Identification and Molecular Mapping of a Gene in Wheat Conferring Resistance to Mycosphaerella graminicola

ABSTRACT Septoria tritici leaf blotch (STB), caused by the ascomycete Mycosphaerella graminicola (anamorph Septoria tritici), is an economically important disease of wheat. Breeding for resistance to STB is the most effective means to control this disease and can be facilitated through the use of molecular markers. However, molecular markers linked to most genes for resistance to STB are not yet available. This study was conducted to test for resistance in the parents of a standard wheat mapping population and to map any resistance genes identified. The population consisted of 130 F(10) recombinant-inbred lines (RILs) from a cross between the synthetic hexaploid wheat W7984 and cv. Opata 85. Genetic analysis indicated that a single major gene controls resistance to M. graminicola in this population. This putative resistance gene is now designated Stb8 and was mapped with respect to amplified fragment length polymorphism (AFLP) and microsatellite markers. An AFLP marker, EcoRI-ACG/MseI-CAG5, was linked in repulsion with the resistance gene at a distance of approximately 5.3 centimorgans (cM). Two flanking microsatellite markers, Xgwm146 and Xgwm577, were linked to the Stb8 gene on the long arm of wheat chromosome 7B at distances of 3.5 and 5.3 cM, respectively. The microsatellite markers identified in this study have potential for use in marker-assisted selection in breeding programs and for pyramiding of Stb8 with other genes for resistance to M. graminicola in wheat.     

Identification of isolate-specific and partial resistance to septoria tritici blotch in 238 European wheat cultivars and breeding lines

From a total of 238 European cultivars and breeding lines screened for isolate-specific resistance to septoria tritici blotch (STB) with eight Mycosphaerella graminicola isolates from five different countries, 142 lines were resistant to Ethiopian isolate IPO88004, and 43 lines were specifically resistant to IPO323, with little or no leaf area bearing pycnidia of M. graminicola . These lines probably all have the resistance gene Stb6 . Specific resistances to isolates CA30JI, IPO001, IPO89011, IPO92006 and ISR398 were less common. Seventy-three per cent of the lines were specifically resistant to at least one isolate and 36 lines were resistant to more than one isolate. The line with the greatest number of specific resistances was the spring cultivar Raffles, with five. The most resistant line in which no specific resistance was identified was the Italian landrace Rieti, an ancestor of many modern European wheat cultivars. There was also a wide range of partial resistance among the lines tested, expressed in detached seedling leaves. Information about the resistance of wheat lines to M. graminicola isolates will assist breeders to choose parents of crosses from which progeny with superior resistance to STB may be selected.     

Quantitative trait loci for adult-plant resistance to Mycosphaerella graminicola in two winter wheat populations

Septoria tritici blotch (STB) is one of the most important leaf spot diseases in wheat worldwide. The goal of this study was to detect chromosomal regions for adult-plant resistance in large winter wheat populations to STB. Inoculation by two isolates with virulence to Stb6 and Stb15, both present in the parents, was performed and STB severity was visually scored plotwise as percent coverage of flag leaves with pycnidia-bearing lesions. 'Florett'/'Biscay' and 'Tuareg'/'Biscay', each comprising a cross of a resistant and a susceptible cultivar, with population sizes of 316 and 269 F(7:8) recombinant inbred lines, respectively, were phenotyped across four and five environments and mapped with amplified fragment length polymorphism, diversity array technology, and simple sequence repeat markers covering polymorphic regions of ≈1,340 centimorgans. Phenotypic data revealed significant (P < 0.01) genotypic differentiation for STB, heading date, and plant height. Entry-mean heritabilities (h(2)) for STB were 0.73 for 'Florett'/'Biscay' and 0.38 for 'Tuareg'/'Biscay'. All correlations between STB and heading date as well as between STB and plant height were low (r = -0.13 to -0.20). In quantitative trait loci (QTL) analysis, nine and six QTL were found for STB ratings explaining, together, 55 and 51% of phenotypic variation in 'Florett'/'Biscay' and 'Tuareg'/'Biscay', respectively. Genotype-environment and QTL-environment interactions had a large impact. Two major QTL were detected consistently across environments on chromosomes 3B and 6D from 'Florett' and chromosomes 4B and 6B from 'Tuareg', each explaining 12 to 17% of normalized adjusted phenotypic variance. These results indicate that adult-plant resistance to STB in both mapping populations was of a quantitative nature.     

