Vc Types Research Articles

High diversity of vegetative compatibility types in Cryphonectria parasitica in Japan and China

We found high diversity of vegetative compatibility (vc) types in native populations of the chestnut blight fungus, Cryphonectria parasitica, in Japan and China; almost every isolate was in a unique vc type. In Japan we found 71 vc types in a sample of 79 isolates pooled from six populations. Within two populations in China, all isolates (n = 28 and 11) had unique vc types; we found 15 vc types among 25 isolates in a third Chinese population where multiple isolates were collected from some trees. None of the isolates from China and only three isolates in the 71 vc types from Japan were compatible with any of 64 vc type testers from Europe, which have known vegetative incompatibility genotypes. To our knowledge this is the first report of vc type diversity for C. parasitica in Japan or of any comparisons of vc types between Asia and Europe. The most significant result of this survey is the identification fungal isolates for expanding knowledge of the genetics of vegetative incompatibility.

High diversity of vegetative compatibility types in Cryphonectria parasitica in Japan and China

We found high diversity of vegetative compatibility (vc) types in native populations of the chestnut blight fungus, Cryphonectria parasitica, in Japan and China; almost every isolate was in a unique vc type. In Japan we found 71 vc types in a sample of 79 isolates pooled from six populations. Within two populations in China, all isolates (n=28 and 11) had unique vc types; we found 15 vc types among 25 isolates in a third Chinese population where multiple isolates were collected from some trees. None of the isolates from China and only three isolates in the 71 vc types from Japan were compatible with any of 64 vc type testers from Europe, which have known vegetative incompatibility genotypes. To our knowledge this is the first report of vc type diversity for C. parasitica in Japan or of any comparisons of vc types between Asia and Europe. The most significant result of this survey is the identification fungal isolates for expanding knowledge of the genetics of vegetative incompatibility.

'Coaching' small biotech companies into success

The paper reports an empirical study on the way Venture Capital organisations (VC here means Venture Capital or the VC organisation) support biotechnology start-ups, not just by providing capital, but through support and advice in strategic management issues, that is, nonfinancial value added. The paper draws attention to differences among assorted types of VC organisations regarding their ways of operating. The study is based on a full population of biotechnology start-ups in Finland and on a survey and interviews with the CEOs of the investee firms. Central findings of the study include an observation that all the investigated VC types did provide value added in the meaning outlined above. Nevertheless, there were clear differences between them in terms of the estimated overall value added as well as in their activity profiles. Informal investors (business angels) were assessed most positively by the CEOs and maintained the closest contacts with their investee firms.

Genetic diversity of Cryphonectria parasitica population in the Štiavnicko-krupinská subpopulation in Slovakia

The structure of <I style="mso-bidi-font-style: normal">C. parasitica</I> populations was evaluated in Štiavnicko-krupinská subpopulation in Slovakia. A total of four vegetative-compatibility (vc) types were detected among the sample of 215 isolates, which respond to following European vc types: EU-12, EU-2, EU-13, and EU-8. Number of vc types on single sites varied between one and four. One vc type (EU-12) was the dominant in Štiavnicko-krupinská subpopulation. This vc type (EU-12) comprised 93% of all isolates and was found on each site. Two vc types were represented by only one or two isolates. The observed vc type frequencies were compared with expected vc type frequencies. The χ<SUP>2</SUP> test showed that the observed vc type frequencies differed significantly from the frequencies expected under random mating.

Identification and geographic distribution of vegetative compatibility types of Cryphonectria parasitica and occurrence of hypovirulence in Greece

Summary 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.

Why Do Contracts Differ Between VC Types? Market Segmentation Versus Corporate Governance Varieties

The main objective of the present paper is to disentangle observed differences in the design of contracts across VC types into firm selection effects and corporate governance differences between VC types (different contracts). Based on a theoretical approach developed in the first part of the paper, we investigate in the second part these issues empirically by using a unique, hand-collected German data set consisting of all contractual details of VC investments into 290 entrepreneurial firms in the period 1990-2004. By employing various matching procedures, we show that VC types differ in both firm choice and corporate governance approach.

