Genetic mapping and inheritance of Russian wheat aphid resistance gene in accession IG 100695

The Russian wheat aphid (RWA), Diuraphis noxia (Kurdjumov), is an important pest of small‐grain cereals, particularly wheat, worldwide. The most efficient strategy against the RWA is to identify sources of resistance and to introduce them into susceptible wheat genotypes. This study was conducted to determine the mode of inheritance of the RWA resistance found in ICARDA accession IG 100695, to identify wheat microsatellite markers closely linked to the gene and to map the chromosomal location of the gene. Simple sequence repeat (SSR) marker scores were identified in a mapping population of 190 F₂ individuals and compared, while phenotypic screening for resistance was performed in F_2 : 3 families derived from a cross between ‘Basribey’ (susceptible) and IG 100695 (resistant). Phenotypic segregation of leaf chlorosis and rolling displayed the effect of a single dominant gene, temporarily denoted Dn100695, in IG 100695. Dn100695 was mapped on the short arm of chromosome 7D with four linked SSR markers, Xgwm44, Xcfd14, Xcfd46 and Xbarc126. Dn100695 and linked SSR markers may be useful for improving resistance for RWA in wheat breeding.     

Inheritance and allelism of resistances to the Russian wheat aphid in seven wheat lines

Summary Studies were conducted to determine the inheritance and allelic relationships of genes controlling resistance to the Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko), in seven wheat germplasm lines previously identified as resistant to RWA. The seven resistant lines were crossed to a susceptible wheat cultivar Carson, and three resistant wheats, CORWA1, PI294994 and PI243781, lines carrying the resistance genes Dn4, Dn5 and Dn6, respectively. Seedlings of the parents, F₁ and F₂ were screened for RWA resistance in the greenhouse by artificial infestation. Seedling reactions were evaluated 21 to 28 days after the infestation using a 1 to 9 scale. All the F₁ hybrids had equal or near equal levels of resistance to the resistant parent indicating dominant gene control. Only two distinctive classes were present and no intermediate types were observed in the F₂ segregation suggesting major gene actions. The resistance in PI225262 was controlled by two dominant genes. Resistance in all other lines was controlled by a single dominant gene. KS92WGRC24 appeared to have the same resistance gene as PI243781 and STARS-9302W-sib had a common allele with PI294994. The other lines had genes different from the three known genes.     

Microsatellite Marker Identification of a Triticum Aestivum -Aegilops Umbellulata Substitution Line with Powdery Mildew Resistance

Summary Aegilops umbellulata acc. Y39 and Triticum carthlicum acc. PS5, immune to many powdery mildew isolates, were crossed to make an amphidiploid line Am9. The powdery mildew resistance of Am9 was transferred to common wheat cultivar Laizhou953 by crossing and backcrossing. In this study, the origin of powdery mildew resistance in a BC₃F_4:5 population derived from a cross of Am9 and Laizhou953 was identified. Microsatellite markers analysis showed that markers Xgwm257, Xgwm296, and Xgwm319, co-segregated with the powdery mildew resistance, whereas markers Xgwm210, Xgwm388/140, Xgwm388/170 and Xgwm526 were related to susceptibility and linked to resistance in repulsion. Of three markers related to resistance, Xgwm257 and Xgwm319 were codominant, whereas Xgwm296 was dominant. All three markers were Ae. umbellulata-specific indicating that resistance in the test population originated from Ae. umbellulata acc. Y39. The chromosome location and mapping of these linked microsatellite markers, the chromosome numbers of derived BC₃F_4:6 families, and chromosome pairing in F₁ plants from a cross of a homozygous resistant BC₃F_4:5 plant and Laizhou953, showed that wheat chromosome 2B was substituted by Ae. umbellulata chromosome 2U. This is the first gene conferring powdery mildew resistance transferred to wheat from Ae. umbellulata, and it should be a novel resistance gene to powdery mildew. It was temporarily designated PmY39.The first two authors made equal contributions     

