韩国栗疫病抗病品种的遗传变异分析

为了分析韩国栗疫病的抗病品种和感病品种的遗传变异和抗病性的筛选,利用抗病性的快速检测法和RAPD(random amplified polymorphic DNA)方法对13个栗树品种进行了抗病性检测和RAPD标记分析。抗病性的快速检测选出了5个抗病品种、5个感病品种和3个中度抗病(或中度感病)品种,并且这一结果与该品种的田间表现相一致。利用筛选的12个随机引物,扩增了100个多态性RAPD片段,但未发现与抗病性或感病性相关的特异RAPD片段。聚类分析结果表明,12个品种大致分为抗病、感病和中度抗病(或中度感病)等3个大组,并与抗病性的快速检测结果基本一致。抗病品种“MANSEKI”表现出了相对于12个品种较远的亲缘关系。     

Hypovirus Transmission to Ascospore Progeny by Field-Released Transgenic Hypovirulent Strains of Cryphonectria parasitica

ABSTRACT Strains of the chestnut blight fungus, Cryphonectria parasitica, have been genetically engineered to contain an integrated full-length cDNA copy of the prototypic virulence-attenuating hypovirus CHV1-EP713. Unlike natural hypovirulent C. parasitica strains, these transgenic hypovirulent strains are able to transmit virus to ascospore progeny under laboratory conditions. This ability provides the potential to circumvent barriers to cytoplasmic virus transmission imposed by the fungal vegetative incompatibility system. During July 1994, transgenic hypovirulent strains were introduced into a Connecticut forest site (Biotechnology Permit 94-010-01). Subsequent analysis of the release site confirmed hypovirus transmission from transgenic hypovirulent strains to ascospore progeny under field conditions. Additionally, it was possible to recover transgenic hypovirulent strains from the test site as long as 2 years after the limited, single-season release. Evidence also was obtained for cytoplasmic transmission of transgenic cDNA-derived hypovirus RNA, including transmission to mycelia of a virulent C. parasitica canker after treatment with conidia of a transgenic strain. Finally, a transgenic hypovirulent strain was recovered from a superficial canker formed on an untreated chestnut tree. Genetic characteristics of the recovered strain suggested that the canker was initiated by an ascospore progeny derived from a cross involving an input transgenic hypovirulent strain. The durability of a molecular marker for field-released cDNA-derived hypovirus RNA is discussed.     

Molecular mapping of the crown rust resistance gene rpc1 in barley

ABSTRACT Crown rust of barley, caused by Puccinia coronata var. hordei, occurs sporadically and sometimes may cause yield and quality reductions in the Great Plains region of the United States and Canada. The incompletely dominant resistance allele Rpc1 confers resistance to P. coronata in barley. Two generations, F(2) and F(2:3), developed from a cross between the resistant line Hor2596 (CIho 1243) and the susceptible line Bowman (PI 483237), were used in this study. Bulked segregant analysis combined with random amplified polymorphic DNA (RAPD) primers were used to identify molecular markers linked to Rpc1. DNA genotypes produced by 500 RAPD primers, 200 microsatellites (SSRs), and 71 restriction fragment length polymorphism (RFLP) probes were applied to map Rpc1. Of these, 15 RAPD primers identified polymorphisms between resistant and susceptible bulks, and 62 SSR markers and 32 RFLP markers identified polymorphisms between the resistant and susceptible parents. The polymorphic markers were applied to 97 F(2) individuals and F(2:3) families. These markers identified 112 polymorphisms and were used for primary linkage mapping to Rpc1 using Map Manager QT. Two RFLP and five SSR markers spanning the centromere on chromosome 3H and one RAPD marker (OPO08-700) were linked with Rpc1 and, thus, used to construct a 30-centimorgan (cM) linkage map containing the Rpc1 locus. The genetic distance between Rpc1 and the closest marker, RAPD OPO08-700, was 2.5 cM. The linked markers will be useful for incorporating this crown rust resistance gene into barley breeding lines.     

