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1.
A. R. STONE 《EPPO Bulletin》1985,15(2):131-137
The co-evolutionary process is believed to have resulted, through interaction of wild populations of potato cyst nematodes and their hosts in geological time, in the resistant hosts now utilized in plant breeding programmes and in nematode populations with genes for resistance-breaking or virulence. It is argued that all such interactions between highly adapted, truly parasitic plant nematodes and their hosts are likely to be governed by gene-for-gene interrelationships. Practical implications of this hypothesis are that only pathotypes (resistance-breaking races) defined against identified resistance genes are scientifically sound and of practical value; that, in the case of potato cyst nematodes, other pathotypes (Ro2, Ro3, Ro5 and Pa2 and Pa3) should be abandoned; and that oligogenically based resistance to potato cyst nematodes, especially important in providing resistance to Globodera pallida, is non-durable. Working definitions of the terms ‘pathotype’, ‘host-race’ and ‘virulence’ are provided.  相似文献   

2.
J. Kort 《EPPO Bulletin》1974,4(4):511-518
Since the discovery of pathotypes of the potato cyst nematode (Heterodera rostochiensis Wollenweber, 1923), surveys on the distribution of these pathotypes have been carried out in different European countries. Test varieties of potato were selected according to findings resulting in the present situation of varying distinctive host-plants and of diverging programs for breeding potatoes resistant to the potato cyst nematode. With respect to rational selection and use of resistant potato varieties, there is a great need for standardization in pathotype identification (nomenclature), maintenance and supply of appropriate genotypes of Solanum species and methods for testing resistance in new potato varieties. Anticipating a cross-experiment with pathotypes and test varieties from Great Britain, the Federal Republic of Germany and the Netherlands in 1974, a preliminary test with all recognized or presumed pathotypes from these countries, but with only part of the potential differential host-plants was carried out by the Plant Protection Service at Wageningen. The results of this experiment are discussed.  相似文献   

3.
The pathotype scheme proposed by Kort et al. (1977) is critically reviewed. It is proposed that many of their pathotypes are artifacts resulting from their using an arbitrary Pf/Pi value of ± 1 and differential clones with quantitatively based polygenic resistance to separate pathotypes. It is concluded that most European populations of potato cyst nematodes are heterogeneous for virulence genes and that Pf/Pi measurements are influenced too readily by several factors, including initial population density, the vigour of plant growth, and the viability of the nematode, to be used as either a measure of nematode virulence or plant resistance. Instead, reproduction should be related to that on appropriate non-resistant or partially resistant controls and the aim should be to quantify the proportion of virulent individuals in the population. For greatest accuracy it will be necessary to use procedures which minimize genotype × environmental interactions.  相似文献   

4.
Results are reported for several international collaborative experiments which examined methods of assessing degrees of partial resistance in potato and virulence in potato cyst nematode (PCN, Globodera pallida). It was demonstrated that absolute rates of multiplication can be extremely variable on both susceptible and partially resistant clones, even when the same population and test procedures are employed. It was therefore concluded that, on clones with quantitatively inherited resistance (i.e. partially resistant), absolute rates of multiplication cannot be used to separate pathotypes. Expression of these rates as percentages of those on the susceptible controls reduced the absolute differences between tests, but the values obtained were still too variable for statutory use. However, whatever the environment or nematode population used, it was observed that the resistance of the test clones and virulence of the nematode populations were generally ranked in a similar order. The main exceptions to this were: (1) a Petri-dish test where cv. Vantage was less resistant than in canisters or pots and (2) a pot test where cv. Darwina tended to be more interactive with environmental factors than the other test clones. It was also observed that with some populations of PCN in pots the susceptible cv. Bintje was a less good host than cv. Désirée. On the basis of these results it is suggested that certain partially resistant clones should be used as internal references in statutory, recommended list and breeders' assessment tests against which the resistance of the test clones are compared. For international comparability it is necessary that the different centres conducting such tests use the same reference clones and nematode populations, and similar test methods.  相似文献   

