Woody Hosts Research Articles

Selection of host plants for vector transmission assays of citrus variegated chlorosis strains of Xylella fastidiosa subsp. pauca

The vector-borne bacterium Xylella fastidiosa subsp. pauca is the etiological agent of important plant diseases, such as citrus variegated chlorosis (CVC). Biological studies are relatively scarce for CVC, in part because citrus is a low titer woody host, in which X. fastidiosa has a long incubation period and low transmission efficiency by vectors. To optimize transmission bioassays, this study was conducted to: i) identify herbaceous plants that allow rapid multiplication and systemic colonization of CVC strains; and ii) evaluate the herbaceous hosts for feeding and survival of the sharpshooter vector, Bucephalogonia xanthophis (Berg), and as indicators of infection after vector inoculation. Mechanical inoculations showed systemic colonization of X. fastidiosa in seven plant species, with higher rates of infection mainly in Catharanthus roseus. The lowest vector mortality was observed on C. roseus, Medicago sativa and Ocimum basilicum. The highest feeding rate was verified on O. basilicum, followed by M. sativa and C. roseus. Infections after vector inoculation were detected in C. roseus, M. sativa, O. basilicum and S. americanum. Among the plant species tested, C. roseus proved to be the most suitable experimental plant for transmission assays with CVC strains of X. fastidiosa subsp. pauca.

The fungal community associated with the ambrosia beetle Xylosandrus compactus invading the mediterranean maquis in central Italy reveals high biodiversity and suggests environmental acquisitions

In summer 2016 a severe infestation of the alien ambrosia beetle Xylosandrus compactus was recorded from the Mediterranean maquis in the Circeo National Park in Central Italy. Trees and shrubs were infested and displayed wilting and necrosis of terminal branches caused by the combined impact of the insect and associated pathogenic fungi. A preliminary screening carried out on captured adults resulted in the isolation of a discrete number of fungal taxa with different life strategies, ranging from true mutualist (e.g. Ambrosiella xylebori) to plant pathogens (Fusarium spp.). In the present study, high-throughput sequencing was applied to determine the total diversity and functionality of the fungal community associated with X. compactus adults collected in the galleries of three Mediterranean woody hosts, Quercus ilex, Laurus nobilis, and Ceratonia siliqua. The effect of season and host in determining the composition of the associated fungal community was investigated. A total of 206 OTUs composed the fungal community associated with X. compactus. Eighteen OTUs were shared among the three hosts, including A. xylebori and members of the Fusarium solani complex. All but two were previously associated with beetles.Sixty-nine out of 206 OTUs were resolved to species level, identifying 60 different fungal species, 22 of which already reported in the literature as associated with beetles or other insects. Functional guild assigned most of the fungal species to saprotrophs and plant pathogens. Effects of seasonality and host on fungal community assemblage were highlighted suggesting the acquisition by the insect of new fungal taxa during the invasion process. The consequences of enriched fungal community on the risk of the insurgence of novel threatful insect–fungus association are discussed considering direct and indirect effects on the invaded habitat.

Transcriptomic analysis reveals insights into the response to Hop stunt viroid (HSVd) in sweet cherry (Prunus avium L.) fruits.

Hop stunt viroid (HSVd) is a member of the genus Hostuviroid of the family Pospiviroidae and has been found in a wide range of herbaceous and woody hosts. It causes serious dapple fruit symptoms on infected sweet cherry, notably inducing cherry tree decay. In order to better understand the molecular mechanisms of HSVd infection in sweet cherry fruit, transcriptome analysis of HSVd-infected and healthy sweet cherry fruits was carried out. A total of 1,572 differentially expressed genes (DEGs) were identified, involving 961 upregulated DEGs and 611 downregulated DEGs. Functional analysis indicated that the DEGs were mainly involved in plant hormone signal transduction, plant–pathogen interactions, secondary metabolism, and the MAPK signaling pathway. In addition, C2H2 zinc finger, MYB, bHLH, AP2/ERF, C2C2-dof, NAC and WRKY transcription factors can respond to HSVd infection. In order to confirm the high-throughput sequencing results, 16 DEGs were verified by RT-qPCR analysis. The results provided insight into the pathways and genes of sweet cherry fruit in response to HSVd infection.