Comparison of Puccinia graminis f.sp. tritici from South America and Europe

Twenty isolates of Puccinia graminis f.sp. tritici from South America were compared with 19 from Europe using virulence, isozymes and random amplified polymorphic DNA (RAPD) markers. The isozyme and virulence patterns for these isolates were also compared with those of 11 isolates representative of the common race clusters in North America. All three types of marker showed a level of similarity between the South American and European isolates comparable with that between isolates from the same continent. The average similarity coefficients between the South American and European isolates were 0.65 for virulence, 0.67 for isozymes, and 0.70 for RAPD markers. Among South American isolates the values were 0.63 for virulence, 0.64 for isozymes and 0.72 for RAPDs. For the South American and European isolates, correlation between the similarity matrices based on RAPDs and on isozyme markers, respectively ( r  = 0.52), was higher than that between the RAPD and virulence matrices ( r  = 0.32) or between isozyme and virulence matrices ( r  = 0.16). The North American isolates had a comparable level of similarity for virulence and isozymes to both the South American and European populations. There was no clear distinction between the South American, North American and European isolates, which is consistent with the hypothesis that these populations may have had a common origin.     

Variation in the Fusarium section Liseola: pathogenicity and genetic studies of isolates of Fusarium moniliforme Sheldon from different hosts in Ghana

Fusarium moniliforme , the imperfect stage of the ascomycete Gibberella fujikuroi , is an economically important pathogen with a very wide host range. The genetic characteristics of isolates of the fungus collected from different regions of Ghana from maize, rice and sorghum were determined using the random amplified polymorphic DNA (RAPD) and restriction fragment length polymorphism (RFLP) techniques. The pathogenicity of the isolates was also compared on maize and rice. DNA fingerprints detected as RFLPs of ribosomal DNA and RAPDs separated the isolates into discrete groups which were generally host-related. The possibility of a sub-structuring of the maize population of the fungus into tissue-related subgroups was suggested by the results. A dendrogram of the relatedness of the isolates is presented. However, the pathogenicity of the isolates on rice, measured by their ability to cause 'bakanae' symptoms, did not resolve the isolates into the clearly defined groups suggested by the genetic studies, and maize isolates of the fungus could cause 'bakanae' symptoms to the same extent as rice isolates. Similarly, some isolates identified as rice-type isolates caused as much shoot stunting in maize as maize isolates. However, the effects of the isolates on root growth of maize seedlings showed a broad correlation with the defined genetic groups, with maize isolates of the fungus showing the greatest tendency to cause root stunting     

陆地棉对黄萎病抗性的分子标记研究

 利用陆地棉标准系TM-1和常抗棉2个陆地棉品种杂交并自交,获得109个F₂单株及F_2:3家系为作图群体,以SSR、RAPD和SRAP 3种分子标记进行抗黄萎病性状的分子标记筛选。结果从1611对(条)引物中仅筛选到70对(条)多态性引物,获得75个多态性位点并进行标记间的连锁性分析。75个标记构建了一个包括15个连锁群,全长535 cM的陆地棉品种间分子标记遗传连锁图,标记间平均距离为11.15 cM,有27个标记不能进入任何连锁群。连锁群的标记数最少2个,最多6个;长度从1.0 cM到92.7 cM不等。对其F_2:3家系的成株期抗黄萎病性状即平均病情指数的分布进行分析,显示其呈正态分布,进一步说明陆地棉对黄萎病的抗性为数量遗传;单标记分析及复合区间作图,检测出与抗黄萎病性相关的3个QTL,分别位于第3、5、6连锁群上,贡献率分别为14.15%、3.45%和18.78%。另外,对该群体生长过程中黄萎病不同发病高峰期的病情也进行了分析。     

Genetic Uniformity Among Isolates of Peronospora tabacina, the Tobacco Blue Mold Pathogen

