DNA and morphological markers for a Russian wheat aphid resistance gene

The Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko), is a significant insect pest of wheat worldwide. Morphological and molecular markers associated with RWA resistance could be used to increase the accuracy and efficiency of selection of resistant germplasm and facilitate transfer to desirable wheat genotypes. The objective of this work was to identify microsatellite (SSR) markers linked to the RWA resistance gene (Dn4) and glume-colour gene (Rg2) using a population of F₂-derived F₃ families originating from a cross between a susceptible line (synthetic hexaploid-11) and a resistance cultivar (Halt). Two microsatellite markers Xgwm106 and Xgwm337 flanked Dn4 on the short arm of chromosome 1D at 5.9 and 9.2 cM, respectively. Two other microsatellite markers, Xpsp2999 and Xpsp3000, at the distal part of this chromosome arm are linked to Dn4 and to Rg2. The accuracy and efficiency of marker-assisted selection were calculated for homozygous Dn4Dn4 genotypes in the F₂ generation. The gene Rg2 for red glume colour can also be used for marker-assisted selection of Dn4 gene individually and in combination with microsatellite markers. When used together, the closest markers Xgwm106 and Xgwm337, provide 100% accuracy and 75% efficiency. One hundred percent accuracy is also achieved when the morphological marker red glume is used in combination with either Xgwm106 or Xgwm337. Using these flanking markers, it may be possible to fix resistance to RWA in the first segregating generation of an F₂ population without infestation with aphids.     

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.     

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。     

Mapping of the leaf rust resistance gene <Emphasis Type="Italic">Lr38</Emphasis> on wheat chromosome arm 6DL using SSR markers

Leaf rust caused by the fungus Puccinia triticina is one of the most important diseases of wheat (Triticum aestivum) worldwide. The use of resistant wheat cultivars is considered the most economical and environment-friendly approach in controlling the disease. The Lr38 gene, introgressed from Agropyron intermedium, confers a stable seedling and adult plant resistance against multiple isolates tested in Europe. In the present study, 94 F₂ plants resulting from a cross made between the resistant Thatcher-derived near-isogenic line (NIL) RL6097, and the susceptible Ethiopian wheat cultivar Kubsa were used to map the Thatcher Lr38 locus in wheat using simple sequence repeat (SSR) markers. Out of 54 markers tested, 15 SSRs were polymorphic between the two parents and subsequently genotyped in the population. The P. triticina isolate DZ7-24 (race FGJTJ), discriminating Lr38 resistant and susceptible plants, was used to inoculate seedlings of the two parents and the segregating population. The SSR markers Xwmc773 and Xbarc273 flanked the Lr38 locus at a distance of 6.1 and 7.9 cM, respectively, to the proximal end of wheat chromosome arm 6DL. The SSR markers Xcfd5 and Xcfd60 both flanked the locus at a distance of 22.1 cM to the distal end of 6DL. In future, these SSR markers can be used by wheat breeders and pathologists for marker assisted selection (MAS) of Lr38-mediated leaf rust resistance in wheat.     

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.     

Development of molecular markers linked to the Leptosphaeria maculans resistance gene Rlm6 and inheritance of SCAR and CAPS markers in Brassica napus × Brassica juncea interspecific hybrids

Leptosphaeria maculans causes blackleg disease on Brassica napus, an economically important oilseed crop. Brassica juncea has high resistance to blackleg and is a source for the development of resistant B. napus varieties. To transfer the Rlm6 resistance gene from B. juncea into B. napus, an interspecific cross between B. napus “Topas DH16516” and B. juncea “Forge” was produced, followed by the development of F₂ and F₃ generations. Sequence characterized amplified region (SCAR) and cleaved amplified polymorphic sequence (CAPS) markers linked to the L. maculans resistance gene Rlm6 were developed. Segregation of SCAR and CAPS markers linked to Rlm6 were confirmed by genotyping of F₂ and F₃ progeny. Segregation of CAPS markers and phenotypes for blackleg disease severity in F₂ plants had a Mendelian ratio of 3:1 in resistant vs. susceptible plants, respectively, supporting the assumption that genetic control of resistance was by a single dominant gene. The molecular markers developed in this study, which show linkage with the L. maculans resistance gene Rlm6, would facilitate marker‐assisted backcross breeding in a variety development programme.     

