Botryosphaeria dothidea: a latent pathogen of global importance to woody plant health

Genetic diversity and population structure of Botryosphaeria dothidea and Neofusicoccum parvum on English walnut (Juglans regia L.) in France

Botryosphaeriaceae species are the major causal agents of walnut dieback worldwide, along with Diaporthe species. Botryosphaeria dothidea and Neofusicoccum parvum are the only two Botryosphaeriaceae species associated with this recently emergent disease in France, and little is known about their diversity, structure, origin and dispersion in French walnut orchards. A total of 381 isolates of both species were genetically typed using a sequence-based microsatellite genotyping (SSR-seq) method. This analysis revealed a low genetic diversity and a high clonality of these populations, in agreement with their clonal mode of reproduction. The genetic similarity among populations, regardless of the tissue type and the presence of symptoms, supports the hypothesis that these pathogens can move between fruits and twigs and display latent pathogen lifestyles. Contrasting genetic patterns between N. parvum populations from Californian and Spanish walnut orchards and the French ones suggested no conclusive evidence for pathogen transmission from infected materials. The high genetic similarity with French vineyards populations suggested instead putative transmission between these hosts, which was also observed with B. dothidea populations. Overall, this study provides critical insight into the epidemiology of two important pathogens involved in the emerging dieback of French walnut orchards, including their distribution, potential to mate, putative origin and disease pathways.

What are the 100 most cited fungal genera?

The global diversity of fungi has been estimated between 2 to 11 million species, of which only about 155 000 have been named. Most fungi are invisible to the unaided eye, but they represent a major component of biodiversity on our planet, and play essential ecological roles, supporting life as we know it. Although approximately 20 000 fungal genera are presently recognised, the ecology of most remains undetermined. Despite all this diversity, the mycological community actively researches some fungal genera more commonly than others. This poses an interesting question: why have some fungal genera impacted mycology and related fields more than others? To address this issue, we conducted a bibliometric analysis to identify the top 100 most cited fungal genera. A thorough database search of the Web of Science, Google Scholar, and PubMed was performed to establish which genera are most cited. The most cited 10 genera are Saccharomyces, Candida, Aspergillus, Fusarium, Penicillium, Trichoderma, Botrytis, Pichia, Cryptococcus and Alternaria. Case studies are presented for the 100 most cited genera with general background, notes on their ecology and economic significance and important research advances. This paper provides a historic overview of scientific research of these genera and the prospect for further research. Citation: Bhunjun CS, Chen YJ, Phukhamsakda C, Boekhout T, Groenewald JZ, McKenzie EHC, Francisco EC, Frisvad JC, Groenewald M, Hurdeal VG, Luangsa-ard J, Perrone G, Visagie CM, Bai FY, Błaszkowski J, Braun U, de Souza FA, de Queiroz MB, Dutta AK, Gonkhom D, Goto BT, Guarnaccia V, Hagen F, Houbraken J, Lachance MA, Li JJ, Luo KY, Magurno F, Mongkolsamrit S, Robert V, Roy N, Tibpromma S, Wanasinghe DN, Wang DQ, Wei DP, Zhao CL, Aiphuk W, Ajayi-Oyetunde O, Arantes TD, Araujo JC, Begerow D, Bakhshi M, Barbosa RN, Behrens FH, Bensch K, Bezerra JDP, Bilański P, Bradley CA, Bubner B, Burgess TI, Buyck B, Čadež N, Cai L, Calaça FJS, Campbell LJ, Chaverri P, Chen YY, Chethana KWT, Coetzee B, Costa MM, Chen Q, Custódio FA, Dai YC, Damm U, de Azevedo Santiago ALCM, De Miccolis Angelini RM, Dijksterhuis J, Dissanayake AJ, Doilom M, Dong W, Alvarez-Duarte E, Fischer M, Gajanayake AJ, Gené J, Gomdola D, Gomes AAM, Hausner G, He MQ, Hou L, Iturrieta-González I, Jami F, Jankowiak R, Jayawardena RS, Kandemir H, Kiss L, Kobmoo N, Kowalski T, Landi L, Lin CG, Liu JK, Liu XB, Loizides M, Luangharn T, Maharachchikumbura SSN, Makhathini Mkhwanazi GJ, Manawasinghe IS, Marin-Felix Y, McTaggart AR, Moreau PA, Morozova OV, Mostert L, Osiewacz HD, Pem D, Phookamsak R, Pollastro S, Pordel A, Poyntner C, Phillips AJL, Phonemany M, Promputtha I, Rathnayaka AR, Rodrigues AM, Romanazzi G, Rothmann L, Salgado-Salazar C, Sandoval-Denis M, Saupe SJ, Scholler M, Scott P, Shivas RG, Silar P, Souza-Motta CM, Silva-Filho AGS, Spies CFJ, Stchigel AM, Sterflinger K, Summerbell RC, Svetasheva TY, Takamatsu S, Theelen B, Theodoro RC, Thines M, Thongklang N, Torres R, Turchetti B, van den Brule T, Wang XW, Wartchow F, Welti S, Wijesinghe SN, Wu F, Xu R, Yang ZL, Yilmaz N, Yurkov A, Zhao L, Zhao RL, Zhou N, Hyde KD, Crous PW (2024). What are the 100 most cited fungal genera? Studies in Mycology 108: 1-411. doi: 10.3114/sim.2024.108.01.

Fungal Trunk Diseases Causing Decline of Apricot and Plum Trees in the Czech Republic

Fungal trunk diseases (FTDs) have been a significant threat to the global stone fruit industry. FTDs are caused by a consortium of wood-decaying fungi. These fungi colonize woody tissues, causing cankers, dieback, and other decline-related symptoms in host plants. In this study, a detailed screening of the fungal microbiota associated with the decline of stone fruit trees in the Czech Republic was performed. The wood fragments of plum and apricot trees showing symptoms of FTDs were subjected to fungal isolation. The partial internal transcribed spacer region, partial beta-tubulin, and translation elongation factor 1-α genes were amplified from genomic DNA extracted from fungal cultures. All isolates were classified, and the taxonomic placement of pathogenic strains was illustrated in phylogenetic trees. The most abundant pathogenic genus was Dactylonectria (31%), followed by Biscogniauxia (13%), Thelonectria (10%), Eutypa (9%), Dothiorella (7%), Diplodia (6%), and Diaporthe (6%). The most frequent endophytic genus was Aposphaeria (17%). The pathogenicity of six fungal species (Cadophora daguensis, Collophorina africana, Cytospora sorbicola, Dothiorella sarmentorum, Eutypa lata, and E. petrakii var. petrakii) to four Prunus spp. was evaluated, and Koch's postulates were fulfilled. All tested isolates caused lesions on at least one Prunus sp. The most aggressive species was E. lata, which caused the largest lesions on all four tested Prunus spp., followed by E. petrakii var. petrakii and D. sarmentorum. Japanese plum (Prunus salicina) and almond (P. amygdalus) were the most susceptible hosts, while apricot (P. armeniaca) was the least susceptible host in the pathogenicity trial.

Endophytic fungal isolates from apple tissue: Latent pathogens lurking within?

Fungal endophytes inhabit a similar ecological niche to that occupied by many phytopathogens, with several pathogens isolated from healthy tissues in their latent phase. This study aimed to evaluate the pathogenicity, the colonisation ability, and the enzyme activity of 37 endophytic fungal isolates recovered from apparently healthy apple shoot and leaf tissues. The pathogenicity of the isolates was assessed on 'Royal Gala' and 'Braeburn' fruit and detached 'Royal Gala' shoots. For the non-pathogenic isolates, their ability to endophytically colonise detached 'Royal Gala' shoots was evaluated. Enzyme activity assays were undertaken to determine whether the pathogenicity of the endophytes was related to the production of the extracellular enzymes, amylase, cellulase, pectinase, protease, and xylanase. Of the 37 isolates studied, eight isolates, representing the genera Colletotrichum, Diaporthe, Fusarium, and Penicillium, were shown to be pathogenic on both apple shoots and fruit. Two isolates identified as Trichoderma atroviride, were pathogenic only on shoots, and three isolates, representing the genus Diaporthe, were pathogenic only on fruit. Of the remaining 24 isolates, 22 (Biscogniauxia (n = 8), Chaetomium (n = 4), Trichoderma (n = 3), Epicoccum (n = 2), Neosetophoma (n = 2), Xylaria (n = 1), Daldinia (n = 1), and Paraphaeosphaeria (n = 1)) were recovered from the inoculated apple shoots but two failed to colonise the shoot tissues. Of the isolates tested, 20 produced amylase, 15 cellulase, 25 pectinase, 26 protease, and 13 xylanase. There was no correlation between the range and type of enzymes produced by the isolates and their pathogenicity or ability to endophytically colonise the shoot tissue. The study showed that approximately one-third (13/37) of the isolates recovered from the apparently healthy apple shoot tissues were observed as latent pathogens. The isolates that did not cause disease symptoms may have the ability to reduce colonisation of apple tissues by pathogens including Neonectria ditissima associated with European canker of apple.