Heterokaryon formation and parasexual recombination between vegetatively incompatible lineages in a population of the chestnut blight fungus, Cryphonectria parasitica

Heterokaryosis was recently reported in the chestnut blight fungus, Cryphonectria parasitica, in which individuals contain nuclei that are isogenic except at the mating-type locus (MAT). MAT heterokaryons were found in several natural populations, including a putatively clonal population in West Salem, Wisconsin, providing an opportunity to address the question of how heterokaryons arise. We represented relationships among RFLP fingerprint haplotypes as networks in which loop formation is considered evidence of recombination. From 1990 to 1995, this population was clonal, as indicated by a simple haplotype network without loops, and the correlation of vegetative compatibility (vc) types and mating types with haplotype lineages. By 1999, we observed loops in the haplotype network involving isolates of two vc types (WS-2 and WS-3). Isolates with haplotypes in the loops were either MAT heterokaryons, carried the opposite mating type from other isolates of the same vc type, and/or had two alleles at two or more codominant SCAR (sequence-characterized amplified region) loci. Segregation of markers and recombination were evident among single-spore isolates from one heterokaryon; these single-spore isolates had novel fingerprint haplotypes, also within the loops. In contrast, vc type WS-1, which comprises 85% of the population, was represented by a simple network with no loops, indicating a clonal lineage varying only by mutation. Almost all isolates of WS-1 had the same mating type; the exceptions were five isolates that were MAT heterokaryons. These results are consistent with the hypothesis that heterokaryons formed between vegetatively incompatible individuals, and recombination occurred by a parasexual process.

The first record of Cryphonectria parasitica in the Czech Republic.

The causal agent of chestnut blight Cryphonectria parasitica (Murrill) M. E. Barr is a quarantine pest that has been recorded for the first time on the territory of the Czech Republic. Cryphonectria parasitica was observed in a sweet chestnut in the town of Uherský Brod. Infected tree was imported as a two-year-old seedling from Bratislava (Slovakia), 25 years ago. The isolate of Cryphonectria parasitica has been compatible with European vc type 13 (EU 13). Castanea sativa Mill. occurs in more than 293 localities in the Czech Republic. Its state of health was checked in 232 localities.

Low diversity of vegetative compatibility types and mating type of Cryphonectria parasitica in the southern Balkans

The diversity of vegetative compatibility (vc) types and mating type was estimated in populations of the chestnut blight fungus, Cryphonectria parasitica, throughout Macedonia and from selected areas in Greece. Nearly all of the 786 isolates (94%) from Macedonia were in a single vc type, EU‐12; all 379 isolates from Greece were EU‐12. Only six of 20 populations in Macedonia had more than one vc type. The diversity of vc types in the most diverse populations of Macedonia was comparable with the least diverse populations found previously in Italy. All but six of the 313 isolates assayed had the same mating type, MAT‐1, and no perithecia of Cryphonectria parasitica were observed in any population. These results lead to the conclusion that sexual reproduction does not occur in these populations. The lack of vc type diversity may indicate a high potential for the spread of hypoviruses and successful biological control with transmissible hypovirulence. However, if sexual reproduction should occur in Macedonian populations, up to 32 vc types would be possible by recombination among vegetative incompatibility loci.

Incomplete movement of Cryphonectria hypovirus 1 within a vegetative compatibility type of Cryphonectria parasitica in natural cankers on grafted American chestnut trees

