Vc Types Research Articles

High frequency of vegetative incompatibility combined with haploid selfing in the native European ash foliage coloniser Hymenoscyphus albidus

Abstract The native European ash fungus Hymenoscyphus albidus is threatened by the morphologically similar introduced ash dieback pathogen Hymenoscyphus fraxineus . H. fraxineus is heterothallic and its populations comprise numerous different vegetative compatibility (vc) types. H. albidus is homothallic with unknown population diversity. In vitro pairings of H. albidus isolates from one French and three UK sites showed compatible (intermingling) and incompatible (gap) reactions similar to those in H. fraxineus. Local vc diversity was high with vc types per isolate ranging from ca. 0.7 to 0.9 and the probability of any two isolates being incompatible ca . 93–98%; suggesting at least four biallelic vic loci in each population. Pairings between single ascospore isolates from the same apothecium, however, were uniformly compatible. All rachis and single ascospore isolates had both MAT1-1-3 and MAT1-2-1 mating type genes, consistent with homothallism. The results suggest local H. albidus populations comprise numerous, vegetatively incompatible genets maintained in part by haploid selfing.

Effects of carbides on abrasive wear properties and failure behaviours of high speed steels with different alloy element content

High speed steels (HSSs) are effective materials applied in aggressive environments where abrasion resistances are required because they have hard carbides and relatively ductile matrix to bind carbides. But there are many kinds of carbides in HSSs, which lead to different effect on wear properties of HSSs. In this paper, three kinds of casting HSSs with VC, M6C or M2C type carbide were prepared respectively through the reasonable design of alloy elements, and then the effects of carbide type on wear behaviours were researched under different abrasive particle size and load using abrasive wear testing machine. The microstructures and failure behaviours of HSSs were analyzed by electron microscopy. The results showed the abrasive particle size and load had obvious effect on wear weight loss of high speed steel (HSS), but the carbide type decided the relative wear resistance of HSS. As the abrasive particle size or load increased, the wear weight loss of any HSS increased obviously. For the fine abrasive wear, the HSS with M6C had higher relative wear resistance than HSS with M2C. But the contrary was the case for the coarse abrasive wear. For any abrasive particle size and load, the HSS with VC had more excellent wear resistance than HSS with M6C or M2C type carbide. The relative wear resistance of HSS with VC was three times higher than that of HSS with M6C or M2C. The excellent wear resistance of HSS with VC was mainly attributed to VC characteristics, such as high hardness and good morphology, which can resist micro-cutting of abrasive particles efficiently.

Occurrence of hypovirus-infected Cryphonectria parasitica isolates in northern Spain: an encouraging situation for biological control of chestnut blight in Asturian forests

The presence of hypovirulent (hypovirus-infected) isolates of the chestnut blight fungus Cryphonectria parasitica in Asturias, northern Spain, is first reported by using both morphological and molecular assessments. Hypovirulence was detected in 16 of the 69 councils where the fungus was previously observed. In total 30 of the 863 C. parasitica isolates analyzed were found to be hypovirus-infected. The isolates belonged to the two main vegetative compatibility (vc) types (EU-1 and EU-13) of the region. Asturian hypoviruses were genetically characterized by sequencing of ORFA and ORFB specific regions of the hypoviral RNA. The results show that 70% of the investigated hypovirulent isolates contained the Spanish subtype (subtype E) while 30% isolates the German subtype (D) of Cryphonectria hypovirus 1 (CHV-1). The presence of hypovirulent isolates compatible with the dominant vc types and the low vc diversity in this region favours the application of biological control. An initial disease management effort could be applied by using the hypovirus of subtype D, whereas further research related to the biocontrol properties of the subtype E hypovirus should be conducted.

