hickory tree (Carya cathayensis Sarg.), which is primarily determined by Botryosphaeriaceae. In our previous work, we identified Botryosphaeria dothidea as the predominant pathogen of this disease. However, it is still unclear about corresponding gene families and mechanisms associated with B. dothidea's pathogenicity on Chinese hickory tree. Here, we present a comparative analysis of high-quality genome assemblies of Botryosphaeria dothidea and other isolated pathogens, showing highly syntenic relationships between B. dothidea and its closely related species and the conservative evolution of the Botryosphaeriaceae family. Higher GC contents were found in the genomes of B. dothidea and three other isolated pathogens (Botryshaeria cortices, Botryshaeria fabicerciana, and Botryshaeria qingyuanensis) compared to Macrophomina phaseolina, Neofusicoccum parvum, Diplodia corticola, and Lasiodiplodia theobromae. An investigation of genes specific to or expanded in B. dothidea revealed that one secreted glucanase, one orsellinic acid biosynthesis enzyme, and two MFS transporters positively regulated B. dothidea's pathogenicity. We also observed an overrepresentation of viral integrase like gene and heterokaryon incompatibility proteins in the B. dothidea's genome. In addition, we observed one LRR-domain-containing protein and two Sec-domain-containing proteins (Sec_1 and Sec_7) that underwent positive selection. This study will help to understand B. dothidea's pathogenicity and potential influence on the infection of Chinese hickory, which will help in the development of disease control and ensure the security of Chinese hickory production.

Chitosan nanoparticle and its effect on Neoscytalidium novaehollandiae, the causal agent of mulberry canker in Tehran

Fungal pathogen “Neoscytalidium novaehollandiae” is the causal agent of trunk canker in mulberry trees. Mulberry is considered as most valuable tree for landscaping in Tehran. Here in, for the first time, chitosan nanoparticles (CSNPs) were used to inhibit canker disease causal agent of mulberry. For this purpose, CSNPs were synthesized with a yield of 86%, and after characterization of the synthesized nanoparticles, the growth inhibition rate of fungus (GI%) was evaluated. The results of in vitro assays showed that the concentration of 1500 ppm significantly (P ≤ 0.05) decreased the radial growth of the fungus in comparison with control. For in vivo experiments, 2-year-old branches from healthy randomly selected mulberry trees in the landscape, were inoculated artificially in the laboratory with mycelial plugs from a 7-day-old culture of fungus. The infected branches were then treated with 500, 1000, and 1500 ppm of CSNPs. The results indicated that the disease severity (DS%) in all the treatments and the control plants increased over time. However, the slope of the changes in DS was less in CSNPs treated compared to control. This effect was concentration dependent so that no disease progress was observed at 1500 ppm of CSNPs. The findings indicate the effectiveness of CSNPs in control of canker disease of mulberry caused by N. novaehollandiae.

High-quality genome assembly and genetic transformation system of Lasiodiplodia theobromae strain LTTK16-3, a fungal pathogen of Chinese hickory.

Lasiodiplodia theobromae, as one of the causative agents associated with Chinese hickory trunk cankers, has caused huge economic losses to the Chinese hickory industry. Although the biological characteristics of this pathogen and the occurrence pattern of this disease have been well studied, few studies have addressed the related mechanisms due to the poor molecular and genetic study basis of this fungus. In this study, we sequenced and assembled L. theobromae strain LTTK16-3, isolated from a Chinese hickory tree (cultivar of Linan) in Linan, Zhejiang province, China. Phylogenetic analysis and comparative genomics analysis presented crucial cues in the prediction of LTTK16-3, which shared similar regulatory mechanisms of transcription, DNA replication, and DNA damage response with the other four Chinese hickory trunk canker-associated Botryosphaeria strains including, Botryosphaeria dothidea, Botryosphaeria fabicerciana, Botryosphaeria qingyuanensis, and Botryosphaeria corticis. Moreover, it contained 18 strain-specific protein clusters (not conserved in the other L. theobromae strains, AM2As and CITRA15), with potential roles in specific host-pathogen interactions during the Chinese hickory infection. Additionally, an efficient system for L. theobromae protoplast preparation and polyethylene glycol (PEG) -mediated genetic transformation was firstly established as the foundation for its future mechanisms study. Collectively, the high-quality genome data and the efficient transformation system of L. theobromae here set up the possibility of targeted molecular improvements for Chinese hickory canker control.IMPORTANCEFungi with disparate genomic features are physiologically diverse, possessing species-specific survival strategies and environmental adaptation mechanisms. The high-quality genome data and related molecular genetic studies are the basis for revealing the mechanisms behind the physiological traits that are responsible for their environmental fitness. In this study, we sequenced and assembled the LTTK16-3 strain, the genome of Lasiodiplodia theobromae first obtained from a diseased Chinese hickory tree (cultivar of Linan) in Linan, Zhejiang province, China. Further phylogenetic analysis and comparative genomics analysis provide crucial cues in the prediction of the proteins with potential roles in specific host-pathogen interactions during the Chinese hickory infection. An efficient PEG-mediated genetic transformation system of L. theobromae was established as the foundation for the future mechanisms exploration. The above genetic information and tools set up valuable clues to study L. theobromae pathogenesis and assist in Chinese hickory canker control.