SummaryAmerican chestnut trees, grafted in 1980 from large survivors, were inoculated in 1982 and 1983 with four white (European) hypovirulent strains of Cryphonectria parasitica, infected with C. hypovirus 1 (CHV1); this hypovirus has been shown to be capable of moving rapidly within the mycelium of a vegetative compatibility (vc) type of C. parasitica in blight cankers. Using a 49‐cell lattice plot, 17.8×17.8 cm, the spatial patterns and frequencies of white and pigmented isolates and white and pigmented vc types were investigated within superficial cankers on the grafts located outside the hypovirulent‐strain‐inoculated zone. Four of six cankers assayed contained white isolates, and three of the four had random spatial patterns of white isolates, based on join‐count statistics. Vc tests, using pigmented isolates and pigmented single‐spore colonies of white isolates, indicated that the majority of white and pigmented isolates recovered from each of two cankers assayed were in one vc type. White and pigmented lattice‐plot cells of the same vc type were frequently in contact with each other, indicating incomplete movement of CHV1 within a vc type. Nine and 10 vc types were found in the two cankers; it is hypothesized that small, white vc type areas in each canker may be a source of CHV1 transmission to the major vc types. Based on join‐count statistics, the spatial pattern of the single, major vc type in one canker was non‐random (aggregated), whereas the other canker had a random major vc type pattern. White and pigmented in vitro variants (sectors) of C. parasitica, that resemble white and pigmented in vivo variants in spatial contact and vc compatibility, were intermediate hypovirulent and virulent on forest American chestnuts, and dsRNA positive and negative, respectively. Incomplete movement of CHV1 within a vc type could be a major cause of the prevalence of pigmented isolates in superficial cankers on chestnut trees.

Spread of Cryphonectria hypovirus1 into 45 vegetative compatibility types of Cryphonectria parasitica on grafted American chestnut trees

A mixture of hypovirulent strains of Cryphonectria parasitica, including four white (European) strains infected with Cryphonectria hypovirus1 (CHV1), was used in 1982 and 1983 to inoculate natural blight cankers located within a zone ranging from the ground to 183 cm on grafted American chestnut trees. These four white strains belonged to three vegetative compatibility (vc) types. Using pigmented, single‐spore colonies from white isolates, 48 vc types were identified among 110 white isolates recovered in 1996, 1998, and 1999 from cankers located outside the inoculated zone. Twenty‐five of the 48 white vc types consisted of two or more isolates. The 25 major white vc types were vegetatively incompatible with all four of the original white hypovirulent strains, providing evidence for spread of CHV1 but not for spread of the original inoculated strains. Forty‐five vc types represent the minimum number of `new' vc types into which CHV1 had spread. The ratio of white vc types to white isolates tested (S/N) and Shannon diversity index were 0.436 and 3.64, respectively. The spatial pattern of white vc types on the grafts was found to be non‐random (p=0.019). White single‐spore colonies of white isolates were placed into four cultural morphology (CM) groups. The two largest groups contained 37 (CM group 3) and 33 (CM group 1) isolates. Single‐spore colonies from the original, white inoculated strain, Ep 49, were classified into CM groups 3 and 1, and colonies of Ep 51 W were classified into CM group 1.

OUTCROSSING AND DIVERSITY OF VEGETATIVE COMPATIBILITY TYPES IN POPULATIONS OF EUTYPA LATA FROM GRAPEVINES

The sources of inoculum of Eutypa dieback of grapevines, caused by Eutypa lata, are not fully understood. Ascospores are thought to be the main source, but in populations with low disease incidence conidia may be important. Earlier studies of this disease in Italy and Germany did not report sexual structures (perithecia) of E. lata on grapevines, leaving open the possibility that populations of this fungus are clonal in some areas. However, we found perithecia in 24% and 43% of symptomatic vines in vineyards in Italy and Germany, respectively. Spatial patterns of symptomatic vines in the German vineyard were significantly aggregated but the aggregation was not strong, as might be expected if the fungus dispersed by conidia or mycelium on pruning tools. In contrast, vines with stromata and perithecia were not significantly aggregated in space. Vegetative compatibility (vc) types segregated among ascospore progeny in all perithecia sampled from both vineyards, indicating that this fungus consistently outcrosses in these populations. Finally, we found a high diversity of vc types in both vineyards, where isolates from different vines (with one exception) had unique vc types. These results reject the hypothesis that clonal reproduction of E. lata is epidemiologically significant, and strongly suggests that ascospores of E. lata are an important source of inoculum. Furthermore, E. lata’s mating system is characterized by outcrossing in nature.