A gene in European wheat cultivars for resistance to an African isolate of Mycosphaerella graminicola

Genes for specific resistance to European and American isolates of Mycosphaerella graminicola , the causal agent of septoria tritici blotch (STB) of wheat, have been identified and mapped in various cultivars and breeding lines and are distributed throughout the genome. The location of a gene for resistance to an Ethiopian isolate, IPO88004, which is currently the most widespread resistance present in European wheat cultivars, is reported. The resistance was mapped in the Swiss cultivar Arina which, besides high partial resistance to STB, also has specific resistance to IPO323, controlled by Stb6 and to IPO88004. An F5 recombinant inbred population from a cross between Arina and the susceptible cultivar Forno was tested in whole seedling trials. Using multiple QTL mapping (MQM), a gene for resistance to M. graminicola isolate IPO88004 in cv. Arina was located to chromosome 6AS. The gene is named Stb15 . Seedling tests on a double haploid population of cvs Arina × Riband indicated that the UK wheat cv. Riband also has Stb15 or another gene for specific resistance to IPO88004 allelic or closely linked to Stb15 .     

Molecular Mapping of the Stb4 Gene for Resistance to Septoria tritici Blotch in Wheat

ABSTRACT Breeding wheat for resistance is the most effective means to control Septoria tritici blotch (STB), caused by the ascomycete Mycosphaerella graminicola (anamorph Septoria tritici). At least eight genes that confer resistance to STB in wheat have been identified. Among them, the Stb4 locus from the wheat cv. Tadinia showed resistance to M. graminicola at both seedling and adult-plant stages. However, no attempt has been made to map the Stb4 locus in the wheat genome. A mapping population of 77 F10 recombinant-inbred lines (RILs) derived from a three-way cross between the resistant cv. Tadinia and the susceptible parent (Yecora Rojo x UC554) was evaluated for disease resistance and molecular mapping. The RILs were tested with Argentina isolate I 89 of M. graminicola for one greenhouse season in Brazil during 1999, with an isolate from Brazil (IPBr1) for one field season in Piracicaba (Brazil) during 2000, and with Indiana tester isolate IN95-Lafayette-1196-WW-1-4 in the greenhouse during 2000 and 2001. The ratio of resistant:susceptible RILs was 1:1 in all three tests, confirming the single-gene model for control of resistance to STB in Tadinia. However, the patterns of resistance and susceptibility were different between the Indiana isolate and those from South America. For example, the ratio of RILs resistant to both the Indiana and Argentina isolates, resistant to one but susceptible to the other, and susceptible to both isolates was approximately 1:1:1:1, indicating that Tadinia may contain at least two genes for resistance to STB. A similar pattern was observed between the Indiana and Brazil isolates. The gene identified with the Indiana tester isolate was assumed to be the same as Stb4, whereas that revealed by the South American isolates may be new. Bulked-segregant analysis was used to identify amplified fragment length polymorphism (AFLP) and microsatellite markers linked to the presumed Stb4 gene. The AFLP marker EcoRI-ACTG/MseI-CAAA5 and microsatellite Xgwm111 were closely linked to the Stb4 locus in coupling at distances of 2.1 and 0.7 centimorgans (cM), respectively. A flanking marker, AFLP EAGG/ M-CAT10, was 4 cM from Stb4. The Stb4 gene was in a potential supercluster of resistance genes near the centromere on the short arm of wheat chromosome 7D that also contained Stb5 plus five previously identified genes for resistance to Russian wheat aphid. The microsatellite marker Xgwm111 identified in this study may be useful for facilitating the transfer of Stb4 into improved cultivars of wheat.     