Host-induced gene silencing in wild apple germplasm Malus hupehensis confers resistance to the fungal pathogen Botryosphaeria dothidea

Host-induced gene silencing (HIGS) is an inherent mechanism of plant resistance to fungal pathogens, resulting from cross-kingdom RNA interference (RNAi) mediated by small RNAs (sRNAs) delivered from plants into invading fungi. Introducing artificial sRNA precursors into crops can trigger HIGS of selected fungal genes, and thus has potential applications in agricultural disease control. To investigate the HIGS of apple (Malus sp.) during the interaction with Botryosphaeria dothidea, the pathogenic fungus causing apple ring rot disease, we evaluated whether apple miRNAs can be transported into and target genes in B. dothidea. Indeed, miR159a from Malus hupehensis, a wild apple germplasm with B. dothidea resistance, silenced the fungal sugar transporter gene BdSTP. The accumulation of miR159a in extracellular vesicles (EVs) of both infected M. hupehensis and invading B. dothidea suggests that this miRNA of the host is transported into the fungus via the EV pathway. Knockout of BdSTP caused defects in fungal growth and proliferation, whereas knockin of a miR159a-insensitive version of BdSTP resulted in increased pathogenicity. Inhibition of miR159a in M. hupehensis substantially enhanced plant sensitivity to B. dothidea, indicating miR159a-mediated HIGS against BdSTP being integral to apple immunity. Introducing artificial sRNA precursors targeting BdSTP and BdALS, an acetolactate synthase gene, into M. hupehensis revealed that double-stranded RNAs were more potent than engineered MIRNAs in triggering HIGS alternative to those natural of apple and inhibiting infection. These results provide preliminary evidence for cross-kingdom RNAi in the apple-B. dothidea interaction and establish HIGS as a potential disease control strategy in apple.

Endophytic Fungi Residing within Cornus florida L. in Mid-Tennessee: Phylogenetic Diversity, Enzymatic Properties, and Potential Role in Plant Health

Endophytic fungi that reside internally in healthy, asymptomatic plants often benefit their hosts by promoting plant growth and/or providing plant protection against abiotic and biotic stresses. However, only a small fraction of the estimated 1.5 million fungal endophytes have been identified. In this study, a total of 369 isolates of fungal endophytes in 59 distinct taxa were isolated from stem samples of Cornus florida (flowering dogwood). All isolates belonged to species of phyla Ascomycota and Basidiomycota distributed across five orders and 11 genera. Isolates belonging to the same family clustered together in a phylogenetic tree generated from a cluster analysis using MEGA 7 software. Diversity indices of the fungi revealed a rich and diverse community that included several species associated with leaf spots, blight, cankers, and/or dieback diseases. Pathogenicity tests confirmed 16 fungal endophytes as C. florida pathogens, including some well-known destructive pathogens Botryosphaera dothidea, Colletotrichum acutatum, and C. gleosporoides. Isolates of the fungal endophytes possess the capacity to produce extracellular hydrolytic enzymes (cellulase, amylase, pectinase, laccase, chitinase, and protease) that are known to function in tissue penetration, plant colonization, nutrient acquisition, and disease suppression in both plant pathogens and endophytes These results support the interchangeable pathogenic-endophytic roles for some taxa.

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.

Prevalent arbuscular mycorrhizae in roots and highly variable mycobiome in leaves of epiphytic subtropical fern Ophioderma pendulum

PREMISE

Endophytic and mycorrhizal fungi are crucial in facilitating plant nutrition acquisition and stress tolerance. In epiphytic habitats, plants face nutrition and water stress, but their roots are mostly nonmycorrhizal and especially lacking in arbuscular mycorrhizal associations. Ophioderma pendulum is an epiphytic fern with a partially mycoheterotrophic lifestyle, likely heavily reliant on symbiotic fungi. To characterize fungal associations in the sporophyte of O. pendulum, we focused on leaves and roots of O. pendulum, seeking to reveal the fungal communities in these organs.

METHODS

Roots and leaves from O. pendulum in a subtropical forest were examined microscopically to observe the morphology of fungal structures and determine the percentage of various fungal structures in host tissues. Fungal composition was profiled using metabarcoding techniques that targeted ITS2 of the nuclear ribosomal DNA.

RESULTS

Roots were consistently colonized by arbuscular mycorrhizal fungi (Glomeromycota), especially Acaulospora. Unlike previous findings on epiphytic ferns, dark septate endophytes were rare in O. pendulum roots. Leaves were predominantly colonized by Ascomycota fungi, specifically the classes Dothideomycetes (46.88%), Eurotiomycetes (11.51%), Sordariomycetes (6.23%), and Leotiomycetes (6.14%). Across sampling sites, fungal community compositions were similar in the roots but differed significantly in the leaves.

CONCLUSIONS

Ophioderma pendulum maintains stable, single-taxon-dominant communities in the roots, primarily featuring arbuscular mycorrhizal fungi, whereas the leaves may harbor opportunistic fungal colonizers. Our study underlines the significance of mycorrhizal fungi in the adaptation of epiphytic ferns.

Taxonomy and pathogenicity of fungi associated with oak decline in northern and central Zagros forests of Iran with emphasis on coelomycetous species

Oak decline is a complex disorder that seriously threatens the survival of Zagros forests. In an extensive study on taxonomy and pathology of fungi associated with oak decline in the central and northern part of Zagros forests, 462 fungal isolates were obtained from oak trees showing canker, gummosis, dieback, defoliation, and partial or total death symptoms. Based on inter-simple sequence repeat (ISSR) fingerprinting patterns, morphological characteristics, and sequences of ribosomal DNA (28S rDNA and ITS) and protein coding loci (acl1, act1, caM, tef-1α, rpb1, rpb2, and tub2), 24 fungal species corresponding to 19 genera were characterized. Forty percent of the isolates were placed in eight coelomycetous species from seven genera, namely, Alloeutypa, Botryosphaeria, Cytospora, Didymella, Gnomoniopsis, Kalmusia, and Neoscytalidium. Of these, four species are new to science, which are introduced here as taxonomic novelties: Alloeutypa iranensis sp. nov., Cytospora hedjaroudei sp. nov., Cytospora zagrosensis sp. nov., and Gnomoniopsis quercicola sp. nov. According to pathogenicity trials on leaves and stems of 2-year-old Persian oak (Quercus brantii) seedlings, Alternaria spp. (A. alternata, A. atra, and A. contlous), Chaetomium globosum, and Parachaetomium perlucidum were recognized as nonpathogenic. All coelomycetous species were determined as pathogenic in both pathogenicity trials on leaves and seedling stems, of which Gnomoniopsis quercicola sp. nov., Botryosphaeria dothidea, and Neoscytalidium dimidiatum were recognized as the most virulent species followed by Biscogniauxia rosacearum.

Biocontrol of almond canker diseases caused by Botryosphaeriaceae fungi

BACKGROUND

Botryosphaeria dieback is a canker disease caused by fungal species of the Botryosphaeriaceae family that threatens almond productivity. The most common control measure to prevent canker development is the application of fungicides which are being phased out by European Union regulations. In the present study, two sets of bacterial strains were evaluated for their antifungal activity against pathogenic Botryosphaeriaceae species through in vitro and in vivo antagonism assays.

RESULTS

The rhizospheric bacteria Pseudomonas aeruginosa AC17 and Bacillus velezensis ACH16, as well as the endophytic bacteria Bacillus mobilis Sol 1-2, respectively inhibited 87, 95, and 63% of the mycelial growth of Neofusicoccum parvum, Botryosphaeria dothidea, Diplodia seriata, and Macrophomina phaseolina. Additionally, they significantly reduced the length of lesions caused by N. parvum and B. dothidea in artificially inoculated detached almond twigs. All these bacterial strains produce hydrolytic enzymes that are able to degrade the fungal cell wall. P. aeruginosa AC17 also produces toxic volatile compounds, such as hydrogen cyanide. This strain was the most effective in controlling Botryosphaeria dieback in planta under controlled conditions at a level similar to the biocontrol agent Trichoderma atroviride and standard chemical fungicide treatments.

CONCLUSION

Pseudomonas aeruginosa AC17 is the best candidate to be considered as a potential biocontrol agent against Botryosphaeriaceae fungi affecting almond. © 2023 Society of Chemical Industry.

