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The chestnut gall wasp (CGW) Dryocosmus kuriphilus is a serious pest of chestnuts (Castanea sativa) in many chestnut growing areas in Turkey. Out of 200 galls randomly collected from four different areas of Yalova and Giresun provinces, 116 showed necrosis, while 84 were asymptomatic. Fungi associated with the necrotic and asymptomatic galls were determined based on morphology and DNA sequencing. Gnomoniopsis smithogilvyi, Colletotrichum acutatum, Penicillium glabrum, Botrysphaeria dothidea, Trichoderma atroviridea, and Botrytis cinerea were found on 49, 11, 10, 8, 7, and 1 necrotic galls, respectively. On the other hand, G. smithogilvyi, Fusarium proliferatum, Aureobasidium sp., C. godetiae, Rhizopus stolonifer, P. glabrum, C. acutatum, Cladosporium sp., Alternaria spp., and Aspergillus sp. were hosted by 37, 35, 15, 14, 12, 8, 6, 3, 1, and 1 asymptomatic galls, respectively. Seven fungi, G. smithogilvyi, C. acutatum, F. proliferatum, B. dothidea, Cryphonectria parasitica, Diplodina castanea, and Penicillium sp. were isolated from 31, 6, 4, 1, 1, 1, and 1 of the dead larvae of D. kuriphilus, respectively. Two fungi, F. proliferatum and Penicillium sp., were isolated from the adults of Torymus sinensis, a parasitoid of CGW. Pathogenicity of G. smithogilvyi, C. acutatum, and F. proliferatum detected from dead larvae of D. kuriphilus and galls was tested on young chestnut saplings: the former two produced necrosis while the third one did not. [ABSTRACT FROM AUTHOR]

Fungi of the genus Cryphonectria are of special interest to tree pathologists because they cause bark disease in numerous species of the Fagaceae and Betulaceae. Despite this special attention, several Cryphonectria species were not recognized as such for a long time. This also affected the identity of eight isolates with outdated names that have been deposited in our laboratory since 1954. The present study reconstructs the history of the Cryphonectria cultures M282–M289 using primary bibliographic sources. To verify the species identity, all isolates were DNA barcoded and taxonomic affiliation was assessed using a phylogenetic approach. The taxonomic identity combined with the history of the isolates confirms that the chestnut blight epidemic (Cryphonectria parasitica) in Spain was caused by the planting of Asian chestnuts and that the first documented case of bark canker in 1940 was caused by Cryphonectria radicalis on Japanese chestnuts imported from France. The history of isolate M289 could be traced back to CBS 165.32, which proved to be the oldest preserved isolate of the rare Cryphonectria naterciae, confirming the presence of this fungus in Europe for at least 100 years. Based on the ITS barcoding of the 32‐year‐old type specimen, Cryphonectria decipiens must be reclassified as a later synonym of Cryphonectria radicalis. The reconstruction of the history of isolates M282–M289 takes us on a scientific journey from Italy to France, Spain and Portugal in the early twentieth century and offers new insights into the historical context of the invasion of Cryphonectria parasitica in Europe. [ABSTRACT FROM AUTHOR]

Sweet chestnut (Castanea sativa) is an ecologically and economically valuable tree species worldwide. Various pathogens, both endemic or introduced, cause severe damage or death to chestnut trees. Chestnut blight, caused by the fungus Cryphonectria parasitica, is one of the most devastating plant diseases known which influences chestnut trees in all major cultivation regions. The work presented here aimed to investigate how the incidence of chestnut blight varied between trees growing at two altitudes (200–400 m vs. 400–600 m) and to determine the impact of chestnut blight on tree‐ring width, morphology and anatomy of C. sativa trees. The incidence of C. parasitica infections was greater at 200–400 m than at 400–600 m. Greater stem diameters were found at 200–400 m than at 400–600 m. There were no differences in stem diameters and heights, however, between healthy and C. parasitica infected chestnut trees. The anatomical characteristics of wood were also compared between healthy and C. parasitica‐infected chestnut trees. Fibre cell traits (length/width, lumen width, lumen area) were higher in healthy trees than in C. parasitica‐diseased trees. Vessel diameters were greater in infected compared with healthy trees. Tree ring widths and wood anatomical characteristics therefore were significantly influenced by C. parasitica infections. [ABSTRACT FROM AUTHOR]

