The dissection and SSR mapping of a high-temperature adult-plant stripe rust resistance gene in American spring wheat cultivar Alturas

Stripe rust is one of major diseases in wheat production worldwide. The best economic and efficient method is to utilize resistant varieties. Alturas has high-temperature adult-plant resistance. In order to determine stripe rust resistance characteristics, resistance gene combination and molecular map of the resistance gene(s), Alturas was crossed with Chinese susceptible cultivar Taichung29. The parents, F₁, F₂ progenies were tested with Chinese predominant mixed races CYR31, CYR32 and CYR33 in field experiments in 2010 and F₃ progenies were evaluated at one site in Beijing, the other site in Langfang, Hebei Province. Infection type (IT) and disease severity (DS) were recorded three times for each plant for F₁ and F₂, and each progeny for F₃ during each growing season. The DS data were used to calculate relative area under the disease progress curve (AUDPC) values. Both IT and AUDPC data showed continuous distributions, indicating that the Alturas HTAP resistance was controlled by quantitative trait loci (QTLs). A major HTAP QTL, designated as QYrAlt.syau-3BS, was consistently detected across environments and was located on chromosome 3BS. The gene contributed to 34.28?% of the phenotypic variation for average AUDPC and 50.20?% for average IT. Markers Xgwm389 and Xbarc238 flanking the major QTL, should be useful in breeding for obtaining durable and high-level resistance by combinations with other non-race-specific resistance genes.     

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.     

小麦抗条锈病一致性数量性状位点(MQTL)图谱构建

 小麦条锈病是造成小麦减产和品质劣化的最重要病害,定位小麦染色体上一致性条锈病抗性基因/位点/区段是小麦条锈病抗性分子育种的重要基础。本研究对至今分子标记和遗传定位的342个条锈病抗性基因/位点/区段进行数据搜集整理,借助Maccaferr和Andrzej的参考图谱,基于元分析技术进行Meta-QTL(MQTL)检测,共获得194个小麦抗条锈病MQTL,包括74个与严重度(Disease severity, DS)相关,46个与反应型(Infection type, IT)相关、19个与病程曲线下面积相关(Area under disease progress curve, AUDPC)、28个与DS和IT共相关、6个与DS和AUDPC共相关、15个与IT和AUDPC共相关、6个与其他条锈病抗性性状相关。这些抗条锈病一致性QTL定位于小麦21条染色体上,呈非均匀分布,且部分MQTL集中成簇。通过与已发表的正式命名抗条锈病基因比较分析,发现大多数正式命名基因定位于MQTL簇区段,说明这些MQTL簇区段很可能是控制小麦条锈病抗性热点区域。控制小麦抗条锈病一致性QTL遗传图谱的构建为小麦条锈病抗性基因精细定位及抗病育种提供了遗传信息参考依据。     

小麦抗条锈病一致性数量性状位点(MQTL)图谱构建

 小麦条锈病是造成小麦减产和品质劣化的最重要病害,定位小麦染色体上一致性条锈病抗性基因/位点/区段是小麦条锈病抗性分子育种的重要基础。本研究对至今分子标记和遗传定位的342个条锈病抗性基因/位点/区段进行数据搜集整理,借助Maccaferr和Andrzej的参考图谱,基于元分析技术进行Meta-QTL(MQTL)检测,共获得194个小麦抗条锈病MQTL,包括74个与严重度(Disease severity, DS)相关,46个与反应型(Infection type, IT)相关、19个与病程曲线下面积相关(Area under disease progress curve, AUDPC)、28个与DS和IT共相关、6个与DS和AUDPC共相关、15个与IT和AUDPC共相关、6个与其他条锈病抗性性状相关。这些抗条锈病一致性QTL定位于小麦21条染色体上,呈非均匀分布,且部分MQTL集中成簇。通过与已发表的正式命名抗条锈病基因比较分析,发现大多数正式命名基因定位于MQTL簇区段,说明这些MQTL簇区段很可能是控制小麦条锈病抗性热点区域。控制小麦抗条锈病一致性QTL遗传图谱的构建为小麦条锈病抗性基因精细定位及抗病育种提供了遗传信息参考依据。     

Inheritance and molecular mapping of barley genes conferring resistance to wheat stripe rust