How megadrought causes extensive mortality in a deep-rooted shrub species normally resistant to drought-induced dieback: The role of a biotic mortality agent

Southern California experienced unprecedented megadrought between 2012 and 2018. During this time, Malosma laurina, a chaparral species normally resilient to single-year intense drought, developed extensive mortality exceeding 60% throughout low-elevation coastal populations of the Santa Monica Mountains. We assessed the physiological mechanisms by which the advent of megadrought predisposed M. laurina to extensive shoot dieback and whole-plant death. We found that hydraulic conductance of stem xylem (Ks, native ) was reduced seven to 11-fold in dieback adult and resprout branches, respectively. Staining of stem xylem vessels revealed that dieback plants experienced 68% solid-blockage, explaining the reduction in water transport. Following Koch's postulates, persistent isolation of a microorganism in stem xylem of dieback plants but not healthy controls indicated that the causative agent of xylem blockage was an opportunistic endophytic fungus, Botryosphaeria dothidea. We inoculated healthy M. laurina saplings with fungal isolates and compared hyphal elongation rates under well-watered, water-deficit, and carbon-deficit treatments. Relative to controls, we found that both water deficit and carbon-deficit increased hyphal extension rates and the incidence of shoot dieback.

Detecting and identifying pathogens and antagonistic bacteria associated with Ginkgo biloba leaf spot disease

Background

Leaf spot disease severely impacts Ginkgo biloba (G. biloba) yield and quality. While microbial agents offer effective and non-toxic biological control for plant diseases, research on controlling leaf spot disease in G. biloba is notably scarce.

Methods

The pathogenic fungi were isolated and purified from diseased and healthy leaves of G. biloba, Subsequent examinations included morphological observations and molecular identification via PCR techniques. A phylogenetic tree was constructed to facilitate the analysis of these pathogenic fungi, and Koch's postulates were subsequently employed to reaffirm their pathogenic nature. The antagonistic experiment was employed to select biocontrol bacteria, and subsequently, the isolated biocontrol bacteria and pathogenic fungi were inoculated onto healthy leaves to assess the inhibitory effects of the biocontrol bacteria.

Results

Two pathologies responsible for the leaf spot disease on G. biloba were identified as Botryosphaeria dothidea and Neofusicoccum parvum via the analysis of phylogenetic tree and the application of Koch's Postulates. Additionally, we isolated two strains of biocontrol bacteria, namely Bacillus velezensis and Bacillus amyloliquefaciens. Their average inhibitory zones were measured at 4.78 cm and 3.46 cm, respectively. The inhibition zone of B. velezensis against N. parvum was 4 cm. B. velezensis showed a stronger inhibitory effect compared to B. amyloliquefaciens on the development of lesions caused by B. dothidea via leaf culture experiment.

Conclusion

This research reports, for the first time, the presence of B. dothidea as a pathogenic fungus affecting G. biloba. Moreover, the biocontrol bacteria, B. velezensis and B. amyloliquefaciens, exhibited the capability to effectively inhibit the growth and reproduction of B. dothidea, indicating their promising potential as environmentally friendly biocontrol resources.

Characterization and Pathogenicity of Fungal Species Associated with Dieback of Apple Trees in Northern Italy

Severe dieback symptoms were recently observed on apple (Malus × domestica) trees in Northern Italy, representing a growing concern for producers. Surveys were conducted over a 3-year period (2019 to 2021), and five apple orchards, from 5 to 12 years old, were monitored. A total of 33 fungal isolates isolated from symptomatic plants was selected for characterization. The species identification was achieved through multilocus phylogenetic analyses performed on sequences of three genomic loci (ITS, tub2, and tef1). Morphological features were assessed, and the average growth rate at different temperatures was determined. Seven species were identified in association with dieback of apple trees: Botryosphaeria dothidea, Cadophora luteo-olivacea, Diaporthe rudis, Diplodia seriata, Eutypa lata, Kalmusia longispora, and Paraconiothyrium brasiliense. All the species were pathogenic when inoculated on healthy apple plants. B. dothidea resulted in the most aggressive infections. This study provides an insight into the fungal species diversity associated with apple dieback and provides basis for further investigations to assess the phytosanitary status of plant materials to recommend and implement effective management strategies.

Molecular characterization of a novel narnavirus infecting the phytopathogenic fungus Botryosphaeria dothidea

Here, a novel mycovirus, Botryosphaeria dothidea narnavirus 5 (BdNV5), was discovered in the plant-pathogenic fungus Botryosphaeria dothidea strain ZM210167-1. The BdNV5 genome sequence is 2,397 nucleotides (nt) in length and contains a putative open reading frame (ORF) encoding an RNA-dependent RNA polymerase (RdRp) with a molecular mass of 72.77 kDa. A BLASTp search using the RdRp amino acid (aa) sequence showed that it was most similar to the RdRp of Botryosphaeria dothidea narnavirus 4 (42.35%). In a phylogenetic tree based on RdRp aa sequences, BdNV5 clustered with members of the family Narnaviridae. BdNV5 is thus a novel member of the family Narnaviridae infecting the phytopathogenic fungus B. dothidea.

Mycobiomes of two distinct clades of ambrosia gall midges (Diptera: Cecidomyiidae) are species-specific in larvae but similar in nutritive mycelia

IMPORTANCE

Ambrosia gall midges are endophagous insect herbivores whose larvae live enclosed within a single gall for their entire development period. They may exhibit phytomycetophagy, a remarkable feeding mode that involves the consumption of plant biomass and mycelia of their cultivated gall symbionts. Thus, AGMs are ideal model organisms for studying the role of microorganisms in the evolution of host specificity in insects. However, compared to other fungus-farming insects, insect-fungus mutualism in AGMs has been neglected. Our study is the first to use DNA metabarcoding to characterize the complete mycobiome of the entire system of the gall-forming insects as we profiled gall surfaces, nutritive mycelia, and larvae. Interestingly, larval mycobiomes were significantly different from their nutritive mycelia, although Botryosphaeria dothidea dominated the nutritive mycelia, regardless of the evolutionary separation of the tribes studied. Therefore, we confirmed a long-time hypothesized paradigm for the important evolutionary association of this fungus with AGMs.

Effects of sample storage temperature and duration on the detection of foliar endophytes of tea plants (Camellia sinensis L.) in summer and winter

Seasonal changes in the diversity of tea plant endophytic fungi and the effects of sample storage conditions on detection were analyzed. Tea leaves were collected from the Saitama Tea Research Institute in Japan during winter (January 2020) and summer (August 2020). The effects of storage temperature (5, 10, 20, 25, and 30°C) and durations (1, 2, 3, 4, 5, 6, and 7 days) on endophytic fungal diversity and community structure were investigated. In summer, storage period and temperature did not affect the fungal colonization rate, frequency, and composition. In winter, storage temperature and period significantly affected the endophytic community structure. Fungal diversity was higher in winter than in summer. Positive relationships between diversity index and storage temperature and period were observed in winter, whereas the opposite trend was observed in summer. Our findings provide insight into the ecology of foliar endophytes of tea plants and the importance of proper sample collection and storage for microbiome studies.

LysM protein BdLM1 of Botryosphaeria dothidea plays an important role in full virulence and inhibits plant immunity by binding chitin and protecting hyphae from hydrolysis

Botryosphaeria dothidea infects hundreds of woody plants and causes a severe economic loss to apple production. In this study, we characterized BdLM1, a protein from B. dothidea that contains one LysM domain. BdLM1 expression was dramatically induced at 6 h post-inoculation in wounded apple fruit, strongly increased at 7 d post-inoculation (dpi), and peaked at 20 dpi in intact shoots. The knockout mutants of BdLM1 had significantly reduced virulence on intact apple shoots (20%), wounded apple shoots (40%), and wounded apple fruit (40%). BdLM1 suppressed programmed cell death caused by the mouse protein BAX through Agrobacterium-mediated transient expression in Nicotiana benthamiana, reduced H2O2 accumulation and callose deposition, downregulated resistance gene expression, and promoted Phytophthora nicotianae infection in N. benthamiana. Moreover, BdLM1 inhibited the active oxygen burst induced by chitin and flg22, bound chitin, and protected fungal hyphae against degradation by hydrolytic enzymes. Taken together, our results indicate that BdLM1 is an essential LysM effector required for the full virulence of B. dothidea and that it inhibits plant immunity. Moreover, BdLM1 could inhibit chitin-triggered plant immunity through a dual role, i.e., binding chitin and protecting fungal hyphae against chitinase hydrolysis.