Vegetative compatibility (vc) and mating types and genetic diversity of Cryphonectria parasitica isolates were determined using 183 isolates obtained from 215 infected chestnut trees growing in 13 provinces of Turkey. Based on the cultural aspects, 143 of these isolates were evaluated as virulent whereas the remaining 40 isolates were hypovirulent. When vc types of 183 isolates were classically differentiated, 135 of them matched to EU‐1 (82.3%), 29 of them to EU‐12 (17.6%) vc type, whereas 19 of them did not match to the two. When molecular vic markers were used, all the isolates were assigned to two EU vc types; 149 to EU‐1 (81.4%) and 34 (18.5%) to EU‐12. Of the majority of the isolates, 134 (73.2%) had mating‐type MAT‐1, while 44 (24%) isolates had MAT‐2 and 5 (2.8%) isolates had both mating types. The population analysis based on two DNA marker systems, Inter‐Primer Binding Site and Start Codon Targeted Polymorphism, showed no intraspecific genetic variation among the C. parasitica isolates. The prevalence of two dominant vc types revealed by this study shows that biological control with hypovirulent EU‐1 and EU‐12 isolates will be significant for the country. The results might be helpful to chestnut breeders carrying out resistance breeding studies to manage this disease based on hypovirulence attributed to Cryphonectria hypovirus 1. [ABSTRACT FROM AUTHOR]

Ink disease of sweet chestnut (Castanea sativa) caused by the oomycetes Phytophthora cinnamomi and P. x cambivora is the limiting factor for chestnut cultivation in several European regions. The objective of this study was to explore how the spatial landscape heterogeneity affects the distribution pattern of ink disease over a large chestnut area in Central Italy using an approach that combined remote sensing, ground truthing activities and GIS. A multivariate model was developed that explained a large proportion of the variance of the impact of the disease using the density of roads and drainage networks as predictor variables. The association of these landscape elements, specifically with ink disease foci, also provides practical tool to improve the accuracy of monitoring of this disease and the preparation of risk maps. [ABSTRACT FROM AUTHOR]

Cryphonectria hypovirus 1 (CHV1) was detected by specific RT‐PCR in two strains of Cryphonectria parasitica from Azerbaijan in which reduction of laccase activity was also observed. This is the first report of a hypovirus in the chestnut blight fungus in Azerbaijan. Our work opens the way to further investigations devoted to characterizing the Azerbaijan CHV1 strain. [ABSTRACT FROM AUTHOR]

A novel real‐time PCR assay based on the TaqMan probe was developed for the detection of Gnomoniopsis castaneae, causal agent of brown rot of chestnut kernels, and responsible for leaf necrosis, shoot blight and bark canker. A part of the pathogen life cycle is endophytic, colonizing all tissues of chestnut and additional hosts, which is suspected to play a key role in its epidemiology. Thus, a molecular tool for sensitive detection and quantification of G. castaneae in symptomatic and asymptomatic host tissues is urgently required to better understand G. castaneae ecology, biology and epidemiology. Primers and a species‐specific probe for G. castaneae were designed based on the sequence of the single‐copy elongation factor 1 alpha (EF1α) gene. The amplification efficiency of target DNA was 105.3% and the limit of detection of the assay was calculated at approximately 40 fg of pure fungal DNA. The pathogen was consistently detected in artificial mixtures of plant and pathogen DNAs with the same Limit of Detection (LOD) as pure fungal DNA. In naturally infected samples, the assay rapidly revealed the presence of the pathogen in all symptomatic specimens, as well as in asymptomatic tissues. Notably, a significant relationship between the results of a metagenomic HTS analysis and the qPCR assay on DNAs extracted from bulk fruit was found. This molecular tool will be of substantial aid in detecting and quantifying G. castaneae, even in the endophytic state, and in different host tissues. [ABSTRACT FROM AUTHOR]

In western Ukraine, forest decline and dieback of several broadleaved tree species have become increasingly evident during recent years, and surveys in some areas have shown symptoms indicative of Phytophthora infections. In this study, we aimed to determine the occurrence and diversity of Phytophthora species associated with several broadleaved tree species (Alnus glutinosa, Betula pendula, Castanea sativa, Fagus sylvatica and Quercus robur) from forest stands where dieback has been observed. Rhizosphere soil samples were collected from 14 forest stands during 2017 and 2018 and tested for the presence of Phytophthora species using morphological and molecular methods. Seven Phytophthora species (P. bilorbang, P. cactorum, P. gallica, P. gonapodyides, P. lacustris, P. plurivora and P. polonica), and two other clade six taxa were detected from the various forest types, several of which are probable agents responsible for decline. Four of the Phytophthora species (P. bilorbang, P. gallica, P. plurivora and P. polonica) have previously never been reported from broadleaf forests in Ukraine. [ABSTRACT FROM AUTHOR]