Identification and location of Stb9, a gene for resistance to septoria tritici blotch in wheat cultivars Courtot and Tonic

This study reports the discovery of a gene for resistance to septoria tritici blotch (STB) in two spring wheat cultivars, Courtot and Tonic. The gene, named Stb9 , confers resistance to Mycosphaerella graminicola isolate IPO89011. It was mapped by quantitative trait loci (QTL) analysis using an existing map of Courtot × Chinese Spring and was located between markers Xfbb226 (3·6 cM) and XksuF1b (9 cM) on the long arm of chromosome 2B. Markers linked to Stb9 in Courtot were then shown to be linked to resistance to IPO89011 in F₃ families of Tonic × Longbow. Allelism tests in which Tonic was crossed with Courtot confirmed that Tonic has a gene for resistance to IPO89011 at or very close to the Stb9 locus. SSR markers flanking Stb9 may be used in marker-assisted selection to introgress this gene into winter cultivars or in spring wheat breeding programmes outside Europe.     

Resistance of wheat line kavkaz-k4500 L.6.a.4 to septoria tritici blotch controlled by isolate-specific resistance genes

ABSTRACT The International Maize and Wheat Improvement Center (CIMMYT), Mexico, germplasm-derived wheat (Triticum aestivum) Kavkaz-K4500 L.6.A.4 (KK) is one of the major sources of resistance to Septoria tritici blotch (STB). KK is resistant to STB in field conditions in the UK even though a large majority of Mycosphaerella graminicola isolates are virulent to it. The genetics of the resistance of KK to four isolates of M. graminicola were investigated. KK has at least five isolate-specific resistance genes including Stb6 on chromosome 3A plus a second gene for resistance to isolate IPO323, two genes on chromosome 4A, both in the region where Stb7 is located with one designated as Stb12, and a gene designated Stb10 on chromosome 1D. Taken together, the widespread use of KK as a source of resistance to STB, its high resistance in field conditions, and its high susceptibility to M. graminicola isolates, which are virulent to all its resistance genes, suggest that high levels of field resistance to STB might be achieved by pyramiding several isolate-specific resistance genes.     

Presence of the Stb6 gene for resistance to septoria tritici blotch (Mycosphaerella graminicola) in cultivars used in wheat-breeding programmes worldwide

Fifty-two wheat cultivars and breeding lines, most of which have been used in breeding programmes worldwide, were tested for isolate-specific resistance to Mycosphaerella graminicola isolate IPO323, which interacts with the Stb6 gene of wheat (first identified in cvs Flame and Hereward) via a gene-for-gene relationship. Twenty-three lines were specifically resistant to this isolate. Sixteen resistant lines were crossed with Flame for a test of allelism. All progeny lines were resistant, suggesting that the 16 parental lines had Stb6 , a gene allelic to it or a gene closely linked to it. In 14 lines, resistance to IPO323 was controlled by Stb6 only. An exception was Kavkaz-K4500 L6.A.4., which has two genes for resistance to IPO323, one of which is Stb6 . The microsatellite marker Xgwm369 was used to examine genetic diversity in the region of the genome containing Stb6 , to which it is closely linked. Eleven alleles of Xgwm369 , with amplified fragments of 10 different sizes, as well as apparent nonamplification of this marker in Bulgaria 88, were detected. Through the use of information about lines' ancestry, combined with Xgwm369 alleles, it was shown that Stb6 entered world wheat-breeding programmes on a minimum of six occasions, and possibly from as many as 11 sources. The presence of Stb6 in both European and Chinese landraces suggests that this gene has been present in cultivated wheat since the earliest times of agriculture.     