Fungal Pathogens Associated with Almond Decline Syndrome, an Emerging Disease Complex in Intensive Almond Crops in Southern Spain

In 2016, an almond (Prunus dulcis) decline syndrome (ADS) emerged in intensive almond plantations in the Andalusia region (southern Spain), showing branch dieback, gummosis, and general tree decline. The aim of this work was to elucidate the etiology of this disease complex. For this purpose, surveys were conducted across the Andalusia region, and a wide collection of fungi was recovered from wood samples showing gum and internal discoloration. Representative isolates were selected and identified by sequencing ITS, TEF1, TUB, ACT, LSU, and/or RPB2 genes. The following fungal species were identified to be associated with the disease: Botryosphaeria dothidea, Diplodia corticola, Di. seriata, Dothiorella iberica, Lasiodiplodia viticola, Macrophomina phaseolina, Neofusicoccum mediterraneum, N. parvum, N. vitifusiforme, Diaporthe neotheicola, Dia. rhusicola, Dia. ambigua, Eutypa lata, E. tetragona, Eutypella citricola, Eu. microtheca, Fusarium oxysporum s.l., Pleurostoma richardsiae, Phaeoacremonium iranianum, Pm. krajdenii, Pm. parasiticum, and Cytospora sp. All isolates were tested for pathogenicity by inoculating detached or attached almond shoots. Di. corticola and N. parvum were the most aggressive species, showing the largest lesions and most gummosis in attached shoots. The results suggest that the species belonging to Botryosphaeriaceae play a key role in disease development, while the remaining identified species may act as secondary pathogens or endophytes. However, further research to determine the interaction between all these fungal species and other biotic and abiotic factors in the ADS progress is needed.

Metabolome and Transcriptome Profiling Reveals the Function of MdSYP121 in the Apple Response to Botryosphaeria dothidea

The vesicular transport system is important for substance transport in plants. In recent years, the regulatory relationship between the vesicular transport system and plant disease resistance has received widespread attention; however, the underlying mechanism remains unclear. MdSYP121 is a key protein in the vesicular transport system. The overexpression of MdSYP121 decreased the B. dothidea resistance of apple, while silencing MdSYP121 resulted in the opposite phenotype. A metabolome and transcriptome dataset analysis showed that MdSYP121 regulated apple disease resistance by significantly affecting sugar metabolism. HPLC results showed that the levels of many soluble sugars were significantly higher in the MdSYP121-OE calli. Furthermore, the expression levels of genes related to sugar transport were significantly higher in the MdSYP121-OE calli after B. dothidea inoculation. In addition, the relationships between the MdSYP121 expression level, the soluble sugar content, and apple resistance to B. dothidea were verified in an F1 population derived from a cross between 'Golden Delicious' and 'Fuji Nagafu No. 2'. In conclusion, these results suggested that MdSYP121 negatively regulated apple resistance to B. dothidea by influencing the soluble sugar content. These technologies and methods allow us to investigate the molecular mechanism of the vesicular transport system regulating apple resistance to B. dothidea.

Identification and Characterization of a Novel Hypovirus from the Phytopathogenic Fungus Botryosphaeria dothidea

Many mycoviruses have been accurately and successfully identified in plant pathogenic fungus Botryosphaeria dothidea. This study discovered three mycoviruses from a B. dothidea strain SXD111 using high-throughput sequencing technology. A novel hypovirus was tentatively named Botryosphaeria dothidea hypovirus 1 (BdHV1/SXD111). The other two were known viruses, which we named Botryosphaeria dothidea polymycovirus 1 strain SXD111 (BdPmV1/SXD111) and Botryosphaeria dothidea partitivirus 1 strain SXD111 (BdPV1/SXD111). The genome of BdHV1/SXD111 is 11,128 nucleotides long, excluding the poly (A) tail. A papain-like cysteine protease (Pro), a UDP-glucose/sterol glucosyltransferase (UGT), an RNA-dependent RNA polyprotein (RdRp), and a helicase (Hel) were detected in the polyprotein of BdHV1/SXD111. Phylogenetic analysis showed that BdHV1/SXD111 was clustered with betahypovirus and separated from members of the other genera in the family Hypoviridae. The BdPmV1/SXD111 genome comprised five dsRNA segments with 2396, 2232, 1967, 1131, and 1060 bp lengths. Additionally, BdPV1/SXD111 harbored three dsRNA segments with 1823, 1623, and 557 bp lengths. Furthermore, the smallest dsRNA was a novel satellite component of BdPV1/SXD111. BdHV1/SXD111 could be transmitted through conidia and hyphae contact, whereas it likely has no apparent impact on the morphologies and virulence of the host fungus. Thus, this study is the first report of a betahypovirus isolated from the fungus B. dothidea. Importantly, our results significantly enhance the diversity of the B. dothidea viruses.

Rapid and Sensitive Detection of the Causal Agents of Postharvest Kiwifruit Rot, Botryosphaeria dothidea and Diaporthe eres, Using a Recombinase Polymerase Amplification Assay

The occurrence of postharvest kiwifruit rot has caused great economic losses in major kiwifruit-producing countries. Several pathogens are involved in kiwifruit rot, notably Botryosphaeria dothidea, and Diaporthe species. In this study, a recombinase polymerase amplification (RPA) assay was developed for the rapid and sensitive detection of the pathogens responsible for posing significant threats to the kiwifruit industries. The RPA primer pairs tested in this study were highly specific for detection of B. dothidea and D. eres. The detection limits of our RPA assays were approximately two picograms of fungal genomic DNA. The optimal conditions for the RPA assays were determined to be at a temperature of 39°C maintained for a minimum duration of 5 min. We were able to detect the pathogens from kiwifruit samples inoculated with a very small number of conidia. The RPA assays enabled specific, sensitive, and rapid detection of B. dothidea and D. eres, the primary pathogens responsible for kiwifruit rots in South Korea.

BdCV1-Encoded P3 Silencing Suppressor Identification and Its Roles in Botryosphaeria dothidea, Causing Pear Ring Rot Disease

Pear ring rot disease is an important branch disease, caused by Botryosphaeria dothidea. With the discovery of fungal viruses, the use of their attenuated properties for biological control provides a new strategy for the biological control of fungal disease. RNA silencing is a major antiviral defense mechanism in plants, insects, and fungi. Viruses encode and utilize RNA silencing suppressors to suppress host defenses. Previous studies revealed that Botryosphaeria dothidea chrysovirus 1 (BdCV1) exhibited weak pathogenicity and could activate host gene silencing by infecting B. dothidea. The aim of our study was to investigate whether BdCV1 can encode a silencing suppressor and what effect it has on the host. In this study, the capability of silencing inhibitory activity of four BdCV1-encoded proteins was analyzed, and the P3 protein was identified as a BdCV1 RNA silencing suppressor in the exotic host Nicotiana benthamiana line 16c. In addition, we demonstrated that P3 could inhibit local silencing, block systemic RNA silencing, and induce the necrosis reaction of tobacco leaves. Furthermore, overexpression of P3 could slow down the growth rate and reduce the pathogenicity of B. dothidea, and to some extent affect the expression level of RNA silencing components and virus-derived siRNAs (vsiRNAs). Combined with transcriptomic analysis, P3 had an effect on the gene expression and biological process of B. dothidea. The obtained results provide new theoretical information for further study of interaction between BdCV1 P3 as a potential silencing suppressor and B. dothidea.

Variations in amino acids caused by drought stress mediate the predisposition of Carya cathayensis to Botryosphaeria canker disease

Abiotic stresses can affect the outcome of plant-pathogen interactions, mostly by predisposing the host plant to infection; however, the crosstalk between pathogens and plants related to such predisposition remains unclear. Here, we investigated the predisposition of Carya cathayensis to infection by the fungal pathogen Botryosphaeria dothidea (Bd) caused by drought in the host plant. High levels of drought stress resulted in a significant increase in plant susceptibility to Bd. Drought significantly induced the accumulation of H2O2 and the free amino acids Pro, Leu, and Ile, and in the phloem tissues of plants, and decreased the content of non-structural carbohydrates. In vitro assays showed that Bd was sensitive to H2O2; however, Pro played a protective role against exogenous H2O2. Leu, Ile, and Pro induced asexual reproduction of Bd. Our results provide the first analysis of how drought predisposes C. cathayensis to Botrysphaeria canker via amino acid accumulation in the host plant, and we propose a model that integrates the plant-pathogen interactions involved.

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.

Climate, host and geography shape insect and fungal communities of trees

Non-native pests, climate change, and their interactions are likely to alter relationships between trees and tree-associated organisms with consequences for forest health. To understand and predict such changes, factors structuring tree-associated communities need to be determined. Here, we analysed the data consisting of records of insects and fungi collected from dormant twigs from 155 tree species at 51 botanical gardens or arboreta in 32 countries. Generalized dissimilarity models revealed similar relative importance of studied climatic, host-related and geographic factors on differences in tree-associated communities. Mean annual temperature, phylogenetic distance between hosts and geographic distance between locations were the major drivers of dissimilarities. The increasing importance of high temperatures on differences in studied communities indicate that climate change could affect tree-associated organisms directly and indirectly through host range shifts. Insect and fungal communities were more similar between closely related vs. distant hosts suggesting that host range shifts may facilitate the emergence of new pests. Moreover, dissimilarities among tree-associated communities increased with geographic distance indicating that human-mediated transport may serve as a pathway of the introductions of new pests. The results of this study highlight the need to limit the establishment of tree pests and increase the resilience of forest ecosystems to changes in climate.