Survival of clones of NAN Ophiostoma novo-ulmi around its probable centre of appearance in North America

275 isolates of Ophiostoma novo-ulmi , sampled across the southern Great Lakes region of North America from Wisconsin to Ohio in 1996, were analysed for vegetative compatibility (vc) types. Over 60% of the sample was a clonal vc component, comprising only two vc types (the AMSG and EUSG); the remainder of the sample was highly heterogeneous for vc types. Vc diversity was highest in Indiana and Michigan; close to where NAN O. novo-ulmi probably first appeared in North America. Each vc clone exhibited a uniform RAPD haplotype and a lower frequency of the A compared with the B mating type. This is consistent with the clones being mainly asexually spread, but with a potential for inbreeding, an unusual feature in a ’genetic clone’. The heterogeneous component, however, exhibited diverse RAPD haplotypes and a near 1:1 ratio of A:B mating types, indicating that the mainly novel vc types of this component arise via sexual recombination. In Europe, dominant vc clones have been quickly replaced by novel vc types. In the Great Lakes region, however, vc clones appear to have survived for over 50 years despite a high potential for emergence of new vc types via sexual recombination. No differences were found between the clonal and heterogeneous components with regard to growth rate and pathogenicity, two important fitness parameters. Two other factors, a low level of selection imposed by deleterious d-factor viruses and a density dependent effect associated with vegetative incompatibility, may have favoured prolonged survival of the clones in North America.

Genetic structure of newly established populations of Cryphonectria parasitica

The genetic structure of three newly established Cryphonectria parasitica populations (Choëx, Weggis, Murg) was analysed and compared to an older, post-epidemic population (Claro). Vegetative compatibility (vc) type and DNA fingerprint analysis revealed an almost clonal C. parasitica population in Choëx, Weggis and Murg. These stands are all situated in northern Switzerland, outside the main range of European chestnut. Only one vc type and one dominant DNA fingerprint was found in Choëx and Murg. In Weggis, two vc types and two dominating DNA fingerprints were found. The European Cryphonectria hypovirus (CHV1) was not detected in these three populations. In contrast, the population in Claro, situated within the main range of European chestnut in southern Switzerland, had much higher vc type and DNA fingerprint diversity. DNA fingerprints were correlated to vc types in Claro and in Weggis. Mating type determination revealed one strongly dominating mating type in each of the three northern populations, but not in Claro. From these results we conclude that C. parasitica disseminated almost exclusively by means of asexual reproduction in Choëx, Weggis and Murg, whereas in Claro sexual reproduction also played an important role. Additionally, founder effects and restricted gene flow were dominating factors in shaping the genetic structure of the three northern populations.

A spatially-structured stochastic model to simulate heterogenous transmission of viruses in fungal populations

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.

Analysis of population structure of the chestnut blight fungus based on vegetative incompatibility genotypes.

Vegetative incompatibility is a self/nonself-recognition system in fungi that has often been used for describing phenotypic diversity in fungal populations. A common hypothesis is that vegetative incompatibility polymorphisms are maintained by balancing selection. However, understanding the evolutionary significance of vegetative incompatibility and the factors that maintain these polymorphisms has been limited by a lack of knowledge of the underlying genetics of vegetative compatibility (vc) types. Genotypes of 64 vc types, controlled by six unlinked vegetative incompatibility (vic) loci, have been identified in the chestnut blight fungus, Cryphonectria parasitica. By interpreting vc type survey data in terms of vic genotypes, we estimated vic-allele frequencies and analyzed the multilocus genetic structure of 13 populations in Europe and 3 populations in the U.S. European populations have less vc type diversity than the US populations because of a combination of lower vic-allele diversity and limited recombination. Genotypic diversity of 10 populations in Italy correlated to the abundance of sexual structures; however, significant deviations from random mating suggest that either sexual reproduction may not contribute many offspring in these populations or that vic genes (or vic genotypes) are under selection. Most vic-allele frequencies deviated from 0.5, the equilibrium frequency predicted under frequency-dependent selection, providing no evidence for selection acting on these loci.