Inheritance of resistance to the Russian wheat aphid in an Iranian durum wheat line

The Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko), is a major economic pest of small grains in many countries. An experiment was therefore conducted to determine the inheritance of gene(s) controlling resistance to RWA in a resistant tetraploid durum wheat line. This resistant line,‘1881′, was crossed to a susceptible line, ‘Orejy‐e‐Kazeroon’, and then F₁ F₂ and BCF₁ (backcross to susceptible line) seedlings were screened in a greenhouse for RWA resistance following artificial infection. Resistance in ‘1881’ was apparently controlled by one dominant gene. Since Dnl, Dn2, dn3, Dn4 and Dn5 have been reported to be located on genome D, it was reasoned that the resistance gene in ‘1881’ is not allelic to them.     

Inheritance of Russian wheat aphid resistance in PI 140207 spring wheat

The Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko), has become a serious, perennial pest of wheat (Triticum aestivum L.) in many areas of the world. This study was initiated to determine the inheritance of RWA resistance in PI 140207 (a RWA-resistant spring wheat) and to determine its allelic relationship with a previously reported RWA resistance gene. Crosses were made between PI 140207 and ‘Pavon’ (a RWA-susceptible spring wheat). Genetic analysis was performed on the parents, F₁, F₂, backcross (BC) population and F₂-derived F₃ families. Analyses of segregation patterns of plants in the F₁, F₂, and BC populations, and F₂-derived F₃ families indicated single dominant gene control of RWA resistance in PI 140207. Results of the allelism test indicated that the resistance gene in PI 140207, while conferring distinctly different seedling reactions to RWA feeding, is the same as Dn 1, the resistance gene in PI 137739.     

Intrachromosomal mapping of genes for dwarfing (Rht12) and vernalization response (Vrn1) in wheat by using RFLP and microsatellite markers

For intrachromosomal mapping of the dominant GA-sensitive dwarfing gene Rht12 and the vernalization response gene Vrn1 on chromosome 5 A, an F₂ population was established using a wide (synthetic) wheat cross. In addition to restriction fragment length polymorphism (RFLP) probes four microsatellite markers were incorporated. Rht12 was mapped distally to four RFLP loci (Xmwg616, Xpsr164, Xwg114, Xpsr1201) and three microsatellite markers (Xgwm179, Xgwm410, Xgwm291), known to be located on the segment of chromosome SAL which was ancestrally translocated and is homoeologous to Triticeae 4 L. The map position of Rht12 suggests that it is homoeologous to the dominant GA-sensitive dwarfing gene Ddw1, present on chromosome 5RL. The vernalization response gene Vrn1 showed linkage to Xwg644, as might be expected from comparative maps.     

Molecular mapping and detection of the yellow rust resistance gene Yr26 in wheat transferred from Triticum turgidum L. using microsatellite markers

Yellow rust (stripe rust), caused by Puccinia striiformis Westend f. sp. tritici, is one of the most devastating diseases of wheat throughout the world. Wheat-Haynaldia villosa 6AL.6VS translocation lines R43, R55, R64 and R77, derived from the cross of three species, carry resistance to both yellow rust and powdery mildew. An F₂ population was established by crossing R55 with the susceptible cultivar Yumai 18. The yellow rust resistance in R55 was controlled by a single dominant gene, which segregated independently of the powdery mildew resistance gene Pm21 located in the chromosome 6VS segment, indicating that the yellow rust resistance gene and Pm21 are unlikely to be carried by the same alien segment. This yellow rust resistance gene was considered to beYr26, originally thought to be also located in chromosome arm 6VS. Bulked Segregation Analysis and microsatellite primer screens of the population F₂ of Yumai 18 × R55 identified three chromosome 1B microsatellite locus markers, Xgwm11, Xgwm18 and Xgwm413, closely linked to Yr26. Yr26 was placed 1.9 cM distal of Xgwm11/Xgwml8, which in turn were 3.2 cM from Xgwm413. The respective LOD values were 21 and 36.5. Therefore, Yr26 was located in the short arm of chromosome 1B. The origin and distribution of Yr26 was investigated by pedigree, inheritance of resistance and molecular marker analysis. The results indicated that Yr26 came from Triticum turgidum L. Three other 6AL.6VS translocation lines, R43, R64 and R77, also carried Yr26. These PCR-based microsatellite markers were shown to be very effective for the detection of the Yr26 gene in segregating populations and therefore can be applied in wheat breeding. This revised version was published online in July 2006 with corrections to the Cover Date.     