ABSTRACT Most barley cultivars are resistant to stripe rust of wheat that is caused by Puccinia striiformis f. sp. tritici. The barley cv. Steptoe is susceptible to all identified races of P. striiformis f. sp. hordei (PSH), the barley stripe rust pathogen, but is resistant to most P. striiformis f. sp. tritici races. To determine inheritance of the Steptoe resistance to P. striiformis f. sp. tritici, a cross was made between Steptoe and Russell, a barley cultivar susceptible to some P. striiformis f. sp. tritici races and all tested P. striiformis f. sp. hordei races. Seedlings of parents and F(1), BC(1), F(2), and F(3) progeny from the barley cross were tested with P. striiformis f. sp. tritici races PST-41 and PST-45 under controlled greenhouse conditions. Genetic analyses of infection type data showed that Steptoe had one dominant gene and one recessive gene (provisionally designated as RpstS1 and rpstS2, respectively) for resistance to races PST-41 and PST-45. Genomic DNA was extracted from the parents and 150 F(2) plants that were tested for rust reaction and grown for seed of F(3) lines. The infection type data and polymorphic markers identified using the resistance gene analog polymorphism (RGAP) technique were analyzed with the Mapmaker computer program to map the resistance genes. The dominant resistance gene in Steptoe for resistance to P. striiformis f. sp. tritici races was mapped on barley chromosome 4H using a linked microsatellite marker, HVM68. A linkage group for the dominant gene was constructed with 12 RGAP markers and the microsatellite marker. The results show that resistance in barley to the wheat stripe rust pathogen is qualitatively inherited. These genes might provide useful resistance against wheat stripe rust when introgressed into wheat from barley.     

Genetic analysis and molecular mapping of wheat genes conferring resistance to the wheat stripe rust and barley stripe rust pathogens

ABSTRACT Stripe rust is one of the most important diseases of wheat and barley worldwide. On wheat it is caused by Puccinia striiformis f. sp. tritici and on barley by P. striiformis f. sp. hordei Most wheat genotypes are resistant to P. striiformis f. sp. hordei and most barley genotypes are resistant to P. striiformis f. sp. tritici. To determine the genetics of resistance in wheat to P. striiformis f. sp. hordei, crosses were made between wheat genotypes Lemhi (resistant to P. striiformis f. sp. hordei) and PI 478214 (susceptible to P. striiformis f. sp. hordei). The greenhouse seedling test of 150 F(2) progeny from the Lemhi x PI 478214 cross, inoculated with race PSH-14 of P. striiformis f. sp. hordei, indicated that Lemhi has a dominant resistance gene. The single dominant gene was confirmed by testing seedlings of the F(1), BC(1) to the two parents, and 150 F(3) lines from the F(2) plants with the same race. The tests of the F(1), BC(1), and F(3) progeny with race PSH-48 of P. striiformis f. sp. hordei and PST-21 of P. striiformis f. sp. tritici also showed a dominant gene for resistance to these races. Cosegregation analyses of the F(3) data from the tests with the two races of P. striiformis f. sp. hordei and one race of P. striiformis f. sp. tritici suggested that the same gene conferred the resistance to both races of P. striiformis f. sp. hordei, and this gene was different but closely linked to Yr21, a previously reported gene in Lemhi conferring resistance to race PST-21 of P. striiformis f. sp. tritici. A linkage group consisting of 11 resistance gene analog polymorphism (RGAP) markers was established for the genes. The gene was confirmed to be on chromosome 1B by amplification of a set of nullitetrasomic Chinese Spring lines with an RGAP marker linked in repulsion with the resistance allele. The genetic information obtained from this study is useful in understanding interactions between inappropriate hosts and pathogens. The gene identified in Lemhi for resistance to P. striiformis f. sp. hordei should provide resistance to barley stripe rust when introgressed into barley cultivars.     