Botryosphaeriaceae species on forest trees in Portugal: diversity, distribution and pathogenicity

Fungi in the family Botryosphaeriaceae are known as pathogens of diverse woody hosts, including forest tree species. Although, several of these fungi have been described in different forest hosts in Portugal, their diversity and distribution is still poorly understood. A survey was conducted across the country to identify Botryosphaeriaceae species associated with the main forest tree species in Portugal, Quercus suber, Eucalyptus globulus and Pinus pinaster. Additionally, a meta-analysis was performed to compile and organize all records known from Portugal. From this meta-analysis, 22 different Botryosphaeriaceae species were reported and 40 different plant hosts were recorded in several studies from agricultural crops to ornamental and forest species. A total of 105 host-pathogen interactions were identified. In the national survey, 12 Botryosphaeriaceae species were identified, with Diplodia corticola being the most frequent. Diplodia insularis, Diplodia pyri, Dothiorella plurivora and Dothiorella yunnana are reported for the first time in Portugal. Of the 23 different host-fungus associations identified, 10 are also recognised as new hosts. Artificial inoculation tests confirmed the pathogenicity of all species, except Dothiorella iberica, Dothiorella plurivora and Dothiorella yunnana, which are regarded as weakly or non-pathogenic to the hosts tested. Pathogenicity tests revealed the host-jump potential of some species, showing high susceptibility of Q. suber to Neofusicoccum parvum and N. eucalyptorum and of P. pinaster to D. corticola. Our results show that Botryosphaeriaceae species have a widespread distribution across the country, however some species such as D. corticola, D. sapinea and N. eucalyptorum exhibit a distribution that overlaps the distribution of their preferred hosts.

Cutting mechanics of wood by beetle larval mandibles

Wood boring is a feature of several insect species and is a major cause of severe and irreparable damage to trees. Adult females typically deposit their eggs on the stem surface under bark scales. The emerging hatchlings live within wood during their larval phase, avoiding possible predation, whilst continually boring and tunneling through wood until pupation. A study of wood boring by insects offers unique insights into the bioengineering principles that drive evolutionary adaptations. We show that larval mandibles of the coffee wood stem borer beetle (Xylotrechus quadripes: Cerambycidae) have a highly sharp cusp edge to initiate fractures in Arabica wood and a suitable shape to generate small wood chips that are suitable for digestion. Cuticle hardness at the tip is significantly enhanced through zinc-enrichment. A hollow architecture significantly reduces bending stresses at the mandibular base without compromising the structural integrity. Finite element model of the mandible showed highest stresses in the tip region; these decreased to significantly lower values at the start of the hollow section. A scaling model based on a fracture mechanics framework shows the importance of the mandible shape in generating optimal chip sizes. These findings contain general principles in tool design and put in focus interactions of insects and their woody hosts.

<p><strong>Additions to Karst Fungi 4:<em> Botryosphaeria</em> spp. associated with woody hosts in Guizhou province, China including <em>B. guttulata</em> <em>sp. nov.</em></strong></p>

Members of Botryosphaeria encompass important plant pathogens, saprobes and endophytes on a wide range of woody hosts worldwide. Botryosphaeria species are difficult to differentiate due to the overlapping morphological characteristics and the molecular data analyses are necessary recently when species identification is carried out. In this study, 28 Botryosphaeria isolates were obtained from decaying woody hosts in six nature reserves in Guizhou province, China. Based on both morphological characteristics and molecular analysis of combined ITS and tef1-α sequence data, four known species (Botryosphaeria dothidea, B. minutispermatia, B. sinensia and B. wangensis) are identified and one new species B. guttulata is introduced. Botryosphaeria sinensia (32% of the isolates obtained from various hosts) is the abundant species, followed by B. dothidea (28.5% of the isolates), B. guttulata (28.5% of the isolates), B. minutispermatia (7% of the isolates) and B. wangensis (4% of the isolates). These results represent the first study of Botryosphaeria species associated with woody hosts from nature reserves in Guizhou province, China. Our findings indicate that there is a potential of Botryosphaeria species remain to be discovered in this unique landform (Karst formations) in Guizhou province, China.

First Report of the Armillaria Root-Disease Pathogen, Armillaria gallica, Associated with Several Woody Hosts in Three States of Central Mexico (Guanajuato, Jalisco, and Michoacan).

