Assemblages of endophytic fungi in coppice shoots ofCastanea sativa

Commodity risk assessment of maple veneer sheets from Canada

The European Commission requested the EFSA Panel on Plant Health to deliver a risk assessment on the likelihood of pest freedom from Union quarantine pests and pests subject to measures adopted pursuant to Article 30 of Regulation (EU) No 2016/2031 for the maple veneer sheets manufactured according to the process set out by Canada, with emphasis on the freedom from Davidsoniella virescens and Phytophthora ramorum (non-EU isolates). The assessment was conducted for veneer sheets of up to 0.7 mm and up to 6 mm thickness, taking into account the different phases in the veneer production in a systems approach. Some of those phases, taken alone, including the heat treatment of logs in a water bath, the cutting into thin veneer sheets and the final high heat drying of veneer sheets are expected to be effective against some of the pests, without uncertainties, making the system approach fully effective. The panel considers that no insects would survive cutting of logs into thin veneer sheets of 0.7 mm and that Xylella fastidiosa will not survive the temperatures in the water bath and final drying of veneers. The degree of pest freedom for the different groups of organisms is generally very high with slightly lower degree of pest freedom for veneer sheets of 6 mm thickness because of lower temperatures reached in the final drying of veneer sheets compared to thinner sheets. P. ramorum is not expected to survive the high heat drying of thin veneer sheets, but it may survive the lower temperatures inside thicker veneer sheets. The Expert Knowledge Elicitation (EKE) indicated, with 95% certainty, that between 9989 and 10,000 veneer sheets (thickness 6 mm) per 10,000 will be free from living P. ramorum. For D. virescens, the EKE indicated, with 95% certainty, that between 9984 and 10,000 veneer sheets (0.7 mm) per 10,000 and that between 9954 and 10,000 veneer sheets (6 mm) per 10,000 will be free from living inoculum. For other relevant groups of pests, the greatest likelihood of pest presence was observed for wood decay fungi. The EKE indicated, with 95% certainty, that between 9967 and 10,000 veneer sheets (0.7 mm) per 10,000 and that between 9911 and 10,000 veneer sheets (6 mm) per 10,000 will be free from living wood decay fungi.

Pest categorisation of Coniella castaneicola

The European Commission requested the EFSA Panel on Plant Health to conduct a pest categorisation of Coniella castaneicola (Ellis & Everh) Sutton, following commodity risk assessments of Acer campestre, A. palmatum, A. platanoides, A. pseudoplatanus, Quercus petraea and Q. robur plants from the UK, in which C. castaneicola was identified as a pest of possible concern to the EU. When first described, Coniella castaneicola was a clearly defined fungus of the family Schizoparmaceae, but due to lack of a curated type-derived DNA sequence, current identification based only on DNA sequence is uncertain and taxa previously reported to be this fungus based on molecular identification must be confirmed. The uncertainty on the reported identification of this species translates into uncertainty on all the sections of this categorisation. The fungus has been reported on several plant species associated with leaf spots, leaf blights and fruit rots, and as an endophyte in asymptomatic plants. The species is reported from North and South America, Africa, Asia, non-EU Europe and Oceania. Coniella castaneicola is not known to occur in the EU. However, there is a key uncertainty on its presence and geographical distribution worldwide and in the EU due to its endophytic nature, the lack of systematic surveys and possible misidentifications. Coniella castaneicola is not included in Commission Implementing Regulation (EU) 2019/2072 and there are no interceptions in the EU. Plants for planting, fresh fruits and soil and other growing media associated with infected plant debris are the main pathways for its entry into the EU. Host availability and climate suitability in parts of the EU are favourable for the establishment and spread of the fungus. Based on the scarce information available, the introduction and spread of C. castaneicola in the EU is not expected to cause substantial impacts, with a key uncertainty. Phytosanitary measures are available to prevent its introduction and spread in the EU. Because of lack of documented impacts, Coniella castaneicola does not satisfy all the criteria that are within the remit of EFSA to assess for this species to be regarded as potential Union quarantine pest.