The Phosphatase Cascade Nem1/Spo7-Pah1 Regulates Fungal Development, Lipid Homeostasis, and Virulence in Botryosphaeria dothidea

Protein phosphatase complex Nem1/Spo7 plays crucial roles in the regulation of various biological processes in eukaryotes. However, its biological functions in phytopathogenic fungi are not well understood. In this study, genome-wide transcriptional profiling analysis revealed that Nem1 was significantly upregulated during the infection process of Botryosphaeria dothidea, and we identified and characterized the phosphatase complex Nem1/Spo7 and its substrate Pah1 (a phosphatidic acid phosphatase) in B. dothidea. Nem1/Spo7 physically interacted with and dephosphorylated Pah1 to promote triacylglycerol (TAG) and subsequent lipid droplet (LD) synthesis. Moreover, the Nem1/Spo7-dependently dephosphorylated Pah1 functioned as a transcriptional repressor of the key nuclear membrane biosynthesis genes to regulate nuclear membrane morphology. In addition, phenotypic analyses showed that the phosphatase cascade Nem1/Spo7-Pah1 was involved in regulating mycelial growth, asexual development, stress responses, and virulence of B. dothidea. IMPORTANCE Botryosphaeria canker and fruit rot caused by the fungus Botryosphaeria dothidea is one of the most destructive diseases of apple worldwide. Our data indicated that the phosphatase cascade Nem1/Spo7-Pah1 plays important roles in the regulation of fungal growth, development, lipid homeostasis, environmental stress responses, and virulence in B. dothidea. The findings will contribute to the in-depth and comprehensive understanding of Nem1/Spo7-Pah1 in fungi and the development of target-based fungicides for disease management.

Plant-Fungi Interactions: Where It Goes?

Fungi live different lifestyles-including pathogenic and symbiotic-by interacting with living plants. Recently, there has been a substantial increase in the study of phytopathogenic fungi and their interactions with plants. Symbiotic relationships with plants appear to be lagging behind, although progressive. Phytopathogenic fungi cause diseases in plants and put pressure on survival. Plants fight back against such pathogens through complicated self-defense mechanisms. However, phytopathogenic fungi develop virulent responses to overcome plant defense reactions, thus continuing their deteriorative impacts. Symbiotic relationships positively influence both plants and fungi. More interestingly, they also help plants protect themselves from pathogens. In light of the nonstop discovery of novel fungi and their strains, it is imperative to pay more attention to plant-fungi interactions. Both plants and fungi are responsive to environmental changes, therefore construction of their interaction effects has emerged as a new field of study. In this review, we first attempt to highlight the evolutionary aspect of plant-fungi interactions, then the mechanism of plants to avoid the negative impact of pathogenic fungi, and fungal strategies to overcome the plant defensive responses once they have been invaded, and finally the changes of such interactions under the different environmental conditions.

Molecular characterization of a novel ourmia‑like virus from the phytopathogenic fungus Botryosphaeria dothidea

Here, we describe a novel ourmia-like virus, Botryosphaeria dothidea ourmia-like virus 2 (BdOLV2), derived from the phytopathogenic fungus Botryosphaeria dothidea strain ZM180192-1 infecting maize in Henan province of China. The complete genome sequence of BdOLV2 consists of a positive-sense single-stranded RNA (+ ssRNA) segment with a length of 2,532 nucleotides (nt). The sequence contains a large open reading frame (ORF) encoding a putative RNA-dependent RNA polymerase (RdRp) consisting of 605 amino acids (aa) with a molecular mass of 68.59 kDa. This RdRp protein contains eight typical conserved motifs associated with ourmia-like viruses. BLASTp analysis revealed that the RdRp protein of BdOLV2 had the highest similarity (62.10%, 58.15%, and 55.75% identity, respectively) to a virus previously identified as "Botourmiaviridae sp.", Macrophomina phaseolina ourmia-like virus 2, and Macrophomina phaseolina ourmia-like virus 2-A. Phylogenetic analysis based on the RdRp aa sequence indicated that BdOLV2 is a new member of the genus Magoulivirus in the family Botourmiaviridae.

Identification and pathogenicity of six fungal species causing canker and dieback disease on golden rain tree in Beijing, China

Golden rain trees (Koelreuteria paniculata) are largely cultivated because of their important ornamental, medicinal, and economic value. However, they are affected by canker and dieback disease to a large extent. To determine the fungi associated with canker and dieback disease of golden rain trees, isolations were obtained from diseased branches and twigs during 2019 and 2020 in greenbelts and nurseries in Beijing, China. Isolates were identified as six species (Allocryptovalsa castaneicola, Botryosphaeria dothidea, Cytospora koelreutericola sp. nov., Dothiorella acericola, Eutypella citricola, and Peroneutypa scoparia) based on morphological features and phylogenetic analyses of ITS, act, rpb2, tef1-α, and tub2. The results of pathogenicity tests indicated that all fungi produced discoloration and Botryosphaeria dothidea was highly aggressive to golden rain tree. In conclusion, this study explored the taxonomy, phylogeny, and pathogenicity of different fungal species associated with canker and dieback disease on golden rain tree and provided fundamental knowledge to improve disease management.

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.

First Report of Botryosphaeria dothidea Causing Stem Blight of Dioscorea oppositifolia in China

Dioscorea oppositifolia Thunb. (Chinese yam) is one of the traditional foods and medicinal plants in China. It has nutritional and medicinal value and plays an important role in treatment of diabetes and hypertension. In 2018, stem blight was first observed on the stalks of D. oppositifolia in fields of Anguo City (115°27' N; 38°46' E), Hebei Province, China. Over 400 plants were surveyed in four fields, and nearly 30% of the plants were infected. At the initial stage of the disease, there were dark brown spots on the stems and in later stages the leaves and stems withered. To identify the pathogen, 10 symptomatic stalks were collected, and one diseased area was taken out from each sample. Small square stalk pieces (3 to 5 mm) were obtained with sterile scissors from the junction of infected and healthy tissues, sterilized with sodium hypochlorite (10%) for 1 min, followed by washing in sterile water three times, then pieces were transferred to potato dextrose agar (PDA) plates for 7 days at 25°C. The fungal isolates were purified by single-spore isolation. A total of three species of fungi were isolated, and initial pathogenicity tests found that one fungal species could cause the disease symptoms on D. oppositifolia stems. This pathogen was grown on PDA plates in the dark at 25 °C for 10 days. In the beginning, the colonies were white, and as the culture time was extended, the color of the colonies became darker and then became black. Conidia forming on pycnidia were one-celled, hyaline, aseptate, and ovoid, with dimensions of 4.6 to 7.6 × 2.6 to 4.8 μm (n=100). Mycelial DNA was extracted from a 7-day-old culture, and PCR amplifications were performed using primers ITS1/ITS4 and β-tubF/β-tubR (Glass and Donaldson 1995; White et al. 1990). BLAST searches at GenBank showed 100.00% nucleotide sequence identity for the ITS sequence with Botryosphaeria dothidea strain sdxf6 (MG282093; 545/545 bp) and for β-tubulin 99.76% identity with B. dothidea strain SD-B8 (KP183131; 411/412 bp). Sequences from these regions were deposited in GenBank (ITS: OP104323; β-tubulin: OK669147). Morphological and molecular results confirmed this species as B. dothidea (Angelica et al. 2017; Bernard et al. 2004). To inoculate plants, pathogen was grown on PDA at 25°C in the dark for 15 days, after which a spore suspension (3×105 spores/mL) was prepared by flooding the agar surface with sterilized double-distilled water. Pathogenicity tests were conducted by stem inoculation of 6-month-old healthy D. oppositifolia plants. The stems were wounded by lightly rubbing with a steel sponge, and the wounded stem was wrapped in sterile cotton treated with 1 mL of the spore suspension, then the plants were covered with plastic to maintain a moist environment for 72 h. Control plants were inoculated with sterile water. Inoculated and control plants (ten each) were kept in a moist chamber (25°C, 16-h light and 8-h dark period, 75% relative humidity). After 15 days, all of the inoculated plants showed dark brown spots on the stems, and the symptoms were the same as those in the field, while the controls were healthy. After 30 days, all of the inoculated but none of the control D. oppositifolia plants showed leaf wilting or leaf withering. Isolates from the inoculated and infected leaves were identified as B. dothidea by DNA sequencing with primers ITS1/ITS4 and β-tubF/β-tubR, fulfilling Koch's postulates. To our knowledge, this is the first report of B. dothidea causing stem blight on D. oppositifolia. The disease poses a threat to the production of D. oppositifolia, and management strategies need to be developed.

