Characterization of <Emphasis Type="Italic">Pm59</Emphasis>, a novel powdery mildew resistance gene in Afghanistan wheat landrace PI 181356

Key message

A new powdery mildew resistance gene, designated Pm59, was identified in Afghanistan wheat landrace PI 181356, and mapped in the terminal region of the long arm of chromosome 7A.

Abstract

Powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), is an important foliar disease of wheat worldwide. In the Great Plains of the USA, Bgt isolates virulent to widely used powdery mildew resistance genes, such as Pm3a, were previously identified. The objectives of this study were to characterize the powdery mildew resistance gene in Afghanistan landrace PI 181356, which exhibited high resistance to Bgt isolates collected in southern Great Plains, and identify molecular markers for marker-assisted selection. An F₂ population and F_2:3 lines derived from a cross between PI 181356 and OK1059060-126135-3 were used in this study. Genetic analysis indicated that PI 181356 carries a single dominant gene, designated Pm59, in the terminal region of the long arm of chromosome 7A. Pm59 was mapped to an interval between sequence tag site (STS) markers Xmag1759 and Xmag1714 with genetic distances of 0.4 cM distal to Xmag1759 and 5.7 cM proximal to Xmag1714. Physical mapping suggested that Pm59 is in the distal bin 7AL 0.99–1.00. Pm59 is a novel powdery mildew resistance gene, and confers resistance to Bgt isolates collected from the Great Plains and the state of Montana. Therefore, Pm59 can be used to breed powdery mildew-resistant cultivars in these regions. Xmag1759 is ideal for marker-assisted selection of Pm59 in wheat breeding.

     

<Emphasis Type="Italic">Pm61</Emphasis>: a recessive gene for resistance to powdery mildew in wheat landrace Xuxusanyuehuang identified by comparative genomics analysis

Key message

A single recessive powdery mildew resistance gene Pm61 from wheat landrace Xuxusanyuehuang was mapped within a 0.46-cM genetic interval spanning a 1.3-Mb interval of the genomic region of chromosome arm 4AL.

Abstract

Epidemics of powdery mildew incited by the biotrophic fungus Blumeria graminis f. sp. tritici (Bgt) have caused significant yield reductions in many wheat (Triticum aestivum)-producing regions. Identification of powdery mildew resistance genes is required for sustainable improvement of wheat for disease resistance. Chinese wheat landrace Xuxusanyuehuang was resistant to several Bgt isolates at the seedling stage. Genetic analysis based on the inoculation of Bgt isolate E09 on the F₁, F₂, and F_2:3 populations produced by crossing Xuxusanyuehuang to susceptible cultivar Mingxian 169 revealed that the resistance of Xuxusanyuehuang was controlled by a single recessive gene. Bulked segregant analysis and simple sequence repeat (SSR) mapping placed the gene on chromosome bin 4AL-4-0.80-1.00. Comparative genomics analysis was performed to detect the collinear genomic regions of Brachypodium distachyon, rice, sorghum, Aegilops tauschii, T. urartu, and T. turgidum ssp. dicoccoides. Based on the use of 454 contig sequences and the International Wheat Genome Sequence Consortium survey sequence of Chinese Spring wheat, four EST-SSR and seven SSR markers were linked to the gene. An F₅ recombinant inbred line population derived from Xuxusanyuehuang?×?Mingxian 169 cross was used to develop the genetic linkage map. The gene was localized in a 0.46-cM genetic interval between Xgwm160 and Xicsx79 corresponding to 1.3-Mb interval of the genomic region in wheat genome. This is a new locus for powdery mildew resistance on chromosome arm 4AL and is designated Pm61.

     

Comparative genetic mapping and genomic region collinearity analysis of the powdery mildew resistance gene Pm41

Key message

By applying comparative genomics analyses, a high-density genetic linkage map narrowed the powdery mildew resistance gene Pm41 originating from wild emmer in a sub-centimorgan genetic interval.

Abstract

Wheat powdery mildew, caused by Blumeria graminis f. sp. tritici, results in large yield losses worldwide. A high-density genetic linkage map of the powdery mildew resistance gene Pm41, originating from wild emmer (Triticum turgidum var. dicoccoides) and previously mapped to the distal region of chromosome 3BL bin 0.63–1.00, was constructed using an F_5:6 recombinant inbred line population derived from a cross of durum wheat cultivar Langdon and wild emmer accession IW2. By applying comparative genomics analyses, 19 polymorphic sequence-tagged site markers were developed and integrated into the Pm41 genetic linkage map. Ultimately, Pm41 was mapped in a 0.6 cM genetic interval flanked by markers XWGGC1505 and XWGGC1507, which correspond to 11.7, 19.2, and 24.9 kb orthologous genomic regions in Brachypodium, rice, and sorghum, respectively. The XWGGC1506 marker co-segregated with Pm41 and could be served as a starting point for chromosome landing and map-based cloning as well as marker-assisted selection of Pm41. Detailed comparative genomics analysis of the markers flanking the Pm41 locus in wheat and the putative orthologous genes in Brachypodium, rice, and sorghum suggests that the gene order is highly conserved between rice and sorghum. However, intra-chromosome inversions and re-arrangements are evident in the wheat and Brachypodium genomic regions, and gene duplications are also present in the orthologous genomic regions of Pm41 in wheat, indicating that the Brachypodium gene model can provide more useful information for wheat marker development.     