5.
Knowledge of pathotype diversity and virulence in local populations of Pyrenophora teres is a prerequisite to screening for durable resistance to net blotch. The current study aimed to quantify the virulence level of Moroccan isolates, identify and designate existing pathotypes, and select resistant genotypes. We developed a method for virulence quantification of P. teres isolates based on a conversion of infection responses into frequencies for use in correspondence analysis. Coordinates of the first axis of this analysis had a virulence spectrum and ranked isolates from virulent to avirulent. Mixed model analysis was also devised for virulence quantification. Coordinates of the first dimension of correspondence analysis were linearly correlated to BLUPs (Best Linear Unbiased Predictors) of the mixed model. A genotype by genotype by environment model (GGE) coupled with cluster analysis differentiated P. teres isolates into ten and nine pathotypes for net- and spot-forms respectively. Populations of these two forms were dissimilar in terms of classes of virulence. For P. teres f. maculata, avirulent, moderately virulent and highly virulent isolates represented one-third of the population, whereas 90% of P. teres f. teres population was composed of avirulent to moderately avirulent isolates. Barley differential sets were subsequently reduced to two new sets that simplified pathotyping through a key code based on resistant or susceptible reactions. Dendrograms of cluster analysis based on GGE analysis depicted the stability of a genotype’s reactions across all isolates, and using only resistant cultivars as sources of resistance to control net blotch disease would, based on this analysis, fail to control all pathotypes. Therefore, we propose an alternative breeding strategy to control net blotch effectively.  相似文献   

6.
Insight into pathogen population dynamics provides a key input for effective disease management of the potato late blight pathogen Phytophthora infestans. Phytophthora infestans populations vary from genetically complex to more simple with a few clonal lineages. The presence or absence of certain strains of P. infestans may impact the efficacy of fungicides or host resistance. Current evidence indicates that genetically, the Irish populations of P. infestans are relatively simple with a few clonal lineages. In this study, P. infestans populations were genetically characterized based on samples collected at the national centre for potato breeding during the period 2012–16. The dominance of clonal lineages within this P. infestans population was confirmed and the potential selection pressure of fungicide treatment (2013–15) and host resistance (2016) on this clonal P. infestans population was then investigated. It was found that fungicide products did not notably affect the genetic structure of sampled populations relative to samples from untreated control plants. In contrast, samples taken from several resistant potato genotypes were found to be more often of the EU_13_A2 lineage than those taken from control King Edward plants or potato genotypes with low resistance ratings. Resistant potato varieties Sarpo Mira and Bionica, containing characterized R genes, were found to strongly select for EU_13_A2 strains.  相似文献   

7.
The interactions of four pathotypes of Diplocarpon rosae with 34 species and hybrids of Rosa were compared in an ongoing search for criteria of potential relevance to rose breeding. There were greater similarities in the resistance‐susceptibility interactions of these roses to the pathotypes DA1, CW1 and ZM1, than to a fourth pathotype, DA2. Among the species roses, only those of the section Cinnamomeae were susceptible to DA2 and this susceptibility was transmitted in several cases to hybrid progeny. CW1 had the greatest pathogenicity of the four pathotypes. In a cross between R. rugosa cv. Scabrosa, which was resistant and R. rugosa f. alba, which was susceptible to all pathotypes, the progeny were tested for resistance to pathotypes DA1, CW1 and ZM1. Each of the 20 progeny was susceptible to all three pathotypes. This shows that, unlike the well characterized Rdr1 gene for resistance to D. rosae, the resistance of R. rugosa cv. Scabrosa is not determined by a dominant major gene. The diploid hybrid, R. rugosa cv. Martin Frobisher × cv. Mistress Quickly, was resistant to all four pathotypes, but an induced tetraploid of this hybrid was susceptible to all pathotypes. The relevance of these findings to the breeding of roses for resistance to black spot disease is discussed.  相似文献   