Sources of resistance to septoria tritici blotch and implications for wheat breeding

Twenty-four wheat cultivars and breeding lines were screened for isolate-specific resistance to septoria tritici blotch (STB) caused by 12 isolates of Mycosphaerella graminicola. New isolate-specific resistances that could be used in wheat breeding were identified. Major sources of resistance to STB used in world breeding programmes for decades, such as Kavkaz-K4500, Veranopolis, Catbird and TE9111, have several isolate-specific resistances. This suggests that 'pyramiding' several resistance genes in one cultivar may be an effective and durable strategy for breeding for resistance to STB in wheat. Several cultivars, including Arina, Milan and Senat, had high levels of partial resistance to most isolates tested as well as isolate-specific resistances. Resistance to isolate IPO323 was common, present in all but one of the major sources of resistance tested. This suggests that resistance to IPO323 may be an indicator of varietal resistance to STB in the field.     

Resistance of wheat to septoria tritici blotch (Mycosphaerella graminicola) and associations with plant ideotype and the 1BL−1RS translocation

Septoria tritici blotch (STB) is a major disease of wheat, reaching epidemic proportions in many parts of the world. In several studies, taller, later-maturing cultivars have had lower disease levels. This study was undertaken to investigate the genetic associations of natural field infection by STB with disease-escape mechanisms related to heading date and height components, mainly leaf spacing, in a population where height and maturity are not controlled by major genes. In field trials of a single seed-descent population of a cross between two nonsemi-dwarf cultivars, Apollo (with strong partial resistance to STB) and Thésée (susceptible), conducted over 3 years, there was a negative correlation between STB and heading date. There was no correlation between STB and distance from stem base to leaf 2; and there was an unexpected positive correlation between STB and distance from flag leaf to leaf 2, which contradicted the so-called 'ladder effect' postulated in STB epidemiology. No effect was detected of the presence of the 1BL−1RS translocation on STB levels. The largest single contributor to variation in STB levels was genetic variation between the progeny lines, and the narrow-sense heritability was 42%. These results suggest that breeders can select for STB resistance alongside optimal stature within the range of height which is adaptive in a particular environment.     

Evaluation of the susceptibility of modern,wild, ancestral,and mutational wheat lines to Septoria tritici blotch disease

Globally, bread wheat production is threatened by fungal diseases, including the devastating disease Septoria tritici blotch (STB). Given the global importance of STB, and the difficulty in identifying novel sources of resistance to this disease, we screened a variety of wheat genotypes, including wild, ancestral, and mutagenized lines, for their STB response. This delineated a panel of wild wheat relatives and Watkins collection lines with exceptional resistance to a range of Zymoseptoria tritici isolates, some of which are highly virulent on modern, elite wheat varieties. Additionally, we characterized the STB susceptibility of 500 lines of the wheat cultivar Cadenza TILLING population and developed backcross derivatives of two TILLING lines that show dominant partial resistance to STB. These backcross lines are partially resistant to multiple isolates of Z. tritici, and, with the wild and ancestral lines identified, provide a useful reservoir of STB-resistant germplasm for use in wheat breeding programmes.     

Partial Resistance to Septoria Tritici Blotch (Mycosphaerella graminicola) in Wheat Cultivars Arina and Riband

ABSTRACT Partial resistance to Septoria tritici blotch (STB) and its inheritance were investigated in a doubled-haploid population of a cross between cvs. Arina and Riband. The former has good partial resistance whereas the latter is susceptible. In adult plant trials in polytunnels, STB disease scores were negatively correlated with heading date. Resistance was not specific to any of the three fungal isolates used in these tests. A quantitative trait locus (QTL) for partial resistance to STB was identified in Riband on chromosome 6B and is named QStb.psr-6B-1. No QTL controlling a major part of the Arina resistance was identified, suggesting that its resistance may be dispersed and polygenic. There was no correlation between the lines' mean disease scores at the seedling and adult stages, implying that partial resistance to STB is developmentally regulated. Seedling resistance to the isolate IPO323 was isolate-specific and controlled by a single gene in Arina, probably allelic with the Stb6 gene in cv. Flame that confers resistance to the same isolate. The implications of these results for wheat breeding programs are discussed.     