ABSTRACT As a first step toward analysis of genetic variation and population structure in Peronospora tabacina, we used a collection of random genomic DNA fragments to survey for restriction fragment length polymorphisms (RFLPs) in DNA from a collection of isolates from Kentucky and other tobacco-growing regions of the United States. Also included in the study were isolates from the wild tobacco species, Nicotiana repanda, and from ornamental tobacco, N. alata. In a preliminary survey using DNA from 10 pathogen isolates, no polymorphisms were detected at six single-copy DNA loci using 22 probe-enzyme combinations. Moderately repetitive and highly repetitive regions of the genome were also remarkably similar between isolates, with only 6 of 15 different probes identifying genetic differences. Some of the polymorphic probes were then used to analyze a larger collection of isolates, most of which were from Kentucky. This resulted in the identification of very few additional polymorphisms, indicating that the population of P. tabacina that infects the Kentucky tobacco crop is genetically very homogeneous. The low level of polymorphism detected in this study overall, suggests that genetic variability may be lacking in P. tabacina populations throughout the United States. Two of the RFLP markers gave hybridization patterns that were consistent with P. tabacina being diploid. Frequencies of alleles at these loci and linkage disequilibrium between different marker loci indicated that genetic recombination does not occur frequently in the pathogen population. DNA polymorphisms that were identified in this study enabled us to differentiate the pathogen population into at least 10 haplotypes. One isolate was analyzed in detail and was shown to be genetically stable through several rounds of single-spore isolation and through several pathogenic cycles.     

Identification and fine-mapping of Xa33, a novel gene for resistance to Xanthomonas oryzae pv. oryzae

Broadening of the genetic base for identification and transfer of genes for resistance to insect pests and diseases from wild relatives of rice is an important strategy in resistance breeding programs across the world. An accession of Oryza nivara, International Rice Germplasm Collection (IRGC) accession number 105710, was identified to exhibit high level and broad-spectrum resistance to Xanthomonas oryzae pv. oryzae. In order to study the genetics of resistance and to tag and map the resistance gene or genes present in IRGC 105710, it was crossed with the bacterial blight (BB)-susceptible varieties 'TN1' and 'Samba Mahsuri' (SM) and then backcrossed to generate backcross mapping populations. Analysis of these populations and their progeny testing revealed that a single dominant gene controls resistance in IRGC 105710. The BC(1)F(2) population derived from the cross IRGC 105710/TN1//TN1 was screened with a set of 72 polymorphic simple-sequence repeat (SSR) markers distributed across the rice genome and the resistance gene was coarse mapped on chromosome 7 between the SSR markers RM5711 and RM6728 at a genetic distance of 17.0 and 19.3 centimorgans (cM), respectively. After analysis involving 49 SSR markers located between the genomic interval spanned by RM5711 and RM6728, and BC(2)F(2) population consisting of 2,011 individuals derived from the cross IRGC 105710/TN1//TN1, the gene was fine mapped between two SSR markers (RMWR7.1 and RMWR7.6) located at a genetic distance of 0.9 and 1.2 cM, respectively, from the gene and flanking it. The linkage distances were validated in a BC(1)F(2) mapping population derived from the cross IRGC 105710/SM//2 × SM. The BB resistance gene present in the O. nivara accession was identified to be novel based on its unique map location on chromosome 7 and wider spectrum of BB resistance; this gene has been named Xa33. The genomic region between the two closely flanking SSR markers was in silico analyzed for putatively expressed candidate genes. In total, eight genes were identified in the region and a putative gene encoding serinethreonine kinase appears to be a candidate for the Xa33 gene.     