Lasiodiplodia iraniensis, a New Causal Agent of Tuber Rot on Yam (Dioscorea Species) Imported into the United States and Implications for Quarantine Decisions

One negative consequence of international trade of agricultural commodities is the inadvertent global spread of crop diseases. Yam (Dioscorea spp.) is a staple food crop in many countries and is traded globally. Most of the commercially traded yams in the United States are imported. In late 2020, samples of yam tubers from a commercial facility were submitted to the plant diagnostic clinic at the UF/IFAS Tropical Research and Education Center in Homestead, Florida. Samples showed rotten symptoms and were drawn from lots that were marked to be destroyed because the source of the rotting symptoms was unknown. Preliminary isolation showed that a fungus was consistently associated with the symptoms and was confirmed in the subsequent pathogenicity test as the causal agent. The fungus grew profusely on potato dextrose agar (PDA) with highly melanized hyphae. Matured conidia showed longitudinal striations. Based on its growth pattern and morphology, it was suspected that this fungus may be in the genus Lasiodiplodia. DNA-based identification using partial sequences of the internal transcribed spacer (ITS), β-tubulin (TUB2), 28S rDNA (LSU), and elongation factor alpha (EF1-α) genes confirmed the identity of the isolates as Lasiodiplodia iraniensis Abdollahz., Zare & A.J.L. Phillips (synonym: L. iranensis). This is the first report of L. iraniensis affecting yam and has implications for international trade. This finding will provide an important foundation for making quarantine decisions to prevent spread of this disease.

The chromosome-scale genome of Phoebe bournei reveals contrasting fates of terpene synthase (TPS)-a and TPS-b subfamilies

Terpenoids, including aromatic volatile monoterpenoids and sesquiterpenoids, function in defense against pathogens and herbivores. Phoebe trees are remarkable for their scented wood and decay resistance. Unlike other Lauraceae species investigated to date, Phoebe species predominantly accumulate sesquiterpenoids instead of monoterpenoids. Limited genomic data restrict the elucidation of terpenoid variation and functions. Here, we present a chromosome-scale genome assembly of a Lauraceae tree, Phoebe bournei, and identify 72 full-length terpene synthase (TPS) genes. Genome-level comparison shows pervasive lineage-specific duplication and contraction of TPS subfamilies, which have contributed to the extreme terpenoid variation within Lauraceae species. Although the TPS-a and TPS-b subfamilies were both expanded via tandem duplication in P. bournei, more TPS-a copies were retained and constitutively expressed, whereas more TPS-b copies were lost. The TPS-a genes on chromosome 8 functionally diverged to synthesize eight highly accumulated sesquiterpenes in P. bournei. The essential oil of P. bournei and its main component, β-caryophyllene, exhibited antifungal activities against the three most widespread canker pathogens of trees. The TPS-a and TPS-b subfamilies have experienced contrasting fates over the evolution of P. bournei. The abundant sesquiterpenoids produced by TPS-a proteins contribute to the excellent pathogen resistance of P. bournei trees. Overall, this study sheds light on the evolution and adaptation of terpenoids in Lauraceae and provides valuable resources for boosting plant immunity against pathogens in various trees and crops.

Two new Botryosphaeria (Botryosphaeriales, Botryosphaeriaceae) species in China

Five ascomycetous strains were isolated from dead branches and leaves of Salix (Salicaceae) and Osmanthusfragrans (Oleaceae), respectively. BLAST searches with ITS sequences in GenBank suggested a high degree of similarity to Botryosphaeriadothidea. To accurately identify these strains, we further analysed their morphological characteristics of asci, ascospores, all conidiophore cells and conidia. Phylogenetic relationships, based on ITS, rpb2, tef1 and tub2 gene sequences, confirmed our strains represented two novel species, which are introduced here as B.salicicola and B.osmanthuse spp. nov.

Reduced Sensitivity to Tebuconazole in Botryosphaeria dothidea Isolates Collected from Major Apple Production Areas of China

China has the largest acreage and is the greatest producer of apples in the world. Apple ring rot (ARR) caused by Botryosphaeria dothidea is one of the major diseases affecting apple fruit production. Tebuconazole, a sterol demethylation-inhibiting (DMI) fungicide, has been increasingly applied to manage ARR in China. Resistance to tebuconazole in field populations of B. dothidea may be selected and accumulate to higher degrees over time. Establishment of tebuconazole sensitivity monitoring programs is critically important for resistance management and effective ARR control. However, the resistance level of B. dothidea to tebuconazole in China remains largely unknown. In this study, in vitro mycelial growth assays of B. dothidea in media amended with tebuconazole were conducted, and the sensitivity of B. dothidea to tebuconazole was determined with a set of 390 isolates collected from the major apple production provinces in China between 2006 and 2014. Results showed that the 50% effective concentration (EC₅₀) value ranged from 0.011 to 0.918, 0.040 to 1.621, and 0.052 to 1.925 μg ml^-1 with a median value of 0.194, 0.386, and 0.782 μg ml^-1 in the isolates collected in 2006, 2010, and 2014, respectively. The frequency distribution of EC₅₀ for tebuconazole was a nonnormal distribution (P < 0.05), suggesting that subpopulations with reduced sensitivity to tebuconazole had emerged in these B. dothidea isolates. The frequency distribution of the B. dothidea isolates collected in 2006 fit a unimodal curve and could be regarded as the baseline sensitivity to tebuconazole. The resistance levels increased over time with the average occurrence frequency of 43.3% and resistance index of 0.38. Positive cross-resistance was observed between tebuconazole and metconazole, which is another DMI fungicide, but multiple resistance was not detected between tebuconazole and non-DMI fungicides. Our results demonstrated that regular long-term resistance monitoring combining with prudent fungicide use should be implemented to prolong the lifespan of tebuconazole in management of ARR in apples.

Stem canker pathogen Botryosphaeria dothidea inhibits poplar leaf photosynthesis in the early stage of inoculation

Fungal pathogens can induce canker lesions, wilting, and even dieback in many species. Trees can suffer serious physiological effects from stem cankers. In this study, we investigated the effects of Botryosphaeria dothidea (B. dothidea) on Populus bolleana (P. bolleana) leaves photosynthesis and stomatal responses, when stems were inoculated with the pathogen. To provide experimental and theoretical basis for preventing poplar canker early. One-year-old poplar stems were inoculated with B. dothidea using an epidermal scraping method. In the early stage of B. dothidea inoculation (2-14 days post inoculation, dpi), the gas exchange, stomatal dynamics, hormone content, photosynthetic pigments content, chlorophyll fluorescence parameters, and non-structural carbohydrate (NSC) were evaluated to elucidate the pathophysiological mechanism of B. dothidea inhibiting photosynthesis. Compared with the control groups, B. dothidea noteworthily inhibited the net photosynthetic rate (P _n), stomatal conductance (G _s), intercellular CO₂ concentration (C _i), transpiration rate (T _r), and other photosynthetic parameters of poplar leaves, but stomatal limit value (L _s) increased. Consistent with the above results, B. dothidea also reduced stomatal aperture and stomatal opening rate. In addition, B. dothidea not only remarkably reduced the content of photosynthetic pigments, but also decreased the maximum photochemical efficiency (F _v/F _m), actual photochemical efficiency (Φ _PSII), electron transfer efficiency (ETR), and photochemical quenching coefficient (q _P). Furthermore, both chlorophyll and Φ _PSII were positively correlated with P _n. In summary, the main reason for the abated P _n under stem canker pathogen was that B. dothidea not merely inhibited the stomatal opening, but hindered the conversion of light energy, electron transfer and light energy utilization of poplar leaves. In general, the lessened CO₂ and P _n would reduce the synthesis of photosynthetic products. Whereas, sucrose and starch accumulated in poplar leaves, which may be due to the local damage caused by B. dothidea inoculation in phloem, hindering downward transport of these products.