Measurement of infection efficiency of a major wheat pathogen using time-resolved imaging of disease progress

Infection efficiency is a key epidemiological parameter that determines the proportion of pathogen spores able to infect and cause lesions once they have landed on a susceptible plant tissue. In this study, an improved method to measure infection efficiency of Zymoseptoria tritici using a replicated greenhouse experiment is presented. Zymoseptoria tritici is a fungal pathogen that infects wheat leaves and causes septoria tritici blotch (STB), a major disease of wheat worldwide. A novel experimental setup was devised, where living wheat leaves were attached to metal plates, allowing for time-resolved imaging of disease progress in planta. Because lesions were continuously appearing, expanding and merging during the period of up to 3 weeks, daily measurements were necessary for accurate counting of lesions. Reference membranes were also used to characterize the density and spatial distribution of spores inoculated onto leaf surfaces. In this way, the relationship between the number of lesions and the number of viable spores deposited on the leaves was captured and an infection efficiency of about 4% was estimated from the slope of this relationship. This study provides a proof of principle for accurate and reliable measurement of infection efficiency of Z. tritici. The method opens opportunities for determining the genetic basis of the component of quantitative resistance that suppresses infection efficiency. This knowledge would improve breeding for quantitative resistance against STB, a control measure considered more durable than deployment of major resistance genes.     

43个中国小麦品种(系)抗叶锈性研究

 选用12个墨西哥叶锈菌生理小种对43个中国小麦品种(系)所携带的抗叶锈病基因进行了推导,在25个品种(系)中推导出6个抗叶锈基因Lr1,Lr10,Lr13,Lr14a,Lr16和Lr26,9个品种(系)对本试验所使有的12个叶锈菌生理小种都表现感病反应,另有9个品种(系)携带未知的抗叶锈基因。在墨西哥2个地点进行的田间成株期抗叶锈性试验表明,12个品种(系)表现慢叶锈性,在将来的抗病育种中有一定的应用价值。     

A Gene-for-Gene Relationship Between Wheat and Mycosphaerella graminicola, the Septoria Tritici Blotch Pathogen

ABSTRACT Specific resistances to isolates of the ascomycete fungus Mycosphaerella graminicola, which causes Septoria tritici blotch of wheat, have been detected in many cultivars. Cvs. Flame and Hereward, which have specific resistance to the isolate IPO323, were crossed with the susceptible cv. Longbow. The results of tests on F1 and F2 progeny indicated that a single semidominant gene controls resistance to IPO323 in each of the resistant cultivars. This was confirmed in F3 families of Flame x Longbow, which were either homozygous resistant, homozygous susceptible, or segregating in tests with IPO323 but were uniformly susceptible to another isolate, IPO94269. None of 100 F2 progeny of Flame x Hereward were susceptible to IPO323, indicating that the resistance genes in these two cultivars are the same, closely linked, or allelic. The resistance gene in cv. Flame was mapped to the short arm of chromosome 3A using microsatellite markers and was named Stb6. Fifty-nine progeny of a cross between IPO323 and IPO94269 were used in complementary genetic analysis of the pathogen to test a gene-for-gene relationship between Stb6 and the avirulence gene in IPO323. Avirulence to cvs. Flame, Hereward, Shafir, Bezostaya 1, and Vivant and the breeding line NSL92-5719 cosegregated, and the ratio of virulent to avirulent was close to 1:1, suggesting that these wheat lines may all recognize the same avirulence gene and may all have Stb6. Together, these data provide the first demonstration that isolate-specific resistance of wheat to Septoria tritici blotch follows a gene-for-gene relationship.     