The diversity of vegetative compatibility (vc) types of chestnut blight fungus, Cryphonectria parasitica, has been reported to be very low in all of Turkey, except in the eastern Black Sea Region. However, risk for increase in vc type diversity has been pointed out regarding the emergence of new vc types as recombinants during sexual reproduction. In this study, the potential increase in the diversity of vc types in Turkish populations of C. parasitica was demonstrated by experimental mating crosses between the two dominant vc types, EU‐1 and EU‐12. Two local isolates of C. parasitica, K5‐5 (EU‐1) and A‐2490 (EU‐12), were used setting crosses on autoclaved chestnut wood. Among the offspring from the crosses, two parental (EU‐1 and EU‐12) and 14 non‐parental vc types (EU‐2, EU‐3, EU‐4, EU‐7, EU‐8, EU‐11, EU‐14, EU‐17, EU‐22, EU‐25, EU‐26, EU‐28, EU‐29 and EU‐30) were detected by a routine test based on co‐culturing. Sixteen vc genotypes were confirmed by a PCR assay using specific primers targeting the alleles of six vic loci in C. parasitica. In field studies, no evidence of new vc types as recombinants was found in western Turkey whereas 14 different vc types were detected among single ascospore isolates isolated from field‐collected perithecia, which were sampled from the eastern Black Sea region. The results of this study indicate that the potential increase in vc type diversity in Turkish population of C. parasitica is high under the conditions where C. parasitica reproduces sexually. [ABSTRACT FROM AUTHOR]

In Europe, fungal pathogens have reduced the overall productivity of sweet chestnut ( Castanea sativa) stands and continue to threaten the economic viability of forestry operations. Chestnut Red Stain ( CRS) in north-eastern Spain, locally referred to as Roig, is capable of decreasing the market value of chestnut timber to the point of rendering chestnut coppices uneconomical. Despite its economic importance, the specific cause of this red discolouration is unknown. With the objective of verifying the presence of fungi within the symptomatic wood, and identifying the fungus or suite of fungi associated with the red stain, wood samples were collected and cultured from 37 stumps found in eight recently harvested stands in the Montseny and Montnegre-Corredor Natural Parks. To separate the fungi associated with CRS from other species inhabiting the chestnut wood, the origin of each fungal culture was mapped in every stump. The fungi were isolated from cultures and identified by sequencing the ITS region. The results provide insight into the fungal community inhabiting chestnut wood and the potential cause of CRS; nine species were identified including two species known to cause decay in chestnut. One of them, Fistulina hepatica, appears to be a likely candidate for the causal agent of CRS. This is the first study reporting the fungi associated with CRS and opens the door to new epidemiological studies focused on F. hepatica. [ABSTRACT FROM AUTHOR]

Cryphonectria parasitica (Murrill.) Barr is a necrotrophic fungus that affects European chestnut populations. In Catalonia (NE Spain), this fungus is widely spread affecting chestnut stands. In addition to vegetative compatibility (VC) types of the fungus, knowledge of the Cryphonectria hypovirus (CHV) occurrence is important to implement a biocontrol programme. We confirmed the presence of hypoviruses in several chestnut subpopulations of Catalonia, and we determined the VC types of CHV-infected isolates. We also studied the nucleotide sequences of these hypoviruses from a variable region located in the hypovirus ORF-A. Our results show a low occurrence of hypoviruses throughout C. parasitica populations in Catalonia, except for a few localized stands. From 312 sampled cankers, we obtained 179 white, pale orange or rickety isolates. In 35 of them, we detected CHV-1. Infected isolates belonged to 5 of the 7 sampled subpopulations. We found 12 CHV-1 haplotypes, based on the nucleotide sequence analysis. Most of the hypoviruses have the same nucleotide sequence or show high homology at nucleotide level with isolates previously included in CHV-1 subtype-I. However, we found that 3 haplotypes share at least 97% of their ORF-A nucleotide sequence with CHV-1 subtype-E. Phylogenetic analysis grouped these 3 isolates in a different cluster than the other hypoviruses. These results suggest that multiple introductions of CHV-1 have occurred recently in Catalonia. Dominant VC types of hypovirus-infected isolates are EU-1, EU-2 and EU-5, which are similar to those previously reported in this region. [ABSTRACT FROM AUTHOR]