Molecular mapping determines that Hessian fly resistance gene H9 is located on chromosome 1A of wheat

Hessian fly [Mayetiola destructor (Say)] is one of the major insect pests of wheat (Triticum aestivum L.) worldwide. Hessian fly resistance gene H9 was previously reported to condition resistance to Hessian fly biotype L that is prevalent in many wheat‐growing areas of eastern USA and an RAPD marker, OPO05₁₀₀₀, linked to H9 in wheat was developed using wheat near‐isogenic lines (NILs). However, marker‐assisted selection (MAS) with RAPD markers is not always feasible. One of the objectives in this study was to convert an RAPD marker linked to the gene H9 into a sequence characterized amplified region (SCAR) marker to facilitate MAS and to map H9 in the wheat genome. The RAPD fragment from OPO05₁₀₀₀ was cloned, sequenced, and converted into a SCAR marker SOPO05₉₀₉, whose linkage relationship with H9 was subsequently confirmed in two F₂ populations segregating for H9. Linkage analysis identified one sequence tagged site (STS) marker, STS‐Pm3, and the eight microsatellite markers Xbarc263, Xcfa2153, Xpsp2999, Xgwm136, Xgdm33, Xcnl76, Xcnl117 and Xwmc24 near the H9 locus on the distal region of the short arm of chromosome 1A, contrary to the previously reported location of H9 on chromosome 5A. Locus Xbarc263 was 1.2 cM distal to H9, which itself was 1.7 cM proximal to loci Xcfa2153, Xpsp2999 and Xgwm136. The loci Xgwm136, Xcfa2153 and SOPO05₉₀₉ were shown to be specific to H9 and not diagnostic to several other Hessian fly resistance genes, and therefore should be useful for pyramiding H9 with other Hessian fly resistance genes in a single genotype.     

小麦花粉致死基因Ki的SSR标记分析

小麦雄性不育主要是通过花粉的败育表现,其不育材料对小麦杂种优势的利用研究具有重要意义和价值,国外研究表明,某些特定普通小麦品种间杂交F₁表现的花粉部分不育现象,受控于核基因组花粉致死基因Ki,为了筛选小麦花粉致死基因Ki的连锁标记,利用现代分子生物学技术通过定位该基因,克隆出花粉致死基因连锁标记片段,为小麦雄性不育种质材料的转育提供有效的选择标记。对小麦花粉致死基因Ki进行了分子标记定位,以‘中国春’和澳大利亚春小麦品种的BC₁F₁代作为定位群体,利用分离群体分组分析法(BSA)对位于小麦6B染色体上85对SSR引物进行多态性筛选,具有多态性的引物再通过BC₁F₁定位群体进行验证,从中筛选出与目的基因连锁的2个SSR标记Xgwm626和Xgpw4138。运用Mapmaker 3.0软件进行连锁分析。结果表明,Xgwm626和Xgpw4138与Ki基因的遗传距离分别为9.2 cM和6.9 cM,且2个SSR标记位于目的基因两侧,并将Ki定位于小麦6BL染色体上。研究结果为Ki基因的分子标记辅助选择和进一步精细定位奠定了基础。     

Inheritance and allelism of Russian wheat aphid resistance in several wheat lines

The Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko) has caused serious reduction in wheat production in 17 Western states of the United States since 1986. Inheritance of resistance to RWA in seven wheat lines and the allelism of the resistance genes in these lines with three known resistance genes Dn4, Dn5, and Dn6 were studied. The seven resistant lines were crossed to a susceptible wheat cultivar ‘Carson’ and three resistant wheats: CORWA1 (Dn4), PI 294994 (Dn5), and PI 243781 (Dn6). Seedlings of the parents, F₁, and F₂ were screened for RWA resistance in the greenhouse by artificial infestation. Seedling reactions were evaluated 21–28 days after the infestation using a 1–9 scale. The resistance level of all the F₁ hybrids was similar to that of the resistant parent, indicating dominant gene control. Only two distinctive classes were present and no intermediate types were observed in the F₂ population, suggesting qualitative, nonadditive gene action, in which the presence of any one of the dominant alleles confers complete resistance to RWA. Resistance in CI 2401 is controlled by two dominant genes. Resistance in CI 6501 and PI 94365 is governed by one dominant gene. Resistance in PI 94355 and PI 151918 may be conditioned by either one dominant gene or one dominant and one recessive gene. No conclusion can be made on how many resistance genes are in AUSVA1-F₃, since the parent population was not a pure line. Allelic analyses showed that one of resistance genes in CI 2401 and PI 151918 was the same allele as Dn4, the resistance gene in CI 6501 was the same allele as Dn6, and AUS-VA1-F₃ had one resistance gene which was the same allele as one of the resistance genes in PI 294994. One non-allelic resistance gene different from the Dn4, Dn5, and Dn6 genes in CI 2401, PI 94355, PI 94365, and PI 222668 was identified and should be very useful in diversifying gene sources in wheat breeding.     

野生二粒小麦导入普通小麦的抗白粉病基因MlWE29分子标记定位

小麦白粉病是严重影响小麦生产的重要病害之一,培育和应用抗病品种是有效控制和减少病害的最经济有效的方法。野生二粒小麦是硬粒小麦和普通小麦的四倍体野生祖先种,是小麦抗病性遗传改良的重要基因资源。本研究利用来自以色列的野生二粒小麦WE29与普通小麦杂交,再用普通小麦连续回交和自交,育成高抗白粉病(Blumeria graminis f. sp. tritici)小麦新品系3D258(系谱为燕大1817/WE29//5*87-1, BC₄F₆)。将3D258和高感小麦白粉病的普通小麦品种薛早配制杂交组合,对其F₁、F₂代分离群体和F₃代家系进行白粉病抗性鉴定和遗传分析。结果表明3D258携带抗白粉病显性单基因,暂命名为MlWE29。利用集群分离分析法(BSA)和分子标记分析,发现6个SSR标记(Xgwm335、Xgwm213、Xgwm639、Xwmc415、Xwmc289和Xwmc75)和5个EST-STS标记(BE494426、BE442763、CD452476、BE445282和BE407068)与抗白粉病基因MlWE29连锁。利用中国春缺体-四体系、双端体系和缺失系将抗白粉病基因MlWE29标记物理定位于5BL染色体的0.59–0.79区域。这一普通小麦抗白粉病种质资源的创制及其连锁分子标记的建立为小麦抗病基因分子标记辅助选择、基因积聚和分子育种提供了新的物质基础。     

