Inheritance and mapping of powdery mildew resistance gene <Emphasis Type="Italic">Pm43</Emphasis> introgressed from <Emphasis Type="Italic">Thinopyrum</Emphasis><Emphasis Type="Italic">intermedium</Emphasis> into wheat

Powdery mildew resistance from Thinopyrum intermedium was introgressed into common wheat (Triticum aestivum L.). Genetic analysis of the F₁, F₂, F₃ and BC₁ populations from powdery mildew resistant line CH5025 revealed that resistance was controlled by a single dominant allele. The gene responsible for powdery mildew resistance was mapped by the linkage analysis of a segregating F₂ population. The resistance gene was linked to five co-dominant genomic SSR markers (Xcfd233, Xwmc41, Xbarc11, Xgwm539 and Xwmc175) and their most likely order was Xcfd233–Xwmc41–Pm43–Xbarc11–Xgwm539–Xwmc175 at 2.6, 2.3, 4.2, 3.5 and 7.0 cM, respectively. Using the Chinese Spring nullisomic-tetrasomic and ditelosomic lines, the polymorphic markers and the resistance gene were assigned to chromosome 2DL. As no powdery mildew resistance gene was previously assigned to chromosome 2DL, this new resistance gene was designated Pm43. Pm43, together with the identified closely linked markers, could be useful in marker-assisted selection for pyramiding powdery mildew resistance genes. Runli He and Zhijian Chang contributed equally to this work.     

Molecular mapping of pea powdery mildew resistance gene <Emphasis Type="Italic">er2</Emphasis> to pea linkage group III

Powdery mildew caused by Erysiphe pisi D.C. is one of the most serious diseases that inflict heavy losses to pea crop world-wide. Identification of resistance sources and their incorporation into susceptible cultivars remains the most effective method of controlling the disease. The present study investigated the resistance phenotype, inheritance, and genomic location of gene(s) controlling resistance to powdery mildew in pea genotype ‘JI2480’. The powdery mildew resistance in ‘JI2480’ appeared to be a spatial phenomenon showing expression only in leaf tissues. By segregation analysis of an F₂ progeny of cross ‘Lincoln/JI2480’, the leaf resistance of ‘JI2480’ was shown to be controlled by a single recessive gene, presumed to be er2. Through linkage analysis of 111 resistant F₂ progeny plants with simple sequence repeat (SSR) and random amplified polymorphic DNA (RAPD) markers adopted from the published linkage maps, the er2 gene was localized on pea linkage group III (LGIII). The assignment of er2 to LGIII, a position different from that reported for er1, has resolved the long standing controversy in the literature regarding the existence and genomic location of er2 gene. A RAPD marker OPX-17_1400, exhibiting cis phase linkage (2.6 cM) to er2 was successfully converted to a sequence characterized amplified region (SCAR) marker, ScX17_1400. The SCAR marker ScX17_1400 will ensure speedy and precise introgression of er2 into susceptible cultivars by permitting selection of er2 heterozygotes amongst BC _n F₁s without progeny tests and resistance screening.     

Molecular mapping of powdery mildew resistance gene <Emphasis Type="Italic">PmHNK</Emphasis> in winter wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) cultivar Zhoumai 22

The Chinese winter wheat cultivar Zhoumai 22 is highly resistant to powdery mildew. The objectives of this study were to map a powdery mildew resistance gene in Zhoumai 22 using molecular markers and investigate its allelism with Pm13. A total of 278 F₂ and 30 BC₁ plants, and 143 F₃ lines derived from the cross between resistant cultivar Zhoumai 22 and susceptible cultivar Chinese Spring were used for resistance gene tagging. The 137 F₂ plants from the cross Zhoumai 22/2761-5 (Pm13) were employed for the allelic test of the resistance genes. Two hundred and ten simple sequence repeat (SSR) markers were used to test the two parents, and resistant and susceptible bulks. Subsequently, seven polymorphic markers were used for genotyping the F₂ and F₃ populations. The results indicated that the powdery mildew resistance in Zhoumai 22 was conferred by a single dominant gene, designated PmHNK tentatively, flanked by seven SSR markers Xgwm299, Xgwm108, Xbarc77, Xbarc84, Xwmc326, Xwmc291 and Xwmc687 on chromosome 3BL. The resistance gene was closely linked to Xwmc291 and Xgwm108, with genetic distances of 3.8 and 10.3 cM, respectively, and located on the chromosome bin 3BL-7-0.63-1.0 in the test with a set of deletion lines. Seedling tests with seven isolates of Blumeria graminis f. sp. tritici (Bgt) and allellic test indicated that PmHNK is different from Pm13, and Pm41 seems also to be different from PmHNK due to its origin from T. dicoccoides and molecular evidence. These results indicate that PmHNK is likely to be a novel powdery mildew resistance gene in wheat.     