Identification of an Avirulence Gene in the Fungus Magnaporthe grisea Corresponding to a Resistance Gene at the Pik Locus

ABSTRACT A rice isolate of Magnaporthe grisea collected from China was avirulent on rice cvs. Hattan 3 and 13 other Japanese rice cultivars. The rice cv. Hattan 3 is susceptible to almost all Japanese blast fungus isolates from rice. The genetic basis of avirulence in the Chinese isolate on Japanese rice cultivars was studied using a cross between the Chinese isolate and a laboratory isolate. The segregation of avirulence or virulence was studied in 185 progeny from the cross, and monogenic control was demonstrated for avirulence to the 14 rice cultivars. The resistance gene that corresponds to the avirulence gene (Avr-Hattan 3) is thought to be located at the Pik locus. Resistance and susceptibility in response to the Chinese isolate in F(3) lines of a cross of resistant and susceptible rice cultivars were very similar to the Pik tester isolate, Ken54-20. Random amplified polymorphic DNA markers and restriction fragment length polymorphism markers from genetic maps of the fungus were used to construct a partial genetic map of Avr-Hattan 3. We obtained several flanking markers and one co-segregated marker of Avr-Hattan 3 in the 144 mapping population.     

Mapping Quantitative Field Resistance Against Apple Scab in a 'Fiesta' x 'Discovery' Progeny

ABSTRACT Breeding of resistant apple cultivars (Malus x domestica) as a disease management strategy relies on the knowledge and understanding of the underlying genetics. The availability of molecular markers and genetic linkage maps enables the detection and the analysis of major resistance genes as well as of quantitative trait loci (QTL) contributing to the resistance of a genotype. Such a genetic linkage map was constructed, based on a segregating population of the cross between apple cvs. Fiesta (syn. Red Pippin) and Discovery. The progeny was observed for 3 years at three different sites in Switzerland and field resistance against apple scab (Venturia inaequalis) was assessed. Only a weak correlation was detected between leaf scab and fruit scab. A QTL analysis was performed, based on the genetic linkage map consisting of 804 molecular markers and covering all 17 chromosomes of apple. With the maximum likelihood-based interval mapping method, eight genomic regions were identified, six conferring resistance against leaf scab and two conferring fruit scab resistance. Although cv. Discovery showed a much stronger resistance against scab in the field, most QTL identified were attributed to the more susceptible parent 'Fiesta'. This indicated a high degree of homozygosity at the scab resistance loci in 'Discovery', preventing their detection in the progeny due to the lack of segregation.     

不同猕猴桃品种RAPD分析及其与抗溃疡病的关系

对不同猕猴桃品种的分子生物学试验表明：猕猴桃的DNA浓度在920 μg/mL符合RAPD分析的要求。通过60个随机引物的PCR扩增,报道了6个不同品种和类型猕猴桃种质资源的RAPD多态性,计算了它们之间的遗传距离,构建了聚类图,并讨论了其亲缘关系。聚类分析图反映出来源于安徽省主要猕猴桃产区的6个样品可以分为3组,其中抗病与感病的相对较为集中,由此可推断出现这种聚类的原因可能是由于它们基因组中有相同的DNA片段。抗病品系都有一条1 458 bp DNA片段,而感病品系均没有该带。故该片段可能与猕猴桃植株抗溃疡病相关。RAPD多态性从分子水平上反映出了猕猴桃种质资源不同品种及不同类型间复杂的遗传背景,为抗病育种的亲本选配提供了依据,也为合成猕猴桃抗溃疡病探针并用于检测猕猴桃抗溃疡病种质和分子标记辅助育种奠定了基础。     

Genetic variability of Colletotrichum lindemuthianum in wild populations of common bean

The genetic structure of wild populations of Colletotrichum lindemuthianum was evaluated for virulence and molecular markers. Forty-five isolates were collected from five wild common bean populations located in their South-Andean centre of origin. The five pathogen populations were monomorphic in their ITS regions, but 45 polymorphic markers were identified using RAPDs. Polymorphism for virulence was also observed; 15 pathotypes were characterized on an international set of 12 differentials. A molecular variance analysis ( AMOVA ) showed that a very large part of the total genetic variation was within populations. Statistical analysis showed that there was a weak though significant differentiation among the five populations for the RAPD and virulence markers. A positive and significant correlation was found between geographic distance and the distances from RAPD and virulence data, suggesting migration between adjacent populations along the Argentinian transect. Our results suggest that the Andean wild isolates of C. lindemuthianum do not reflect all the putative diversity found in the isolates from cultivated common bean.     