野生二粒小麦导入普通小麦的抗白粉病基因MlWE29分子标记定位

小麦白粉病是严重影响小麦生产的重要病害之一,培育和应用抗病品种是有效控制和减少病害的最经济有效的方法。野生二粒小麦是硬粒小麦和普通小麦的四倍体野生祖先种,是小麦抗病性遗传改良的重要基因资源。本研究利用来自以色列的野生二粒小麦WE29与普通小麦杂交,再用普通小麦连续回交和自交,育成高抗白粉病(Blumeria graminis f. sp. tritici)小麦新品系3D258(系谱为燕大1817/WE29//5*87-1, BC₄F₆)。将3D258和高感小麦白粉病的普通小麦品种薛早配制杂交组合,对其F₁、F₂代分离群体和F₃代家系进行白粉病抗性鉴定和遗传分析。结果表明3D258携带抗白粉病显性单基因,暂命名为MlWE29。利用集群分离分析法(BSA)和分子标记分析,发现6个SSR标记(Xgwm335、Xgwm213、Xgwm639、Xwmc415、Xwmc289和Xwmc75)和5个EST-STS标记(BE494426、BE442763、CD452476、BE445282和BE407068)与抗白粉病基因MlWE29连锁。利用中国春缺体-四体系、双端体系和缺失系将抗白粉病基因MlWE29标记物理定位于5BL染色体的0.59–0.79区域。这一普通小麦抗白粉病种质资源的创制及其连锁分子标记的建立为小麦抗病基因分子标记辅助选择、基因积聚和分子育种提供了新的物质基础。     

Microsatellite mapping of powdery mildew resistance allele <Emphasis Type="Italic">Pm5d</Emphasis> from common wheat line IGV1-455

The powdery mildew resistance allele Pm5d in the backcross-derived wheat lines IGV1-455 (CI10904/7*Prins) and IGV1-556 (CI10904/7*Starke) shows a wide spectrum of resistance and virulent pathotypes have not yet been detected in Germany. Although this allele may be distinguished from the other documented Pm5 alleles by employing a differential set of Blumeria graminis tritici isolates, the use of linked molecular markers could enhance selection, especially for gene pyramiding. Pm5d was genetically mapped relative to six microsatellite markers in the distal part of chromosome 7BL using 82 F₃ families of the cross Chinese Spring × IGV1-455. Microsatellite-based deletion line mapping placed Pm5d in the terminal 14% of chromosome 7BL. The closely linked microsatellite markers Xgwm577 and Xwmc581 showed useful variation for distinguishing the different Pm5 alleles except the ones originating from Chinese wheat germplasm. Their use, however, would be limited to particular crosses because they are not functional markers. The occurrence of resistance genes closely linked to the Pm5 locus is discussed. Ghazaleh Nematollahi and Volker Mohler equally contributed to this work.     

Mapping antixenosis genes on chromosome 6A of wheat to greenbug and to a new biotype of Russian wheat aphid

Greenbug and Russian wheat aphid (RWA) are two devastating pests of wheat. The first has a long history of new biotype emergence and recently. RWA resistance has just started to break down. Thus, it is necessary to find new sources of resistance that will broaden the genetic base against these pests in wheat. Seventy‐five doubled haploid recombinant (DHR) lines for chromosome 6A from the F₁ of the cross between “Chinese Spring’ and the “Chinese Spring (Synthetic 6A) (Triticum dicoccoides × Aegilops tauschii)” substitution line were used as a mapping population for testing resistance to greenbug biotype C and to a new strain of RWA that appeared in Argentina in 2003. A quantitative trait locus (QTL) (br antixenosis to greenbug was significantly associated with the marker loci Xgwm1009 and Xgwm1185 located in the centromere region of chromosome 6A. Another QTL which accounted for most of the antixenosis against RWA was associated with the marker loci Xgwm1291 and Xiinni1150. both located on the long arm of chromosome 6A. This is the first report of greenbug and RWA resistance genes located on chromosome 6A. It is also the first report of antixenosis against the new strain of RWA. As most of the RWA resistance genes present in released cultivars have been located in [he D‐ genome, it is highly desirable to find new sources in other genomes to combine the existing resistance genes with new sources.     

