Characterization and expression profiling of a novel cereal cyst nematode resistance gene analog in wheat

Based on the conserved regions of known resistance genes, an NBS-LRR-type CCN resistance gene analog was isolated from the CCN resistant E-10 near isogenic lines (NILs) of wheat, designated as CreZ (GenBank accession number: EU327996). It contained a complete ORF that was 2775 bp in length and encoded 924 amino acids. Sequence comparison indicated that it shared 92% nucleotide and 87% amino acid identity with those of the known CCN-resistance gene Cre3 and had similar characteristic conserved motifs to those in other established NBS-LRR disease resistance genes. The expression profiling of CreZ indicated that it was specifically expressed in the roots of resistant plants and real-time PCR analysis demonstrated that expression levels drastically increased when the plants were inoculated with cereal cyst nematodes. It could be inferred, then, that CreZ belongs to the NBS-LRR resistance gene family and is a candidate gene for potential resistance to the cereal cyst nematode. Published in Russian in Molekulyarnaya Biologiya, 2008, Vol. 42, No. 6, pp. 1070–1077. The text was submitted by the authors in English.     

Identification of RFLP markers linked to the cereal cyst nematode resistance gene (Cre) in wheat

The cereal cyst nematode (CCN) (Heterodera avenae Woll.) is an economically damaging pest of wheat in many of the worlds cereal growing areas. The development of CCN-resistant cultivars may be accelerated by the use of molecular markers. The Cre gene of the wheat line AUS 10894 confers resistance to CCN. Using a pair of near-isogenic lines (NILs) that should differ only in a small chromosome segment containing the Cre locus, we screened 58 group-2 probes and found two (Tag605 and CDO588) that detect polymorphism between the NILs. Nulli-tetrasomic and ditelosomic lines confirmed that the restriction fragment length polymorphism (RFLP) markers identified were derived from the long arm of wheat chromosome 2. Crosses between AUS 10894 and Spear and the NIL AP and its recurrent parent Prins were used to produce F₂ populations that gave the expected 31 segregation ratio for the resistance gene. Linkage analysis identified two RFLP markers flanking the resistance gene. Xglk605 and Xcdo588 mapped 7.3 cM (LOD=6.0) and 8.4 cM (LOD=6.7), respectively, from the Cre locus.     

Mapping QTL for resistance to eyespot of wheat in Aegilops longissima

Eyespot is an economically important disease of wheat caused by the soilborne fungi Oculimacula yallundae and O. acuformis. These pathogens infect and colonize the stem base, which results in lodging of diseased plants and reduced grain yield. Disease resistant cultivars are the most desirable control method, but resistance genes are limited in the wheat gene pool. Some accessions of the wheat wild relative Aegilops longissima are resistant to eyespot, but nothing is known about the genetic control of resistance. A recombinant inbred line population was developed from the cross PI 542196 (R) × PI 330486 (S) to map the resistance genes and better understand resistance in Ae. longissima. A genetic linkage map of the S(l) genome was constructed with 169 wheat microsatellite markers covering 1261.3 cM in 7 groups. F(5) lines (189) were tested for reaction to O. yallundae and four QTL were detected in chromosomes 1S(l), 3S(l), 5S(l), and 7S(l). These QTL explained 44 % of the total phenotypic variation in reaction to eyespot based on GUS scores and 63 % for visual disease ratings. These results demonstrate that genetic control of O. yallundae resistance in Ae. longissima is polygenic. This is the first report of multiple QTL conferring resistance to eyespot in Ae. longissima. Markers cfd6, wmc597, wmc415, and cfd2 are tightly linked to Q.Pch.wsu-1S ( l ), Q.Pch.wsu-3S ( l ), Q.Pch.wsu-5S ( l ), and Q.Pch.wsu-7S ( l ), respectively. These markers may be useful in marker-assisted selection for transferring resistance genes to wheat to increase the effectiveness of resistance and broaden the genetic diversity of eyespot resistance.     