Triplex real-time qPCR for the simultaneous detection of Botryosphaeriaceae species in woody crops and environmental samples.

Species of Botryosphaeriaceae fungi are relevant pathogens of almond causing trunk cankers, extensive gumming, necrosis of internal tissues and plant dieback and dead, threatening almond productivity. A novel triplex quantitative real-time PCR (qPCR) assay was designed for the simultaneous detection and quantification of Neofusicoccum parvum, Botryosphaeria dothidea and the Botryosphaeriaceae family. The method was validated in symptomatic and asymptomatic almond, avocado, blueberry and grapevine plants and in environmental samples, such as cropping soil and rainwater and in artificially inoculated trapped spores, demonstrating the same performance on several matrices. The limit of detection of the triplex qPCR was 10 fg of genomic DNA for the three fungal targets, with high correlation coefficients (R2) and amplification efficiencies between 90 and 120%. Although the triplex qPCR demonstrated to be more sensitive and accurate than the traditional plate culturing and further sequencing method, a substantial agreement (kappa index = 0.8052 ± 0.0512) was found between the two detection methods. The highly sensitive qPCR assay allows for accurate diagnosis of symptomatic plants and early detection of Botryosphaeriaceae fungi in asymptomatic plants (rootstocks and grafting scions from almond nurseries). Furthermore, the triplex qPCR successfully detected Botryosphaeriaceae fungi in environmental samples, such as cropping soils and rainwater. It was also capable of detecting as few as 10 conidia in artificially inoculated tapes. Therefore, the triplex qPCR is a valuable tool for accurate diagnosis, aiding in the implementation of suitable control measures. It enables preventive detection in asymptomatic samples, helping to avoid the introduction and spread of these pathogens in production fields. Moreover, it assists in identifying inoculum sources and quantifying inoculum levels in crop environments, contributing to a precise phytosanitary application schedule, thereby reducing production costs and preserving the environment.

First report of Trunk Canker Caused by Botryosphaeria dothidea on Cinnamomum camphora in China.