普通小麦DH155抗白粉病基因的分子作图及应用分子标记辅助选择将其转移

普通小麦品系DH155对白粉病菌表现高抗。为明确DH155所携带抗白粉病基因的遗传方式及与抗病基因连锁SSR标记,利用DH155与高感小麦品系SN2890杂交获得的F2和F2:3群体进行接种鉴定和遗传分析,发现DH155对白粉菌菌株E09的抗性受1对显性基因控制,暂命名为Ml DH155。BSA和分子标记分析结果显示,Ml DH155与SSR标记Xcfd81和Xcfd18连锁。利用已发表的中国春和粗山羊草D基因组序列开发新标记,进一步将Ml DH155定位于标记Xsdau K525和Xsdau K527之间,其遗传距离分别为0.2 c M和0.8 c M。将DH155与感白粉病优良品系HB133-4和旱10杂交,在F2~F4代,结合优良农艺性状选择、分子标记辅助选择和抗白粉病鉴定,获得3个高抗白粉病且农艺性状优异的株系(SDAU2100、SDAU2101和SDAU2102)。利用14个白粉菌菌株对DH155进行苗期接种鉴定表明,DH155对13个菌株表现抗病反应型。这些菌株对DH155的毒力谱与已知抗白粉病基因Pm2相似,但DH155对Bg78-3和Bg44-5菌株的反应型与携带Pm2的Ulka/8*Cc不同。结合本试验结果和Pm2基因的相关报道,推测Ml DH155可能是Pm2或其等位基因。     

Molecular mapping of two recessive genes controlling resistance to bacterial leaf pustule disease in soybean (Glycine max)

Bacterial leaf pustule (BLP) caused by Xanthomonas axonopodis pv. glycines (Xag) is a serious soybean disease. A BLP resistant genotype ‘TS-3’ was crossed with a BLP susceptible genotype ‘PK472’, and a segregating F₂ mapping population was developed for genetic analysis and mapping. The F₂ population segregation pattern in 15:1 susceptible/resistance ratio against Xag inoculum indicated that the resistance to BLP in ‘TS-3’ was governed by two recessive genes. A total of 12 SSR markers, five SSR markers located on chromosome 2 and seven SSR markers located on chromosome 6 were identified as linked to BLP resistance. One of the resistance loci (r1) was mapped with flanking SSR markers Sat_183 and BARCSOYSSR_02_1613 at a distance of 0.9 and 2.1 cM, respectively. Similarly, SSR markers BARCSOYSSR_06_0024 and BARCSOYSSR_06_0013 flanked the second locus (r2) at distances of 1.5 and 2.1 cM, respectively. The identified two recessive genes imparting resistance to BLP disease and the SSR markers tightly linked to these loci would serve as important genetic and molecular resources to develop BLP resistant genotypes in soybean.     

Chromosomal location of powdery mildew resistance gene Pm16 in wheat using SSR marker analysis

The use of resistant cultivars is a most economical way to control powdery mildew (Blumeria graminis f.sp. tritici) in wheat (Triticum aestivum L.). Identification of molecular markers closely linked to resistance genes can greatly increase the efficiency of pyramiding resistance genes in wheat cultivars. The objective of this study was to identify molecular markers closely linked lo the powdery mildew resistance gene Pm16. An F₂ population with 156 progeny was produced from the cross‘Chancellor’(susceptible) ב70281’ (resistant), A total of 45 SSR markers on chromosomes 4A and 5B of wheat and 15 SSRs on chromosome 3 of rice was used lo lest the parents, as well as the resistant and susceptible bulks: the resulting polymorphic markers were used to genotype the F₂ progeny. Results indicated that the SSR marker Xgwm159, located on the short arm of chromosome 5B, is closely linked to Pm16 (genetic distance: 5.3 CM). The cytogenetical data presented in an original report, in combination with this molecular analysis, suggests that Pm16 may he located on a translocated 4A.5BS chromosome.     

Mapping of male sterility gene ms10 in chilli pepper (Capsicum annuum L.)