116个小麦品种（系）抗叶锈基因Lr9-Lr26、Lr19-Lr20的复合PCR检测

[目的]建立简单、快速、有效的小麦抗叶锈基因复合PCR体系,从而提高分子标记辅助选择效率。[方法]以28个‘Thatcher’为背景的近等基因系和16个已知基因载体品系作为试材,测试了小麦抗叶锈病基因Lr9、Lr26、Lr19和Lr20的STS标记特异性,通过优化PCR反应体系和循环条件,构建了抗叶锈基因Lr9-Lr26和Lr19-Lr20的复合PCR检测体系。对116个小麦品种(系)所含有的抗叶锈病基因进行了分子检测。[结果]供试品种均不含有Lr9和Lr20,47个品种含有Lr26(基因频率为40.5%),‘中梁22’含有Lr19。经反复验证,Lr9-Lr26和Lr19-Lr20复合PCR技术检测结果可靠,且与上述单个分子标记检测结果一致。[结论]建立的Lr9-Lr26和Lr19-Lr20的复合PCR检测体系可以准确、稳定、高效地检测小麦抗叶锈基因Lr9、Lr26、Lr19和Lr20。     

Predicting quantitative host plant resistance against phoma black stem in sunflower

Phoma black stem is an important disease in sunflower, against which no specific management method is currently deployed in France. Relevant phenotyping methods for quantitative resistance are critical for integration of this trait into breeding programmes. Components of resistance associated with physiological resistance, and morphological traits associated with disease escape were measured on 21 sunflower genotypes under growth chamber (on seedlings), greenhouse (on adult plants), and field conditions, together with disease intensity in the field. Potential predictors were first selected for sensitivity and robustness from mixed model anova s. Analyses involving ranking tests and logistic regressions were then performed to identify predictors for field resistance. The identification of predictors for resistance involved analyses conducted in two broad steps: process‐oriented experiments, and epidemic‐oriented experiments. This stepwise approach departs from many studies aimed at identifying predictors for field resistance, which rely mainly on the computation of correlation coefficients between predictors and measured field disease variables. Predictors for quantitative resistance were identified: (i) lesion length and lesion expansion on stems of plants before flowering stage, and (ii) lesion length on first leaf petioles of seedlings. A high number of leaves and tall plants were associated with disease escape. Control genotypes for susceptibility and quantitative resistance were identified, and implications for breeding and improvements were derived from this work.     

1992~1996年我国小麦叶锈菌毒性动态

 利用已知抗叶锈病基因的小麦近等基因系(或单基因系)作鉴别寄主,监测来自我国12个省(市、区)的499份叶锈标样。结果表明:(1)在发现的诸多致病类型(毒性基因组合)中,PHT出现频率较高(26.6%),为优势类型,其余类型的出现频率均在7.4%以下;(2)毒性基因V2a、V9、V15、V19、V20、V24、V28、V29、V37、V38和V13+3Ka的出现频率小于30%,V2b、V18、V25、V27+31和V33+34的出现频率在30%~60%之间,其对应的抗性基因可视为我国小麦叶锈菌的有效抗病基因;(3)不同生态区的叶锈菌株,毒性基因(或基因组合)的组成特点、出现频率及多样性等差异较大。文中建议采用"固定鉴别基因+辅助鉴别基因"的复合鉴定系统,并对小麦抗叶锈病生态育种及抗锈基因分区部署等问题进行了讨论。     

Mapping quantitative resistance to septoria tritici blotch in spelt wheat

The foliar wheat disease septoria tritici blotch can cause significant yield losses. A source of resistance has been mapped on chromosome 7D of spelt wheat, Triticum aestivum L. subsp. spelta (L.) Thell. The microsatellite-based genetic map was constructed from a set of 87 single-chromosome recombinant doubled-haploid lines bred from the cross between the landrace ‘Chinese Spring’ and a ‘Chinese Spring’-based line carrying chromosome 7D from spelt wheat. Two regions of the chromosome were associated with isolate-specific QTL expressed one at the seedling and another at the adult plant stage. The seedling resistance locus QStb.ipk-7D1 was found in the centromeric region of chromosome 7D, which corresponds to the location of the major resistance genes Stb4 originating from bread wheat cultivar ‘Tadinia’ and Stb5 originating from Triticum tauschii. The adult resistance locus QStb.ipk-7D2 was found on the short arm of chromosome 7D in a similar position to the locus Lr34/Yr18 known to be effective against multiple pathogens. Composite interval mapping confirmed QStb.ipk-7D1 and QStb.ipk-7D2 to be two distinct loci.