Molecular identification of a new powdery mildew resistance gene <Emphasis Type="Italic">Pm41</Emphasis> on chromosome 3BL derived from wild emmer (<Emphasis Type="Italic">Triticum turgidum</Emphasis> var. <Emphasis Type="Italic">dicoccoides</Emphasis>)

Powdery mildew caused by Blumeria graminis f. sp. tritici is an important wheat disease in China and other parts of the world. Wild emmer (Triticum turgidum var. dicoccoides) is the immediate progenitor of cultivated tetraploid and hexaploid wheats and thus an important resource for wheat improvement. Wild emmer accession IW2 collected from Mount Hermon, Israel, is highly resistant to powdery mildew at the seedling and adult plant stages. Genetic analysis using an F₂ segregating population and F_2:3 families, derived from a cross between susceptible durum cultivar Langdon and wild emmer accession IW2, indicated that a single dominant gene was responsible for the resistance of IW2. Bulked segregant and molecular marker analyses detected that six polymorphic SSR, one ISBP, and three EST-STS markers on chromosome 3BL bin 0.63–1.00 were linked to the resistance gene. Allelic variations of resistance-linked EST-STS marker BE489472 revealed that the allele was present only in wild emmer but absent in common wheat. Segregation distortion was observed for the powdery mildew resistance allele and its linked SSR markers with preferential transmission of Langdon alleles over IW2 alleles. The resistance gene was introgressed into common wheat by backcrossing and marker-assisted selection. Since no designated powdery mildew resistance gene has been found on chromosome 3BL, the resistance gene derived from wild emmer accession IW2 appears to be new one and was consequently designated Pm41. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Development of SCAR markers linked to powdery mildew (<Emphasis Type="Italic">Uncinula necator</Emphasis>) resistance in grapevine (<Emphasis Type="Italic">Vitis vinifera</Emphasis> L. and <Emphasis Type="Italic">Vitis</Emphasis> sp.)

Sequence-characterized amplified regions markers (SCARs) were developed from six randomly amplified polymorphic DNA (RAPD) markers linked to the major QTL region for powdery mildew (Uncinula necator) resistance in a test population derived from the cross of grapevine cultivars “Regent” (resistant) × “Lemberger”(susceptible). RAPD products were cloned and sequenced. Primer pairs with at least 21 nucleotides primer length were designed. All pairs were tested in the F1 progeny of “Regent” × “Lemberger”. The SCAR primers resulted in the amplification of specific bands of expected sizes and were tested in additional genetic resources of resistant and susceptible germplasm. All SCAR primer pairs resulted in the amplification of specific fragments. Two of the SCAR markers named ScORA7-760 and ScORN3-R produced amplification products predominantly in resistant individuals and were found to correlate to disease resistance. ScORA7-760, in particular, is suitable for marker-assisted selection for powdery mildew resistance and to facilitate pyramiding powdery mildew resistance genes from various sources.     

<Emphasis Type="Italic">MlAG12</Emphasis>: a <Emphasis Type="Italic">Triticum timopheevii</Emphasis>-derived powdery mildew resistance gene in common wheat on chromosome 7AL