8.
Clubroot resistance derived from the oilseed rape/canola Brassica napus ‘Mendel’ has been overcome in some fields in Alberta, Canada, by the emergence of ‘new’ strains of the protist Plasmodiophora brassicae. Resistance to the pathogen was assessed in 112 doubled haploid (DH) lines, derived from B. rapa subsp. rapifera (European clubroot differential (ECD) 04). The lines were evaluated against five single‐spore isolates representing the ‘old’ pathotypes 2, 3, 5, 6 and 8, and 15 field populations representing new strains of P. brassicae. The disease severity index (ID%) data revealed that none of the DH lines were resistant or moderately resistant to the new pathotype 5X (field populations L‐G1, L‐G2, L‐G3) and D‐G3, while 3–42% were resistant or moderately resistant to the other 11 new strains. Using the mean ID induced by the old pathotype 3 (approx. 13.5%) as the baseline, clubroot severity increased by 300–600% when inoculated with the new pathotypes. A significant finding of this study was the fact that ECD 04 showed absolute resistance to all of the old and new P. brassicae strains while the B. napus ‘Mendel’, although resistant to all of the old pathotypes, was resistant to only about 50% of the new strains. Similarly, all of the selected clubroot‐resistant commercial canola cultivars evaluated in this study were susceptible to 87% of the new P. brassicae strains. The molecular data revealed that the breakdown of clubroot resistance in Mendel and the canola cultivars was in part due to the non‐inheritance of the Crr1 gene on the A08 chromosome from ECD 04.  相似文献   

9.
The two closely related nematode species Globodera rostochiensis and G. pallida are one of the major problems encountered in potato cultivation. There is a spectrum of potato plant genes known, which confer resistance to these species and their pathotypes. Potato growing in The Netherlands has to follow strict rules to control spread of the pests. Since distinction between the two nematode species is difficult, a rapid and reliable identification method is needed to allow better use of existing and forthcoming resistant potato cultivars. The aims of this project were: (1) identification and partial purification of species-specific proteins from the nematodes, (2) production of species-specific monoclonal antibodies, and (3) development of a screening test for qualitative and quantitative determination of Globodera spp. in soil samples.  相似文献   

10.
Solanum nigrum, black nightshade, is a wild non-tuber bearing hexaploid species with a high level of resistance to Phytophthora infestans (Colon et al. 1993), the causal agent of potato late blight, the most devastating disease in potato production. However, the genetic mode of resistance in S. nigrum is still poorly understood. In the present study, two S. nigrum accessions, 984750019 (N19) and #13, resistant (R) and susceptible (S), respectively, to three different isolates of P. infestans, were sexually crossed. The various kinds of progeny including F1, F2, F3, and backcross populations (BC1; F1 × S), as well as two populations produced by self-pollinating the R parent and S parent, were each screened for susceptibility to P. infestans isolate MP 324 using detached leaf assays. Fifty seedling plant individuals of the F1 progeny were each resistant to this specific isolate, similarly to the seedling plants resulting from self-pollination of the resistant R parent. Thirty seedling plants obtained from self-pollination of the S parent were susceptible. Among a total of 180 F2 plants, the segregation ratio between resistant and susceptible plants was approximately 3: 1. Among the 66 seedling plants of the BC1 progeny originating from crossing an F1 plant with the susceptible S parent, there were 26 susceptible and 40 resistant plants to P. infestans. The segregation patterns obtained indicated monogenic dominant inheritance of resistance to P. infestans isolate MP 324 in S. nigrum acc. 984750019. This gene, conferring resistance to P. infestans, may be useful for the transformation of potato cultivars susceptible to late blight.  相似文献   