In July-August 2019, seven Armillaria isolates (derived from rhizomorphs and mycelial fans of infected roots) were collected in association with woody hosts in the central Mexico: states of Guanajuato (MEX204), Jalisco (MEX206, MEX208, MEX209), and Michoacan (MEX211, MEX214, MEX216). All seven isolates were identified as Armillaria gallica based on translation elongation factor 1α (tef1) gene sequences (GenBank accession Nos.: MN839636 - MN839642 for MEX204, MEX206, MEX208, MEX209, MEX211, MEX214, and MEX216) and somatic pairing tests against known tester isolates. GenBank nucleotide BLAST results showed tef1 similarity for all isolates was highest for with A. gallica (≥ 97%; GenBank Accession Nos. KF156775 and KF156772). In replicated pairings against three tester isolates each for A. gallica, A. mellea, and A. mexicana, all isolates showed the highest compatibility with A. gallica (67-100%), with lower compatibility against A. mellea and A. mexicana, with 3-11% and 2-11%, respectively. Variations in compatibility among different tester isolates could reflect cryptic speciation within A. gallica (Klopfenstein et al., 2017). In Tarimoro, Guanajuato, MEX204 was isolated from infected Quercus jonesii (20°13'46.2"N 100°42'51.1"W, elevation 2286 m) that displayed root disease symptoms/signs (wilting/defoliation and mycelial fans within the roots). In a forested area of Mazamitla, Jalisco, MEX206 was isolated from infected Quercus laevis (19°54´52"N 103°00´07"W, elevation 2564 m) with root disease symptoms/signs (e.g., wilting, foliar chlorosis, and mycelial fans within the root crown); MEX208 was isolated from infected Pinus pseudostrobus (19°54´53"N 102°59´54"W, elevation 2554 m) with basal resinosis and mycelial fans; and MEX209 was collected from a symptomless P. devoniana (19°54'13.1"N 103°00'14.1"W, elevation 2566 m). In Zinapecuaro, Michoacan, MEX211 (19°53'28.8"N 100°39'44.0"W, elevation 2587 m) was isolated from infected Malus domestica with root disease that resulted in mortality; in Hidalgo, Michoacan, MEX214 (19°46'49"N 100°39'25.2"W, elevation 2961 m) and MEX216 (19°46'58"N 100°39'24"W, elevation 2958 m) were isolated from infected P. devoniana and P. teocote, respectively, which both displayed root disease symptoms/signs (basal resinosis and mycelial fans). Previously, A. gallica was reported in the State of Mexico, Veracruz, Oaxaca, Mexico (Elías-Román et al. 2013; Klopfenstein et al. 2014), but this represents the first report of A. gallica in Guanajuato, Jalisco, and Michoacan, Mexico. In contrast to other regions of North America (e.g., Bruhns et al. 2000), A. gallica was demonstrated to be a virulent pathogen on peach (Prunus persica) in central Mexico (Elías-Román et al. 2013). Unfortunately, tree seedlings cannot be used for Armillaria pathogenicity tests in a greenhouse or nursery; however, all root-diseased trees in this report showed Armillaria mycelial fans under the bark of a living tree, which are reliable indicators of pathogenicity, and no other root diseases were found. This report demonstrates that A. gallica is distributed across central Mexico, where it is associated with disease on Quercus, Pinus, and Malus. Such information is critical to increase our understanding of Armillaria root disease across diverse geographic regions and climates.

Isolation, Characterization, and Pathogenicity of Two Pseudomonas syringae Pathovars from Populus trichocarpa Seeds.

Pseudomonas syringae is a ubiquitous plant pathogen, infecting both woody and herbaceous plants and resulting in devastating agricultural crop losses. Characterized by a remarkable specificity for plant hosts, P. syringae pathovars utilize a number of virulence factors including the type III secretion system and effector proteins to elicit disease in a particular host species. Here, two Pseudomonas syringae strains were isolated from diseased Populus trichocarpa seeds. The pathovars were capable of inhibiting poplar seed germination and were selective for the Populus genus. Sequencing of the newly described organisms revealed similarity to phylogroup II pathogens and genomic regions associated with woody host-associated plant pathogens, as well as genes for specific virulence factors. The host response to infection, as revealed through metabolomics, is the induction of the stress response through the accumulation of higher-order salicylates. Combined with necrosis on leaf surfaces, the plant appears to quickly respond by isolating infected tissues and mounting an anti-inflammatory defense. This study improves our understanding of the initial host response to epiphytic pathogens in Populus and provides a new model system for studying the effects of a bacterial pathogen on a woody host plant in which both organisms are fully genetically sequenced.