Chestnut blight destroyed the native chestnut forests in North America and also severely affected the European chestnut trees after its introduction in the 20th century. The ascomycete fungus Cryphonectria parasitica is responsible for this serious disease and causes lethal bark cankers on susceptible chestnut trees. In Europe, however, an infection of C. parasitica with Cryphonectria hypovirus 1 ( CHV-1) causes hypovirulence in C. parasitica and reduces the severity of the disease. Hypovirulence biologically controls chestnut blight in many regions to date. In this study, our goal was to determine morphological canker characteristics that are indicative of virus presence or absence in C. parasitica. We investigated 677 chestnut blight cankers from seven different geographic locations across Europe. For each canker, we assessed canker length, stem encircling, canker depth, presence of sporulation, canker activity and virus infection. We statistically analysed the informative value of these morphological characteristics for the presence or absence of CHV-1. However, we did not find reliable indicators. Our logistic regression analysis revealed that virus infection of C. parasitica is not clearly related to canker morphology. This implies that fungal isolations from chestnut blight cankers and assessments in the laboratory are required to determine infection with CHV-1 unequivocally. [ABSTRACT FROM AUTHOR]

The research was performed in a new and isolated ink disease outbreak. Nine sweet chestnuts of comparable age, growing under same environmental and site conditions, and belonging to three phytosanitary classes (healthy, infected but asymptomatic and symptomatic) were randomly selected. Their ectomycorrhizal community was monitored during two periods, with regard to species abundance, to verify whether the community composition can be useful as an ink disease bioindicator. From the 216 samples, 29 ectomycorrhizal species were recorded, with abundances that changed with the health status of the tree. The results demonstrated that the mycorrhizal community composition was highly related to the ink disease level, allowing the consideration of the use of this parameter as a tool for the quick detection and control of the early stages of the disease. [ABSTRACT FROM AUTHOR]

Summary Chestnut blight caused by Cryphonectria parasitica has recently been reported from Guilan province, the only region with natural chestnut ( Castanea sativa) stands in Iran. During the past few years, chestnut stands in Iran have been seriously threatened by the fungus, incidence of the disease is increasing and vast canopies are reduced to sprouts. As yet, there is no report on the disease distribution and severity in this region. Six sites from three main growing regions of chestnut in Guilan province were selected for investigation. We report occurrence and evaluation of the damage of the disease caused by C. parasitica. To evaluate the scale of damage, the investigated trees were classified into six categories based on the degree of crown damage, the number of canker wounds and the presence of the fungus. Index of health condition was calculated for all sites. During this study, a total of 250 isolates of Cryphonectria species were obtained, of which 232 isolates were C. parasitica and 18 were Cryphonectria radicalis. Castanea parasitica was observed in all regions. Index of health condition was scored from 0 to 6 with 0 being disease free and six being the most severe infection. Index results in the investigated sites varied between 0.69-5.45 and 0.93-5.55 for years 2006 and 2007, respectively. The highest damage was found in Doran ( I [ABSTRACT FROM AUTHOR]

Summary The occurrence of chestnut blight ( Cryphonectria parasitica) on oaks in mixed chestnut-oak forests was studied in 2003-2008 in Slovakia. Infections on living Quercus trees were found at four of seven localities. The disease incidence on oaks ranged from 1.3% to 15.8%. The symptoms on infected oaks were similar to those on chestnut, but less conspicuous. Cankers of C. parasitica were found only on Quercus robur and Q. petraea. A total of 22 isolates of C. parasitica, all virulent, were isolated. Each site yielded only a single vc type (EU12 or EU13). Field inoculation experiments on chestnuts with seven strains of C. parasitica from oaks and an isolate from Castanea sativa showed no differences in virulence. On Quercus robur stems, the cankered area was significantly smaller than on C. sativa and the cankers developed very slowly. [ABSTRACT FROM AUTHOR]

Distribution and gradient analysis of Ink disease caused by Phytophthora cambivora were studied over a 2 years period in a chestnut forest in Italy. Ink disease incidence, severity and tree mortality increased during the period over the studied chestnut forest. Disease descriptors and landform datasets were analysed by Geographic Information System software and displayed as a multilayer thematic map. Indices of dispersion and empirical dispersion models were used to study spatial distribution of disease in the investigated area. Semivariograms were used to interpolate spatial data and to map Ink disease. A logical spatial dependence of the studied variables was found. Ink disease occurred preferentially along natural drainages routes where multicyclic inoculum build up was likely to occur. A negative relationship was found between Ink disease incidence, severity and tree mortality with respect to distance from the drainage. [ABSTRACT FROM AUTHOR]