11.
Puccinia horiana is the causal agent of chrysanthemum white rust or Japanese rust. This microcyclic autoecious rust has a quarantine status and can cause major damage in the commercial production of Chrysanthemum x morifolium. Given the international and often trans-continental production of planting material and cut flowers of chrysanthemum and the decreasing availability of registered fungicides in specific regions, breeding for resistance against P. horiana will gain importance and will need to involve the appropriate resistance genes for the pathotypes that may be present. As pathotypes have not been well characterized in this system, the main objective was to build an international collection of isolates and screen these on a large collection of cultivars to identify different pathotypes. Using a robust and high throughput bioassay, we tested 36 selected cultivars with 22 individual single-pustule isolates of P. horiana. The isolates originated from three different continents over 4 different collection years and included some isolates from cultivars previously reported as resistant. In most cases the bioassays resulted in a clear scoring of interaction phenotypes as susceptible or resistant, while in several cases consistent intermediate phenotypes were found, often on specific cultivars. Twenty-four of the cultivars gave a differential interaction phenotype profile. All isolates produced a unique profile, infecting a minimum of 4 and a maximum of 19 differential cultivars. Based on the Person analysis of these profiles, this pathosystem contains at least seven resistance genes (and seven avirulence genes), demonstrating the highly complex race structure in this pathosystem.  相似文献   

12.
Genetic resistance is the main tool used to manage clubroot of canola (Brassica napus) in Canada. However, the emergence of new virulent strains of the clubroot pathogen, Plasmodiophora brassicae, has complicated canola breeding efforts. In this study, 386 Brassica accessions were screened against five single-spore isolates (represented by pathotypes 2F, 3H, 5I, 6M and 8N on the Canadian Clubroot Differential Set) and 17 field isolates (represented by 12 unique pathotypes: 2B, 3A, 3D, 3O, 5C, 5G, 5K, 5L, 5X, 8E, 8J and 8P) of P. brassicae to identify resistance sources effective against these strains. The results showed that one B. rapa accession (CDCNFG-046, mean index of disease (ID) = 3.3%) and two B. nigra accessions (CDCNFG-263, mean ID = 3.1%; and CDCNFG-262, mean ID = 4.7%) possessed excellent resistance to all 22 of the isolates evaluated. Fifty other accessions showed differential clubroot reactions (resistant, moderately resistant or susceptible), including 27 (one B. napus, two B. rapa, four B. oleracea and 20 B. nigra) accessions that were each resistant to 8–21 P. brassicae isolates, but developed mean IDs in the range of 5.3–29.6%. The remaining 23 accessions (two B. napus, one B. rapa, five B. oleracea and 15 B. nigra) were each resistant to 3–13 isolates, but developed mean IDs in the range of 30.3–47.0%. The three accessions that showed absolute resistance and the 50 accessions that showed differential clubroot reactions could be used to breed for resistance to the new P. brassicae strains.  相似文献   

13.
The variability of resistance durability in different potato genotypes harbouring the same resistance QTL but differing by their genetic background was explored. The indirect consequences of the resistance adaptation in terms of local (i.e. genotype‐specific) adaptation and cross‐virulence was also investigated. Following the virulence of the potato cyst nematode Globodera pallida in a long‐term experimental evolution protocol, the results showed that nematode populations were able to adapt to the resistance of four potato genotypes carrying the QTL GpaV from Solanum vernei, and that the plant genetic background has an impact upon the durability of resistance. The pattern of local adaptation observed here indicates that divergent selection has occurred during the experimental evolution performed from the same initial nematode population, and revealed a trade‐off between the adaptation to a resistant potato genotype and the adaptation to another resistant genotype differing in its genetic background. In terms of cross‐virulence between potato genotypes derived from different resistance sources (S. sparsipilum and S. spegazzinii), this study shows that the adaptation to resistance QTL GpaVvrn does not necessarily allow the adaptation to collinear GpaV loci. The results presented here could be useful for predicting evolution of nematode populations in natural agro‐ecosystems and identifying durable strategies for resistance deployment.  相似文献   