Molecular characterization of a new fusarivirus infecting Botryosphaeria dothidea, the causal agent of pear ring rot disease

Here, a novel mycovirus, tentatively designated as "Botryosphaeria dothidea fusarivirus 2" (BdFV2), was discovered in Botryosphaeria dothidea strain JZ-3. The complete genome sequence is 6,271 nucleotides (nt) in length, excluding the poly(A) tail, and contains two putative open reading frames (ORFs). The larger ORF1 encodes a polypeptide of 1,552 amino acids (aa) with conserved RNA-dependent RNA polymerase (RdRp) domains and a viral helicase domain. The ORF1-encoded polypeptide shares 19.47-78.70% sequence identity with those of other fusariviruses and shares the highest sequence identity (78.70%) with the corresponding protein aa sequences of Neofusicoccum luteum fusarivirus 1 (NlFV1) isolate CBS110299. The small ORF2 encodes a hypothetical protein with 479 aa, which is predicted to contain a chromosome segregation protein SMC domain of unknown function. Sequence alignments and phylogenetic analysis indicated that BdFV2 is a distinct member of the recently established family Fusariviridae. BdFV2 appears to be a novel fusarivirus infecting a pathogenic B. dothidea strain that causes pear ring rot disease.

Effects of Temperature on Development of Canker-Causing Pathogens in Almond and Prune

Between 2000 and 2020, canker diseases of nut and stone fruit trees have become very widespread and severe in California. This study determined the effects of temperature on the development of canker-causing pathogens of almond and prune. Five pathogen taxa, Botryosphaeria dothidea, Cytospora leucostoma, Diaporthe (Phomopsis) neotheicola, Lasiodiplodia citricola, and Neofusicoccum mediterraneum, were used. Colony growth on medium and canker lesion development on detached shoots were measured at 10, 15, 20, 25, 30, and 35°C. The effects of temperature on colony growth differed among different pathogen taxa, although 25°C was the optimal temperature for most of the pathogens tested. The patterns of lesion growth as response to temperature were different among the different pathogens and tree crops. On almond, the highest growth rates appeared at 30°C for B. dothidea and L. citricola, but at 20°C for N. mediterraneum. The growth rates for C. leucostoma were lower than those of the other three pathogen taxa, with the highest rates recorded at 25°C. However, on prune, C. leucostoma showed greater lesion growth rates at different temperatures than the other pathogen taxa and maximum growth at 30 to 35°C. Similar trends were observed for L. citricola. The growth rates of B. dothidea and N. mediterraneum were comparatively lower than those of C. leucostoma and L. citricola.

Involvement of the Autophagy Protein Atg1 in Development and Virulence in Botryosphaeria dothidea

Botryosphaeria canker and fruit rot caused by the fungus Botryosphaeria dothidea is one of the most destructive diseases of apple worldwide. Autophagy is an evolutionarily conserved self-degradation process that is important for maintaining homeostasis to ensure cellular functionality. To date, the role of autophagy in B. dothidea is not well elucidated. In this study, we identified and characterized the autophagy-related protein Atg1 in B. dothidea. The BdAtg1 deletion mutant ΔBdAtg1 showed autophagy blockade and phenotypic defects in mycelial growth, conidiation, ascosporulation and virulence. In addition, ΔBdAtg1 exhibited an increased number of nuclei in the mycelial compartment. Comparative transcriptome analysis revealed that inactivation of BdAtg1 significantly influenced multiple metabolic pathways. Taken together, our results indicate that BdAtg1 plays an important role in vegetative differentiation and the pathogenicity of B. dothidea. The results of this study will provide a reference for the development of new target-based fungicides.

Pathogenicity Factors of Botryosphaeriaceae Associated with Grapevine Trunk Diseases: New Developments on Their Action on Grapevine Defense Responses

Botryosphaeriaceae are a family of fungi associated with the decay of a large number of woody plants with economic importance and causing particularly great losses in viticulture due to grapevine trunk diseases. In recent years, major advances in the knowledge of the pathogenicity factors of these pathogens have been made possible by the development of next-generation sequencing. This review highlights the knowledge gained on genes encoding small secreted proteins such as effectors, carbohydrate-associated enzymes, transporters and genes associated with secondary metabolism, their representativeness within the Botryosphaeriaceae family and their expression during grapevine infection. These pathogenicity factors are particularly expressed during host-pathogen interactions, facilitating fungal development and nutrition, wood colonization, as well as manipulating defense pathways and inducing impacts at the cellular level and phytotoxicity. This work highlights the need for further research to continue the effort to elucidate the pathogenicity mechanisms of this family of fungi infecting grapevine in order to improve the development of control methods and varietal resistance and to reduce the development and the effects of the disease on grapevine harvest quality and yield.

Molecular characterization of a novel victorivirus isolated from Botryosphaeria dothidea, the causal agent of longan leaf spot disease

Mycoviruses are widespread in all major taxonomic groups of filamentous fungi. Previous research has indicated that mycoviruses are associated with the phytopathogenic fungus Botryosphaeria dothidea. In this study, three distinct double-stranded RNA viruses were detected in B. dothidea strain YCLYY11 isolated from a leaf spot of longan (Dimocarpus longana). The results of BLAST analysis revealed that the predicted amino acid sequences of those viruses were similar to those of Botryosphaeria dothidea chrysovirus 1, Botryosphaeria dothidea partitivirus 1, and an apparent novel victorivirus. Sequencing and analysis of the complete genome of the novel victorivirus indicated it is 5218 bp in length and contains two open reading frames (ORFs) that overlap at the tetranucleotide AUGA. BLASTp analysis of the proteins encoded by ORF1 and ORF2 showed that they were most similar to the coat protein and RNA-dependent RNA polymerase of Sphaeropsis sapinea RNA virus 2 (81.37% and 74.09% identical, respectively). A phylogenetic tree showed that the novel virus clustered together with victoriviruses and was separate from members of the other four genera of the family Totiviridae. Based on its genome structure and the results of phylogenetic analysis, we propose that this novel victorivirus should be named "Botryosphaeria dothidea victorivirus 3". This is also the first report of these three mycoviruses coinfecting a strain of B. dothidea.

The Effect of Temperature and Moisture on Colonization of Apple Fruit and Branches by Botryosphaeria dothidea

Botryosphaeria dothidea causes severe disease of apple trees in China. The process of conidium germination, colonization, and infection of apple fruit and branches was examined on 'Fuji' apple and the effect of temperature, surface wetness and relative humidity (RH), and host surface washates on these processes was studied in controlled environments. Initial germ tube development and hyphal growth resulted in the colonization of the host surface without forming an infection structure. Hyphae expanded radially across the host surface and, after entering lenticels, developed into a dense mycelium mass or differentiated pseudoparenchyma. Hyphae from the bottom of the pseudoparenchyma either directly penetrated the lenticel surface intercellularly through the cell layer, or formed an undifferentiated hypha that invaded the lenticel through cracks formed during the lenticel development. Conidial germination and hyphal colonization occurred at 10 to 40°C, with an optimum of approximately 28°C. Conidial germination required an RH > 95% or surface wetness but, for hyphal colonization, an RH > 90% was sufficient. Conidia germinated and formed germ tubes within 1 h under optimum conditions. However, the pathogen required a longer period at RH > 90% or surface wetness for hyphae to colonize and form pseudoparenchyma or dense mycelia on the host surface. Hyphal colonization is a crucial stage for infection of apple tissues by B. dothidea.

Stilbocrea banihashemiana sp. nov. a New Fungal Pathogen Causing Stem Cankers and Twig Dieback of Fruit Trees

Stem cankers and twig dieback were the most serious disease of fig (Ficus carica) and loquat (Eriobotrya japonica) noticed in a survey of fruit tree orchards in the Fars Province, Iran. Isolates of Bionectriaceae were consistently recovered from symptomatic fig and loquat trees. Phylogenetic analyses of multiple nuclear loci, internal transcribed spacer regions (ITS) of rDNA, RNA polymerase II subunit 2 (rpb2), and translation elongation factor 1-α (tef1), combined with morphological observations, revealed that isolates could be referred to a still unknown taxon, which was formally described as Stilbocrea banihashemiana sp. nov. Phylogenetically, isolates from fig and loquat trees clustered in a well-supported monophyletic group within the Stilbocrea clade of Bionectriaceae, closely related to S. walteri. Stilbocrea banihashemiana sp. nov. was characterized by the lack of stilbella-like asexual structure in both natural substrates and pure cultures and produced two morphologically distinct types of conidia, globose and cylindrical, formed on short and long simple phialides. In pathogenicity tests, S. banihashemiana sp. nov. induced stem cankers in both fig and loquat, wood discoloration in fig and twig dieback in loquat. Pathogenicity tests also showed that the potential host range of this novel pathogen includes other economically relevant horticultural trees.

Identification of the Pathogens and Laboratory Bioactivity Determination of the Rot Disease of Kiwifruit (Actinidia spp.)