中国不同地区致病疫霉遗传多样性的RAPD分析

 本文应用RAPD技术检测了我国主要马铃薯产区致病疫霉的遗传分化情况及不同地区菌株间的亲缘关系。用筛选出的10个随机引物对1997-2001年间采自我国9省市的82株及3株来自日本的致病疫霉DNA进行了PCR扩增,获得了79条谱带,其中多态性标记75条,占95%。根据扩增结果,运用UPGMA分析,获得了表现菌株间亲缘关系的树状图。菌株间的最大遗传距离为0.5,以距离0.3为阈值,可将供试菌株划分为10个组(RG1-10)。结果发现:A1交配型菌株群体内的差异大于A1和A2菌株群体之间的;RAPD分组与菌株的地理来源、交配型及对甲霜灵的敏感性无明显相关性。研究结果显示,来自中国北方甘肃、内蒙、吉林、黑龙江地区的菌株与一些来自云南、四川等西南地区的菌株亲缘关系相近。病原菌随种薯的迁移可能是导致这种现象的原因之一。     

Gene and Genotypic Diversity of Phytophthora cinnamomi in South Africa and Australia Revealed by DNA Polymorphisms

Phytophthora cinnamomi isolates from South Africa and Australia were compared to assess genetic differentiation between the two populations. These two populations were analysed for levels of phenotypic diversity using random amplified polymorphic DNAs (RAPDs) and gene and genotypic diversity using restriction fragment length polymorphisms (RFLPs). Sixteen RAPD markers from four decanucleotide Operon primers and 34 RFLP alleles from 15 putative loci were used. A few isolates from Papua New Guinea known to posses alleles different from Australian isolates were also included for comparative purposes. South African and Australian P. cinnamomi populations were almost identical with an extremely low level of genetic distance between them (D_m=0.003). Common features for the two populations include shared alleles, low levels of phenotypic/genotypic diversity, high clonality, and low observed and expected levels of heterozygosity. Furthermore, relatively high levels of genetic differentiation between mating type populations (D_m South Africa=0.020 and D_m Australia=0.025 respectively), negative fixation indices, and significant deviations from Hardy–Weinberg equilibrium, all provided evidence for the lack of frequent sexual reproduction in both populations. The data strongly suggest that both the South African and Australian P. cinnamomi populations are introduced.     

Association mapping of quantitative resistance to Phaeosphaeria nodorum in spring wheat landraces from the USDA National Small Grains Collection

Stagonospora nodorum blotch (SNB), caused by Phaeosphaeria nodorum, is a destructive disease of wheat (Triticum aestivum) found throughout the United States. Host resistance is the only economically feasible option for managing the disease; however, few SNB-resistant wheat cultivars are known to exist. In this study, we report findings from an association mapping (AM) of resistance to P. nodorum in 567 spring wheat landraces of diverse geographic origin. The accessions were evaluated for seedling resistance to P. nodorum in a greenhouse. Phenotypic data and 625 polymorphic diversity array technology (DArT) markers have been used for linkage disequilibrium (LD) and association analyses. The results showed that seven DArT markers on five chromosomes (2D, 3B, 5B, 6A, and 7A) were significantly associated with resistance to P. nodorum. Genetic regions on 2D, 3B, and 5B correspond to previously mapped quantitative trait loci (QTL) conferring resistance to P. nodorum whereas the remaining QTL appeared to be novel. These results demonstrate that the use of AM is an effective method for identifying new genomic regions associated with resistance to P. nodorum in spring wheat landraces. Additionally, the novel resistance found in this study could be useful in wheat breeding aimed at controlling SNB.     