A cereal cyst nematode (Heterodera avenae Woll.) resistance gene transferred from Aegilops triuncialis to hexaploid wheat

 The cereal cyst nematode (Heterodera avenae) is an important root parasite of common wheat. A high level of resistance was transferred to wheat from Aegilops triuncialis (TR lines) using the cross [(T. turgidum×Ae. triuncialis)×T. aestivum]. Low fertility (3–5 viable kernels per plant) was observed during the process but the surviving hybrid plants were highly vigorous. To obtain stable resistant lines further crosses to T. aestivum were performed. The resistance in TR lines seems to be transferred from the C genome of Ae. triuncialis (genomes CCUU). Ae. triuncialis was highly resistant to the two Spanish populations of H. avenae tested, as well as to four French races and two Swedish populations. The histological analysis showed a hypersensitive reaction in the roots of a resistant TR line inoculated with the Ha71 pathotype of H. avenae, whereas well-formed syncytia were observed in the roots of the susceptible control. Resistance to the H. avenae Ha71 pathotype seemed to be inherited as determined by a single dominant factor in the crosses between resistant TR lines and susceptible cultivars. Received: 11 November 1997 / Accepted: 9 December 1997     

Impact of Cre1, Cre8 and Cre3 genes on cereal cyst nematode resistance in wheat

The cereal cyst nematode (CCN; Heterodera avenae), a root disease of cereal crops, is a major economic constraint in many wheat (Triticum aestivum)-growing areas of the world. The objective of this study was to assess the impact of the Cre1, Cre8 and Cre3 genes on CCN resistance. A population of 92 doubled-haploid (DH) lines derived from a cross between wheat cvs. Frame and Silverstar as well as 1,851 wheat breeding lines were screened for CCN resistance at the Primary Industries Research Victoria (PIRVic). A second population of 9,470 wheat breeding lines was screened at the South Australian Research and Development Institute (SARDI). Cre3 had the largest impact on reducing the number of female cysts, followed by Cre1 and Cre8. There was no significant difference in number of cysts between DH lines with or without the Cre8 marker, suggesting that the marker is not perfectly linked to Cre8. The estimated heritabilities were 0.32 in the DH population, 0.48 in the PIRVic data set and 0.32 in the SARDI data set, which confirm that this is a trait of low heritability. The repeatability of CCN resistance improved with an increase in the number of plants assessed per line—up to ten. However, 85–88% of the improvement was achieved with the assessments of the first five plants.     

A QTL for broad-spectrum resistance to cyst nematode species (Globodera spp.) maps to a resistance gene cluster in potato

 Broad-spectrum resistance in potato to the potato cyst nematode (PCN) species Globodera rostochiensis and G. pallida is commonly regarded as a polygenically inherited trait. Yet, by use of QTL analysis and a selected set of PCN populations, resistance to both PCN species could be ascribed to the action of locus Grp1. Grp1 confers major resistance to G. rostochiensis line Ro₅-22 and G. pallida population Pa₂-D383 and partial resistance to G. pallida population Pa₃-Rookmaker. Grp1 was mapped on chromosome 5 using previously characterized AFLP markers. Cleaved amplified polymorphic sequence (CAPS) markers available for RFLP loci GP21 and GP179 revealed that Grp1 maps on a genomic region harboring other resistance factors to viral, fungal and nematodal pathogens. The present data indicate that Grp1 is a compound locus which contains multiple genes involved in PCN resistance. Received: 10 September 1997 / Accepted: 6 October 1997     

QTL for resistance to root lesion nematode (Pratylenchus thornei) from a synthetic hexaploid wheat source

Key message

A whole genome average interval mapping approach identified eight QTL associated with P. thornei resistance in a DH population from a cross between the synthetic-derived wheat Sokoll and cultivar Krichauff.

Abstract

Pratylenchus thornei are migratory nematodes that feed and reproduce within the wheat root cortex, causing cell death (lesions) resulting in severe yield reductions globally. Genotypic selection using molecular markers closely linked to Pratylenchus resistance genes will accelerate the development of new resistant cultivars by reducing the need for laborious and expensive resistance phenotyping. A doubled haploid wheat population (150 lines) from a cross between the synthetic-derived cultivar Sokoll (P. thornei resistant) and cultivar Krichauff (P. thornei moderately susceptible) was used to identify quantitative trait loci (QTL) associated with P. thornei resistance. The resistance identified in the glasshouse was validated in a field trial. A genetic map was constructed using Diversity Array Technology and the QTL regions identified were further targeted with simple sequence repeat (SSR) and single-nucleotide polymorphism (SNP) markers. Six significant and two suggestive P. thornei resistance QTL were detected using a whole genome average interval mapping approach. Three QTL were identified on chromosome 2B, two on chromosome 6D, and a single QTL on each of chromosomes 2A, 2D and 5D. The QTL on chromosomes 2BS and 6DS mapped to locations previously identified to be associated with Pratylenchus resistance. Together, the QTL on 2B (QRlnt.sk-2B.1–2B.3) and 6D (QRlnt.sk-6D.1 and 6D.2) explained 30 and 48 % of the genotypic variation, respectively. Flanking PCR-based markers based on SSRs and SNPs were developed for the major QTL on 2B and 6D and provide a cost-effective high-throughput tool for marker-assisted breeding of wheat with improved P. thornei resistance.     