Host Range Determinants of Pseudomonas savastanoi Pathovars of Woody Hosts Revealed by Comparative Genomics and Cross-Pathogenicity Tests.

The study of host range determinants within the Pseudomonas syringae complex is gaining renewed attention due to its widespread distribution in non-agricultural environments, evidence of large variability in intra-pathovar host range, and the emergence of new epidemic diseases. This requires the establishment of appropriate model pathosystems facilitating integration of phenotypic, genomic and evolutionary data. Pseudomonas savastanoi pv. savastanoi is a model pathogen of the olive tree, and here we report a closed genome of strain NCPPB 3335, plus draft genome sequences of three strains isolated from oleander (pv. nerii), ash (pv. fraxini) and broom plants (pv. retacarpa). We then conducted a comparative genomic analysis of these four new genomes plus 16 publicly available genomes, representing 20 strains of these four P. savastanoi pathovars of woody hosts. Despite overlapping host ranges, cross-pathogenicity tests using four plant hosts clearly separated these pathovars and lead to pathovar reassignment of two strains. Critically, these functional assays were pivotal to reconcile phylogeny with host range and to define pathovar-specific genes repertoires. We report a pan-genome of 7,953 ortholog gene families and a total of 45 type III secretion system effector genes, including 24 core genes, four genes exclusive of pv. retacarpa and several genes encoding pathovar-specific truncations. Noticeably, the four pathovars corresponded with well-defined genetic lineages, with core genome phylogeny and hierarchical clustering of effector genes closely correlating with pathogenic specialization. Knot-inducing pathovars encode genes absent in the canker-inducing pv. fraxini, such as those related to indole acetic acid, cytokinins, rhizobitoxine, and a bacteriophytochrome. Other pathovar-exclusive genes encode type I, type II, type IV, and type VI secretion system proteins, the phytotoxine phevamine A, a siderophore, c-di-GMP-related proteins, methyl chemotaxis proteins, and a broad collection of transcriptional regulators and transporters of eight different superfamilies. Our combination of pathogenicity analyses and genomics tools allowed us to correctly assign strains to pathovars and to propose a repertoire of host range-related genes in the P. syringae complex.

Ectomycorrhizal Flora Formed by Main Forest Trees in the Irtysh River Region of Central and Northeastern Kazakhstan

In this study, the aim was to determine and identify symbiotically living ectomycorrhizas of the main tree species forming forests in central and northeastern Kazakhstan. Surveys were conducted on the right bank of the Irtysh River in a mixed forest of Pinus sylvestris, Picea obovata and Betula pendula trees. The collection was formed and the primary identification of voucher samples of fruiting bodies of macromycetes collected as ectomycorrhiza forming fungi was completed. In the collection and species identification of fruiting bodies, standard methods were used. A total of 30 ectomycorrhizas belonging to Agaricomycetes were identified. The distribution of 30 species into families is as follows: Suillaceae (8), Russulaceae (7), Cortinariaceae (4), Boletaceae (3), Tricholomataceae (2), Amanitaceae (1), Cantharellaceae (1), Gomphaceae (1), Gomphidiaceae (1), Paxillaceae (1), and Bankeraceae (1). The richest genus on account of the number of species was Suillus (8). Concerning the woody host species, 17 mycorrhizas were determined to build symbiosis with P. sylvestris, 8 mycorrhizas with B. pendula, 6 mycorrhizas with Populus tremula, 1 mycorrhiza with P. obovata, 1 mycorrhiza with Quercus robur, 1 mycorrhiza with Salix sp., and 1 mycorrhiza with Pinus densiflora Siebold and Zuccarini. Ectomycorrhizas should be used as a major performance-enhancing tool in afforestation and restoration studies in the Irtysh River basin under extreme ecological conditions and under climate change effects.