Factors influencing growth, sporulation and virus transfer in Cryphonectria parasitica isolates from Castilla and León (Spain)

Biological control with Cryphonectria hypovirus CHV1 of the chestnut blight, caused by the fungus Cryphonectria parasitica, has reduced the impact of the disease in Europe. The virus reduces the virulence of the fungus so that it causes non-lethal cankers, thus enabling the chestnut trees to overcome the disease. The virus can be transmitted horizontally by hyphal anastomosis or vertically to the conidia. In this study, we investigated growth and sporulation of the fungus as well as rates of horizontal transmission of the virus at different temperatures. We used fungal isolates of the vegetative compatibility types (vc types) that are most prevalent in Castilla and Leon (central northern Spain) to evaluate the effects of fungal strain on the parameters tested. In addition, we infected four isolates of C. parasitica with hypovirus subtypes CHV1-F1 and CHV1-I, to determine the influence of virus subtype on growth, sporulation and virus transfer. We assessed growth of fungal colonies and horizontal transmission of the virus at 15 °C and 25 °C. Colony growth was affected by an interaction between fungal isolates included in vc type EU1 or EU11 and virus at both 15 °C and 25 °C. However, horizontal transmission of the virus was only influenced by the fungal genotype of isolates included in vc type EU1 or EU11, and spore production was only affected by the virus subtype. Vertical transmission was also influenced by the fungal isolate and virus subtype. Growth of the fungal isolates varied depending on the virus subtype with which they were infected. This supports the theory that fungal host and virus subtype influence transmission and dissemination of hypovirulence. The fungal genotype affects colony growth and horizontal transmission of the virus. It is common to expect a good dissemination of the hypovirus with a low vc type diversity but the selection of the best combination of hypovirus and fungal isolate is crucial for the success of biological control not only for small areas but in larger chestnut populations as well.

Cryphonectria parasitica isolates of the same vegetative compatibility type display different rates of transfer of CHV1 hypovirus

Hypovirulent strains of the chestnut blight fungus Cryphonectria parasitica have not been registered in the autonomous region of Castilla y Leon (Spain), except in the province of Leon. In this laboratory-based study, we analyzed the rates of horizontal transmission of hypovirus CHV1 subtype F1, isolated from chestnut stands in Leon. We tested the conversion capacity of the six vegetative compatibility (vc) types of C. parasitica isolates most commonly distributed in Castilla y Leon (EU1, EU11, EU12, EU66, CL5 and CL6). We investigated conversion rates of virulent isolates into hypovirulent isolates between pairings of isolates of the same vc type (EU1, EU11 and CL6) and also tested cross conversion rates between isolates of different vc types (EU1, EU11 and CL6 as donors and EU12, EU66, CL5 and CL6 as recipients). We carried out the hypovirus transmission assay with 1700 pairings, of which 700 had donor and recipient isolates of the same vc type and 1000 pairings of isolates had different vc types. Our results show that the conversion frequency to hypovirulent isolates was significantly affected by the vc type, the genotype of isolates with the same origin (province) and the interaction between both factors. In the conversion between isolates of the same vc type, the conversion rates were better with EU1 (ranging between 56 and 94 %) than with EU11 (varying from 4 to 58 %). In the cross conversion between donor and recipient isolates of different vc types, only CL5 and CL6 recipients were converted and the conversion of recipient isolates of EU12 and EU66 failed in all cases. For CL5 as recipient isolate, the conversion rates were similar with EU11 and CL6 as the donor isolates. Recipient isolates of CL6 had good conversion with donor isolates from the same vc type (CL6) and in cross conversion the results were better with donor EU1. Fungal isolates from chestnut stands in Leon displayed the best conversion rates, followed by those from Zamora, Salamanca and Avila when the donor and the recipient isolates were of the same vc type. The fungal isolates appear to have a strong influence on the transmission rate of the hypovirus, at least between strains isolated from chestnut stands in Castilla y Leon. EU1 isolates were more susceptible to conversion than the isolates from EU11. The results highlight the differences in hypovirus transmission, regarding vc types and the genotype of isolates from the same province, when donor and recipient isolates are of the same vc type. Further transmission assays would be useful to determine why hypovirus transmissions, when compared to the hypovirus transmission of other European assays, have different conversion rates with fungal isolates from Castilla y Leon.