Diversity of Endophytic Fungi in Annual Shoots of Prunus mandshurica (Rosaceae) in the South of Amur Region, Russia

Prunus mandshurica is a rare species of the Russian Far East; it is cultivated for fruits and as an ornamental tree. The objective was to determine the fungi associated with young shoots of the Manchurian apricot, which is an important biotic factor for plant viability and productivity. Fungi were isolated by incubation of shoot fragments (unsterilized or surface-sterilized) on a growth medium and identified according to their cultural and morphological characteristics. Diaporthe eres and Nothophoma quercina isolates were identified by multilocus phylogenetic analysis (apn2, cal, tef1-α, tub2 for D. eres, and ITS, rpb2, tub2 for N. quercina). In total, 12 species (Alternaria alternata, A. tenuissima, Aureobasidium pullulans, Cladosporium cladosporioides, C. herbarum, D. eres, Epicoccum nigrum, Fusarium graminearum, F. oxysporum, N. quercina, Sarocladium strictum, and Tripospermum myrti) and one genus (Gliocladium sp.) were found. Alternaria alternata, N. quercina, and D. eres were the most frequent species of the shoots. Alternaria tenuissima and F. oxysporum were also frequent in some collections, while all other species were rare or occasional in occurrence. Molecular analysis of D. eres and N. quercina revealed redundancy of some species within the D. eres species complex and the genus Nothophoma. This is the first report on the fungal inhabitants of asymptomatic shoots of P. mandshurica. Nothophoma quercina was identified in Russia for the first time.

The Use of qPCR to Detect Cryphonectria parasitica in Plants

Cryphonectria parasitica is a fungal pathogen that causes lethal bark necrosis in chestnut. A duplex qPCR allowing detection of the pathogen and its host, Castanea sativa, is described. The method can be used for early detection of the pathogen in chestnut bark tissues with an internal control of false-negative results caused by PCR inhibitors and/or DNA extraction failure. A positive amplification control of qPCR that allows detection of any deviation from a normal qPCR run based on a control chart is also described. As C. parasitica is a regulated pathogen in Europe, the protocol also provides information on the way to collect and handle bark samples to fulfil biosecurity rules.

Endophytic Fungi and Ecological Fitness of Chestnuts

Chestnuts (Castanea spp.) are plants of relevant economic interest in the agro-sylvicultural contexts of mountain regions throughout the temperate zone, particularly in the northern hemisphere. In recent years, several biological adversities have repeatedly endangered species belonging to this genus, calling for coordinated actions addressed to contrast their decline. These actions have mainly focused on the control of key pests/pathogens and the improvement of resistance/tolerance by the plant host, while the role of microorganisms as mediators of interactions between plants and the noxious agents has been less considered, essentially by reason of a limited knowledge on their ecological impact. In line with the increasing awareness of the basic importance of microbial symbionts in regulating plant fitness in both natural and crop contexts, this paper offers an overview on the occurrence and effects of endophytic fungi of chestnuts.

Cork Oak Endophytic Fungi as Potential Biocontrol Agents against Biscogniauxia mediterranea and Diplodia corticola

An increase in cork oak diseases caused by Biscogniauxia mediterranea and Diplodia corticola has been reported in the last decade. Due to the high socio-economic and ecologic importance of this plant species in the Mediterranean Basin, the search for preventive or treatment measures to control these diseases is an urgent need. Fungal endophytes were recovered from cork oak trees with different disease severity levels, using culture-dependent methods. The results showed a higher number of potential pathogens than beneficial fungi such as cork oak endophytes, even in healthy plants. The antagonist potential of a selection of eight cork oak fungal endophytes was tested against B. mediterranea and D. corticola by dual-plate assays. The tested endophytes were more efficient in inhibiting D. corticola than B. mediterranea growth, but Simplicillium aogashimaense, Fimetariella rabenhorstii, Chaetomium sp. and Alternaria alternata revealed a high potential to inhibit the growth of both. Simplicillium aogashimaense caused macroscopic and microscopic mycelial/hyphal deformations and presented promising results in controlling both phytopathogens' growth in vitro. The evaluation of the antagonistic potential of non-volatile and volatile compounds also revealed that A. alternata compounds could be further explored for inhibiting both pathogens. These findings provide valuable knowledge that can be further explored in in vivo assays to find a suitable biocontrol agent for these cork oak diseases.

Hail-Induced Infections of the Chestnut Blight Pathogen Cryphonectria parasitica Depend on Wound Size and May Lead to Severe Diebacks

This study combined phytosanitary surveys, laboratory analyses, and mathematical modeling to show how hail-induced wounds can foster the infections of the blight pathogen Cryphonectria parasitica, locally associated with extensive dieback of chestnut (Castanea sativa). Orchards and coppices located within and outside the assessed dieback area in a single location in the North West of Italy were inspected to appraise the abundance of hail-induced wounds and C. parasitica infections. The incidence of C. parasitica was significantly higher within the dieback area compared with outside (92% versus 60%; P < 0.05). Hail-induced wounds were observed on small branches and shoots of all trees sampled within the dieback area, whereas they were less abundant outside (20% of trees), suggesting either that the dieback was directly associated with the injuries caused by the hailstorms or that those injuries may have facilitated infections of C. parasitica. Isolations conducted on 359 branches and shoots showed that hail-induced wounds served as infection courts for C. parasitica and that infections depended on the size rather than on the number of hail wounds. We fitted a logistic model showing that hail-induced wounds whose perimeter was larger than 66 mm were at particular risk of C. parasitica infection. A newly designed geometrical-based model is proposed to relate hailstones size, hail wound perimeter, and the risk of infection. We established that hail-induced wounds are entry points for virulent and hypovirulent strains of C. parasitica, since 6.5% of isolates were infected by Cryphonectria hypovirus-1.