Most of the hybrid seed in chilli are produced manually, but the use of male sterility (MS) can reduce the cost of hybrid seed production. MS‐12, a nuclear male‐sterile (NMS) line developed at Punjab Agricultural University, Ludhiana (India), has been utilized to develop commercial F₁ hybrids. A recessive gene, designated as ms10, governs MS in MS‐12. Due to recessive gene control, development of new NMS lines incorporating ms10 gene is tedious and time‐consuming. We identified SSR markers AVRDC‐PP12 and AVRDC_MD997* linked to the ms10 gene. A total of 558 primer pairs were screened following bulked segregant analysis (BSA). Linkage analysis in 210 F₂ plants indicated that the two SSR markers were linked to the ms10 gene and the marker AVRDC‐PP12 was closest to the gene at 7.2 cM distance. The marker was mapped to chromosome 1 at genome position 175 694 513 to 175 694 644. Until more closely linked markers are developed, the marker AVRDC‐PP12 would facilitate transfer of ms10 gene through marker‐assisted selection (MAS). Fine mapping would lead to cloning of the ms10 gene.     

Development of a SCAR marker linked with a MYMV resistance gene in mungbean (Vigna radiata L. Wilczek)

Yellow mosaic disease (YMD) caused by mungbean yellow mosaic virus (MYMV) is the most important disease of mungbean, causing great yield loss. The present investigation was carried out to study the inheritance and identify molecular markers linked with MYMV resistance gene by using F₁, F₂ and 167 F_2 : 8 recombinant inbred lines (RILs) developed from the cross ‘TM‐99‐37’ (resistant) × Mulmarada (susceptible). The F₁ was susceptible, F₂ segregated in 3S:1R phenotypic ratio and RILs segregated in 1S:1R ratio in the field screening indicating that the MYMV resistance gene is governed by a single recessive gene. Of the 140 RAPD primers, 45 primers showing polymorphism in parents were screened using bulked segregant analysis. Three primers amplified specific polymorphic fragments viz. OPB‐07_600, OPC‐06₁₇₅₀ and OPB‐12₈₂₀. The marker OPB‐07₆₀₀ was more closely linked (6.8 cM) with a MYMV resistance gene as compared to OPC‐06₁₇₅₀ (22.8 cM) and OPB‐12₈₂₀ (25.2 cM). The resistance‐specific fragment OPB‐07₆₀₀ was cloned, sequenced and converted into a sequence‐characterized amplified region (SCAR) marker and validated in twenty genotypes with different genetic backgrounds.     

Mapping a gene conferring resistance to <Emphasis Type="Italic">Wheat yellow mosaic virus</Emphasis> in European winter wheat cultivar ‘Ibis’ (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.)

Wheat yellow mosaic, caused by Wheat yellow mosaic virus (WYMV), is one of the most devastating soil-borne diseases of winter wheat (Triticum aestivum L.) in Japan. Yellow-striped leaves and stunted spring growth, symptomatic of WYMV infection, result in severe yield loss. A new putative WYMV resistance gene in the European wheat cultivar ‘Ibis’ was mapped in the cluster of microsatellite markers including Xcfd16, Xwmc41, Xcfd168 and Xwmc181 on the long arm of chromosome 2D at the distances of 2.0 cM, 4.0 cM, 7.1 cM and 12.4 cM, respectively. WYMV-resistant cultivars contained a common haplotype of the four markers, whereas moderately susceptible and susceptible cultivars did not. These results should be useful in marker-assisted selection for WYMV resistance in wheat.     

Stripe rust resistance gene Yr18 and its suppressor gene in Chinese wheat landraces

The slow‐rusting and mildewing gene Yr18/Lr34/Pm38/Sr57 confers partial, durable resistance to multiple fungal pathogens and has its origins in China. A number of diagnostic markers were developed for this gene based on the gene sequence, but these markers do not always predict the presence of the resistant phenotype as some wheat varieties with the gene are susceptible to stripe rust in China. We hypothesized that these varieties have a suppressor of Yr18. This study was undertaken to determine the presence of Yr18, the suppressor and/or another resistance gene in 144 Chinese wheat landraces using molecular markers and stripe rust field data. Forty‐three landraces were predicted to have Yr18 based on the presence of the markers, but had final disease severities higher than 70%, indicating that this gene may be under the influence of a suppressor. Four of these landraces, ‘Sichuanyonggang 2’, ‘Baikemai’, ‘Youmai’ and ‘Zhangsihuang’, were chosen for genetic studies. Crosses were made between the lines and ‘Avocet S’, with further crosses of Sichuanyonggang 2 ×  ‘Huixianhong’ and Sichuanyonggang 2 ×  ‘Chinese Spring’. The F₁ plants of Sichuanyonggang 2/Chinese Spring was susceptible indicating the presence of a dominant suppressor gene. The results of genetic analyses of F_2:3 and BC₁F₂ families derived from these crosses indicated the presence of Yr18, a Yr18 suppressor and another additive resistance gene. The Yr18 region in Sichuanyonggang 2 was sequenced to ensure that it contained the functional allele. This is the first report of a suppressor of Yr18/Lr34/Pm38/Sr57 gene with respect to stripe rust response.     