5个持久抗条锈病小麦品种的抗性组分和遗传距离的研究

 小麦数量抗病品种Aquileja(AQ)、Libellula(LB)、Luke(LK)、Nugaines(NG)和咸农4号(XN)具有持久抗条锈病特点,本文对这5个品种的抗性组分及它们之间的遗传距离进行了研究,以铭贤169(MX)为感病对照品种。苗期室内抗性组分试验表明:LB、XN、AQ 3个品种与LK、NG 2个品种相比,前者的气孔下泡囊密度低于后者;前者的菌落长度短于后者。其中AQ和XN的吸器密度低于LK和NG而高于LB;LK和NG的气孔下泡囊密度甚至高于感病对照品种MX。田间抗性组分试验表明:5个数量抗病品种AQ、LB、LK、NG和XN的反应型(IT)、严重度(DS)、病情发展曲线下面积(AUDPC)和病斑长度(LL)值均低于感病对照品种MX;数量抗病品种AQ、LB、LK、NG、XN之间相比,AQ的IT值最高而LB最低;NG的DS和AUDPC值最高而LB最低;AQ、NG和XN的LL值高于LB和LK;AQ的病斑密度值低于NG和LK而高于XN和LB。由此可见,LK和NG没有抗侵入能力而在成株期具有抗扩展能力,LB、AQ和XN除了具有抗扩展能力外,还具有降低侵入频率能力。基于SSR DNA指纹数据的聚类分析,AQ与LB为同一类,NG与XN为同一类,LK单独为一类。由此推测,AQ或LB与其它3个数量抗病品种之间杂交的后代中可能会出现性状超亲分离,本实验室报道的AQ/NG杂交组合的结果证明了这一点。本文为进一步的抗病遗传育种工作提供了有用信息。     

Quantitative trait loci for high-temperature adult-plant and slow-rusting resistance to Puccinia striiformis f. sp. tritici in wheat cultivars

Stripe rust, caused by Puccinia striiformis f. sp. tritici, is one of the most damaging diseases of wheat (Triticum aestivum) globally. High-temperature adult-plant resistance (HTAPR) and slow-rusting have great potential for sustainable management of the disease. The wheat cultivars Luke and Aquileja have been previously reported to possess HTAPR and slow-rusting to stripe rust, respectively. Aquileja displayed less number of stripes per unit leaf area than Luke, while Luke showed lower infection type than Aquileja at adult-plant stages of growth under high-temperature conditions. The objectives of this study were to confirm the resistances and to map the resistance genes in Luke and Aquileja. Luke was crossed with Aquileja, and 326 of the F(2) plants were genotyped using 282 microsatellite primer pairs. These F(2) plants and their derived F(3) families were evaluated for resistance to stripe rust by inoculation in the fields and greenhouses of high- and low-temperatures. Infection type was recorded for both seedlings and adult plants, and stripe number was recorded for adult plants only. Two quantitative trait loci (QTL) were identified, on the short arm of chromosome 2B, to be significantly associated with infection type at adult-plant stages in the fields and in the high-temperature greenhouse. The locus distal to centromere, referred to as QYrlu.cau-2BS1, and the locus proximal to centromere, referred to as QYrlu.cau-2BS2, were separated by a genetic distance of about 23 cM. QYrlu.cau-2BS1 was flanked by the microsatellite markers Xwmc154 and Xgwm148, and QYrlu.cau-2BS2 was flanked by Xgwm148 and Xabrc167. QYrlu.cau-2BS1 and QYrlu.cau-2BS2 explained up to 36.6 and 41.5% of the phenotypic variation of infection type, respectively, and up to 78.1% collectively. No significant interaction between the two loci was detected. Another QTL, referred to as QYraq.cau-2BL, was detected on the long arm of chromosome 2B to be significantly associated with stripe number. QYraq.cau-2BL was flanked by the microsatellite markers Xwmc175 and Xwmc332, and it explained up to 61.5% of the phenotypic variation of stripe number. It is possible that these three QTL are previously unmapped loci for resistance to stripe rust.     

Mechanism and molecular markers associated with rust resistance in a chickpea interspecific cross (Cicer arietinum × Cicer reticulatum)