Wheat powdery mildew is an economically important disease in cool and humid environments. Powdery mildew causes yield losses as high as 48% through a reduction in tiller survival, kernels per head, and kernel size. Race-specific host resistance is the most consistent, environmentally friendly and, economical method of control. The wheat (Triticum aestivum L.) germplasm line NC06BGTAG12 possesses genetic resistance to powdery mildew introgressed from the AAGG tetraploid genome Triticum timopheevii subsp. armeniacum. Phenotypic evaluation of F₃ families derived from the cross NC06BGTAG12/‘Jagger’ and phenotypic evaluation of an F₂ population from the cross NC06BGTAG12/‘Saluda’ indicated that resistance to the ‘Yuma’ isolate of powdery mildew was controlled by a single dominant gene in NC06BGTAG12. Bulk segregant analysis (BSA) revealed simple sequence repeat (SSR) markers specific for chromosome 7AL segregating with the resistance gene. The SSR markers Xwmc273 and Xwmc346 mapped 8.3 cM distal and 6.6 cM proximal, respectively, in NC06BGTAG12/Jagger. The multiallelic Pm1 locus maps to this region of chromosome 7AL. No susceptible phenotypes were observed in an evaluation of 967 F₂ individuals in the cross NC06BGTAG12/‘Axminster’ (Pm1a) which indicated that the NC06BGTAG12 resistance gene was allelic or in close linkage with the Pm1 locus. A detached leaf test with ten differential powdery mildew isolates indicated the resistance in NC06BGTAG12 was different from all designated alleles at the Pm1 locus. Further linkage and allelism tests with five other temporarily designated genes in this very complex region will be required before giving a permanent designation to this gene. At this time the gene is given the temporary gene designation MlAG12.     

Pea powdery mildew <Emphasis Type="Italic">er1</Emphasis> resistance is associated to loss-of-function mutations at a <Emphasis Type="Italic">MLO</Emphasis> homologous locus

The powdery mildew disease affects several crop species and is also one of the major threats for pea (Pisum sativum L.) cultivation all over the world. The recessive gene er1, first described over 60 years ago, is well known in pea breeding, as it still maintains its efficiency as a powdery mildew resistance source. Genetic and phytopathological features of er1 resistance are similar to those of barley, Arabidopsis, and tomato mlo powdery mildew resistance, which is caused by the loss of function of specific members of the MLO gene family. Here, we describe the obtainment of a novel er1 resistant line by experimental mutagenesis with the alkylating agent diethyl sulfate. This line was found to carry a single nucleotide polymorphism in the PsMLO1 gene sequence, predicted to result in premature termination of translation and a non-functional protein. A cleaved amplified polymorphic sequence (CAPS) marker was developed on the mutation site and shown to be fully co-segregating with resistance in F₂ individuals. Sequencing of PsMLO1 from three powdery mildew resistant cultivars also revealed the presence of loss-of-function mutations. Taken together, results reported in this study strongly indicate the identity between er1 and mlo resistances and are expected to be of great breeding importance for the development of resistant cultivars via marker-assisted selection.     

<Emphasis Type="Italic">Pm37</Emphasis>, a new broadly effective powdery mildew resistance gene from <Emphasis Type="Italic">Triticum </Emphasis><Emphasis Type="Italic">timopheevii</Emphasis>

Powdery mildew is an important foliar disease in wheat, especially in areas with a cool or maritime climate. A dominant powdery mildew resistance gene transferred to the hexaploid germplasm line NC99BGTAG11 from T. timopheevii subsp. armeniacum was mapped distally on the long arm of chromosome 7A. Differential reactions were observed between the resistance gene in NC99BGTAG11 and the alleles of the Pm1 locus that is also located on chromosome arm 7AL. Observed segregation in F_2:3 lines from the cross NC99BGTAG11 × Axminster (Pm1a) demonstrate that germplasm line NC99BGTAG11 carries a novel powdery mildew resistance gene, which is now designated as Pm37. This new gene is highly effective against all powdery mildew isolates tested so far. Analyses of the population with molecular markers indicate that Pm37 is located 16 cM proximal to the Pm1 complex. Simple sequence repeat (SSR) markers Xgwm332 and Xwmc790 were located 0.5 cM proximal and distal, respectively, to Pm37. In order to identify new markers in the region, wheat expressed sequence tags (ESTs) located in the distal 10% of 7AL that were orthologous to sequences from chromosome 6 of rice were targeted. The two new EST-derived STS markers were located distal to Pm37 and one marker was closely linked to the Pm1a region. These new markers can be used in marker-assisted selection schemes to develop wheat cultivars with pyramids of powdery mildew resistance genes, including combinations of Pm37 in coupling linkage with alleles of the Pm1 locus.     