Kiwifruit is an important economic crop in the world today with a high nutritional value. It can cause huge damage by causing kiwifruit rot disease; however, at present, the control methods for this disease are limited. In this study, the rotten fruits of kiwifruit (Cultivar “Jinyan”) were collected from Pujiang city (Sichuan province), Xixia city, (Henan province), Zhouzhi (Shaanxi province), Meixian city (Shaanxi province), and Bijie (Guizhou province), China, and the pathogenic fungi were identified by isolation and purification, pathogenicity test, morphological characteristics, and analysis of ribosomal DNA internal transcribed spacer (rDNA-ITS) sequences. The results showed that the pathogenic fungi of kiwifruit rot disease were Botryosphaeria dothidea and Dothiorella gregaria. Meanwhile, the in vitro antifungal activity of 11 kinds of fungicides and 5 kinds of plant essential oils against B. dothidea and D. gregaria were determined and the results showed that all the tested fungicides and plant essential oils had a certain inhibitory effect on B. dothidea and D. gregaria. Among them, propiconazole had the best inhibitory effect on B. dothidea with an EC50 value of 4.10 mg/L, and quinolinone had the best inhibitory effect on D. gregaria with the EC50 value of 10.05 mg/L. Moreover, the pesticides and essential oils have practical application values for prevention and treatment of fruit rot diseases pathogens.

MicroRNA candidate miRcand137 in apple is induced by Botryosphaeria dothidea for impairing host defense

MicroRNA (miRNA)-mediated gene silencing is a master gene regulatory pathway in plant-pathogen interactions. The differential accumulation of miRNAs among plant varieties alters the expression of target genes, affecting plant defense responses and causing resistance differences among varieties. Botryosphaeria dothidea is an important phytopathogenic fungus of apple (Malus domestica). Malus hupehensis (Pamp.) Rehder, a wild apple species, is highly resistant, whereas the apple cultivar "Fuji" is highly susceptible. Here, we identified a 22-nt miRNA candidate named miRcand137 that compromises host resistance to B. dothidea infection and whose processing was affected by precursor sequence variation between M. hupehensis and "Fuji." miRcand137 guides the direct cleavage of and produced target-derived secondary siRNA against Ethylene response factor 14 (ERF14), a transcriptional activator of pathogenesis-related homologs that confers disease resistance to apple. We showed that miRcand137 acts as an inhibitor of apple immunity by compromising ERF14-mediated anti-fungal defense and revealed a negative association between miRcand137 expression and B. dothidea sensitivity in both resistant and susceptible apples. Furthermore, MIRCAND137 was transcriptionally activated by the invading fungi but not by the fungal elicitor, implying B. dothidea induced host miRcand137 as an infection strategy. We propose that the inefficient miRcand137 processing in M. hupehensis decreased pathogen-initiated miRcand137 accumulation, leading to higher resistance against B. dothidea.

Grapevine trunk diseases of cold-hardy varieties grown in Northern Midwest vineyards coincide with canker fungi and winter injury

Grapevine trunk diseases make up a disease complex associated with several vascular fungal pathogenic species. Surveys to characterize the composition of grapevine trunk diseases have been conducted for most major grape growing regions of the world. This study presents a similar survey characterizing the fungi associated with grapevine trunk diseases of cold-hardy interspecific hybrid grape varieties grown nearly exclusively in the atypical harsh winter climate of Northern Midwestern United states vineyards. From the 172 samples collected in 2019, 640 isolates obtained by culturing were identified by ITS sequencing and represent 420 sample-unique taxa. From the 420 representative taxa, opportunistic fungi of the order Diaporthales including species of Cytospora and Diaporthe were most frequently identified. Species of Phaeoacremonium, Paraconiothyrium, and Cadophora were also prevalent. In other milder Mediterranean growing climates, species of Xylariales and Botryosphaeriales are often frequently isolated but in this study they were isolated in small numbers. No Phaeomoniellales taxa were isolated. We discuss the possible compounding effects of winter injury, the pathogens isolated, and management strategies. Additionally, difficulties in researching and understanding the grapevine trunk disease complex are discussed.

A Secreted Lignin Peroxidase Required for Fungal Growth and Virulence and Related to Plant Immune Response

Botryosphaeria spp. are important phytopathogenic fungi that infect a wide range of woody plants, resulting in big losses worldwide each year. However, their pathogenetic mechanisms and the related virulence factors are rarely addressed. In this study, seven lignin peroxidase (LiP) paralogs were detected in Botryosphaeria kuwatsukai, named BkLiP1 to BkLiP7, respectively, while only BkLiP1 was identified as responsible for the vegetative growth and virulence of B. kuwatsukai as assessed in combination with knock-out, complementation, and overexpression approaches. Moreover, BkLiP1, with the aid of a signal peptide (SP), is translocated onto the cell wall of B. kuwatsukai and secreted into the apoplast space of plant cells as expressed in the leaves of Nicotiana benthamiana, which can behave as a microbe-associated molecular pattern (MAMP) to trigger the defense response of plants, including cell death, reactive oxygen species (ROS) burst, callose deposition, and immunity-related genes up-regulated. It supports the conclusion that BkLiP1 plays an important role in the virulence and vegetative growth of B. kuwatsukai and alternatively behaves as an MAMP to induce plant cell death used for the fungal version, which contributes to a better understanding of the pathogenetic mechanism of Botryosphaeria fungi.

Giant Starship Elements Mobilize Accessory Genes in Fungal Genomes

Accessory genes are variably present among members of a species and are a reservoir of adaptive functions. In bacteria, differences in gene distributions among individuals largely result from mobile elements that acquire and disperse accessory genes as cargo. In contrast, the impact of cargo-carrying elements on eukaryotic evolution remains largely unknown. Here, we show that variation in genome content within multiple fungal species is facilitated by Starships, a newly discovered group of massive mobile elements that are 110 kb long on average, share conserved components, and carry diverse arrays of accessory genes. We identified hundreds of Starship-like regions across every major class of filamentous Ascomycetes, including 28 distinct Starships that range from 27 to 393 kb and last shared a common ancestor ca. 400 Ma. Using new long-read assemblies of the plant pathogen Macrophomina phaseolina, we characterize four additional Starships whose activities contribute to standing variation in genome structure and content. One of these elements, Voyager, inserts into 5S rDNA and contains a candidate virulence factor whose increasing copy number has contrasting associations with pathogenic and saprophytic growth, suggesting Voyager's activity underlies an ecological trade-off. We propose that Starships are eukaryotic analogs of bacterial integrative and conjugative elements based on parallels between their conserved components and may therefore represent the first dedicated agents of active gene transfer in eukaryotes. Our results suggest that Starships have shaped the content and structure of fungal genomes for millions of years and reveal a new concerted route for evolution throughout an entire eukaryotic phylum.

The hidden world within plants: metatranscriptomics unveils the complexity of wood microbiomes

The importance of plants as complex entities influenced by genomes of the associated microorganisms is now seen as a new source of variability for a more sustainable agriculture, also in the light of ongoing climate change. For this reason, we investigated through metatranscriptomics whether the taxa profile and behaviour of microbial communities associated with the wood of 20-year-old grapevine plants are influenced by the health status of the host. We report for the first time a metatranscriptome from a complex tissue in a real environment, highlighting that this approach is able to define the microbial community better than referenced transcriptomic approaches. In parallel, the use of total RNA enabled the identification of bacterial taxa in healthy samples that, once isolated from the original wood tissue, displayed potential biocontrol activities against a wood-degrading fungal taxon. Furthermore, we revealed an unprecedented high number of new viral entities (~120 new viral species among 180 identified) associated with a single and limited environment and with potential impact on the whole holobiont. Taken together, our results suggest a complex multitrophic interaction in which the viral community also plays a crucial role in raising new ecological questions for the exploitation of microbial-assisted sustainable agriculture.

A New Disease for Europe of Ficus microcarpa Caused by Botryosphaeriaceae Species

The Indian laurel-leaf fig (Ficus microcarpa) is an important ornamental tree widely distributed in the urban areas of Italy. Surveys conducted in 2019 and 2020 on several tree-lined streets, squares, and public parks in Catania and Siracusa provinces (Sicily, southern Italy) revealed the presence of a new disease on mature trees. About 9% of approximately 450 mature plants showed extensive branch cankers and dieback. Isolations from woody tissues obtained from ten symptomatic plants consistently yielded species belonging to the Botryosphaeriaceae family. The identification of the recovered fungal isolates was based on a multi-loci phylogenetic (maximum parsimony and maximum likelihood) approach of the ITS, tef1-α, and tub2 gene regions. The results of the analyses confirmed the presence of three species: Botryosphaeria dothidea, Neofusicoccum mediterraneum, and N. parvum. Pathogenicity tests were conducted on potted, healthy, 4-year-old trees using the mycelial plug technique. The inoculation experiments revealed that all the Botryosphaeriaceae species identified in this study were pathogenic to this host. Previous studies conducted in California showed similar disease caused by Botryosphaeriaceae spp., and the pathogenic role of these fungi was demonstrated. To our knowledge, this is the first report of Botryosphaeriaceae affecting Ficus microcarpa in Europe.