A molecular technique was used to detect the bacterium Pseudomonas syringae pv. aesculi in horse chestnut trees ( Aesculus hippocastanum), affected by the recently recognized European ‘ Pseudomonas horse chestnut bark disease’. The technique helped identify the pathogen within 6 h of sample preparation including DNA extraction, polymerase chain reaction (PCR) and electrophoresis until gel documentation. PCR primer pairs derived from the gyrase B gene sequence were used. Because of the great similarity in the gyrase B gene sequences of the numerous closely related P. syringae pathovars, the primers were not only totally specific to the pathovar aesculi, but also detected a few other pathovars. The assumption that other bacteria should not occur at least near to a necrotic lesion of a horse chestnut tree was corroborated by sequence identity of the PCR products obtained with the gyrase B gene sequence of P. syringae pv. aesculi. Koch’s postulates were fulfilled for an isolate of P. syringae pv. aesculi obtained from a diseased horse chestnut tree sampled in Hamburg in 2007. [ABSTRACT FROM AUTHOR]

The chestnut blight fungus [ Cryphonectria parasitica (Murill) Barr] has threatened European chestnut stands ( Castanea sativa Mill.) in the 20th century, but infected trees recovered because of the appearance of hypovirulent strains. However, within a dry inner Alpine valley (Italy), blight-infected C. sativa showing various degrees of crown dieback and dead trees were found. We conducted a dendroecological analysis to retrospectively evaluate a possible synergistic effect of blight infection in the early 1970s and climate stress on the growth decline of C. sativa. In the Eisack Valley (Italy), where annual precipitation is <700 mm, increment cores were taken from blight-infected C. sativa (n = 103) showing different levels of decline symptoms, i.e. extent of crown dieback (healthy, moderate, severe), and from dead trees. Ring width and basal area increment (BAI) chronologies were developed based on dendroecological methods. Growth–climate relationships were explored using response function analysis and Pearson correlation coefficients. Major findings of our study were: (i) C. sativa growth is limited by low precipitation from December to February and high temperatures in June, (ii) BAI of all vitality classes except healthy trees shows a decreasing trend since 1980; and (iii) a severe drought in 1996 accelerated growth decline and caused death of infected C. sativa individuals. Because of the strong influence of climate on radial tree growth within the study area and observed divergent growth trends in selected vitality classes after infestation by hypovirulent C. parasitica strains in the early 1970s, we conclude that although blight infection is a prerequisite for observed growth declines, soil water availability in the years of drought strongly affects susceptibility to tree death. [ABSTRACT FROM AUTHOR]

Cryphonectria parasitica, the causal agent of chestnut blight, has been responsible for the decline in chestnut in Portugal for the last two decades. In order to improve understanding of C. parasitica diversity, a total of 617 isolates from all affected chestnut-growing areas in continental Portugal, Madeira and the Azores archipelagos were studied. Nine vegetative compatibility (vc) types were identified among the isolates. EU-11 was the most widespread vc type comprising 80.2% of the isolates, followed by EU-12 (7.1%) and EU-66 (6.6%). Two of the Portuguese vc types could not be assigned to a known European vc type. The diversity of vc types was low in the Portuguese populations of C. parasitica, but comparable with other areas where C. parasitica was introduced recently. The frequent occurrence of perithecia and both mating types of C. parasitica indicates that sexual reproduction of the chestnut blight fungus is common in Portugal. One C. parasitica isolate from Trás-os-Montes showed a white culture morphology and contained dsRNA, indicating the presence of hypovirulence in this area. [ABSTRACT FROM AUTHOR]

Castanea sativa, one of the most precious forest trees in Greece, is affected by the spread of chestnut blight all over the country. Identification and mapping of the vegetative compatibility (vc) types of the fungus Cryphonectria parasitica was carried out and the occurrence of hypovirulence was checked. In 11 chestnut populations distributed all over Greece, 627 isolates were obtained and their vc type was determined. Four vc types were identified by means of tester isolates: EU-12 was found to be the dominant vc type reaching a percentage of 88%, with EU-2 (6%), EU-10 (3%) and EU-1 (2%) following. EU-12 was found in all 11 populations investigated whereas EU-2 was isolated from five populations and EU-10 and EU-1 were found only in one population each. Natural hypovirulence was also found in five populations of 11 examined. Perithecia were not found in either population, a finding supported by the fact that all Greek isolates examined belonged to a single mating type, MAT-1. The low diversity in vc types, the absence of the perithecial stage and the occurrence of natural hypovirulence in some areas support the feasibility of successful application of biological control on the national level in Greece. [ABSTRACT FROM AUTHOR]