Cinnamomum camphora, an essential woody plant in China, experienced a severe outbreak of trunk canker affecting an area of 540,000 square meters in the Xiaoshan District of Zhejiang province during the early summer of 2022. The observed symptoms included stem canker, dieback, twig blight, and extensive vascular discoloration, with an incidence rate ranging from 45% to 70%. To investigate the etiology of the disease, symptomatic plant samples were subjected to rigorous surface sterilization involving washing with running tap water, followed by surface sterilization using 75% ethanol. The samples were then rinsed twice with sterile distilled water, plated on potato dextrose agar (PDA) medium, and incubated at a temperature of 28°C. The isolated fungi exhibited characteristics consistent with the species Botryosphaeria dothidea. Fungal isolates displayed abundant white aerial mycelium, which darkened to grey after five to seven days, eventually giving rise to black pycnidia. Single hyphal tip cultures of putative two isolates were stored at the Agricultural Experiment Station of Zhejiang University. Conidia formed on pycnidia were one-celled, hyaline, aseptate, and fusiform, with dimensions of 18.34-27.12 μm x 3.77-6.84 μm (average 22.90 μm x 5.20 μm) (one hundred conidia were measured). To determine the fungal species, genomic DNA was extracted from individual isolates ZJUP0868, and subjected to DNA sequence analysis of four gene regions: the internal transcribed spacer (ITS) using the primer-pair ITS4 and ITS1 (White et al., 1990), the large subunit (LSU) gene with LR0R and LR5 (Rehner and Samuels, 1995), the small subunit (SSU) gene with SR1R and SR7 (Zoller et al., 1999), and the translation elongation factor 1-alpha (tef1) with EF1-983F and EF1-2218R (Rehner and Buckley, 2005). Furthermore, DNA sequence analysis of above four genes was performed. BLAST analysis indicated the highest nucleotide sequence identity with Botryosphaeria dothidea CBS 115476 reference sequence (ITS: 99.59%, KF766151; LSU: 99.88%, DQ377852; SSU: 100%, NG_062738; tef1: 98.93%, AY236898). Representative sequences of isolate ZJUP0868 from these regions were deposited in GenBank (ITS: Accession No. OR192838; LSU: Accession No:OR248147; SSU: Accession No:OR248174; tef1: Accession No. OR262053). A phylogenomic analysis was conducted to determine the phylogenetic position of Botryosphaeria dothidea in the family Botryosphaeriaceae. The combined morphological and molecular findings confirmed the identification of the pathogen as Botryosphaeria dothidea. Pathogenicity tests were conducted by stem inoculation of two-year-old Cinnamomum camphora baranches. Mycelial plugs (2-3 mm in diameter) from actively growing colonies of B. dothidea (PDA) were applied to bark of similar size on the middle point of the stems. Inoculated barks were wrapped with Parafilm, while control branches received sterile PDA plugs. Inoculated and control branches (7 each) were maintained in a greenhouse at 28°C. After two weeks, all inoculated plants exhibited dark vascular stem tissue, whereas the control plants remained healthy. B. dothidea was re-isolated from symptomatic tissues, thus fulfilling Koch's postulates. No symptoms were observed in the control branched, and B. dothidea was not re-isolated from their tissues. B. dothidea , the type species of Botryosphaeria (Botryosphaeriaceae, Botryosphaeriales), is commonly associated with cankers and dieback in woody plants. Previous reports have identified Botryosphaeria dothidea as a pathogen causing stem dieback and trunk canker on Glycine max (Chen et al., 2020), Camellia oleifera (Hao et al., 2022), and Gleditsia sinensis (Huang et al., 2020). Additionally, B. dothidea has been reported to cause leave wilt on various plant species in China, including Daimyo oak (Liu et al., 2023) and Cornus officinalis (Zhang et al., 2022). To the best of our knowledge, this is the first report of B. dothidea on C. camphora in China. This findings contribute to a better understanding of the pathogens affecting Cinnamomum camphora in the China.

Sensitivity and resistance risk of Botryosphaeria dothidea causing Chinese hickory trunk canker to fludioxonil

Hickory trunk canker (HTC), primarily caused by Botryosphaeria dothidea, is an aggravating disease that threatens an important regional economic tree species of Chinese hickory and few information is available in the control of this disease. Here, the sensitivity of 93 isolates to fludioxonil and the resistance risk were investigated. All the isolates tested were sensitive to fludioxonil and the EC50 ranged from 0.0028 to 0.0569 μg/mL. The tamed fludioxonil-resistant mutants remained highly resistant to fludioxonil even after 10 consecutive transfers to fludioxonil-free PDA plates. As for fitness penalty, the fludioxonil-resistant mutants demonstrated a reduction in conidia production and virulence as well as increased sensitivity to high osmotic stress. While, variations in mycelial growth and responses to SDS and H2O2 were not detected in all the resistant mutants. In addition, the resistant mutants demonstrated positive cross-resistance to iprodione but not to fungicides of other modes of action. Sequential analysis of BdNik1 showed that premature stop codon occurred in all the resistant mutants despite of point mutation (BD16–22R9 and BD16–22R20) or frameshift mutation (BD16–22R8, BD16–22R11 and BD16–22R18). Our study suggested that fludioxonil exhibited excellent inhibition activity on mycelial growth of B. dothidea in vitro, the resistance risk of B. dothidea to fludioxonil should be low to moderate and fludioxonil would be a nice candidate in controlling HTC caused by B. dothidea.