Establishment and dissemination of hypovirulent strains of Cryphonectria parasitica in Greece

SummaryChestnut blight caused by Cryphonectria parasitica has been one of the major reasons for the decline of chestnut cultivation in Greece over the last 50 years. A previous detailed study of the vc types of the fungus has revealed only four vc types in the entire country, those of EU‐1, EU‐2 and EU‐10 with the dominant being EU‐12 counting for 88% of the isolates. As the loss in orchard trees reached in some chestnut producing prefectures over 35% of the trees, the decision was taken to apply biological control on a nationwide scale. The project was implemented in 17 prefectures during the period 2007–2009. Hypovirulent (hv) strains of C. parasitica which were infected by the CHV‐1 subtype I (Italian subtype) viruses which occur naturally in Greece were used. The necessary hypovirulent inoculum was prepared at the Forest Research Institute during the period 2007–2009 on a large scale, however, with laboratory care. Three million inoculations were made around accessible developing cankers over three consecutive years by trained personnel. An extensive evaluation conducted in 2011 in the 12 of the 17 treated prefectures, where no natural hypovirulence had been found before, demonstrated not only the successful establishment of hypovirulence but also profound dissemination and healing of non‐inoculated cankers. The extent of dissemination varied significantly among sampling plots and among prefectures. The conclusion is drawn that CHV‐1 subtype I has successfully established and spread into chestnut orchards and coppice forests resulting in a gradual decline of chestnut blight.

75 years of the chestnut blight fungus Cryphonectria parasitica (Murr.) Barr in Europe

The chestnut blight fungus Cryphonectria parasitica is a native pathogen in East Asia and has been introduced into North America and Europe. Historical records and population genetic studies revealed at least three major introduction events from Asia into Europe.
 Nowadays, chestnut blight is present in almost the entire distribution range of European chestnut, i.e. from the Iberian Peninsula to the Caucasus. The C. parasitica population in most countries has been studied in respect to the diversity of vegetative compatibility (vc) types and the occurrence of hypovirulence. The vc type diversity of the different populations varied considerably. Typically, a high diversity of vc types has been found in areas with a long history of chestnut blight and where sexual recombination between divergent genotypes commonly has occurred. On the other hand, newly established populations often showed a low diversity with only one, or a few vc types present.
 Hypovirulence, i.e. the occurrence of C. parasitica isolates infected by Cryphonectria hypovirus 1 has been found widespread in Europe. Natural dissemination and active biological control applications have lead to a high prevalence of the hypovirus and to the recovery of many chestnut stands. Virulent cankers became hypovirus-infected within a short time and ceased expansion. There is concern that the diversity of vegetative compatibility types could increase in Europe through sexual reproduction between C. parasitica genotypes originating from different introductions. A higher level of vegetative incompatibility would not only hamper hypovirus spread within a population but could also select for lower virulence in CHV-1 and subsequently lead to an erosion of biological control. Recent studies, however, indicate that the vc type barriers are not so restrictive than previously assumed and that so far no evidence for an erosion of biological control system in high diversity populations can be observed.

Dynamics of Cryphonectria hypovirus Infection in Chestnut Blight Cankers

Virulent strains of the chestnut blight fungus Cryphonectria parasitica cause lethal bark cankers on chestnut trees. Infection of C. parasitica with Cryphonectria hypovirus 1 in Europe biologically controls this disease, leading to nonlethal and inactive cankers. Unexpectedly, virus-free C. parasitica strains have been isolated from inactive cankers. In this study, we compared the virulence of virus-infected and virus-free C. parasitica strains isolated from either inactive or active cankers on chestnut seedlings and sprouts. In the seedling experiment, we assessed canker growth and seedling mortality. In the sprout experiment, we also assessed canker growth and made fungal reisolations to determine virus infection and immigration of foreign vegetative compatibility (vc) types over a period of 13 years in a coppice forest. Overall, the virulence of virus-free C. parasitica strains isolated from inactive versus active cankers did not differ. Significant differences were only attributed to virus infection. Virus infection and fungal strain composition in cankers changed over time. Foreign vc types immigrated into cankers and virus-free cankers became virus-infected within a few years. Most of the cankers were callused over time and became inactive. However, we observed that the virus did not always persist in these cankers. This study demonstrates that virus spread occurs effectively in European chestnut forests and that this biocontrol system is highly dynamic.