Genetics of vegetative incompatibility in cryphonectria parasitica

Vegetative incompatibility in the chestnut blight fungus, Cryphonectria parasitica, in Europe is controlled by six unlinked vic loci, each with two alleles. Four previously identified vic loci (vic1, vic2, vic3, and vic4) were polymorphic in European vegetative compatibility (vc) types. Two new loci, vic6 and vic7, also were identified among European vc types. In one cross, vic genes segregated independently at five loci, and 194 progeny were assigned to 32 vc types; none of these loci were linked. A total of 64 vc types were identified from all crosses. All 64 genotypes possible from six vic loci, each with two alleles (2(6) = 64), were identified and assigned to vc types. Based on our model, vc types v-c 5 and v-c 10, which had been used in previous genetic studies, differ by only five vic genes. Future studies of vc types in C. parasitica can use knowledge of vic genotypes for analysis of population genetic structure based on vic allele frequencies and to determine the effect of each vic gene on virus transmission between vc types.

Comparison of vegetative compatibility types in Italian and Swiss subpopulations of Cryphonectria parasitica

SummaryTester isolates of 20 vegetative compatibility (vc) types from 11 Italian subpopulations and tester isolates of 26 vc types from five Swiss subpopulations of Cryphonectria parasitica were compared by two different vc test methods. A total of 31 different vc types was identified; 15 vc types were common to both countries, five Italian vc types were not found in Switzerland and 11 Swiss vc types were not found in Italy. These 31 vc types were labelled with the acronym EU, followed by progressive numbers and may constitute the base for a common European nomenclature. The vc type EU‐2 was the most common vc type in both countries and dominated in all Swiss and in seven Italian subpopulations. The vc types EU‐1 and EU‐5 were found primarily in northern Italy and Switzerland, while EU‐10 and EU‐12 were most common in southern Italy. The diversity of vc types was greater in the subpopulations of Switzerland and northern Italy than in the subpopulations of southern Italy. The geographical distribution of vc types in Europe should therefore be taken into consideration for biological control measures of chestnut blight and quarantine regulations.

Potential Diversity in Vegetative Compatibility Types of Ophiostoma novo-ulmi in North America

The diversity of vegetative compatibility (vc) types of the Dutch elm disease fungus, Ophiostoma novo-ulmi, in North America was recently shown to be very low compared to populations in Europe (Brasier, 1996, Mycologia 88:951–964). To determine if low diversity was caused by a lack of polymorphism at vegetative incompatibility (vic) loci, we made crosses between isolates in the three common vc types and estimated the number of vic genes segregating. The most common vc type (vc type 1) differed from the next two most common vc types (vc types 2 and 10) by at least five and seven vic loci, respectively. Therefore, mating between vc types 1 and 2 or between 1 and 10 could potentially result in at least 32 or 128 vc types, respectively, which is much greater than the 16 vc types previously observed among 112 field isolates from North America. Because vc types 2 and 10 were almost always found in the same population as vc type 1, lack of polymorphism at vic loci can be eliminated as a cause of the low diversity observed. Two vc types produced in crosses were the same as vc types present in the North American sample, suggesting that recombination occurs in nature. Restricted recombination and/or selection against recombinant vc types are the simplest hypotheses to explain the limited number of vc types observed in nature.

Potential diversity in vegetative compatibility types of Ophiostoma novo-ulmi in North America

The diversity of vegetative compatibility (vc) types of the Dutch elm disease fungus, Ophiostoma novo-ulmi, in North America was recently shown to be very low compared to populations in Europe (Brasier, 1996, Mycologia 88:951–964). To determine if low diversity was caused by a lack of polymorphism at vegetative incompatibility (vic) loci, we made crosses between isolates in the three common vc types and estimated the number of vic genes segregating. The most common vc type (vc type 1) differed from the next two most common vc types (vc types 2 and 10) by at least five and seven vic loci, respectively. Therefore, mating between vc types 1 and 2 or between 1 and 10 could potentially result in at least 32 or 128 vc types, respectively, which is much greater than the 16 vc types previously observed among 112 field isolates from North America. Because vc types 2 and 10 were almost always found in the same population as vc type 1, lack of polymorphism at vic loci can be eliminated as a cause of the low diversity observed. Two vc types produced in crosses were the same as vc types present in the North American sample, suggesting that recombination occurs in nature. Restricted recombination and/or selection against recombinant vc types are the simplest hypotheses to explain the limited number of vc types observed in nature.