Identification and characterization of a novel powdery mildew resistance gene <Emphasis Type="Italic">PmG3M</Emphasis> derived from wild emmer wheat, <Emphasis Type="Italic">Triticum dicoccoides</Emphasis>

Powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt) is one of the most important wheat diseases worldwide. Wild emmer wheat, Triticum turgidum ssp. dicoccoides, the tetraploid ancestor (AABB) of domesticated bread and durum wheat, harbors many important alleles for resistance to various diseases, including powdery mildew. In the current study, two tetraploid wheat mapping populations, derived from a cross between durum wheat (cv. Langdon) and wild emmer wheat (accession G-305-3M), were used to identify and map a novel powdery mildew resistance gene. Wild emmer accession G-305-3M was resistant to all 47 Bgt isolates tested, from Israel and Switzerland. Segregation ratios of F₂ progenies and F₆ recombinant inbred line (RIL) mapping populations, in their reactions to inoculation with Bgt, revealed a Mendelian pattern (3:1 and 1:1, respectively), indicating the role of a single dominant gene derived from T. dicoccoides accession G-305-3M. This gene, temporarily designated PmG3M, was mapped on chromosome 6BL and physically assigned to chromosome deletion bin 6BL-0.70-1.00. The F₂ mapping population was used to construct a genetic map of the PmG3M gene region consisted of six simple sequence repeats (SSR), 11 resistance gene analog (RGA), and two target region amplification polymorphism (TRAP) markers. A second map, constructed based on the F₆ RIL population, using a set of skeleton SSR markers, confirmed the order of loci and distances obtained for the F₂ population. The discovery and mapping of this novel powdery mildew resistance gene emphasize the importance of the wild emmer wheat gene pool as a source for crop improvement.     

Identification and genetic mapping of <Emphasis Type="Italic">pm42</Emphasis>, a new recessive wheat powdery mildew resistance gene derived from wild emmer (<Emphasis Type="Italic">Triticum turgidum var. dicoccoides</Emphasis>)

Powdery mildew, caused by Blumeria graminis f. sp. tritici, is one of the most important wheat diseases worldwide in areas with cool or maritime climates. Wild emmer (Triticum turgidum var. dicoccoides) is an important potential donor of disease resistances and other traits for common wheat improvement. A powdery mildew resistance gene was transferred from wild emmer accession G-303-1M to susceptible common wheat by crossing and backcrossing, resulting in inbred line P63 (Yanda1817/G-303-1 M//3*Jing411, BC₂F₆). Genetic analysis of an F₂ population and the F_2:3 families developed from a cross of P63 and a susceptible common wheat line Xuezao showed that the powdery mildew resistance in P63 was controlled by a single recessive gene. Molecular markers and bulked segregant analysis were used to characterize and map the powdery mildew resistance gene. Nine genomic SSR markers (Xbarc7, Xbarc55, Xgwm148, Xgwm257, Xwmc35, Xwmc154, Xwmc257, Xwmc382, Xwmc477), five AFLP-derived SCAR markers (XcauG3, XcauG6, XcauG10, XcauG20, XcauG22), three EST–STS markers (BQ160080, BQ160588, BF146221) and one RFLP-derived STS marker (Xcau516) were linked to the resistance gene, designated pm42, in P63. pm42 was physically mapped on chromosome 2BS bin 0.75–0.84 using Chinese Spring nullisomic-tetrasomic, ditelosomic and deletion lines, and was estimated to be more than 30 cM proximal to Xcau516, a RFLP-derived STS marker that co-segregated with the wild emmer-derived Pm26 which should be physically located in 2BS distal bin 0.84–1.00. pm42 was highly effective against 18 of 21 differential Chinese isolates of B. graminis f. sp. tritici. The closely linked molecular markers will enable the rapid transfer of pm42 to wheat breeding populations thus adding to their genetic diversity. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. W. Hua, Z. Liu, and J. Zhu contributed equally to this work.     