Control of chestnut blight by the use of hypovirulent strains of the fungus Cryphonectria parasitica in northwestern Spain

Chestnut blight is controlled in Europe by using Cryphonectria hypovirus CHV1, a non-encapsulated RNA virus. The chestnut blight fungus, Cryphonectria parasitica, is weakened by the virus, and healing tissue growth occurs in the host tree. Transmission of this cytoplasmic hypovirus is restricted by the incompatibility system of the fungus, so that the hypovirus can be transmitted only between isolates of the same or closely related vegetative compatibility (vc) types. Hypovirulent isolates of C. parasitica (all of the French subtype CHV1-F1) from Castilla y León (NW Spain) were compared with virulent isolates in both laboratory (cut stems) and field inoculations (in two orchards in the province of León and one orchard in the province of Zamora). The tests were performed with the most common vc types in the region, EU1 and EU11. The cut stem assay revealed that the hypovirulent isolates of vc type EU1 did not reduce the growth of virulent cankers. By contrast, four hypovirulent strains H1, H4, H5 and H6 (all vc type EU11) reduced the growth of virulent isolates in the cut stem assay. Field tests showed that hypovirulent isolates of EU1 and EU11 were effective in reducing canker in both orchards in León with all treatments tested; however, in Zamora, where only EU11 was tested, all the treatments failed except H1, which was able to reduce growth of the canker eighteen months after the inoculation. The development of hypovirulence suggests that hypovirus subtype F1 is well adapted in the province of León. Both naturally extended and inoculated hypoviruses appear to have reduced the incidence of the canker, thus improving chestnut stands. However, the inoculations were not as effective in the orchards in Zamora. This indicates that the disease could be controlled in Castilla y León by inoculation of trees with hypovirulent strains, but that more tests should be done in provinces where the hypovirus is still not present.

Trouble de la posture : avis chirurgical

A spatially explicit, interacting particle system model was developed to simulate the heterogeneous transmission of viruses in fungal populations. This model is based primarily on hypoviruses in the chestnut blight fungus, Cryphonectria parasitica, which debilitate their hosts and function as biological control agents. An important characteristic of this system is that virus transmission occurs freely between individuals in the same genetically defined vegetative compatibility (vc) type, but is restricted among individuals in different vc types, resulting in heterogeneous transmission. An additional source of heterogeneity is spatial structure in host populations; viruses are dispersed by fungal spores which disperse relatively short distances. The model showed that vc type diversity is highly correlated to the horizontal transmission rate and therefore significantly affects virus invasion. The probability of virus invasion decreased as the diversity of vc types increased. We also demonstrated that virus transmission would be overestimated if we assumed virus transmission was homogeneous, ignoring both genetic and spatial heterogeneity. Genetic and spatial heterogeneity are not independent because both are affected by the reproductive biology of the fungus. In asexual populations, restricted fungus dispersal resulted in nonrandom spatial patterns of vc types, increasing the chance of contact between vegetatively compatible individuals, and promoting virus transmission. In contrast, virus transmission was poor in sexual populations due to spatial randomization of vc types by long distance dispersed sexual spores. Finally, this model was used to evaluate the release of genetically engineered virus-infected strains for disease management. The release of transgenic strains resulted in only marginally greater virus establishment than for non-transgenic strains. Virus invasion was still restricted by vc type diversity in the resident fungus population. Simulation of inundative releases of transgenic virus-infected strains slightly improved virus establishment, but viruses did not persist after treatment was terminated.

Genetic diversification of the chestnut blight fungus Cryphonectria parasitica and its associated hypovirus in Germany

Chestnut blight in south-western Germany was first reported in 1992 and is since expanding in distribution. Here we investigated the invasion history of Cryphonectria parasitica and its associated hypovirus. For this, we characterized 284 isolates collected between 1992 and 2012 for hypovirulence, vegetative compatibility (vc), mating type, and microsatellite haplotype. A total of 27 haplotypes and 15 vc types were observed, although the C. parasitica population analyzed is currently dominated to 50 % by one haplotype and to 64 % by the vc type EU-2. Structure analysis indicated two divergent genetic pools. Over 66 % of the haplotypes belonged to a pool probably originating from northern Italy. Further diversification is expected due to ongoing sexual recombination, but also to new migration and additional introductions. Cryphonectria hypovirus 1 (CHV-1) was found in four of five C. parasitica populations from Baden-Württemberg. Genetic analysis of the 35 CHV-1 isolates obtained revealed that they all belong to the German subtype, although they have clearly diverged from the first German hypovirus isolated in 1992. Our study suggests that C. parasitica has been introduced into Germany several times from two different gene pools, whereas the hypovirus most probably has a single origin.