First Report of Duranta leaf curl virus Infecting Ficus virens Showing Leaf Curl Symptoms in Pakistan

Ficus virens (family: Moraceae) is a deciduous tree found in the Indian subcontinent, some other Southeast Asian countries, and northern Australia. It is valued for its latex, wood, and medicinal and edible products. In December 2018, during a routine survey to record begomoviruses other than cotton infecting viruses in Pakistan, curling of young leaves, which is a typical symptom of infection by viruses of the genus Begomovirus, was observed in F. virens trees in a park in Lahore, central Punjab, Pakistan. The total DNA of three trees was extracted using the Viral Gene-spin Viral DNA/RNA Extraction Kit (iNtRON Biotechnology, Seongnam, Korea) and used as a template in PCR amplification with begomovirus-specific primers: Beg-F (5′-CCGTGCTGCTGCCCCCATTGTCCGCGTCAC-3′) and Beg-R (5′- CTGCCACAACCATGGATTCACGCACAGGG-3′). The amplified 1-kb DNA was cloned into the pGEM-3Zf (+) vector (Promega, Madison, WI) and sequenced by a commercial sequencing service (Macrogen, Seoul, Korea). NCBI BLAST results revealed a nucleotide (nt) sequence identity of 95, 93, and 92% with chilli leaf curl India virus, rose leaf curl virus, and papaya leaf crumple virus, respectively. Based on the sequence obtained, new primers, DCP-F (5′-AGCACATTGGTAAAGTCATGTGTG-3′) and DCP-R (5′-GGATATCATGTCTGGACTCAAATG-3′), were designed to obtain full-length DNA-A of the begomovirus. An approximately 2.8-kb product was amplified and cloned. The resulting sequence (GenBank accession no. MN537564) showed 97.43% nt identity with duranta leaf curl virus (DLCV; KT948069), a Begomovirus species reported in the ornamental shrub Duranta erecta in Pakistan by Iram et al. (2005) and by Anwar et al. (2017). In the former case, only DNA-A of DLCV was found without any associated molecules such as DNA-B or DNA β, whereas, in the latter case, tomato leaf curl New Delhi virus DNA-B was found in association with the DNA-A of DLCV, like in many other Old World begomoviruses. The attempt to amplify DNA-B through PCR using newly designed primers NDB-F (5′-AAACACAGGAGGGATCGGAG-3′) and NDB-R (5′-CACAGATTTCCTTACGCGTATATT-3′) based on the sequence KT948071 was unsuccessful. Similarly, efforts to detect alphasatellite and betasatellite molecules in infected F. virens using universal primers (Bull et al. 2003; Briddon et al. 2002) were unsuccessful. Furthermore, Southern blot hybridization was carried out using [³²P]-radiolabeled PCR product of 1 kb obtained with Beg-F/R primers as a probe. This produced dsDNA bands of different conformations as well as a ssDNA band, which confirms the presence of DLCV in F. virens. Members of the family Geminiviridae, to which begomoviruses belong, mainly infect herbaceous hosts, but they have also been reported in a few woody hosts, such as citrus chlorotic dwarf associated virus in citrus (Loconsole et al. 2012), grapevine red blotch virus in grape (Al Rwahnih et al. 2013), jatropha mosaic virus in Jatropha multifida (Polston et al. 2014), and apple geminivirus 1 in apple tree (Liang et al. 2015). To our knowledge, this is the first report of DLCV infecting F. virens in Pakistan. The results obtained here indicate that F. virens may serve as an alternative host of DLCV and a possible source of infection to the commonly grown D. erecta ornamental garden hedge.

Diversity of woody-host infecting Phytophthora species in public parks and botanic gardens as revealed by metabarcoding, and opportunities for mitigation through best practice