Amplified fragment length polymorphism markers linked to a major quantitative trait locus controlling scab resistance in wheat

ABSTRACT Scab is a destructive disease of wheat. To accelerate development of scab-resistant wheat cultivars, molecular markers linked to scab resistance genes have been identified by using recombinant inbred lines (RILs) derived by single-seed descent from a cross between the resistant wheat cultivar Ning 7840 (resistant to spread of scab within the spike) and the susceptible cultivar Clark. In the greenhouse, F(5), F(6), F(7), and F(10) families were evaluated for resistance to spread of scab within a spike by injecting about 1,000 conidiospores of Fusarium graminearum into a central spikelet. Inoculated plants were kept in moist chambers for 3 days to promote initial infection and then transferred to greenhouse benches. Scab symptoms were evaluated four times (3, 9, 15, and 21 days after inoculation). The frequency distribution of scab severity indicated that resistance to spread of scab within a spike was controlled by a few major genes. DNA was isolated from both parents and F(9) plants of the 133 RILs. A total of 300 combinations of amplified fragment length polymorphism (AFLP) primers were screened for polymorphisms using bulked segregant analysis. Twenty pairs of primers revealed at least one polymorphic band between the two contrasting bulks. The segregation of each of these bands was evaluated in the 133 RILs. Eleven AFLP markers showed significant association with scab resistance, and an individual marker explained up to 53% of the total variation (R(2)). The markers with high R(2) values mapped to a single linkage group. By interval analysis, one major quantitative trait locus for scab resistance explaining up to 60% of the genetic variation for scab resistance was identified. Some of the AFLP markers may be useful in marker-assisted breeding to improve resistance to scab in wheat.     

Development and application of new molecular markers for analysis of genetic diversity in Verticillium dahliae populations

The aim of this study was to develop new polymorphic markers for analysis of genetic diversity in the fungal soilborne plant pathogen Verticillium dahliae. Twelve polymorphic markers (five microsatellites and seven polymorphic sequences) were developed from a genomic library enriched for microsatellites. Screening of polymorphic loci was done using a collection of 25 V. dahliae isolates of diverse geographic origins, host sources and vegetative compatibility groups (VCGs). Three methods were used to score alleles: polyacrylamide gel electrophoresis (PAGE), sequencing of PCR‐amplified loci, and capillary electrophoresis. The new markers were used to assess genetic differentiation between isolates associated with different host plants. Two collections of isolates were analysed, obtained from artichoke (30 isolates) and potato (20 isolates) from crops grown in rotation located in the same area in eastern‐central Spain. The resolution of genetic differentiation between these two collections using the new markers was compared to that provided by other often‐used markers (SCARs and VCGs). Sequence analysis of the alleles proved to be the most unambiguous technique for scoring microsatellite data. The relatively high genetic differentiation observed between isolates from different crops (genetic differentiation coefficient, G_ST = 0·24) and their high genotypic diversity suggest a divergence between V. dahliae from artichoke and potato. It is hypothesized that evolution of V. dahliae from the local resident population in association with the two host crops has occurred. The new markers are useful for resolving population structure within V. dahliae and may contribute to a better understanding of the population biology of this fungus.     

High diversity and clonality are hallmarks of Fusarium circinatum in South Africa

Pitch canker on plantation-grown Pinus species, caused by the fungal pathogen Fusarium circinatum, first appeared in the western and southern Cape regions of South Africa. However, outbreaks have subsequently been reported from the major plantation growing regions of KwaZulu-Natal and Limpopo in the eastern, summer rainfall regions of the country. It is more than 10 years since the last detailed population genetics studies on F. circinatum in the region were conducted. To shed light on the population biology of F. circinatum in this region of South Africa, we used microsatellite markers and mating-type assays to study a collection of 296 isolates from different nurseries and plantation sites. Our results showed that populations in the region are highly diverse, but strongly interconnected, with various genotypes shared across nursery and plantation collection sites. In contrast to nursery populations, those associated with pitch canker outbreaks were characterized by the presence of relatively small numbers of dominant genotypes that were generally widespread across the region. Opposite mating-type individuals occurred in most of the isolate collections, but multilocus linkage disequilibrium analyses pointed towards clonality being the main reproductive mode of F. circinatum in the region. Most of the pathogen's genetic variation could probably have resulted from multiple different introductions into the country and more specifically, into the summer rainfall region. Because the spread and establishment of invasive pathogens are typically driven by aggressive clones, the results of this study provide important considerations for current and future Pinus disease management strategies.     