A gene that controls resistance to chickpea rust (Uromyces ciceris-arietini) has been identified in a recombinant inbred line (RIL) population derived from an interspecific cross between Cicer arietinum (ILC72) × Cicer reticulatum (Cr5-10), susceptible and resistant to rust, respectively. Both parental lines and all RILs displayed a compatible interaction but differed in the level of infection measured as Disease Severity (DS) and Area Under the Disease Progress Curve (AUDPC). Histological studies of the seedlings of resistant parental Cr5-10 line revealed a reduction in spore germination, appressorium formation, number of haustoria per colony and colony size, with little host cell necrosis, fitting the definition of partial resistance. A Quantitative Trait Locus (QTL) explaining 31% of the total phenotypic variation for DS in seedlings and 81% of the AUDPC in adult plants in the field was located on linkage group 7 of the chickpea genetic map. The AUDPC displayed a bimodal distribution with high frequency of susceptible lines and both the AUDPC and markers showed the same distorted segregation. Consequently, it was hypothesised that a single dominant gene (proposed as Uca1/uca1) controlled resistance to rust in adult plants. This allowed us to locate the gene on the genetic linkage map. Two Sequence Tagged Microsatellite Sites (STMS) markers, TA18 and TA180 (3.9 cM apart) were identified that flank the resistance gene. These findings could be the starting point for a Marker-Assisted Selection (MAS) programme for rust resistance in chickpea.     

Microsatellite markers for genes lr34/yr18 and other quantitative trait Loci for leaf rust and stripe rust resistance in bread wheat

ABSTRACT Leaf rust and stripe rust, caused by Puccinia triticina and P. striiformis, respectively, are important diseases of wheat in many countries. In this study we sought to identify molecular markers for adult plant resistance genes that could aid in incorporating such durable resistance into wheat. We used a doubled haploid population from a Japanese cv. Fukuho-komugi x Israeli wheat Oligoculm cross that had segregated for resistance to leaf rust and stripe rust in field trials. Joint and/or single-year analyses by composite interval mapping identified two quantitative trait loci (QTL) that reduced leaf rust severity and up to 11 and 7 QTLs that might have influenced stripe rust severity and infection type, respectively. Four common QTLs reduced stripe rust severity and infection type. Except for a QTL on chromosome 7DS, no common QTL for leaf rust and stripe rust was detected. QTL-7DS derived from 'Fukuho-komugi' had the largest effect on both leaf rust and stripe rust severities, possibly due to linked resistance genes Lr34/Yr18. The microsatellite locus Xgwm295.1, located almost at the peak of the likelihood ratio contours for both leaf and stripe rust severity, was closest to Lr34/Yr18. QTLs located on 1BL for leaf rust severity and 3BS for stripe rust infection type were derived from 'Oligoculm' and considered to be due to genes Lr46 and Yr30, respectively. Most of the remaining QTLs for stripe rust severity or infection type had smaller effects. Our results indicate there is significant diversity for genes that have minor effects on stripe rust resistance, and that successful detection of these QTLs by molecular markers should be helpful both for characterizing wheat genotypes effectively and combining such resistance genes.     

Resistance in Australian barley (Hordeum vulgare) germplasm to the exotic pathogen Puccinia striiformis f. sp. hordei,causal agent of stripe rust

Eighty‐eight Australian and 10 international barley cultivars were assessed for resistance to the barley stripe (yellow) rust pathogen, Puccinia striiformis f. sp. hordei (Psh). All cultivars were tested for seedling resistance to two UK‐derived isolates of Psh (11.01 and 83.39) that were shown to differ in virulence based on responses on 16 differential barley genotypes. The 98 barley cultivars differed substantially in stripe rust response; 45% were susceptible to Psh 11.01, 53% to Psh 83.39 and 44% to both isolates. The observed diverse infection types (ITs) suggest the presence of both known and uncharacterized resistance. However, further multipathotype tests are required for accurate gene postulation. The Yerong × Franklin (Y×F) doubled haploid (DH) population was phenotypically assessed as seedlings using both Psh isolates. Yerong and Franklin were immune and highly resistant, respectively, to both isolates used in this study. Marker‐trait and QTL mapping identified a major effect on the long arm of chromosome 7H contributed by Franklin in response to all isolates. The resistance of Yerong was mapped to 113·96 and 169·38 cM on chromosome 5HL in response to Psh 11.01 and 83.39, respectively. The Psh resistance sources identified in this study can be used for further genetic analysis and introgression for varietal improvement.     