Phylogenetic and phenotypic characterisation of Sirococcus castaneae comb. nov. (synonym Diplodina castaneae), a fungal endophyte of European chestnut

In this paper we resolve the taxonomic status of the fungus Diplodina castaneae (Ascomycetes, Diaporthales, Gnomoniaceae) which occurs on the European chestnut (Castanea sativa) as endophyte and as the causal agent of Javart disease. Specimens from Switzerland, Spain, and Azerbaijan were sequenced at five nuclear loci (β-tubulin, EF-1α, ITS, LSU, and RPB2). Phylogenies were inferred to place D. castaneae in the Gnomoniaceae family. Moreover, growth rates and morphological characteristics on different agar media were assessed and compared to those of Gnomoniopsis castaneae, which can easily be confused with D. castaneae. Based on morphological and phylogenetic characteristics, we propose to reallocate D. castaneae to the genus Sirococcus, as S. castaneae comb. nov.

Saprophytic Activity and Sporulation of Cryphonectria parasitica on Dead Chestnut Wood in Forests with Naturally Established Hypovirulence

ABSTRACT Sustainable biological control of the chestnut blight fungus Crypho-nectria parasitica with hypovirulence depends on the production and dissemination of hypovirus-infected propagules of the pathogen. We investigated the ability of C. parasitica to sporulate and produce hypo-virus-infected spores on recently dead chestnut wood in coppice stands in southern Switzerland where hypovirulence has been naturally established. The number and type (active, inactive, or none) of cankers was assessed on experimentally cut and stacked stems, firewood stacks, and natural dead wood. Hypovirus-free and hypovirus-infected strains readily survived for more than 1 year in the chestnut blight cankers of the stacked stems. Sporulation of C. parasitica was observed on the surface of preexisting inactive and active cankers, as well as on newly colonized bark areas and was significantly more abundant than on comparable cankers on living stems. On all types of dead wood, we observed more stromata with perithecia than with pycnidia; however, a large proportion of the stromata was not differentiated. All perithecia examined yielded only hypovirus-free ascospores. The incidence of pycnidia that produced hypovirus-infected conidia ranged from 5% on natural dead wood to 41% on the experimental stacks. The mean virus transmission rate into conidia was 69%. Our study demonstrates a considerable saprophytic activity of C. parasitica on recently dead chestnut wood and supports the hypothesis of a role of this saprophytic phase in the epidemiology of hypovirulence.

Forest endophytes: pattern and process

Studies on taxonomy, distribution, and possible function have dominated the literature on forest endophytes since these fungi were first noted. Endophyte distributions have been described at a variety of scales ranging from those at a landscape level to those at the finest scales of resolution within a single leaf or patch of bark. At a landscape level, distribution patterns seem to be determined by host specificity, liquid precipitation, canopy cover, and geographic continuity or disjunctness. At the level of the individual stand or tree, height in the crown may become important. At the level of individual branch systems, age of substrate appears the most important factor. At a microscopic scale, tissue specificity, leaf topography, and phenology of the infection process with respect to leaf development all play a role. Endophytic fungi have seldom been found to cause widespread disease in trees; furthermore, their age-specific infection frequencies in conifer needles show continuous increases with needle age, in contrast to needle pathogens in which infections are largely confined to young needles. Endophytes are usually viewed as protective mutualists acting against herbivorous insects and pathogenic fungi. Proof of mutualism requires not only that endophytes be present in tissues under attack and their presence be correlated with, for example, increased insect mortality, but that inoculation experiments and comparisons with uninoculated plant tissues also be done. Such experiments often show no differences between treatment and control plants, results that may be related to unsuccessful inoculation of the endophyte. Such results may also be rooted in an inability to reproduce the biological complexity present in natural forest stands. Multiple infections of single leaves may lead to synergistic interactions of toxins produced by endophytes. Insect herbivores have evolved behavioral responses to the presence of endophytes, and protective mutualism by endophytes may occur only intermittently. Key words: endophyte, distribution, mutualism, gall midge, toxins, coevolution.