The diversity of Phytophthora species in soils collected from 14 highly disturbed sites in northern Britain, including botanic gardens, arboreta, public parks and other amenity woodland sites, was analysed using a molecular technique known as DNA metabarcoding. This technique enables the identification of multiple species present in a single environmental sample based on a DNA ‘barcode’ unique to each species. The genus Phytophthora was targeted in this study due to its increasing impact on Britain’s forests and woodlands over thelast 20 years. The introduction and spread of new Phytophthora species into Britain has been strongly associated with the movement of traded containerised plants, with a number of Phytophthora outbreaks reported on host trees located in public gardens and parks that had recently undergone planting or landscape regeneration schemes. This study was undertaken to assess the extent to which these highly disturbed sites with extensive planting regimes act as harbours for woody-host infecting Phytophthora species. A total of 23 Phytophthora species, the majority of which are known to be pathogens of woody hosts, were detected across the 14 sites sampled. These included four quarantine-regulated pathogens and four species notpreviously recorded in Britain. Also detected were three as-yet undescribed Phytophthora species and nine oomycete sequences with no clear match to any known genus. There was no effect of geographical location, elevation, underlying soil type, host family or host health status on the Phytophthora assemblages at each site, suggesting that the Phytophthora communities detected are likely to comprise introduced species associated with planting programmes. P. austrocedri and P. pseudosyringae were two of the most abundant Phytophthoraspecies detected, both of which cause serious damage to trees and are regarded as fairly recent introductions to Britain. The practical implications of the findings in terms of mitigating Phytophthora introduction, spread and impact at botanic gardens, arboreta and urban parks are discussed.

Spittlebugs of Mediterranean Olive Groves: Host-Plant Exploitation throughout the Year.

Spittlebugs are the vectors of the bacterium Xylella fastidiosa Wells in Europe, the causal agent of olive dieback epidemic in Apulia, Italy. Selection and distribution of different spittlebug species on host-plants were investigated during field surveys in 2016–2018 in four olive orchards of Apulia and Liguria Regions of Italy. The nymphal population in the herbaceous cover was estimated using quadrat samplings. Adults were collected by sweeping net on three different vegetational components: herbaceous cover, olive canopy, and wild woody plants. Three species of spittlebugs were collected: Philaenus spumarius L., Neophilaenus campestris (Fallén), and Aphrophora alni (L.) (Hemiptera: Aphrophoridae). Philaenus spumarius was the predominant species both in Apulia and Liguria olive groves. Nymphal stages are highly polyphagous, selecting preferentially Asteraceae Fabaceae plant families, in particular some genera, e.g., Picris, Crepis, Sonchus, Bellis, Cichorium, and Medicago. Host-plant preference of nymphs varies according to the Region and through time and nymphal instar. In the monitored sites, adults peak on olive trees earlier in Apulia (i.e., during inflorescence emergence) than in Liguria (i.e., during flowering and beginning of fruit development). Principal alternative woody hosts are Quercus spp. and Pistacia spp. Knowledge concerning plant selection and ecological traits of spittlebugs in different Mediterranean olive production areas is needed to design effective and precise control strategies against X. fastidiosa vectors in olive groves, such as ground cover modifications to reduce populations of spittlebug vectors.

Phenology, seasonal abundance and stage-structure of spittlebug (Hemiptera: Aphrophoridae) populations in olive groves in Italy

Spittlebugs (Hemiptera: Aphrophoridae) are the dominant xylem-sap feeders in the Mediterranean area and the only proven vectors of Xylella fastidiosa ST53, the causal agent of the olive dieback epidemic in Apulia, Italy. We have investigated the structured population phenology, abundance and seasonal movement between crops and wild plant species of both the nymphal and adult stages of different spittlebug species in olive groves. Field surveys were conducted during the 2016–2018 period in four olive orchards located in coastal and inland areas in the Apulia and Liguria regions in Italy. The nymphal population in the herbaceous cover was estimated using quadrat samplings. Adults were collected through sweep nets on three different vegetational components: herbaceous cover, olive canopy and wild woody plants. Philaenus spumarius was the most abundant species; its nymphs were collected from early March and reached a peak around mid-April, when the 4th instar was prevalent. Spittlebug adults were collected from late April until late autumn. P. spumarius adults were abundant on the herbaceous cover and olive trees in late spring, and they then dispersed to wild woody hosts during the summer and returned to the olive groves in autumn when searching for oviposition sites in the herbaceous cover. A relatively high abundance of P. spumarius was observed on olive trees during summer in the Liguria Region. The present work provides a large amount of data on the life cycle of spittlebugs within an olive agroecosystem that can be used to design effective control programmes against these vectors in infected areas and to assess the risk of the establishment and spread of X. fastidiosa to Xylella-free areas.