14.
Common scab is one of the most important soil‐borne diseases of potato and is difficult to control. Selection of potato breeding lines for resistance to common scab is also cumbersome due to environmental factors influencing symptom development and an erratic spatial distribution of the scab pathogens (Streptomyces spp.) in the field. The bacterial phytotoxin thaxtomin A, which causes scab symptoms, can be used to screen large numbers of potato seedlings for tolerance in vitro, but few studies have investigated whether the results correspond to resistance to common scab observed in the field. In this study, 120 F1 potato progeny from a single cross were screened in vitro by exposing the seedlings to thaxtomin A added to the culture medium. Eighteen genotypes were selected based on high sensitivity or tolerance using shoot growth as the criterion, multiplied in vitro, and tested for resistance to common scab caused by S. turgidiscabies and S. scabies in a glasshouse and in three different fields. Evaluation of ca. 6500 tubers showed that the 18 potato genotypes differed in scab indices and disease severity (P < 0·0001). The relative shoot height in vitro (thaxtomin A used at 0·5 μg mL?1) and the scab index in the field showed significant correlation (rs = ?0·463, P = 0·0528, n = 18), also consistent with the results obtained under controlled conditions in the glasshouse. Hence, the in vitro bioassay may be used to discard scab‐susceptible genotypes and elevate the overall levels of common scab resistance in the potato breeding populations.  相似文献   

15.
During 1983–1989 about 1,200 infested plots in the Czech republic were investigated for the occurrence of new pathotypes of the potato cyst nematodes (PCN) Globoderu rostochiensis and G. pallida. Only eight populations of the pest were suspected of containing another pathotype than Ro1. Glasshouse pot trials were performed with those eight natural populations, two populations of Ro1, 10 potato cultivars resistant to Ro1 and 10 cultivars resistant to more pathotypes, G. pallida included. The multiplication rates (Pf/Pi) showed that four of the PCN populations were probably mixtures, with pathotype Ro1 prevailing. Three populations were suspected of containing G. pallida , but their morphological characters corresponded only with G. rostochiensis. One population corresponded with pathotype Ro5. The extent of the occurrence of pathotypes or virulence groups different from Ro1 can be estimated at 0.3–0.4% of infested plots.  相似文献   

16.
The goal of this research was to identify quantitative trait loci (QTLs) for potato tuber resistance to the soil- and seedborne bacterium Dickeya solani and for tuber starch content, to study the relationship between these traits. A resistant diploid hybrid of potato, DG 00-270, was crossed with a susceptible hybrid, DG 08-305, to generate the F1 mapping population. Tubers that were wound-inoculated with bacteria were evaluated for disease severity, expressed as the mean weight of rotted tubers, and disease incidence, measured as the proportion of rotten tubers. Diversity array technology (DArTseq) was used for genetic map construction and QTL analysis. The most prominent QTLs for disease severity and incidence were identified in overlapping regions on potato chromosome IV and explained 22.4% and 22.9% of the phenotypic variance, respectively. The second QTL for disease severity was mapped to chromosome II and explained 16.5% of the variance. QTLs for starch content were detected on chromosomes III, V, VI, VII, VIII, IX, XI, and XII in regions different from the QTLs for soft rot resistance. Two strong and reproducible QTLs for resistance to D. solani on potato chromosomes IV and II might be useful for further study of candidate genes and marker development in potato breeding programmes. The relationship between tuber resistance to bacteria and the starch content in potato tubers was not confirmed by QTL mapping, which makes the selection of genotypes highly resistant to soft rot with a desirable starch content feasible.  相似文献   

17.
Late blight caused by Phytophthora infestans is the most devastating disease of potato worldwide. To understand the P. infestans population structure and dynamics in northwestern China, 959 single‐lesion isolates were purified in three consecutive years (2009–2011) and were characterized for mating type, pathotype, mtDNA haplotype and molecular variation at eight SSR loci. The results showed that the distribution of mating types changed significantly over years, with self‐fertile isolates dominant in 2010 and 2011. SSR genotyping distinguished 959 isolates into 151 genotypes, and association analysis indicated that P. infestans populations in 2010 and 2011 were strictly asexual while in 2009 they showed signs of sexual reproduction. Population analysis showed that the majority of genetic variation was within P. infestans populations. Isolates sharing identical SSR genotypes were detected in distant regions, indicating that migration of P. infestans could have occurred between regions. Pathogenicity assays on a set of potato differential lines containing R1 to R11 resistance genes detected four pathotypes from 74 selected isolates, with the pathotype virulent against all 11 R genes being dominant. Three mtDNA haplotypes (Ia, IIa, IIb) were detected with Ia being dominant among 507 isolates examined. Phylogenetic analysis indicated that P. infestans populations in northwestern China are distant from European lineages including 13‐A2 (blue‐13) at the time of this survey. The results have implications for the trade of healthy seed tubers as a means of managing late blight.  相似文献   