Paramicrosphaeropsis eriobotryae sp. nov., a new agent of loquat canker in Iran

AbstractLoquat (Eriobotrya japonica) is a subtropical evergreen plant, important in terms of both horticulture and green space in the urban environment. In recent years, symptoms of branch and trunk canker, dieback and decline have been observed in the main cultivation areas of this tree in Iran. To study the aetiology of loquat canker in Fars Province, branches and trunks of loquat trees with disease symptoms were sampled from 2018 to 2019. Several isolates of an unknown Paramicrosphaeropsis species (Didymellaceae, Pleosporales, Dothideomycetes) were recovered from the trunks and branches of infected loquat trees. Phylogenetic analysis of the isolates based on a multigene phylogeny of the ribosomal internal transcribed spacer (ITS), partial β‐tubulin gene (tub2) and the second‐largest subunit of RNA polymerase II (rpb2) loci revealed that the isolates belonged to a new taxon, Paramicrosphaeropsis eriobotryae sp. nov. Pathogenicity tests revealed that this species was able to cause canker, trunk flaking, dieback, decline, leaf yellowing, defoliation and growth reduction in loquat trees. A host range evaluation on detached branches of some important horticultural trees occurring adjacent to loquat tree orchards of Fars Province showed that P. eriobotryae might have a broader host range, as it was also able to infect almond and olive trees.

Trunk canker of Juglans sigillata caused by Lasiodiplodia pseudotheobromae in China.

Iron walnut (Juglans sigillata Dode) is a temperate deciduous tree indigenous to China. It is mainly distributed in southwestern China, and valued for its wood and nuts (Feng et al. 2018). In September 2020, symptoms of canker on J. sigillata were observed in an orchard measuring 2 hectares located in Chongzhou City, Sichuan Province (31°5' 25″N, 105°27'36″E, 365 m altitude). Twenty percent of plants showed canker symptoms during the 50 surveyed plants. The infected trunk showed necrotic lesions with black pycnidia, that led to necrosis of branches and death of the whole plant in severe cases (Fig. 1). Six specimens from different diseased plants were collected for pathogen isolation and morphological observation. Pure cultures were obtained from single conidium on potato-dextrose agar (PDA) media according to the method described by Chomnunti (Chomnunti et al. 2014). Colonies grew fast and reached 3 cm after 5 days. The aerial mycelium was abundant, which was initially white and then grayish. Conidiomata on the host were measured 160-280 µm × 140-190 µm (average: 220 × 165 µm, n = 20), stromatic, uniloculate, dark brown to black, immersed, and erumpent when mature. Pycnidial walls 32-58 µm wide, were composed of 5-7 layers of brown to dark brown cells. Conidia were hyaline, and ellipsoidal with rounded apex and base, widest at the middle, thick-walled, and unicellular, with a size 21.5-31 µm × 11.5-15.7 µm (average: 27 × 13.5 µm, n = 50). Morphological characteristics fit the description of Lasiodiplodia pseudotheobromae A.J.L. Phillips, A. Alves & Crous (Aives et al. 2008). The internal transcribed spacers (ITS), 18S small subunit rRNA (SSU), 28S large subunit rDNA (LSU), translation elongation factor 1-alpha (tef1-α), and beta-tubulin (tub2) were amplified by polymerase chain reaction and sequenced with primers ITS1/ITS4, NS1/NS4, LR0R/LR5, EF1-728F/EF1-986R and Bt2a/Bt2b, respectively (Li et al. 2018). The sequences of the representative isolate (SICAUCC 22-0079) were deposited in NCBI with accession numbers ON090365 (ITS), ON090406 (SSU), ON090418 (LSU), ON112377 (tef1-α), and ON112378 (tub2), respectively. Nucleotide blast showed 100% similarity of all the analyzed and NCBI submitted isolates with L. pseudotheobromae (CBS116459; holotype) (accession numbers EF622077, EU673199, EU673256, EF622057, EU673111). Phylogenetic analyses based on a combined dataset showed 100% bootstrap support values in a clade with L. pseudotheobromae complexes (Fig. 2). Based on morphological and molecular analyses, the fungal pathogen was identified as L. pseudotheobromae. To conduct Koch's postulates, four 2-year-old healthy plants of J. sigillata were inoculated with 10 μL spore suspension (105 conidia/mL) onto the wounded sites via sterile pin. As control, four healthy plants were treated with sterile distilled water. The inoculated and untreated plants were placed in a growth chamber at 25°C with relative humidity >90% and 12-h photoperiod. Trunk canker symptoms appeared on inoculated plants after 15-20 days, and the pathogen was re-isolated and the controls were symptomless, confirming Koch's postulates. L. pseudotheobromae is widely distributed in various plants all over the world, usually as a pathogen associated with damping-off, wilt, die-back, root rot, collar rot, witches' brooms, or fruit rots (Zhao et al. 2010). To our knowledge, this is the first report of trunk canker on J. sigillata caused by L. pseudotheobromae in China. Trunk canker caused by L. pseudotheobromae is becoming a potential threat to walnut production, and some necessary measures for integrated management should be made.