The Effect of Arbuscular Mycorrhizal Fungi on Photosystem II of the Host Plant Under Salt Stress: A Meta-Analysis

As important components of the photosynthetic apparatus, photosystems I (PS I) and II (PS II) are sensitive to salinity. Salt stress can destroy the PS II reaction center, disrupt electron transport from PS II to PS I, and ultimately lead to a decrease in the photosynthetic capacity of the plant. Arbuscular mycorrhizal fungi (AMF) can enhance the photosynthetic capacity of a host plant under salinity stress. However, this specific effect of AMF is not always predictable. Here, we conducted a meta-analysis including 436 independent observations to compare chlorophyll fluorescence parameters in response to AMF inoculation under salt stress. The results showed that AMF inoculation had a positive total impact on photosynthesis in the host plant. Subgroup analysis showed that annual host plants had better performance in terms of photosynthesis after inoculation. The mitigating effects of AMF on the photosynthetic rate (Pn), actual quantum yield of photochemical energy conversion in PS II (ɸPS II), and electron transfer rate (ETR) in C4 species were higher than those in C3 species. Moreover, the photosynthesis performance of monocotyledon species was better than that of dicotyledon species after AMF inoculation. The woody host plants had higher energy utilization by way of an enhanced electron transfer rate to reduce energy dissipation after AMF inoculation. Finally, the mitigating effect of AMF on plants under moderate salinity was stronger than that under high salinity. Among AMF species, Funneliformis mosseae was found to be the most effective in enhancing the photosynthesis performance of plants. For the analyzed dataset, AMF inoculation alleviated the detrimental effects of salinity on photosystem II of the host plant by improving the utilization of photons and photosynthetic electron transport, and also by reducing the susceptibility of photosystem II to photoinhibition.

Botryosphaerialean fungi causing canker and dieback of tree hosts from Mount Yudu in China

The order Botryosphaeriales includes many latent fungal pathogens with a wide range of woody hosts. The taxonomy of these pathogens has been difficult due to the use of poorly informing markers in phylogenetic analyses and the lack of good morphological characters. Many genera and families in this order have not yet been systematically studied in different hosts and from different regions. In this study, a total of 29 fungal strains from the Aplosporellaceae and Botryosphaeriaceae were isolated from branches or twigs with symptoms of canker and dieback disease in Mount Yudu of China. Morphology and multigene analyses (ITS, LSU and TEF1-α) indicated five distinct lineages, including Aplosporella javeedii, Botryosphaeria dothidea, Diplodia quercicola sp. nov., Phaeobotryon aplospora sp. nov. and Phaeobotryon rhois. Diplodia quercicola is characterized by multiloculate conidiomata, producing oblong to cylindrical, thick-walled, hyaline, aseptate conidia. Phaeobotryon aplospora is characterized by pulvinate, multiloculate conidiomata, producing ellipsoid to oblong, brown, aseptate conidia. The new species differ from related species phylogenetically and ecologically and in morphological features.

Diaporthalean fungi associated with canker and dieback of trees from Mount Dongling in Beijing, China.

Diaporthales is a fungal order comprising important plant pathogens, saprobes and endophytes on a wide range of woody hosts. It is often difficult to differentiate the pathogens in this order, since both the morphology and disease symptoms are similar among the various species. In the current study, we obtained 15 representative diaporthalean isolates from six tree hosts belonging to plant families Betulaceae, Fagaceae, Juglandaceae, Rosaceae, and Ulmaceae from Mount Dongling in China. Six species were identified residing in four families of Diaporthales (Diaporthaceae, Erythrogloeaceae, Juglanconidaceae and Melanconidaceae). Based on morphological comparison and the phylogenetic analyses of partial ITS, LSU, cal, his3, rpb2, tef1-α and tub2 gene sequences, we identified five known species (Diaporthe betulina, D. eres, D. rostrata, Juglamconis oblonga and Melanconis stilbostoma) and one novel species (Dendrostoma donglinensis). These results represent the first study of diaporthalean fungi associated with canker and dieback symptoms from Mount Dongling in Beijing, China.