Molecular Mapping of the rps1.a Recessive Gene for Resistance to Stripe Rust in BBA 2890 Barley

ABSTRACT Stripe rust, caused by Puccinia striiformis f. sp. hordei, is one of the most important diseases of barley in the south-central and western United States. Growing resistant cultivars is the best approach for controlling the disease. The barley genotype BBA 2890 has all-stage resistance against all races of P. striiformis f. sp. hordei (PSH) identified thus far in the United States. The resistance in BBA 2890 is controlled by a single recessive gene, rps1.a. The objectives of this study were to identify resistance gene analog polymorphism (RGAP) markers for the all-stage resistance gene rps1.a, to map the gene on a barley chromosome using chromosome-specific simple sequence repeat (SSR) markers, and to determine the presence or absence of the flanking RGAP markers for the gene in 24 barley genotypes. Seedlings of the parents and 200 F(8) recombinant inbred lines (RILs) were tested for resistance to pathogen races PSH-14, PSH-48, and PSH-54 in the greenhouse in 2005. Genomic DNA was extracted from the parents and 150 F(8) RILs. The RGAP technique was used to identify molecular markers for the rps1.a gene. Twelve primer pairs generating repeatable polymorphic bands were selected for genotyping the 150 F(8) RILs. A genetic linkage group was constructed for the resistance gene with 13 RGAP markers and four chromosome-specific SSR markers. The four SSR markers mapped the gene on the long arm of barley chromosome 3H. The closest RGAP marker for the resistant allele was within a genetic distance of 2.1 centimorgans (cM). The closest marker for the susceptible allele was 6.8 cM away from the locus. The two closest RGAP markers for the resistant allele detected polymorphisms in 67 and 71% of the 24 barley genotypes when used individually, and detected polymorphism in 88% of the genotypes when used in combination. This information should be useful in incorporating the resistance gene into barley cultivars and in pyramiding the gene with other resistance genes for superior stripe rust resistance.     

Experimentally evolved populations of the potato cyst nematode Globodera pallida allow the targeting of genomic footprints of selection due to host adaptation

In the current agronomical context of pesticide use reduction, deciphering the genetic bases of pathogen adaptation to plant defences is of major importance to improve durability of resistance. Indeed, knowledge of virulence gene frequencies in pathogen populations could allow the prediction of resistance durability before deployment. Globodera pallida is a major pest of potato crops for which a promising resistance QTL, GpaV_vrn, has been identified in Solanum vernei. An experimental evolution study, in which G. pallida lineages evolved on resistant or susceptible potato genotypes for up to eight generations, previously showed that G. pallida was able to rapidly overcome GpaV_vrn resistance. However, it was not known if enough genetic mixing occurred in these lineages to be able to detect islands of differentiation in a genome scan approach. Here, this question was investigated using 53 polymorphic microsatellite markers distributed along the genome and three different tests based on genetic differentiation and heterozygosity. Eight outlier loci were identified, indicative of genomic regions putatively involved in host adaptation. Several loci were identified by multiple detection methods and/or in two independent adapted lineages. Some candidate genomic regions identified also seemed to be involved in overcoming resistance to nematodes in a plant genotype harbouring the same resistance QTL in a different genetic background. These results validate the feasibility of a genome scan approach on biological material coming from short experimental evolution, and encourage the use of a high coverage genome scan by whole genome resequencing.