RFLP mapping of the Ha 2 cereal cyst nematode resistance gene in barley

 The cereal cyst nematode (CCN), Heterodera avenae Woll., is an economically damaging pest of barley in many of the world’s cereal-growing areas. The development of CCN-resistant cultivars may be accelerated through the use of molecular markers. A number of resistance genes against the pest are well known; one of them, the single dominant Ha 2 resistance gene, has been shown to be effective against the Australian pathotype and maps to chromosome 2 of barley. Segregation analysis identified two restriction fragment length polymorphism (RFLP) markers flanking the resistance gene in two doubled-haploid populations of barley. AWBMA 21 and MWG 694 mapped 4.1 and 6.1 cM respectively from the Ha 2 locus in the Chebec×Harrington cross and 4.0 and 9.2 cM respectively in the Clipper×Sahara cross. Analysis of a further seven sources of CCN resistance in the form of near-isogenic lines (NILs) indicates that all available sources of resistance to the Australian pathotype of CCN in barley represent the Ha 2 locus. Received: 5 December 1996 / Accepted: 20 December 1996     

QTL associated with horizontal resistance to soybean cyst nematode in Glycine soja PI464925B

Soybean cyst nematode (Heterodera glycines Ichinohe; SCN) is the primary disease responsible for yield loss of soybean [Glycine max (L.) Merr.]. Resistant cultivars are an effective management tool; however, the sources currently available have common resistant genes. Glycine soja Sieb. and Zucc., the wild ancestor of domesticated soybean, represents a diverse germplasm pool with known SCN resistance. The objectives of this research were to: (1) determine the genetic variation and inheritance of SCN resistance in a G. max (‘S08-80’) × G. soja (PI464925B) F _4:5 recombinant inbred line (RIL) population; and (2) identify and evaluate quantitative trait loci (QTL) associated with SCN resistance. Transgressive segregation for resistance was observed, although neither parent was resistant to the Chatham and Ruthven SCN isolates. Broad sense heritability was 0.81 for the Ruthven and 0.91 for the Chatham isolate. Root dry weight was a significant covariate that influenced cyst counts. One RIL [female index (FI) = 5.2 ± 1.11] was identified as resistant to the Chatham isolate (FI < 10). Seventeen and three RILs infected with Chatham and Ruthven isolates, respectively, had mean adjusted cyst counts of zero. Unique and novel QTL, which derived resistance from G. soja, were identified on linkage groups I, K, and O, and individually explained 8, 7 and 5% (LOD = 2.1–2.7) of the total phenotypic variation, respectively. Significant epistatic interactions were found between pairs of SSR markers that individually may or may not have been associated with SCN resistance, which explained between 10 and 15% of the total phenotypic variation. Best-fit regression models explained 21 and 31% of the total phenotypic variation in the RIL population to the Chatham and Ruthven isolates, respectively. The results of this study help to improve the understanding of the genetic control of SCN resistance in soybean caused by minor genes resulting in horizontal resistance. The incorporation of the novel resistance QTL from G. soja could increase the durability of SCN-resistance in soybean cultivars, especially if major gene resistance breaks down.     

Identification of a new major QTL associated with resistance to soybean cyst nematode (Heterodera glycines)

Resistance of soybean [Glycine max (L.) Merr.] to cyst nematode (SCN) (Heterodera glycines Ichinohe), one of the most destructive pathogens affecting soybean, involves a complex genetic system. The identification of QTLs associated with SCN resistance may contribute to the understanding of such system. The objective of this work was to identify and map QTLs for resistance to SCN Race 14 with the aid of molecular markers. BC₃F_2:3 and F_2:3 populations, both derived from an original cross between resistant cv. Hartwig and the susceptible line BR-92–31983 were screened for resistance to SCN Race 14. Four microsatellite (Satt082, Sat_001, Satt574 and Satt301) and four RAPD markers (OPAA-11₇₉₅, OPAE-08₈₃₇, OPR-07₅₄₈ and OPY-07₂₀₃₀) were identified in the BC₃F_2:3 population using the bulked segregant analysis (BSA) technique. These markers were amplified in 183 F_2:3 families and mapped to a locus that accounts for more than 40% of the resistance to SCN Race 14. Selection efficiency based on these markers was similar to that obtained with the conventional method. In the case of the microsalellite markers, which identify homozygous resistant genotypes, the efficiency was even higher. This new QTL has been mapped to the soybean linkage group D2 and, in conjunction with other QTLs already identified for SCN resistance, will certainly contribute to our understanding of the genetic basis of resistance of this important disease in soybean. Received: 12 October 1999 / Accepted: 14 April 2000     