Three novel Ambrosia Fusarium Clade species producing clavate macroconidia known (F. floridanum and F. obliquiseptatum) or predicted (F. tuaranense) to be farmed by Euwallacea spp. (Coleoptera: Scolytinae) on woody hosts

ABSTRACTThe Ambrosia Fusarium Clade (AFC) comprises at least 16 genealogically exclusive species-level lineages within clade 3 of the Fusarium solani species complex (FSSC). These fungi are either known or predicted to be farmed by Asian Euwallacea ambrosia beetles (Coleoptera: Curculionidae: Scolytinae) in the tribe Xyleborini as a source of nutrition. To date, only 4 of the 16 AFC lineages have been described formally. In the absence of Latin binomials, an ad hoc nomenclature was developed to distinguish the 16 species lineages as AF-1 to AF-16. Herein, Fusarium species AF-3, AF-5, and AF-7 were formally described as F. floridanum, F. tuaranense, and F. obliquiseptatum, respectively. Fusarium floridanum farmed by E. interjectus on box elder (Acer negundo) in Gainesville, Florida, was distinguished morphologically by the production of sporodochial conidia that were highly variable in size and shape together with greenish-pigmented chlamydospores. Fusarium tuaranense was isolated from a beetle-damaged Paŕa rubber tree (Hevea brasiliense) in North Borneo, Malaysia, and was diagnosed by production of the smallest sporodochial conidia of any species within the AFC. Lastly, F. obliquiseptatum was farmed by an unnamed ambrosia beetle designated Euwallacea sp. 3 (E. fornicatus species complex) on avocado (Persea americana) in Queensland, Australia. It uniquely produces some clavate sporodochial conidia with oblique septa. Maximum likelihood analysis of a multilocus data set resolved these three novel AFC taxa as phylogenetically distinct species based on genealogical concordance. Particularly where introduced into exotic environments, these exotic mutualists pose a serious threat to the avocado industry, native forests, and urban landscapes in diverse regions throughout the world.

Xanthomonas perforans: a tomato and pepper pathogen associated with bacterial blight and dieback of Eucalyptus pellita seedlings in Indonesia

Leaf and shoot blight, often accompanied by die-back symptoms, on Eucalyptus species, hybrids and clones have been reported from a number of countries. More than one bacterial species has been found to cause these symptoms. In this study, a leaf disease of E. pellita in Indonesia was investigated. The disease was found primarily on nursery plants and young trees that recovered within the first year of growth. Leaf samples were collected from symptomatic trees, and isolations consistently yielded a Xanthomonas sp. Sequencing of the 16S rRNA gene region and multilocus sequence analysis (MLSA) was performed on 19 of the 61 Xanthomonas isolates obtained. In the MLSA, four genes, namely, dnaK, fyuA, gyrB and rpoD, were sequenced and the isolates were identified as X. perforans. Four representative isolates, at a concentration of 106 CFU/ml, were leaf-infiltrated and spray-inoculated on to E. pellita, tomato and pepper seedlings. The type isolate of X. perforans was included in the pathogenicity trials as a positive control. All four isolates of X. perforans, inclusive of the type isolate, induced bacterial spot symptoms on tomato and pepper seedlings. They also caused water-soaked lesions on the leaves of E. pellita seedlings, characteristic of the symptoms observed in the field. This is the first report of X. perforans infecting leaves of a woody host.

Quambalaria cyanescens, a new fungal trunk pathogen associated with grapevine decline in Iran

During surveys on grapevines trunk diseases in vineyards at different localities in East and WestAzerbaijan and Ardabil provinces, Iran, wood samples (two, three year-old cordons) were collected from grapevine showing decline symptoms, including leaf yellowing and necrosis, stunted growth, internal wood necrosis, black vascular discolouration. Nine fungal isolates with similar morphology were recovered from grapevines with decline symptoms in five different areas, which one-third of the isolates were recovered as the sole fungal agents. The identity of fungal isolates was determined as Quambalaria cyanescens based on the combination of cultural and morphological characteristics and DNA phylogeny. Pathogenicity trials based on excised shoot assay and potted grapevine under greenhouse conditions confirmed Q. cyanescens being pathogenic on grapevines; the isolates induced symptoms similar to those observed in naturally infected grapevines. Our findings confirm Q. cyanescens as a new fungal trunk pathogen of grapevine. Members of the genus Quambalaria are known to cause leaf spot, shoot blight and canker disease on Eucalyptus and its relative Corymbia. The current study is the first regarding pathogenicity of the Q. cyanescens on woody hosts; in previous studies Q. cyanescens has proven to be non-pathogenic to Corymbia spp. The host range, extent of geographical distribution and economic significance of this new pathogen on grapevine remains to be studied.