Molecular tagging of a stripe rust resistance gene in <Emphasis Type="Italic">Aegilops tauschii</Emphasis>

Stripe rust, caused by Puccinia striiformis f. sp. tritici (PST), is one of the most important diseases of common wheat (Triticum aestivum L.). China has the largest stripe rust epidemic areas in the world and yield losses can be large. Aegilops tauschii Coss, the D-genome progenitor of common wheat, includes two subspecies, tauschii and strangulata (Eig) Tzvel. The ssp. strangulata accession AS2388 is highly resistant to the prevailing physiological races of PST in China, and possesses a single dominant gene for stripe rust resistance. In order to tag this gene, AS2388 was crossed with the highly susceptible ssp. tauschii accession AS87. The parents, F₂ plants, and F_2:3 families were tested at adult plant stage in field trials with six currently prevailing races. Simple sequence repeat (SSR) primers were used to identify molecular markers linked to the resistance gene. SSR markers Xwmc285 and Xwmc617 were linked to the resistance gene on chromosome arm 4DS flanking it at 1.7 and 34.6 cM, respectively. Based on the chromosomal location, this gene temporarily designated as YrAS2388 is probably novel. The resistance in Ae. tauschii AS2388 was partially expressed in two newly developed synthetic hexaploid backgrounds.     

A new rice gall midge resistance gene in the breeding line CR57-MR1523, mapping with flanking markers and development of NILs

Gall midge is the third most destructive insect pests of rice after stem borers and planthoppers. Host plant resistance has been recognized as the most effective and economic, means for gall midge management. With the characterization of a new gall midge biotype (GMB) 4M, unique feature of gall midge resistance in the breeding line CR57-MR1523 was highlighted. Multi-location evaluation of F₃ families derived from the cross TN1 × CR57-MR1523 against different gall midge biotypes helped to identify a new dominant gene conferring resistance against GMB4. This gene has been designated as Gm11t. Though CR57-MR1523 has been extensively used in breeding gall midge resistant rice varieties like Suraksha, neither the genetics of resistance nor chromosomal location of the resistance gene(s) is known. In the present study we have tagged and mapped the new gall midge resistance gene, Gm11t, on chromosome 12, using SSR markers. To map the gene locus, 466 F₁₀ generation Recurrent Inbred Lines (RILs), from the cross of TN1 × CR57-MR1523 were used. Of the 471 SSR markers spread across the rice genome, 56 markers showed polymorphism and were used to screen a subset of the mapping population consisting of 10 resistant (R) and 10 susceptible (S) F₁₀ RILs. Six SSR markers, RM28706, RM235, RM17, RM28784, RM28574 and RM28564 on chromosome 12 were initially found to be associated with resistance and susceptibility. Based on the linkage analysis in selected 158 RILs, we were able to map the locus between two flanking SSR markers, RM28574 and RM28706, on chromosome 12 within 4.4 and 3.8 cM, respectively. Further, two NILs with 99% genetic similarity, were identified from the RILs which differed in gall midge resistance. The tightly linked flanking SSR markers will facilitate marker-assisted gene pyramiding and map-based cloning of the resistant gene. NILs would be valuable materials for functional analysis of the identified candidate gene.     

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.     