Mapping resistance to cereal aphids in barley

 A set of 150 doubled-haploid (DH) barley (Hordeum vulgare L.) lines derived from the cross of Harrington/TR306 was used to determine the number and chromosomal location of quantitative trait loci (QTLs) controlling resistance to cereal aphids. The experiments were conducted under natural infestation in the field during two growing seasons: 1994 and 1995. Aphid resistance was measured by counting the number of aphids per plot. Counts were made on a weekly basis. Each year at the time of maximum aphid density there was an obvious difference in reaction between the parental genotypes. The DH lines showed continuous variation for aphid density. Simple interval mapping and simplified composite interval mapping revealed that the principal QTL determining cereal aphid resistance is on the distal region of the short arm of chromosome 1. This aphid-resistance QTL is linked with a heading-date QTL. At the time of highest aphid infestation, this QTL accounted for 31% and 22% of the total variance of aphid density in 1994 and 1995, respectively. A QTL on chromosome 5 was also detected but only by simplified composite interval mapping. However, the largest consistent effect was due to the QTL on the short arm of chromosome 1. This QTL may be a useful target for marker-assisted selection for adult plant cereal aphid resistance in barley. Received: 10 September 1996/Accepted: 11 October 1996     

A directed search for DNA sequences tightly linked to cereal cyst nematode resistance genes in Triticum tauschii.

An improved system for identifying DNA sequences linked to a targeted region was developed by fractionating DNA sequences prior to polymerase chain reaction (PCR) analysis. In an attempt to identify DNA markers linked to a strong CCN resistance gene, Ccn-D1, in Triticum tauschii, DNA samples from individuals homozygous for resistance and susceptibility at the Ccn-D1 locus in a segregating progeny were bulked separately to produce "near isogenic" DNA pools. The polymerase chain reaction was employed to generate several DNA amplification products from each of the bulked DNA segregants using 240 random (RAPD) and 4 semirandom (consensus sequences of intron-splice junctions) primers. A DNA polymorphic fragment was apparent between the resistant and susceptible bulks using one of the semirandom primers. Hydroxylapatite chromatography of reannealed DNA (to Cot values > 100) was used to enrich low copy DNA sequences in the bulk DNA segregants (resistant and susceptible DNA pools). PCR analysis on the low copy enriched DNA pool increased the level of polymorphism detected between bulked segregants. One of the RAPD fragments present in only the resistant low copy DNA pool was cloned and mapped to the distal region of the long arm of chromosome 2D. By using the cloned RAPD fragment, csE20-2, to assay an RFLP locus in three independent F2 progenies, complete cosegregation was obtained with the Ccn-D1 locus. Joint segregation analysis from a genome-wide mapping of RFLP markers and a second CCN resistance in T. tauschii, Ccn-D2, showed this locus to be loosely linked to the proximal region of chromosome 2.     

Root responses to cereal cyst nematode (Heterodera avenae) in hosts with different resistance genes

The development of cereal cyst nematode (CCN; Heterodera avenae ) induced syncytia in the host roots of infected resistant bread wheat ( Triticum aestivum cv. AUS10894), diploid wheat ( Aegilops tauschii ), barley ( Hordeum vulgare cv. Chebec and cv. Galleon) and in the susceptible wheat cv. Meering and barley cv. Clipper were studied over a period of 13 d. The resistance to CCN in these cereal plants is conferred by the resistance genes Cre1 in the wheat cv. AUS10894, Cre3 in A. tauschii , Ha2 in barley cv. Chebec and Ha4 in barley cv. Galleon. Anatomical observations were made on the development of the syncytia in CCN-infected wheat and barley roots, which carry each of these four sources of resistance genes. Accelerated development of the syncytia in resistant plants, especially in the barley cultivars, was observed. The sites of syncytia development in susceptible wheat and barley were also closely associated with the vascular tissues in the stele, but less so in the resistant plants. The syncytia in the infected susceptible wheat and barley were also metabolically active at day 13. By contrast, the syncytia of resistant wheat plants carrying the Cre1 or Cre3 genes remained extensively vacuolated and less metabolically active. In barley plants with the Ha2 or Ha4 genes, the syncytia appeared non-functional and in early stages of degeneration by day 13 after inoculation.     