Molecular mapping of leaf rust resistance gene <Emphasis Type="Italic">Rph14</Emphasis> in <Emphasis Type="Italic">Hordeum vulgare</Emphasis>

An incompletely dominant gene conferring resistance to Puccinia hordei, Rph14, identified previously in an accession of Hordeum vulgare, confers resistance to all known pathotypes of P. hordei in Australia. Knowledge of the chromosomal location of Rph14 and the identification of DNA markers closely linked to it will facilitate combining it with other important leaf rust resistance genes to achieve long lasting resistance. The inheritance of Rph14 was confirmed using 146 and 106 F₃ lines derived from the crosses ‘Baudin’/‘PI 584760’ (Rph14) and ‘Ricardo’/‘PI 584760’ (Rph14), respectively. Bulk segregant analysis on DNA from the parental genotypes and resistant and susceptible DNA bulks using DArT markers located Rph14 to the short arm of chromosome 2H. DArT marker bPb-1664 was identified as having the closest genetic association with Rph14. PCR based marker analysis identified a single SSR marker, Bmag692, linked closely to Rph14 at a map distance of 2.1 and 3.8 cm in the ‘Baudin’/‘PI 584760’and ‘Ricardo’/‘PI 584760’ populations, respectively.     

Identification and validation of RAPD and SCAR markers linked to the gene <Emphasis Type="Italic">Er3</Emphasis> conferring resistance to <Emphasis Type="Italic">Erysiphe pisi</Emphasis> DC in pea

Three genes, er1, er2 and Er3, conferring resistance to powdery mildew (Erysiphe pisi) in pea have been described so far. Because single gene-controlled resistance tends to be overcome by evolution of pathogen virulence, accumulation of several resistance genes into a single cultivar should enhance the durability of the resistance. Molecular markers linked to genes controlling resistance to E. pisi may facilitate gene pyramiding in pea breeding programs. Molecular markers linked to er1 and er2 are available. In the present study, molecular markers linked to Er3 have been obtained. A segregating F₂ population derived from the cross between a breeding line carrying the Er3 gene, and the susceptible cultivar ‘Messire’ was developed and genotyped. Bulk Segregant Analysis (BSA) was used to identify Random Amplified Polymorphic DNA (RAPD) markers linked to Er3. Four RAPD markers linked in coupling phase (OPW04_637, OPC04_640, OPF14_1103, and OPAH06_539) and two in repulsion phase (OPAB01_874 and OPAG05_1240), were identified. Two of these, flanking Er3, were converted to Sequence Characterized Amplified Region (SCAR) markers. The SCAR marker SCW4₆₃₇ co-segregated with the resistant gene, allowing the detection of all the resistant individuals. The SCAR marker SCAB1₈₇₄, in repulsion phase with Er3, was located at 2.8 cM from the gene and, in combination with SCW4₆₃₇, was capable to distinguish homozygous resistant individuals from heterozygous with a high efficiency. In addition, the validation for polymorphism in different genetic backgrounds and advanced breeding material confirmed the utility of both markers in marker-assisted selection.     

Genetic linkage map of melon (<Emphasis Type="Italic">Cucumis melo</Emphasis> L.) and localization of a major QTL for powdery mildew resistance

Powdery mildew caused by Podosphaera xanthii has become a major problem in melon since it occurs all year round irrespective of the growing system. The TGR-1551 melon genotype was found to be resistant to several melon diseases, among them powdery mildew. However, the corresponding resistance genes have been never mapped. We constructed an integrated genetic linkage map using an F2 population derived from a cross between the multi-resistant genotype TGR-1551 and the susceptible Spanish cultivar ‘Bola de Oro’. The map spans 1,284.9 cM, with an average distance of 3.6 cM among markers, and consists of 354 loci (188 AFLP, 39 RAPD, 111 SSR, 14 SCAR/CAPS/dCAPS, and two phenotypic traits) distributed in 14 linkage groups. QTL analysis identified one major QTL (Pm-R) on LG V for resistance to races 1, 2, and 5 of powdery mildew. The PM4-CAPS marker is closely linked to the Pm-R QTL at a genetic distance of 1.9 cM, and the PM3-CAPS marker is located within the support interval of this QTL. These codominant markers, together with the map information reported here, could be used for melon breeding, and particularly for genotyping selection of resistance to powdery mildew in this vegetable crop species.     