大麦抗条纹病基因的定位分析

为发掘大麦中抗条纹病的新基因,采用三明治法通过人工接种大麦条纹病菌Pyrenophora graminea强致病力菌株QWC对甘啤2号(免疫)与Alexis(高感)杂交F_1代及F_2代分离群体进行抗性遗传分析,利用群体分离分析法鉴定与抗病基因连锁的SSR标记,并通过QTL IciMapping软件构建遗传连锁图谱完成对抗病基因的定位。结果显示,甘啤2号与Alexis杂交F_1代对大麦条纹病菌强致病力菌株QWC表现为免疫,F_2代表现3∶1抗感分离,表明甘啤2号对菌株QWC的抗性由1个显性抗性基因控制,将该抗病基因暂命名为Rdg3;该基因位于大麦7H染色体上的SSR标记Bmag206和Bmag7之间,与二者的遗传距离分别为1.78 cM和2.86 cM。经与已定位于7H染色体上的抗病基因比较,发现Rdg3是一个新的抗条纹病基因,可作为大麦抗病育种的新种质资源。     

大麦种质对叶斑病的抗性鉴定与评价

 由麦根腐平脐蠕胞菌引起的叶斑病在世界各大麦种植区均有发生,严重影响大麦的产量和品质。选育和应用抗性品种是防控该病害最有效的策略,然而可利用的抗源非常有限。在本研究中对中国233份具有代表性的大麦种质资源进行成株期抗叶斑病田间人工接种鉴定,发现只有垦啤麦5号等10份材料对3个供试菌株都表现抗病,仅占供试材料的4.3%。另外对37份国内外重要的叶斑病抗源材料进行苗期及成株期抗叶斑病鉴定,结果显示成株期抗叶斑病材料所占比例为41%~46%,苗期抗性材料所占比例为50%~64%,其中ND17293等11份材料在苗期和成株期对3个菌株均表现为抗病,可作为抗源继续加以利用;基于上述鉴定结果,进一步分析发现供试大麦苗期对三个菌株的抗病比例均高于成株期抗病比例,说明大麦在不同生育期对叶斑病的抗性存在较大差异。另外发现大麦对B. sorokiniana不同致病类型的抗性也存在明显的专化性。     

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.     

Quantitative trait Loci mapping for adult-plant resistance to powdery mildew in bread wheat

ABSTRACT Powdery mildew, caused by Blumeria graminis f. sp. tritici, is a major disease to wheat (Triticum aestivum) worldwide. Use of adult-plant resistance (APR) is an effective method to develop wheat cultivars with durable resistance to powdery mildew. In the present study, 432 molecular markers were used to map quantitative trait loci (QTL) for APR to powdery mildew in a doubled haploid (DH) population with 107 lines derived from the cross Fukuho-komugi x Oligoculm. Field trials were conducted in Beijing and Anyang, China during 2003-2004 and 2004-2005 cropping seasons, respectively. The DH lines were planted in a randomized complete block design with three replicates. Artificial inoculation was carried out in Beijing with highly virulent isolate E20 of B. graminis f. sp. tritici and the powdery mildew severity on penultimate leaf was evaluated four times, and the maximum disease severity (MDS) on penultimate leaf was investigated in Anyang under natural inoculation in May 2004 and 2005. The heritability of resistance to powdery mildew for MDS in 2 years and two locations ranged from 0.82 to 0.93, while the heritability for area under the disease progress curve was between 0.84 and 0.91. With the method of composite interval mapping, four QTL for APR to powdery mildew were detected on chromosomes 1AS, 2BL, 4BL, and 7DS, explaining 5.7 to 26.6% of the phenotypic variance. Three QTL on chromosomes 1AS, 2BL, and 7DS were derived from the female, Fukuho-komugi, while the one on chromosome 4BL was from the male, Oligoculm. The QTL on chromosome 1AS showed high genetic effect on powdery mildew resistance, accounting for 19.5 to 26.6% of phenotypic variance across two environments. The QTL on 7DS associated with the locus Lr34/Yr18, flanked by microsatellite Xgwm295.1 and Ltn (leaf tip necrosis). These results will benefit for improving powdery mildew resistance in wheat breeding programs.     

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.     