Quantitative and molecular characterization of heat tolerance in hexaploid wheat

Understanding the genetic basis of tolerance to high temperature is important for improving the productivity of wheat (Triticum aestivum L.) in regions where the stress occurs. The objective of this study was to estimate inheritance of heat tolerance and the minimum number of genes for the trait in bread wheat by combining quantitative genetic estimates and molecular marker analyses. Two cultivars, Ventnor (heat-tolerant) and Karl92 (heat-susceptible), were crossed to produce F₁, F₂, and F₃populations, and their grain-filling duration (GFD) at 30/25 ^°C 16/8 h day/night was determined as a measure of heat tolerance. Distribution of GFD in the F₁ and F₂ populations followed the normal model (χ², p > 0.10). A minimum of 1.4 genes with both additive and dominance effects, broad-sense heritability of 80%, and realized heritability of 96%for GFD were determined from F₂ and F₃ populations. Products from 59primer pairs among 232 simple sequence repeat (SSR) pairs were polymorphic between the parents. Two markers, Xgwm11 andXgwm293, were linked to GFD by quantitative trait loci (QTL) analysis of the F₂ population. The Xgwm11-linked QTL had only additive gene action and contributed 11% to the total phenotypic variation in GFD in the F₂population, whereas the Xgwm293-linked QTL had both additive and dominance action and contributed 12% to the total variation in GFD. The results demonstrated that heat tolerance of common wheat is controlled by multiple genes and suggested that marker-assisted selection with microsatellite primers might be useful for developing improved cultivars. This revised version was published online in August 2006 with corrections to the Cover Date.     

普通小麦品种Brock抗白粉病基因分子标记定位

为明确利用Brock转育成的小麦抗白粉病品系3B529(京411*7//农大015/Brock, F₆)抗性的遗传基础,将高感白粉病小麦品系薛早和3B529杂交,获得F₁代、F₂分离群体和F_2:3家系。抗病性鉴定和遗传分析结果表明,3B529对E09小种的抗性受1对显性基因控制,暂被定名为MlBrock。利用BSA和分子标记分析,获得了与MlBrock连锁的3个SSR标记Xcfd81、Xcfd78、Xgwm159和2个SCAR标记SCAR203和SCAR112,根据SSR和SCAR标记在中国春缺体四体、双端体和缺失系的定位结果,将MlBrock定位在小麦染色体臂5DS Bin 0~0.63区间上。MlBrock与Xcfd81和SCAR203共分离,与SCAR112的遗传距离为0.5 cM。这些分子标记的建立有利于今后Brock抗白粉病基因分子标记辅助选择和基因聚合。综合抗白粉病基因MlBrock的染色体定位和抗谱分析结果,推测MlBrock很可能是Pm2基因。     

Inheritance of root traits and phosphorus uptake in common bean (Phaseolus vulgaris L.) under limited soil phosphorus supply

Heterosis is an important way to improve yield and quality for many crops. Hybrid rice and hybrid maize contributed to enhanced productivity which is essential to supply enough food for the increasing world population. The success of hybrid rice in China has led to a continuous interest in hybrid wheat, even when most research on hybrid wheat has been discontinued in other countries for various reasons including low heterosis and high seed production costs. The Timopheevii cytoplasmic male sterile system is ideal for producing hybrid wheat seeds when fertility restoration lines with strong fertility restoration ability are available. To develop PCR-based molecular markers for use in marker-assisted selection of fertility restorer lines, two F₂ populations derived from crosses R18/ND36 and R9034/ND36 were used to map fertility restoration genes in the two elite fertility restorer lines (R-lines) R18 and R9034. Over 678 SSR markers were analyzed, and markers closely linked to fertility restoration genes were identified. Using SSR markers, a major fertility restoration gene, Rf3, was located on the 1B chromosome in both populations. This gene was partially dominant in conferring fertility restoration in the two restorer lines. SSR markers Xbarc207, Xgwm131, and Xbarc61 are close to this gene. These markers may be useful in marker-assisted selection of new restorer lines with T. timopheevii cytoplasm. Two minor QTL conferring fertility restoration were also identified on chromosomes 5A (in R18) and 7D (in R9034) in two R-lines.     