Molecular mapping of rice blast resistance gene <Emphasis Type="Italic">Pi-1</Emphasis>(<Emphasis Type="Italic">t</Emphasis>) in the elite <Emphasis Type="Italic">indica</Emphasis> variety Samba mahsuri

Samba mahsuri (BPT 5204) is a cultivar of the medium slender grain indica variety of Oryza sativa grown across India for its high yield and quality. However, this cultivar is susceptible to several diseases and pests including rice blast. The analysis of near isogenic lines indicated the presence of a resistance gene, Pi-1(t) in the donor cultivar C101LAC which is highly resistant to the rice blast fungus Magnaporthe grisea (M. grisea). C101LAC was crossed with susceptible indica rice cultivar (BPT 5204) to generate the mapping population. A mendelian segregation ratio of 3:1 for resistant to susceptible F₂ plants using bulk segregation analysis confirmed the presence of a major gene pi-1(t) by simple sequence repeats marker RM224 to the highly virulent blast isolate DRR 001.     

Molecular mapping of <Emphasis Type="Italic">Rym17</Emphasis>, a dominant and <Emphasis Type="Italic">rym18</Emphasis> a recessive barley yellow mosaic virus (BaYMV) resistance genes derived from <Emphasis Type="Italic">Hordeum vulgare</Emphasis> L.

PK23-2, a line of six-rowed barley (Hordeum vulgare L.) originating from Pakistan, has resistance to Japanese strains I and III of the barley yellow mosaic virus (BaYMV). To identify the source of resistance in this line, reciprocal crosses were made between the susceptible cultivar Daisen-gold and PK23-2. Genetic analyses in the F₁ generation, F₂ generation, and a doubled haploid population (DH45) derived from the F₁ revealed that PK23-2 harbors one dominant and one recessive resistance genes. A linkage map was constructed using 61 lines of DH45 and 127 DNA markers; this map covered 1268.8 cM in 10 linkage groups. One QTL having a LOD score of 4.07 and explaining 26.8% of the phenotypic variance explained (PVE) for resistance to BaYMV was detected at DNA marker ABG070 on chromosome 3H. Another QTL having a LOD score of 3.53 and PVE of 27.2% was located at marker Bmag0490 on chromosome 4H. The resistance gene on chromosome 3H, here named Rym17, showed dominant inheritance, whereas the gene on chromosome 4H, here named rym18, showed recessive inheritance in F₁ populations derived from crosses between several resistant lines of DH45 and Daisen-gold. The BaYMV recessive resistance genes rym1, rym3, and rym5, found in Japanese barley germplasm, were not allelic to rym18. These results revealed that PK23-2 harbors two previously unidentified resistance genes, Rym17 on 3H and rym18 on 4H; Rym17 is the first dominant BaYMV resistance gene to be identified in primary gene pool. These new genes, particularly dominant Rym17, represent a potentially valuable genetic resource against BaYMV disease.     

Linkage of a RAPD marker with powdery mildew resistance

The aim of this study was to investigate the inheritance of powdery mildew disease and to tag it with a DNA marker to utilize for the marker-assisted selection (MAS) breeding program. The powdery mildew resistant genotype Fallon(er) and susceptible genotype 11760-3ER were selected from 177 genotypes by heavy infestation of germplasm with Erysiphe pisi through artificial inoculation. The F1 plants of the cross Fallon/11760-3 indicated the dominance of the susceptible allele, while F2 plants segregated in 3 : 1 ratio (susceptible : resistant) that fit for goodness of fitness by chi2 (P > 0.07), indicating monogenic recessive inheritance for powdery mildew resistance in Pisum sativum. A novel RAPD marker OPB18 (5'-CCACAGCAGT-3') was linked to the er-1 gene with 83% probability with a LOD score of 4.13, and was located at a distance of 11.2 cM from the er-1 gene.     

Homoeologous recombination-based transfer and molecular cytogenetic mapping of powdery mildew-resistant gene <Emphasis Type="Italic">Pm57</Emphasis> from <Emphasis Type="Italic">Aegilops searsii</Emphasis> into wheat

Key message

Pm57, a novel resistant gene against powdery mildew, was transferred into common wheat from Ae. searsi and further mapped to 2S ^s #1L at an interval of FL0.75 to FL0.87.