In Macedonia, hypoviruses in the chestnut blight fungus, Cryphonectria parasitica, were first identified in 1995, more than 20 years after the discovery of chestnut blight. Between 1995 and 2000, 488 isolates of the fungus were collected from 19 sites throughout Macedonia. These isolates were screened for hypoviruses by extraction of double-stranded RNA (dsRNA) and electrophoresis on agarose gels. We found dsRNA of approximately 12 kb in length in 95 isolates in eight subpopulations of the fungus. Subpopulations with the highest virus incidence were Skudrinje (63%) and Jepiste (43%) in the Debar region, and Frangovo (46%) in the Struga region. Virus incidence in other subpopulations was much lower. To test whether the 12-kb dsRNAs are Cryphonectria hypovirus 1 (CHV-1), we subjected a sample of 27 isolates to reverse transcription (RT)-PCR and RFLP analyses. All 27 were identified as CHV-1 and belonged to the Italian subtype (subtype-I); all of these isolates were white in culture, typical of CHV-1-containing isolates. Most isolates had RFLPs identical to those previously found in other countries of southern Europe. Future studies will investigate hypoviruses from various origins in Macedonia for their biological control potential. Preliminary field surveys identified superficial cankers at all chestnut populations where CHV-1 was found. [ABSTRACT FROM AUTHOR]

The bark miner Spulerina simploniella (Lepidoptera: Gracilariidae) was found in coppice chestnut ( Castanea sativa) forests in Greece but was not found in chestnut orchards. Its larvae mine under the thin periderm of young trees, 4–10 years old, while the stem bark is still smooth. Under normal conditions it does not cause any damage to the trees. However, when chestnut blight caused by Cryphonectria parasitica is present in the area, the insect may be an agent of disease spread. Experiments revealed that spraying of 23 pupation sites with a C. parasitica conidiospore suspension caused canker formation at a rate of 100% in the coppice chestnut forests of Mount Athos, North Greece. It is believed that rain during the pupation period (approximately May 23 to June 15) may deposit conidiospores on the freshly exposed phloem and cause cankers. This bark miner has been detected in several parts of Greece, however, always in intensively managed chestnut coppice forests. [ABSTRACT FROM AUTHOR]

Three indigenous field strains of the chestnut blight fungus, Cryphonectria parasitica collected in 1996 from a test site in the Meshomasic State Forest, Connecticut, USA, were engineered to contain a chromosomally integrated full-length infectious cDNA copy of the severe, virulence-attenuating hypovirus CHV1-EP713. These transgenic hypovirulent strains were introduced into the test site after it had been clear-cut, as sprayed conidia in multiple applications over 4 years, beginning in 1997. Evidence was obtained for cytoplasmic transmission of cDNA-derived hypovirus RNA and for recovery of transgenic strains from canker tissue of the spray-treated trees. However, there was no indication of spread of transgenic strains or cDNA-derived viral RNA to the control plot or outside the treatment plot. A single transgenic C. parasitica isolate was identified from a total of 156 isolates recovered from 1330 insects representing five insect orders. Only 2.6% of the 1082 C. parasitica bark isolates recovered during the course of this study were vegetatively compatible with the untransformed input strains. Transgenic ascospore progeny were produced by 40% of the perithecia collected in 1999 and by only 7.3% of the perithecia collected in 2000. A concurrent field release study performed in the Monongahela National Forest in West Virginia in 1998 and 1999 with transgenic hypovirulent strains constructed with the same CHV1-EP713 cDNA-containing plasmid identified seasonal application dates and delivery methods that resulted in very high levels of transgenic ascospore production. Results of the combined field release studies are discussed in terms of requirements for improved formulations and delivery methods and the importance of balancing ecological fitness and virulence attenuation. [ABSTRACT FROM AUTHOR]

Summary Seasonal variation in the development of chestnut blight, caused by Cryphonectria parasitica , was investigated by inoculating in situ chestnut trees and in vitro excised chestnut segments, at either monthly or 3-monthly intervals throughout 30 months. Inoculations were made with conidia and mycelium of a virulent isolate and with mycelium of a hypovirulent isolate. Conidial inoculations of living sprouts or excised segments between May and July resulted in the greatest incidence of infection whereas inoculations in autumn and winter, in vitro as well as in situ , did not reveal any visible disease. However, from these symptomless inoculated stems, C. parasitica was isolated 3 months after inoculation. Inoculations with the mycelium of the virulent isolate always resulted in lesions, except in January 1999, and the greatest rate of lesion development occurred for inoculations made in the spring and summer. There was a significant seasonal effect on lesion development. Lesions caused by the hypovirulent isolate, smaller than those caused by the virulent isolate, followed a similar seasonal pattern. The same seasonal variations were observed for inoculations in vitro of excised segments. Relative water content (RWC) of chestnut bark significantly varied with bark sampling date. The rate of lesion development in sprouts significantly correlated with average minimum (ATn) and maximum (ATx) temperatures and the sum of rainfall during inoculation period, with the rate of lesion development measured in excised segments 10 days after inoculation (R10d) and with RWC measured on the day of inoculation. In multiple regression models, variables ATx and R10d best explained variation in lesion development. [ABSTRACT FROM AUTHOR]