Mapping and diagnostic marker development for Soil-borne cereal mosaic virus resistance in bread wheat

Monogenically-inherited resistance to Soil-borne cereal mosaic virus (SBCMV) in hexaploid bread wheat cultivars ‘Tremie’ and ‘Claire’ was mapped on chromosome 5D. The two closest flanking markers identified in the Claire-derived mapping population, Xgwm469-5D and E37M49, are linked to the resistance locus at distances of 1 and 9 cm, respectively. Xgwm469-5D co-segregated with the SBCMV resistance in the Tremie-derived population and with the recently identified Sbm1 locus in the cv. Cadenza. This suggested that Tremie and Claire carry a resistance gene allelic to Sbm1, or one closely linked to it. The diagnostic value of Xgwm469-5D was assessed using a collection of SBCMV resistant and susceptible cultivars. Importantly, all susceptible genotypes carried a null allele of Xgwm469-5D, whereas resistant genotypes presumably related to either Claire and Tremie or Cadenza revealed a 152 or 154 bp allele of Xgwm469-5D, respectively. Therefore, Xgwm469-5D is well suited for marker assisted selection for SBCMV resistance.     

28份人工合成小麦对禾谷孢囊线虫、纹枯病、条锈病和叶锈病的抗性

为了发现具有兼抗多种病害的小麦种质,本研究采用田间病圃法和人工接种法,对28份人工合成小麦的禾谷孢囊线虫、纹枯病、条锈病和叶锈病进行了抗性鉴定。人工合成小麦对这些病害表现不同程度的抗性反应。C2和C20对鉴定的4种病害都具有抗性,C5、C10和C25对这些病害都表现感病。8份材料对Heterodera avenae和H. filipjevi两种病原线虫都表现抗性反应型,也有的材料只抗一种线虫。供试材料对纹枯病的抗性表现较好,其中19份材料表现抗性反应型。9份材料对接种的条锈菌小种CY30、CY31、CY32和CY33均表现抗性反应型,5份材料对叶锈菌小种THT和PHT都具抗性。     

A major QTL for resistance to soil-borne cereal mosaic virus derived from an old Italian durum wheat cultivar

Abstract

The genetic basis of resistance to soil-borne cereal mosaic virus (SBCMV) in the Triticum turgidum L. var. durum cv. Neodur was analyzed in this study, using a linkage mapping approach. We performed phenotypic and molecular analyses of 146 recombinant inbred lines derived from the cross Cirillo (highly susceptible)×Neodur (highly resistant). A major quantitative trait locus (QTL) that explained up to 87% of the observed variability for symptom severity was identified on the short arm of chromosome 2B, within the 40-cM interval between the markers Xwmc764 and Xgwm1128, with wPt-2106 as the peak marker. Three minor QTLs were found on chromosomes 3B and 7B. Two markers coding for resistance proteins co-segregate with the major QTL on chromosome 2B and the minor QTL on chromosome 3B, representing potential candidate genes for the two resistance loci. Microsatellite markers flanking the major QTL were evaluated on a set of 25 durum wheat genotypes that were previously characterized for SBCMV resistance. The allelic composition of the genotypes at these loci, together with pedigree data, suggests that the old Italian cultivar Cappelli provided the SBCMV-resistance determinants to durum cultivars that have been independently bred in different countries over the last century.     

Mapping QTL for water regime in spring bread wheat

For the first time, the authors assessed and mapped the chromosome QTLs (Quantitative Trait Loci) for the manifestation of morpho-physiological and agronomic indices of plant water status and related quantitative traits, such as plant height, weight, and dry matter content in spring bread wheat (Triticum aestivum L.). Following the study of ten agronomic traits, 13 QTLs were mapped on linkage groups 1A, 1B, 2B, 2D, 4A, 5A, 5B, 5D, 6A, and 6D. Some of the identified QTLs concurrently determined several traits. The physiological components of water status were shown to correlate with quantitative traits in wheat plants, such as plant height, weight, and dry matter content, and the correlation coefficients were calculated for all traits under study. Water retention capacity after 3 h correlated with water retention capacity after 24 h (r _xy = 0.47). The correlations were also established between water retention capacity after 3 h and plant height at booting stage (r _xy = 0.29) and between water retention capacity after 3 h and plant dry weight (r _xy = 0.33). Statistical calculations supported generally observed negative correlation (up to ?1) between leaf water and dry matter contents, as well as between the root indices of variance in the mapping population of wheat lines. The results obtained in the present study will promote future efforts to fine-map the genes residing within the identified QTLs, to eventually clone these genes in order to establish the physiological mechanisms for maintaining water homeostasis in higher plant cells and to accomplish the practical implementation of marker-assisted assessment of water status in wheat plants studied on the basis of morpho-physiological and economical indices.