Phenotypic and Genomic Difference among Four Botryosphaeria Pathogens in Chinese Hickory Trunk Canker.

Botryosphaeria species are amongst the most widespread and important canker and dieback pathogens of trees worldwide, with B. dothidea as one of the most common Botryosphaeria species. However, the information related to the widespread incidence and aggressiveness of B. dothidea among various Botryosphaeria species causing trunk cankers is still poorly investigated. In this study, the metabolic phenotypic diversity and genomic differences of four Chinese hickory canker-related Botryosphaeria pathogens, including B. dothidea, B. qingyuanensis, B. fabicerciana, and B. corticis, were systematically studied to address the competitive fitness of B. dothidea. Large-scale screening of physiologic traits using a phenotypic MicroArray/OmniLog system (PMs) found B. dothidea has a broader spectrum of nitrogen source and greater tolerance toward osmotic pressure (sodium benzoate) and alkali stress among Botryosphaeria species. Moreover, the annotation of B. dothidea species-specific genomic information via a comparative genomics analysis found 143 B. dothidea species-specific genes that not only provides crucial cues in the prediction of B. dothidea species-specific function but also give a basis for the development of a B. dothidea molecular identification method. A species-specific primer set Bd_11F/Bd_11R has been designed based on the sequence of B. dothidea species-specific gene jg11 for the accurate identification of B. dothidea in disease diagnoses. Overall, this study deepens the understanding in the widespread incidence and aggressiveness of B. dothidea among various Botryosphaeria species, providing valuable clues to assist in trunk cankers management.

Biological characteristics of Diplodia sapinea f. sp. cupressi infecting Cupressus sempervirens L. in Tunisia

Cupressus sempervirens L. (Italian cypress), is a Mediterranean evergreen coniferous tree. Due to its ecological values, this cypress has been used in forest protection against desertification and soil conservation. Last decades, cypress dieback has been commonly observed in Tunisian forests. Symptoms of shoot dieback, necrosis, twig blight, and trunk cankers have been observed on cypress trees in Bou Chrik (Nabeul) region. The causal agent was identified as Diplodia pinea f. sp. cupressi. The mycelial growth rate of the fungus was evaluated by using four different media culture at 25 °C and at seven temperatures ranging from (5 °C to 35 °C) on PDA medium. The results showed that the species was able to grow in a range of temperatures ranging from 20 to 25 °C and showed a higher growth rate on PDA medium. A pathogenicity test was conducted on C. sempervirens seedlings, and the aggressiveness of the fungus was approved.

Whole-Genome Resource of Lasiodiplodia pseudotheobromae BaA, the Causative Agent of Black Root Rot Morinda officinalis.

Whole-Genome Resource of Lasiodiplodia pseudotheobromae BaA, the Causative Agent of Black Root Rot Morinda officinalis.