Inheritance and allelism for resistance to Russian Wheat Aphid in an Iranian Spring Wheat

Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko), is an important pest of wheat (Triticum aestivum L.) in the United States of America. Developing adapted wheat cultivars with genetic resistance to RWA is an effective control strategy. Genetic studies were conducted to determine the mode of inheritance of gene(s) conferring resistance to RWA in an Iranian landrace wheat line, G 5864. For the inheritance study, G 5864 was crossed with the susceptible wheats ‘Yecora Rojo’ and ND 2375. Seedlings of F1, reciprocal F1, F2, BC1 to the susceptible parent (BCS), and BC1 to the resistant parent (BCR) were screened for RWA reaction. Several phenotypic segregation ratios were tested in the F2 populations for goodness of fit; the 9:3:3:1 ratio (resistant: rolled leaves: stunted plants: susceptible) was an acceptable fit in all cases. Thus, resistance in G 5864 seemed to be controlled by two independent dominant genes with additive gene effects. The allelic relationships of gene(s) in this line with genes in other resistant lines, PI 137739 (Dn1), PI 262660 (Dn2), PI 372129 (Dn4), PI 294994 (Dn5), and PI 243781 (Dn6), were also studied. Segregation patterns observed in G 5864 × resistant (R × R) F2 populations were inconclusive. However, no susceptible plants were observed in these F2 populations. If previous reports concerning the number of resistance genes present in the other resistant lines are correct, then given the high manifestation of resistance observed in G 5864, and given the absence of susceptible plants in the R × R F2 populations, it is indicated that RWA resistance in G 5864 is either controlled by different alleles at the same loci as the other resistance genes, or that G 5864 shares a resistance gene with each of the other resistant lines. This revised version was published online in July 2006 with corrections to the Cover Date.     

Inheritance and allelic relationships of resistances to the Russian wheat aphid in two Iranian wheat lines

Russian wheat aphid (RWA), Diuraphis noxia (Kurdjumov), is a serious pest of small grains in many countries. A previous study screened 70 genotypes, collected from different parts of Iran, for RWA resistance. Four crosses were made between two resistant lines (Shz.W-102 and Shz.W-104) and two susceptible lines (Shz.W-101 and Shz.W-103). Parents, F₁, F₂, and BCF₁ seedlings were screened for RWA resistance in the greenhouse by artificial infection. To determine allelism, the two resistant lines were intercrossed and F₁, and F₂ seedlings were evaluated. Resistance in Shz.W-102 and Shz.W-104, when crossed with Shz.W-101, was controlled by one dominant gene. However, resistance in Shz.W-102 and Shz.W-104, when crossed with Shz.W-103, was controlled by two dominant genes. Genes in two resistant lines segregated independently of each other. A three-gene system was proposed to govern resistance in the lines under study . This revised version was published online in July 2006 with corrections to the Cover Date.     

Microsatellite marker for yellow rust resistance gene Yr5 in wheat introgressed from spelt wheat

Yellow rust of wheat caused by Puccinia striiformis f sp. tritici has been periodically epidemic and severely damaged wheat production in China and throughout the world. Breeding for resistant cultivars has been proved to be an effective way to resolve the problem. A yellow rust resistance gene, Yr5, derived from Triticum spelta shows immunity or high resistance to the most popular isolates Tiaozhong 30 and 31 in China. Establishment of DNA markers for the Yr5 gene will facilitate marker‐assisted selection and gene pyramiding in the breeding programme. Since the Yr5 gene was cytologically located on the long arm of chromosome 2B, By33, the donor of Yr5, was crossed and backcrossed with the susceptible line 441, and BC₃F₂ and BC₃F₃ segregating populations were screened for polymorphism by using 11 microsatellite primers mapped on chromosome 2B. A marker, Xgwm501‐195 bp/160 bp, was found to be linked to Yr5, with a genetic distance of 10.5‐13.3 cM.