Distribution of chestnut blight and diversity of Cryphonectria parasitica in chestnut forests in Bulgaria

SummaryWe surveyed chestnut stands at 18 sites in 11 locations in Bulgaria in 2005 and 2007 for the presence of chestnut blight. We found chestnut blight in seven locations (Belogradchik, Berkovitsa, Brezhani, Barziya, Govezhda, Petrich and Petrovo) but not in four others (Tsaparevo, Kresna, Dupnica and Botevgrad). We successfully isolated Cryphonectria parasitica from cankers on 606 trees with symptoms of chestnut blight and assayed them for vegetative compatibility (vc) types and mating type. Three vc types were identified among the 606 isolates; all three were among the European vc types with known vegetative incompatibility (vic) genotypes. Vc type EU‐12 was the most common, representing 80% of the isolates, and was found at all locations with blight, with the exception of Belogradchik in north‐west Bulgaria, where all isolates were vc type EU‐2. Only one population (Barziya) had more than one vc type, with a combination of EU‐12 and EU‐10 in almost equal frequencies. Similarly, the diversity of mating types was very low. All but three of 536 isolates assayed were in mating‐type MAT‐1; MAT‐2 was only found in one population in the north‐west (Berkovitsa). We inspected 671 bark samples from chestnut blight cankers with stromata of C. parasitica and found perithecia in only 33, of which 28 were from Berkovitsa where MAT‐2 was present. We did not detect hypoviruses in any of the 270 isolates screened using the standard double‐stranded RNA extraction protocol. Similar to results from previous studies in south‐eastern Europe, the diversity of vc types and mating type of C. parasitica in Bulgaria is low, and reproduction of the fungus is mainly asexual. Unfortunately, naturally occurring hypovirulence was not detected. Nevertheless, we observed a small number of superficial cankers typical of those caused by C. parasitica isolates infected with a hypovirus.

English

Bursa and Yalova provinces are very important centers of chestnut production and processing. Chestnut blight is a serious disease of Castanea spp. and the only feasible method to control it is the use of hypovirulence. Hypovirulence and vegetative compatibility (vc) types of 198 isolates of Cryphonectria parasitica obtained from 15 different locations from Bursa and Yalova provinces in three years were determined and discussed. Vc types of C. parasitica isolates were evaluated by using six European vc types; EU–1, EU–2, EU–5, EU–6, EU–12 and EU–14. All strains were found to belong to EU1 vc type. White mycelial growth which is typical for hypovirulence was observed in 12% of the isolates. All these white-growing isolates were found to contain ds-RNA. Presence of only one fungal vc type and one hypovirus subtype (Subtype I) which was determined by analyzing gene sequences of dsRNA of the hypovirus in our previous work suggests that a possible biological control of the disease might be applied in this region.

Patterns of Venture Capital Investments in Europe

We study the investment strategies of different types of Venture Capital investors (VCs) using a unique dataset that includes 1,663 VC first investments made by 846 investors in 737 young high-tech entrepreneurial ventures located in seven European countries between 1994 and 2004. Using a transformed Balassa index, we analyze the relative investment specialization of independent VCs, corporate VCs, bank-affiliated VCs and governmental VCs along several dimensions that characterize investments (e.g., syndication, duration and exit mode) and investee companies (e.g., industry of operation, age, size, development stage, location and distance from investor’s premises at the time of the investment). Our findings indicate that VC types in Europe differ markedly in their patterns of investment specialization, especially governmental VC on the one side and private VC on the other. We compare our findings with evidence from the USA and find some interesting differences, notably regarding independent and governmental VCs.