普通小麦-华山新麦草易位系H9015-17抗条锈病基因的标记定位

 采用我国当前流行的小麦条锈菌小种和重要致病类型, 在常温条件下对普通小麦-华山新麦草易位系H9015-17进行苗期抗条锈性鉴定, 并用当前主要流行小种CYR32对H9015-17与铭贤169的杂交后代及其双亲进行抗条锈性遗传分析, 以揭示H9015-17抗条锈性遗传基础。结果显示, H9015-17对小麦条锈菌小种CYR31、CYR32、CYR33和致病类型Su11-4、Su11-7、V26、Su11-11均有良好的抗病性, 对当前主要流行小种CYR32的抗病性由1对显性基因控制, 暂命名为YrHua1。 采用分子标记定位技术,筛选到5个与抗病基因YrHua1连锁的RGAP标记(M1、M2、M3、M4和M5)和1个SSR标记(Xgwm292),这些标记与抗病基因YrHua1的遗传距离分别为17.3、15.7、13.1、3.3、2.9和11.2,并将基因YrHua1定位在小麦染色体5DL上。研究结果将为分子标记辅助选择改良小麦抗条锈性提供宝贵的种质材料,建议在抗病育种加以利用。     

小麦-滨麦易位系M8657-1抗条锈病基因遗传分析和分子标记

 M8657-1, one of the wheat translocation lines derived from Leymus mollis Trin. Hara, is possessed of effective resistance at all stages to Su-ll and other dominant races of Puccinia striiformis f. sp. tritici in China. Seedlings of the parents, F₁, and F₂ progeny derived from the cross of M8657-1 (resistant) Mingxian169 (susceptible) were inoculated with Su-ll in greenhouse to identify and map the probable new stripe rust resistance gene. The results suggested that the stripe rust resistance in M8657-1 was conferred by a pair of recessive genes. Simple sequence repeat (SSR) technique was used to detect molecular marker associated with the resistance gene:208 pairs of wheat SSR primers were used to screen the two parents, as well as resistant and susceptible bulks and then three SSR markers were selected for genotyping the F₂ population. The geue, temporarily designated as YrLml, was found to be located on the chromosome 7DL and flanked by three SSR markers GDM67, WMC150 and WMC671, with the genetic distance of 5.0, 9.7 and 11.8cM, respectively.     

Identifying quantitative trait loci for resistance to Sclerotinia head rot in two USDA sunflower germplasms

Sclerotinia head rot is a major disease of sunflower in the world, and quantitative trait loci (QTL) mapping could facilitate understanding of the genetic basis of head rot resistance and breeding in sunflower. One hundred twenty-three F2:3 and F2:4 families from a cross between HA 441 and RHA 439 were studied. The mapping population was evaluated for disease resistance in three field experiments in a randomized complete block design with two replicates. Disease incidence (DI) and disease severity (DS) were assessed. A genetic map with 180 target region amplification polymorphism, 32 simple sequence repeats, 11 insertion-deletion, and 2 morphological markers was constructed. Nine DI and seven DS QTL were identified with each QTL explaining 8.4 to 34.5% of phenotypic variance, suggesting the polygenic basis of the resistance to head rot. Five of these QTL were identified in more than one experiment, and each QTL explained more than 12.9% of phenotypic variance. These QTL could be useful in sunflower breeding. Although a positive correlation existed between the two disease indices, most of the respective QTL were located in different chromosomal regions, suggesting a different genetic basis for the two indices.     

Genetic analysis and molecular mapping of quantitative trait loci in common bean against Pythium ultimum

Pythium ultimum is a soil pathogen that can cause seed decay and damage to roots in common bean. In this study, the response of a set of 40 common bean genotypes to P. ultimum and inheritance of the resistance in the 92 F? recombinant inbred lines (RIL) developed from a cross between Xana and Cornell 49242 was investigated by using emergence rate and seedling vigor. Emergence of the 40 genotypes showed a significant association between white seed coat and response to this pathogen. Among these, 11 common bean genotypes, all with colored seeds, exhibited a high percentage of emergence and seedling vigor not significantly different (P > 0.05) to noninoculated plants. Response of the RIL population revealed both qualitative and quantitative modes of inheritance. A major gene (Py-1) controlling the emergence rate was mapped in the region of the gene P, a basic color gene involved in control of seed coat color, located on LG 7. Using the RIL subpopulation with colored seeds, a significant quantitative trait loci (QTL) associated with the emergence rate (ER3(XC)) and another with seedling vigor (SV6(XC)) were identified on the LG 3 and 6, respectively. QTL SV6(XC) was mapped in the region of the gene V, another gene involved the genetic control of color. QTLs associated with seed traits were mapped in the same relative position as regions involved in responses to P. ultimum suggesting the possible implication of avoidance mechanisms in the response to this pathogen.