User‐friendly markers linked to Fusarium wilt race 1 resistance Fw gene for marker‐assisted selection in pea

Fusarium wilt is one of the most widespread diseases of pea. Resistance to Fusarium wilt race 1 was reported as a single gene, Fw, located on linkage group III. The previously reported AFLP and RAPD markers linked to Fw have limited usage in marker‐assisted selection due to their map distance and linkage phase. Using 80 F₈ recombinant inbred lines (RILs) derived from the cross of Green Arrow × PI 179449, we amplified 72 polymorphic markers between resistant and susceptible lines with the target region amplified polymorphism (TRAP) technique. Marker–trait association analysis revealed a significant association. Five candidate markers were identified and three were converted into user‐friendly dominant SCAR markers. Forty‐eight pea cultivars with known resistant or susceptible phenotypes to Fusarium wilt race 1 verified the marker–trait association. These three markers, Fw_Trap_480, Fw_Trap_340 and Fw_Trap_220, are tightly linked to and only 1.2 cM away from the Fw locus and are therefore ideal for marker‐assisted selection. These newly identified markers are useful to assist in the isolation of the Fusarium wilt race 1 resistance gene in pea.     

小麦品种小偃9323抗条锈基因的遗传分析和分子作图

小偃9323是小偃6号的同源材料,具有早熟、抗逆性强、适应性广、抗条锈性强等许多优良的生物学特性。为明确其抗条锈性及遗传规律,利用当前流行的中国条锈菌小种CYR32对抗病品种小偃9323与感病品种铭贤169及其杂交后代F₁、F₂、F₃和BC₁代进行苗期抗条锈性遗传分析,并对其抗条锈基因进行SSR分子标记。结果表明,小偃9323对CYR32小种具有良好的抗性,由1对隐性基因所控制。利用F₂代分离群体,筛选到6个与抗病基因连锁的SSR标记,分别是Xwmc807、Xbarc3、Xwmc684、Xwmc201、Xwmc553和Xwmc179;该抗病基因位于小麦6AL染色体上,其最近的标记为Xwmc201和Xwmc553,遗传距离分别是2.6 cM和3.7 cM。分析表明,该基因不同于已知抗条锈基因,暂被命名为YrXY9323。用YrXY9323两侧遗传距离最近的标记Xwmc201和Xwmc553对42个黄淮麦区主栽小麦品种进行分子检测,结果表明有19%的品种具有与YrXY9323相同的标记位点。本结果对YrXY9323在小麦抗条锈病育种中的应用提供了理论依据。     

QTL mapping of a partial resistance to the corn delphacid‐transmitted viruses in Lepidopteran‐resistant maize line Mp705

A partial resistance to maize mosaic virus (MMV) and maize stripe virus (MStV) was mapped in a RILs population derived from a cross between lines MP705 (resistant) and B73 (susceptible). A genetic map constructed from 131 SSR markers spanned 1399 cM with an average distance of 9.6 cM. A total of 10 QTL were detected for resistance to MMV and MStV, using composite interval mapping. A major QTL explaining 34–41% of the phenotypic variance for early resistance to MMV was detected on chromosome 1. Another major QTL explaining up to 30% of the phenotypic variation for all traits of resistance to MStV was detected in the centromeric region of chromosome 3 (3.05 bin). After adding supplementary SSR markers, this region was found to correspond well to the one where a QTL of resistance to MStV already was located in a previous mapping study using an F₂ population derived from a cross between Rev81 and B73. These results suggested that these QTL of resistance to MStV detected on chromosome 3 could be allelic in maize genome.     

Identification and molecular mapping of a leaf rust resistance gene in spelt wheat landrace Altgold

Leaf rust, caused by Puccinia triticina, is an important disease for wheat production, both in China and worldwide. In laboratory studies spelt wheat (Triticum aestivum ssp. spelta) landrace Altgold was resistant to P. triticina races THT and PHT and genetic analysis indicated that it possessed a dominant leaf rust resistance gene, temporarily designated LrAlt. F₆ recombinant inbred lines (RILs) derived from a cross with the susceptible common wheat cultivar Nongda 3338 were used to map LrAlt with SSR markers. The resistance gene was distal to SSR loci Xbarc212, Xwmc382, Xgwm636, and Xwmc407 on the short arm of chromosome 2A. The closest markers Xbarc212 and Xwmc382 which co-segregated were 1.8 cM away from LrAlt. The relationships of LrAlt and other wheat leaf rust resistance genes located on the short arm of chromosome 2A were discussed, suggesting that LrAlt might be a new leaf rust resistance gene.