18.
L. M. HANSEN 《EPPO Bulletin》1985,15(2):193-198
Clones from the international test assortment were tested for resistance to Globodera pallida (Pa2 and Pa3) and estimated by root-ball counting and by extraction of the total number of cysts to show the practicability of the root-ball test. New clones in a breeding programme were tested by root-ball counting for resistance to Globodera rostochiensis (Ro1) and G. pallida (Pa2 and Pa3), and the statistical aspects are discussed. The conclusion is that testing new clones early in a breeding programme by root-ball counting of cysts with four to five replicates is a sufficient method to separate the susceptible clones from resistant and moderately resistant ones.  相似文献   

19.
Worldwide Puccinia striiformis f. sp. tritici (Pst) epidemics have been reported to be driven by few genetic lineages, while a high diversity is evident at the Pst Himalayan centre of diversity. This study investigated the relationship between pathotype diversity and genetic structure in Nepal, the eastern Himalayan region, which has been largely unexplored. Despite the high genetic diversity and recombinant structure detected through microsatellite genotyping, characterization of virulence phenotypes for 62 isolates identified only eight pathotypes, with two pathotypes predominant over all the populations. This is in contrast to the Pakistani and Chinese recombinant populations, where high pathotype diversity is associated with genetic diversity. The most prevalent Nepali pathotype was not a unique clonal lineage, but was represented by seven multilocus genotypes from four distinct genetic subgroups, suggesting strong directional selection on virulence genes, resulting in convergent pathotypes in distinct genetic groups. This convergent selection is discussed in comparison with clonal French and recombinant Pakistani populations. Additionally, the Nepali Pst population carried virulence to 17 out of 24 tested yellow rust resistance genes (Yr), with the absence of virulence to Victo and Early Premium and resistance genes Yr5, Yr10, Yr15, Yr24 and Yr26. Virulence to Yr2, Yr7, Yr27 and YrSu were fixed in all isolates, in line with the deployment of these resistance genes in Nepal. The results reflect the influence of resistance gene deployment on selection of virulence and pathotypes in a recombinant pathogen population, which must be considered in the context of durable resistance gene deployment.  相似文献   

20.
Phakopsora pachyrhizi is a biotrophic fungus that causes rust on soybean, leading to devastating yield losses. Development of resistant cultivars for deployment in different geographic regions requires a comprehensive understanding of the prevalent P. pachyrhizi pathotypes. To determine the pathotypes existing in four East African countries, 65 isolates were tested on 11 soybean host differentials. In addition, the virulence spectrum of isolates collected from the same region over multiple years was compared. The majority of the isolates (54%) belonged to pathotype 1000, which was found in all countries. The pathotypes with the most complex virulence spectrum, which comprised isolates from Kenya and Malawi, were virulent on four differentials. All pathotypes were virulent on soybean genotypes carrying the Rpp1 resistance gene to P. pachyrhizi, but they were avirulent on cultivars carrying the Rpp1b, Rpp2, or Rpp3 gene, as well as on cultivar No6-12-1 that carries Rpp2, Rpp4, and Rpp5. Two of the pathotypes were virulent on cultivar UG 5 that carries Rpp1 and Rpp3 and on Hyuuga that carries Rpp3 and Rpp5. The isolates collected from different countries differed in their virulence spectrum across the years. Shannon's index (H) and Simpson's index (S) of diversity indicated that the isolates from Malawi were more diverse (H = 1.55, S = 0.90) while those from Uganda had lower diversity (H = 0.78, S = 0.46 ). The Rpp genes that were found to provide resistance to all pathotypes of P. pachyrhizi can be employed for soybean breeding aimed at durable rust resistance.  相似文献   

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