The occurrence of Colletotrichum acutatum J. H. Simmonds in necrotized galls of Dryocosmus kuriphilus Yasumatsu in chestnut ( Castanea sativa Miller) stands is reported for the first time in Italy. Morphological and biomolecular analyses confirmed the isolation of the fungus. No damage by the fungus has been observed. [ABSTRACT FROM AUTHOR]

Infection of American and European chestnuts with the chestnut blight fungus Cryphonectria parasitica results in the formation of cankers, lesions caused by the growth of mycelia within bark tissue of the host plant. Infection of the fungus with Cryphonectria hypovirus 1 (CHV‐1) results in conversion of the mycelial phenotype from virulent to hypovirulent, thus allowing production of callus around cankers as a reaction by infected trees, rendering active into inactive cankers. In this study, we sampled one USA and six European chestnut stands and assessed frequency of hypovirulent C. parasitica and diversity of vegetative compatibility (vc) types present in calluses and randomly sampled cankers. Callused cankers on C. dentata at West Salem in the USA yielded significantly more hypovirulent C. parasitica isolates compared with four sampled populations on C. sativa, while all six sampled European populations did not show any statistically significant differences among themselves. We observed no correlation between hypovirulence frequencies in randomly sampled cankers and calluses, as well as no correlation of C. parasitica vc type diversity in calluses and residential populations of the fungus. Furthermore, even though we have observed calluses with more than one vc type, they do not occur regularly. Even when present in C. parasitica populations with high vc type diversity, no more than three different vc types were observed in a single callus. [ABSTRACT FROM AUTHOR]

Chestnut blight is a stem‐girdling disease of Castanea caused by the fungal pathogen Cryphonectria parasitica. Chestnut blight affects all Castanea species to some degree. In Asian species, chestnut blight is a commercially relevant disease which primarily affects nut production. In American and European species, chestnut blight has caused significant declines in wild populations and continues to negatively affect nut production in the European chestnut (C. sativa). Despite the profound effect of this disease in the Castanea genus, very little is known concerning the factors involved in the host–pathogen interaction between C. parasitica and its Castanea hosts. This review summarizes information on known mechanisms and metabolites involved in the host–pathogen interaction and contributes original information on the pathogen in relation to susceptible and putatively resistant genotypes with a view to furthering research that will promote a better understanding of this devastating disease and enable its control. [ABSTRACT FROM AUTHOR]

Sweet chestnut (Castanea sativa) is an important tree species in the Marmara and Aegean regions of Turkey as these two regions produce the great majority of edible nuts, especially those used for marron glacé production. Chestnut forests and orchards in these regions showing severe dieback symptoms not associated with chestnut blight were investigated to determine the role of Phytophthora spp. in the decline syndrome. Soil samples were collected from around 108 symptomatic chestnut trees at 29 sites and Phytophthora spp. isolated using soil baiting technique and selective medium. Species isolated were identified by cultural characteristics and ITS sequencing. Phytophthora x cambivora was the dominant species detected in 13 sites, followed by P. cinnamomi (5 sites), P. plurivora (3 sites) and P. cryptogea (1 site). Phytophthora x cambivora was present in both regions, while P. cinnamomi was found only in the Marmara region in coastal areas around Istanbul. When inoculated at the stem bases of 3‐year‐old chestnut saplings, P. cinnamomi produced significantly longer necrotic lesions (7.8–12.0 cm) than P. x cambivora (2.6–6.3 cm) by 12 days after inoculation. Phytophthora plurivora was the least aggressive species causing only small lesions. Phytophthora cryptogea, which represents the first record on chestnut in Turkey, produced intermediate sized lesions in between P. x cambivora and P. plurivora. These results indicate that P. x cambivora and in some areas P. cinnamomi play major roles in the observed dieback of sweet chestnut in western Turkey. [ABSTRACT FROM AUTHOR]