Susceptibility of fig cultivars to Diaporthe canker in Iran

AbstractFig canker is a serious concern in the major fig‐growing region of Iran, Fars Province. The disease reduces yield and the lifespan of fig trees, particularly the dominant commercial dried fig cultivar, Sabz. Four consecutive years of surveys (2019–2022) led to the identification of four distinct canker types (A–D) in infected fig orchards in southern Iran. Morphological identification and multiple gene phylogenetic analyses indicated that 218 (>66% of the total) isolates from infected fig cultivars belonged to Diaporthe cinerascens, all of which were recovered from Type A cankers, that is, trunk cankers with zonation. Based on scales developed by the principal component analysis (PCA) approach of pathogenicity characteristics, D. cinerascens isolates were clustered into three groups: low, moderate and highly aggressive. The susceptibility of 10 drought and/or salinity‐tolerant fig cultivars to a highly aggressive D. cinerascens isolate was evaluated based on five pathogenicity characteristics. These cultivars were clustered into nonsusceptible (cultivar Matti), semisusceptible (the majority of the cultivars) and susceptible (cultivars Dehdez and Gilasi). The present study is the first attempt to assess the response of fig cultivars to the most significant and common pathogen causing fig canker, D. cinerascens, by phenotyping techniques.

Diplodia scrobiculata and Neofusicoccum luteum causing dieback of Pinus halepensis in Tunisia

AbstractForest trees withering is an increasingly ubiquitous phenomenon throughout the Mediterranean basin. Aleppo pine (Pinus halepensis Mill.) is one of the dominant conifer species in this region. In the northeastern pine coastal woodland of Tunisia, Pinus halepensis stands originally afforested to stabilize sand dunes are often damaged. Fungal pathogens are among the main causes of forest tree diseases. Species of the Botryosphaeriaceae family, having a worldwide distribution, are well known as plant pathogens including Pinus spp. Pinus halepensis trees are suffering from shoot dieback, branch cankers and trunk cankers in two Tunisian forests. The objective of the present work was to characterize Botryosphaeriaceae species associated with P. halepensis branch canker in Bizerte (Rimel forest). A total of 43 isolates were obtained from infected branches of P. halepensis trees. Using morphological characteristics and phylogenetic analysis, two Botryosphaeriaceae species were identified, that is Diplodia scrobiculata and Neofusicoccum luteum. Pathogenicity tests were performed on 3‐year‐old P. halepensis plants and both isolates were found to be pathogenic. Diplodia scrobiculata was the more virulent species had a greater virulence than Neofusicoccum luteum based on the length of vascular necrosis in the wood of the P. halepensis inoculated stem. To our knowledge, this is the first record of Neofusicoccum luteum and Diplodia scrobiculata associated with P. halepensis branch canker and dieback in Tunisia and worldwide.

High-Quality Genome Assembly and Annotation Resource of Three Botryosphaeria Pathogens Causing Chinese Hickory Canker.

Tree trunk canker is the most critical disease threatening the Chinese hickory (Carya cathayensis). Except for the well-known pathogen Botryosphaeria dothidea, our group has previously reported three new pathogenic species, including B. corticis, B. fabicerciana, and B. qingyuanensis. Here, we reported almost chromosome-scale genome assemblies of the representative strains of these Botryosphaeria species using the Oxford Nanopore Technologies (ONT) sequencing platform. The assemblies were 44 to 46 Mb in size, and contained less than 14 contigs (13 - 14) with the contig N50 of around 4 Mb. The BUSCO completeness of genome assemblies was around 99% at the Ascomycota level. These genome assemblies contained no more than 8% repeats and around 13,000 (12,876 - 13,677) protein-coding genes. Gene functional annotations, including pathogen-host interaction, carbohydrate active enzymes (CAZymes), cytochrome P450 enzymes (CYPs), putative secreted proteins, and secondary metabolite biosynthesis gene clusters (SMBGCs) were performed. Comparative genomics analysis shows that these stains shared 11,489 core orthologous gene clusters with our previously reported B. dothidea strain BDLA16-7. The almost chromosomal-level and well-annotated genome assemblies will provide valuable comparative genomic resources for Botryosphaeria species.