CpBir1 is required for conidiation, virulence and anti-apoptotic effects and influences hypovirus transmission in Cryphonectria parasitica

Inhibitors of apoptosis proteins (IAPs) are critically important in the regulation of unicellular yeast and metazoan apoptosis. All IAPs contain one to three baculovirus IAP repeat (BIR) domains, which are essential for the anti-apoptotic activity of the IAPs. A homolog of IAPs, CpBir1, which bears two BIR domains, was recently identified from the chestnut blight fungus Cryphonectria parasitica genome. CpIAP was deleted by gene replacement, and the phenotypes of ΔIAP were characterized. CpBir1 was significantly down-regulated by hypovirus infection but up-regulated by H2O2. Similar to Saccharomyces cerevisiae Bir1p, the Cpbir1 mutant was sensitive to H2O2, and constitutive overexpression of CpBir1 increased resistance to H2O2. The Cpbir1 mutant also showed defects in aerial hyphal formation, colony growth, mycelial morphology, conidiogenesis, pigmentation, resistance to stress conditions and virulence. Genetic complementation with native Cpbir1 fully recovered all these defective phenotypes. The CpBir1-eGFP fusion protein was localized to the nucleus in juvenile cultures, while it was found in the cytoplasm in old cultures, suggesting that the localization pattern of CpBir1 may correlate with the process of anti-apoptosis. Increased accumulation of reactive oxygen species (ROS) in the Cpbir1 deletion mutant further supports the anti-apoptotic function of CpBir1. Among five selected vegetative compatible (vc) types of C. parasitica, Cpbir1 deletion was found to block virus from transferring between Cpbir1 mutants. However, hypovirus infected Cpbir1 mutants showed a similar ability to transmit virus to other virus-free isolates compared with the infected wild-type strain. In summary, Cpbir1 encodes an IAP CpBir1 that is down-regulated by hypovirus infection and required for conidiation, virulence and anti-apoptosis, as well as affects hypovirus transmission in chestnut blight fungus C. parasitica.

Characterization of hypovirulent isolates of the chestnut blight fungus, Cryphonectria parasitica from the Marmara and Black Sea regions of Turkey

Chestnut blight caused by the introduced fungus Cryphonectria parasitica has been responsible for the decline of Castanea sativa in Turkey since the 1960s. In this study, 72 C. parasitica isolates were recovered from the Marmara and Black Sea regions of Turkey showing white or cream-coloured culture morphology and were subjected to various tests to determine if they were infected by Cryphonectria hypovirus 1 (CHV-1). The vast majority of the isolates (69 out of 72) were vc type EU-1. Both mating types were found among a subsample of the isolates. The hypovirus was detected in 55 isolates by dsRNA extraction and/or virus specific RT-PCR on total RNA extracts. All but one isolates showed no or only weak phenol oxidase activity on agar medium containing tannic acid, typical of CHV-1 infected isolates. Through sequencing of a specific region of the hypovirus genome, we found that 24 hypovirus isolates belonged to the CHV-1 subtype I and six to the CHV-1 subtype F2. The distribution of the two CHV-1 subtypes in Turkey showed a clear geographic pattern. CHV-1 subtype I was only detected in the Marmara and western Black Sea region, whereas subtype F2 was restricted to the eastern part of the Black Sea region. The effectiveness of 23 hypovirulent isolates was tested against a virulent isolate on 2–3 years old chestnut sprouts. Ten hypovirulent isolates, all infected by CHV-1 subtype I, prevented canker development by more than 80 % suggesting that they might be suitable for biological control of chestnut blight in Turkey.

Diversity of Cryphonectria parasitica in western Spain and identification of hypovirus‐infected isolates

SummaryIsolates of the chestnut blight fungus Cryphonectria parasitica were obtained from 44 localities in four provinces in Western Spain and characterized for vegetative compatibility (vc) types, mating types and the presence of Cryphonectria hypovirus 1 (CHV1). Among the 1232 isolates recovered from chestnut blight cankers, 11 vc types were identified: five known vc types included in EU1 to EU74 (EU1, EU11, EU12, EU28 and EU66) and six unknown vc types (CL4, CL5 CL6, CL8, CL9 and CL10). The number of vc types found per province varied between two and seven. The vc type EU11 was present in all provinces and accounted for 48.9% of all isolates. EU1 was detected in three provinces and accounted for 39.1% of the isolates. The vc types EU12, EU66, CL5 and CL6 were present in one or two provinces and comprised between 2.4% and 3% of the isolates. The other vc types were represented by only one or very few isolates. The mating type MAT‐1 was largely dominant in the provinces Leon and Avila, while both mating types MAT‐1 and MAT‐2 were found in Salamanca and Zamora. Fourteen hypovirus‐infected C. parasitica isolates were found, nine were in vc type EU1 and five in EU11, and they were detected only in the province León. All isolates analysed contained the French hypovirus subtype CHV1‐F1.