Castanea sativa forests in north‐eastern Spain have historically been healthy and have been good producers of timber and non‐wood forest products. In the last quarter of a century, Fistulina hepatica has gained relevance in this ecosystem and is believed to be responsible for Chestnut Red Stain (CRS), which inflicts heart rot in trees and causes severe economic losses. The fungus grows in the heartwood and produces no external symptoms that would enable early detection. With the objective of developing an inexpensive method to detect heart rot and to discover possible relationships between the severity of F. hepatica attack and the silvicultural management or site characteristics of chestnut stands, 38 pure C. sativa plots were selected, sampled and analysed for the presence of the fungus. DNA was extracted from the heartwood samples, and PCR was used to amplify target sequences with specific F. hepatica primers for non‐homologous ITS1 and ITS2 regions. Correlation analysis was used to inspect the multiple interactions among the environmental and management variables examined, and a predictive model was designed for forest managers to estimate the risk of infection. Both analyses revealed that stress variables were related to CRS severity. This result is especially relevant since temperatures are expected to rise in coming decades throughout the northern rim of the Mediterranean region, where chestnut is an important species. This study provides two tools for better managing chestnut forests in the coming years: an inexpensive and fast tool for diagnosis and a predictive model to estimate the risk of infection. [ABSTRACT FROM AUTHOR]

Phytophthora cinnamomi was repeatedly isolated from the rhizosphere of recently dead sweet chestnut trees in the upper Rhine valley. Identification was genetically confirmed by RFLP and sequencing of the ITS‐region. This is the first record of P. cinnamomi on forest land in Germany. Mode of introduction of this invasive species and potential factors favouring establishment are discussed. [ABSTRACT FROM AUTHOR]

The Valdivian rainforest, one of the global hotspots of biodiversity, is a temperate rainforest originating as a Tertiary relic from the supercontinent Gondwana. In November 2014, a survey of Phytophthora diversity was performed in 13 natural forest stands and 20 forest streams and rivers in two protected areas near Valdivia and in a temperate montane forest in the Concepción area. One planted stand each of the introduced tree species Castanea sativa and Fagus sylvatica were also included. Using baiting assays, eight described species and four previously unknown taxa of Phytophthora were isolated from 86% of the 50 rhizosphere soil samples from seven of the eight tree species sampled in 12 forest stands, and from 20 streams: P. chlamydospora, P. cinnamomi, P. kernoviae, P. lacustris, P. plurivora, P. pseudosyringae, P. ×cambivora, P. ×stagnum, P. valdiviana nom. prov. from Clade 2b, P. madida nom. prov. from Clade 8a, and P. chilensis nom. prov. and P. pseudokernoviae nom. prov. The latter two species are the closest relatives of P. kernoviae from Clade 10. Phytophthora pseudokernoviae nom. prov. was also isolated from necrotic leaves of Drimys winteri. From the Valdivia river, a swarm of three Clade 6 hybrids was recovered. Each hybrid isolate resulted from multiple reticulation events with P. thermophila as maternal and both P. amnicola and P. chlamydospora as paternal parents. In addition, three previously unknown and recently described Nothophytophthora species, N. caduca, N. chlamydospora and N. valdiviana, were isolated from several forest streams. Phytophthora cinnamomi, the most common and widespread species in soils of native forests, was associated with severe dieback of Valdivian rainforest trees, in particular D. winteri, Luma apiculata, Nothofagus dombeyi and the endangered Saxegothaea conspicua. A first pathogenicity test demonstrated high aggressiveness of P. cinnamomi to several native tree species, including N. dombeyi, Blepharocalyx cruckshanksii and Gevuina avellana. [ABSTRACT FROM AUTHOR]

To extend our knowledge of population structure of Cryphonectria parasitica in the Aegean region, 264 isolates obtained from eight subpopulations in Izmir, Manisa and Denizli provinces were studied. Only three vegetative compatibility (vc) types, EU‐1, EU‐12 and EU‐2, were identified. EU‐1 (59%) was dominant and was found in all eight subpopulations. EU‐12 (32%) was detected in six subpopulations and was highly dominant (71%) in the Ödemiş subpopulation (İzmir province). EU‐2 was restricted to only one subpopulation, Tire, but, there, had the highest frequency (50%). This is the first reported occurrence of EU‐2 in western Turkey. Regarding sexual compatibility, both MAT1‐1 and MAT1‐2 were detected in all subpopulations; however, 85% of the isolates were MAT1‐1 and no perithecia were found in any of the subpopulations. Multilocus linkage disequilibrium analysis determined that all subpopulations were clonal. Indicator co‐kriging representations showed that vc types and mating types were spatially aggregated. In combination, these results indicate that the dispersal of the pathogen most likely occurs via localized short‐distance transport of rain‐splashed asexual conidia, rather than the long‐distance dispersal of wind‐borne ascospores. Because of the presence four polymorphic vegetative incompatibility (vic) loci in certain subpopulations, C. parasitica has the potential to generate new vc types in the future. [ABSTRACT FROM AUTHOR]