Abstract

Powdery mildew, caused by the fungus Blumeria graminis f. sp. tritici, is one of the most severe foliar diseases of wheat causing reduction in grain yield and quality. Host plant resistance is the most effective and environmentally safe approach to control this disease. Tests of a set of Chinese Spring–Ae. searsii (S^sS^s, 2n?=?2x?=?14) Feldman & Kislev ex K. Hammer disomic addition lines with a mixed isolate of the powdery mildew fungus identified a novel resistance gene(s), designed as Pm57, which was located on chromosome 2S^s#1. Here, we report the development of ten wheat–Ae. searsii recombinants. The wheat chromosomes involved in five of these recombinants were identified by FISH and SSR marker analysis and three of them were resistant to powdery mildew. Pm57 was further mapped to the long arm of chromosome 2S^s#1 at a fraction length interval of FL 0.75 to FL 0.87. The recombinant stocks T2BS.2BL-2S^s#1L 89-346 (TA5108) with distal 2S^s#1L segments of 28% and 89(5)69 (TA5109) with 33% may be useful in wheat improvement. The PCR marker X2L4g9p4/HaeIII was validated to specifically identify the Ae. searsii 2S^s#1L segment harboring Pm57 in T2BS.2BL-2S^s#1L against 16 wheat varieties and advanced breeding lines, and the development of more user-friendly KASP markers is underway.

     

Molecular mapping of powdery mildew resistance gene <Emphasis Type="Italic">Eg-3</Emphasis> in cultivated oat (<Emphasis Type="Italic">Avena sativa</Emphasis> L. cv. Rollo)

Powdery mildew is a prevalent fungal disease affecting oat (Avena sativa L.) production in Europe. Common oat cultivar Rollo was previously shown to carry the powdery mildew resistance gene Eg-3 in common with cultivar Mostyn. The resistance gene was mapped with restriction fragment length polymorphism (RFLP) markers from Triticeae group-1 chromosomes using a population of F₃ lines from a cross between A. byzantina cv. Kanota and A. sativa cv. Rollo. This comparative mapping approach positioned Eg-3 between cDNA-RFLP marker loci cmwg706 and cmwg733. Since both marker loci were derived from the long arm of barley chromosome 1H, the subchromosomal location of Eg-3 was assumed to be on the long arm of oat chromosome 17. Amplified fragment length polymorphism (AFLP) marker technology featured as an efficient means for obtaining markers closely linked to Eg-3.     

Identification and comparative mapping of a powdery mildew resistance gene derived from wild emmer (<Emphasis Type="Italic">Triticum turgidum</Emphasis> var. <Emphasis Type="Italic">dicoccoides</Emphasis>) on chromosome 2BS

Powdery mildew, caused by Blumeria graminis f. sp. tritici, is an important foliar disease of wheat worldwide. Wild emmer (Triticum turgidum var. dicoccoides) is a valuable genetic resource for improving disease resistance in common wheat. A powdery mildew resistance gene conferring resistance to B. graminis f. sp. tritici isolate E09 at the seedling and adult stages was identified in wild emmer accession IW170 introduced from Israel. An incomplete dominant gene, temporarily designated MlIW170, was responsible for the resistance. Through molecular marker and bulked segregant analyses of an F₂ population and F₃ families derived from a cross between susceptible durum wheat line 81086A and IW170, MlIW170 was located in the distal chromosome bin 2BS3-0.84-1.00 and flanked by SSR markers Xcfd238 and Xwmc243. MlIW170 co-segregated with Xcau516, an STS marker developed from RFLP marker Xwg516 that co-segregated with powdery mildew resistance gene Pm26 on 2BS. Four EST–STS markers, BE498358, BF201235, BQ160080, and BF146221, were integrated into the genetic linkage map of MlIW170. Three AFLP markers, XPaacMcac, XPagcMcta, XPaacMcag, and seven AFLP-derived SCAR markers, XcauG2, XcauG3, XcauG6, XcauG8, XcauG10, XcauG20, and XcauG25, were linked to MlIW170. XcauG3, a resistance gene analog (RGA)-like sequence, co-segregated with MlIW170. The non-glaucousness locus Iw1 was 18.77 cM distal to MlIW170. By comparative genomics of wheat–Brachypodium–rice genomic co-linearity, four EST–STS markers, CJ658408, CJ945509, BQ169830, CJ945085, and one STS marker XP2430, were developed and MlIW170 was mapped in an 2.69 cM interval that is co-linear with a 131 kb genomic region in Brachypodium and a 105 kb genomic region in rice. Four RGA-like sequences annotated in the orthologous Brachypodium genomic region could serve as chromosome landing target regions for map-based cloning of MlIW170.