Identification of novel genetic regions associated with resistance to European canker in apple

BackgroundEuropean canker, caused by the fungal pathogen Neonectria ditissima, is an economically damaging disease in apple producing regions of the world – especially in areas with moderate temperatures and high rainfall. The pathogen has a wide host range of hardwood perennial species, causing trunk cankers, dieback and branch lesions in its hosts. Although apple scion germplasm carrying partial resistance to the disease has been described, little is still known of the genetic basis for this quantitative resistance.ResultsResistance to Neonectria ditissima was studied in a multiparental population of apple scions using several phenotyping methods. The studied population consists of individuals from multiple families connected through a common pedigree. The degree of disease of each individual in the population was assessed in three experiments: artificial inoculations of detached dormant shoots, potted trees in a glasshouse and in a replicated field experiment. The genetic basis of the differences in disease was studied using a pedigree-based analysis (PBA). Three quantitative trait loci (QTL), on linkage groups (LG) 6, 8 and 10 were identified in more than one of the phenotyping strategies. An additional four QTL, on LG 2, 5, 15 and 16 were only identified in the field experiment. The QTL on LG2 and 16 were further validated in a biparental population. QTL effect sizes were small to moderate with 4.3 to 19% of variance explained by a single QTL. A subsequent analysis of QTL haplotypes revealed a dynamic response to this disease, in which the estimated effect of a haplotype varied over the field time-points.ConclusionsThis study describes the first identified QTL associated with resistance to N. ditissima in apple scion germplasm. The results from this study show that QTL present in germplasm commonly used in apple breeding have a low to medium effect on resistance to N. ditissima. Hence, multiple QTL will need to be considered to improve resistance through breeding.

Neocosmospora caricae sp. nov. and N. metavorans, two new stem and trunk canker pathogens on Ficus carica in Iran

During 2018–2021, a survey was conducted in rainfed fig (Ficus carica L.) orchards throughout the Fars Province of Iran to investigate the occurrence of canker diseases, and to identify the causal organisms. Morphological and cultural characteristics, as well as multilocus phylogenetic analyses of the internal transcribed spacer (ITS) region of rDNA, RNA polymerase II second largest subunit (RPB2), and the translation elongation factor 1-alpha (TEF1), revealed that the recovered isolates from the infected fig trees clustered in clade 3 of Neocosmospora (Nectriaceae), including N. metavorans, and a new taxon described here as N. caricae sp. nov. Neocosmospora caricae is characterised by falcate, multiseptate, gently dorsoventrally curved macroconidia with poorly developed foot-shaped basal cells, ovoid, aseptate microconidia that cluster in false heads, and abundant terminal or intercalary chlamydospores. Pathogenicity tests indicated that isolates of both Neocosmospora species were pathogenic, causing stem canker and wood discolouration on fig saplings of “Sabz” and “Shah Anjeer” cultivars. The present study adds to existing knowledge on the aetiology of fig stem and trunk canker, and may provide essential information for developing effective integrated management strategies against canker diseases affecting fig orchards in Iran.

First Report of Leaf Spot on Malania oleifera Caused by Botryosphaeria fabicerciana in China.