Chestnut blight in south‐western Germany: multiple introductions of Cryphonectria parasitica and slow hypovirus spread

SummaryCryphonectria parasitica was discovered in the sweet chestnut forests of south‐western Germany in 1992. Two main areas affected by chestnut blight were discerned, one to the east and one to the west of the Rhine valley. The occurrence of the fungal pathogen with respect to vegetative compatibility (vc) type and hypovirulence was analysed by sampling chestnut blight cankers between 1992 and 2010. Among 368 C. parasitica isolates sampled in south‐western Germany, 9 different vc types were found. East of the Rhine valley, EU‐2 is the most widespread vc type. In addition, two isolated forest areas infected with C. parasitica of the vc types EU‐14 and EU‐28 were detected. West of the Rhine valley, C. parasitica of the vc type EU‐65 was repeatedly isolated from an infection focus, the spread of which was successfully suppressed for several years by sanitation measures. Since 2003, additional outbreaks of C. parasitica belonging to the vc types EU‐2 and EU‐5 were detected in the vicinity. Several other vc types (EU‐1, EU‐12, EU‐33 and one vc type incompatible with any of the 74 European testers) were identified on isolated trees mainly in urban areas across the study area and were subsequently eradicated. The spatial and temporal distribution of the different vc types indicates at least nine different introductory events of C. parasitica into south‐western Germany. Natural hypovirulence was only found in the infection area in Baden‐Württemberg. A total of four hypovirulent isolates of the vc type EU‐2 were obtained, one in 1992 and three in recent years. The four hypoviruses were genetically closely related and belonged to the Spanish/German subtype of Cryphonectria hypovirus 1. As the different vc types in south‐western Germany occur mostly in spatially separated, single stands, the introduction of hypovirulence as biological control is expected to be effective.

Spread and population structure of Cryphonectria parasitica in a young chestnut orchard in Slovakia

Abstract The chestnut blight pathogen Cryphonectria parasitica was studied in a chestnut collection composed of both seedlings and grafts derived from selected Castanea sativa and C. sativa × C. crenata trees located in south-east Slovakia, near village Príbelce on an area of approximately 3.5 ha. The study was conducted during eight years (2003–2010). During this period 133 trees were infected, which represents 59.82% of chestnut trees of all chestnut accessions. Based on the phenotype of the fungus culture and the type of cankers in the field, all isolates were determined to be virulent. No hypovirulent strains were found. No vegetative compatibility (vc) type diversity was observed. More than 130 isolates were analyzed for vc and all were in single vc type, which was identical with EU 12. All isolates assayed for mating type were MAT-1. No perithecia were observed. No significant differences were found between the proportion of cankered and dead cankered trees in seedlings and grafts of hybrid origin (C. sativa × C. crenata) and of C. sativa origin. However, particular seedlings and grafts of hybrid origin seemed to exhibit certain resistance to chestnut blight.

Population Structure of Cryphonectria Parasitica in The Modrý Kameň Region

The European chestnut was evaluated for Chestnut blight disease in the Modrý Kameň region, in 2010. A total of 1321 trees and sprouts were selected. There were 140 healthy trees, without any symptoms of Cryphonectria parasitica infection. Nearly 90% of the evaluated trees and sprouts were diseased. The health condition index (I HC ) on 11 experimental plots varied from 2.31 to 4.03. Ev- ery collected sample was identified as having C. parasitica. All isolates had the orange culture morphology; all isolates were virulent. Among the isolates, 8 vc types were detected. Vc type EU-2 was dominant, it comprised 37.14% of the tested isolates. Two other vc types: EU 1 and EU 12 were frequently detected.