HomePlant DiseaseVol. 106, No. 6First Report of Leaf Spot on Malania oleifera Caused by Botryosphaeria fabicerciana in China PreviousNext DISEASE NOTE OPENOpen Access licenseFirst Report of Leaf Spot on Malania oleifera Caused by Botryosphaeria fabicerciana in ChinaYue Pan, Pengfei Wang, Wandong Chen, Guichai Yang, Yingjie Gu, Junwei Wang, and Juan WangYue Panhttps://orcid.org/0000-0002-2092-2366Eco-development Academy, Southwest Forestry University, Kunming 650224, ChinaSearch for more papers by this author, Pengfei WangCollege of Forestry, Southwest Forestry University, Kunming 650224, ChinaSearch for more papers by this author, Wandong ChenCollege of Forestry, Southwest Forestry University, Kunming 650224, ChinaSearch for more papers by this author, Guichai YangCollege of Garden and Horticulture, Southwest Forestry University, Kunming 650224, ChinaSearch for more papers by this author, Yingjie GuCollege of Forestry, Southwest Forestry University, Kunming 650224, ChinaSearch for more papers by this author, Junwei WangSchool of Geography and Ecotourism, Southwest Forestry University, Kunming 650224, ChinaSearch for more papers by this author, and Juan Wang†Corresponding author: J. Wang; E-mail Address: schima@163.comEco-development Academy, Southwest Forestry University, Kunming 650224, ChinaSearch for more papers by this authorAffiliationsAuthors and Affiliations Yue Pan1 Pengfei Wang2 Wandong Chen2 Guichai Yang3 Yingjie Gu2 Junwei Wang4 Juan Wang1 † 1Eco-development Academy, Southwest Forestry University, Kunming 650224, China 2College of Forestry, Southwest Forestry University, Kunming 650224, China 3College of Garden and Horticulture, Southwest Forestry University, Kunming 650224, China 4School of Geography and Ecotourism, Southwest Forestry University, Kunming 650224, China Published Online:11 May 2022https://doi.org/10.1094/PDIS-09-21-2038-PDNAboutSectionsView articlePDFSupplemental ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmailWechat View articleMalania oleifera Chun & S. K. Lee is an endangered plant species in China with rich nervonic acid in seeds, and, thus, has important ecological and economic value (Fu 1992; Tang et al. 2013). Brown leaf spots were observed on 3-year-old M. oleifera plants in summer 2019 in Guangnan County, Yunnan Province, China (24°05′26″N, 105°05′07″E). A total of 100 trees within 0.3 ha of mountainous area were investigated, and eight (8%) showed disease symptoms. Initially, small, brown irregular spots appeared on the tip and margin of the leaf, and then gradually expanded to the whole leaf. Ten symptomatic leaves were randomly collected from different plants for fungal isolation. They were washed with running tap water, sterilized with 75% ethanol for 3 min and 1% NaOCl for 2 min, and rinsed in sterile distilled water three times. The leaves were cut into 5 × 5 mm2 segments and cultured on potato dextrose agar (PDA) at 25°C in the dark after air drying. In total, 12 morphologically similar fungal isolates were obtained. Colonies of the fungal culture initially appeared white, turned gray from the center between 3 to 6 days, and then became dark gray with cottony aerial mycelium 9 days later. To induce sporulation, the cultures were placed on 2% water agar (WA) with autoclaved pine needles and were incubated at 25°C under near-ultraviolet light as described by Chen et al. (2011). Globose conidiomata developed on pine needle surfaces after 10 days. Conidia were hyaline, unicellular, aseptate, fusiform with apex acute and base truncate, and 18.62 to 26.14 × 4.80 to 7.63 μm (average 21.77 × 5.91 μm, n = 50). The morphological characteristics resembled those of Botryosphaeria fabicerciana (S.F. Chen, D. Pavlic, M.J. Wingf. & X.D. Zhou) A.J.L. Phillips & A. Alves (Phillips et al. 2013). The internal transcribed spacer (ITS) region and the translation elongation factor 1-α gene (EF1-α) regions of a representative isolate (CGMCC3.20320) were amplified using primers ITS1F/ITS4 and EF1-728F/EF1-986R (Carbone and Kohn 1999; White et al. 1990), respectively. The obtained sequences (GenBank accession nos. MW642163 and MW651965) showed 99.80% (identity = 505/506) and 99.27% (identity = 272/274) similarity with the corresponding genes of ex-type CMW 27094 of Fusicoccum fabicercianum S.F. Chen, D. Pavlic, M.J. Wingf. & X.D. Zhou, now B. fabicerciana (GenBank accession nos. HQ332197 and HQ332213). The pathogenicity of the selected isolate (CGMCC3.20320) was evaluated by leaf inoculation of 1-year-old M. oleifera seedlings. Mycelial plugs (5 mm) of B. fabicerciana from a 7-day-old culture were applied on leaves wounded with sterile scalpels. Controls were inoculated with sterile PDA plugs. Each treatment was repeated six times. Inoculated and control plants were kept in a greenhouse at 25°C and 80% relative humidity, with a 12-h photoperiod. After 10 days, irregular brown spots appeared on all inoculated leaves, whereas there were no spots from control plants. Botryosphaeria fabicerciana was reisolated only from symptomatic leaves, fulfilling Koch’s postulates. Previous studies indicated that this fungus can cause stem lesions on Eucalyptus and trunk cankers on Carya cathayensis in China (Chen et al. 2011; Zhuang et al. 2021). To our knowledge, this represents the first report of B. fabicerciana causing leaf spot on M. oleifera in China.The author(s) declare no conflict of interest.