Molecular detection of a gene effective against powdery mildew in the wheat cultivar Liangxing 66

Since it was commercialized in 2008, Liangxing 66 is one of the most widely grown cultivars of wheat (Triticum aestivum L.) in winter and facultative wheat-producing regions in northern China. This cultivar displays broad-spectrum resistance to isolates of powdery mildew. To identify the powdery mildew resistance gene in Liangxing 66, genetic analysis and molecular mapping were conducted using the F₂ populations and F_2:3 families derived from the reciprocal crosses of Liangxing 66 and the susceptible cultivar Jingshuang 16. A single dominant gene, tentatively designated PmLX66, conferred resistance in Liangxing 66 to the powdery mildew isolate E09. The results of molecular mapping indicated that this gene was located on the short arm of chromosome 5D and flanked by SCAR203 and Xcfd81 at genetic distances of 0.4 and 2.8?cM, respectively, which is similar to the position of locus Pm2. However, PmLX66 and Pm2 showed different reactions to five of the 42 isolates of powdery mildew tested. Together, these results indicated that PmLX66 was most likely an allele of Pm2. Based on its superior yield and agronomic performance, in combination with powdery mildew resistance, Liangxing 66 is useful as a promising parent for control of powdery mildew and for the development of new disease-resistant cultivars.     

Pyramiding of transgenic <Emphasis Type="Italic">Pm3</Emphasis> alleles in wheat results in improved powdery mildew resistance in the field

Key message

The combined effects of enhanced total transgene expression level and allele-specificity combination in transgenic allele-pyramided Pm3 wheat lines result in improved powdery mildew field resistance without negative pleiotropic effects.

Abstract

Allelic Pm3 resistance genes of wheat confer race-specific resistance to powdery mildew (Blumeria graminis f. sp. tritici, Bgt) and encode nucleotide-binding domain, leucine-rich repeat (NLR) receptors. Transgenic wheat lines overexpressing alleles Pm3a, b, c, d, f, and g have previously been generated by transformation of cultivar Bobwhite and tested in field trials, revealing varying degrees of powdery mildew resistance conferred by the transgenes. Here, we tested four transgenic lines each carrying two pyramided Pm3 alleles, which were generated by crossbreeding of lines transformed with single Pm3 alleles. All four allele-pyramided lines showed strongly improved powdery mildew resistance in the field compared to their parental lines. The improved resistance results from the two effects of enhanced total transgene expression levels and allele-specificity combinations. In contrast to leaf segment tests on greenhouse-grown seedlings, no allelic suppression was observed in the field. Plant development and yield scores of the pyramided lines were similar to the mean scores of the corresponding parental lines, and thus, the allele pyramiding did not cause any negative effects. On the contrary, in pyramided line, Pm3b × Pm3f normal plant development was restored compared to the delayed development and reduced seed set of parental line Pm3f. Allele-specific RT qPCR revealed additive transgene expression levels of the two Pm3 alleles in the pyramided lines. A positive correlation between total transgene expression level and powdery mildew field resistance was observed. In summary, allele pyramiding of Pm3 transgenes proved to be successful in enhancing powdery mildew field resistance.

     

Identification and marker-assisted transfer of a new powdery mildew resistance gene at the <Emphasis Type="Italic">Pm4</Emphasis> locus in common wheat

Powdery mildew, a wheat (Triticum aestivum L.) foliar disease caused by Blumeria graminis (DC.) E.O. Speer f. sp. tritici, imposes a constant challenge on wheat production in areas with cool or maritime climates. This study was conducted to identify and transfer the resistance gene in the newly identified common wheat accession ‘D29’. Genetic analysis of the F₂ population derived from a cross of D29 with the susceptible elite cultivar Y158 suggested a single dominant gene is responsible for the powdery mildew resistance in this germplasm. This gene was mapped to chromosome 2AL in a region flanked by microsatellite markers Xgdm93 and Xhbg327, and co-segregated with sequence-tagged site (STS) markers Xsts_bcd1231 and TaAetPR5. An allelic test indicated that the D29 gene was allelic to the Pm4 locus. To further evaluate the resistance conferred by this gene and develop new germplasms for breeding, this gene, as well as Pm4a and Pm4b, was transferred to Y158 through backcross and marker-assisted selection. In the resistance spectrum analysis, the D29 gene displayed a resistance spectrum distinguishable from the other Pm4 alleles, including Pm4a, Pm4b, and Pm4c, and thus was designated as Pm4e. The identification of new allelic variation at the Pm4 locus is important for understanding the resistance gene evolution and for breeding wheat cultivars with powdery mildew resistance.     

Identification of <Emphasis Type="Italic">Pm58</Emphasis> from <Emphasis Type="Italic">Aegilops tauschii</Emphasis>

Key message

A novel powdery mildew-resistance gene, designated Pm58, was introgressed directly from Aegilops tauschii to hexaploid wheat, mapped to chromosome 2DS, and confirmed to be effective under field conditions. Selectable KASP? markers were developed for MAS.

Abstract

Powdery mildew caused by Blumeria graminis (DC.) f. sp. tritici (Bgt) remains a significant threat to wheat (Triticum aestivum L.) production. The rapid breakdown of race-specific resistance to Bgt reinforces the need to identify novel sources of resistance. The d-genome species, Aegilops tauschii, is an excellent source of disease resistance that is transferrable to T. aestivum. The powdery mildew-resistant Ae. tauschii accession TA1662 (2n?=?2x?=?DD) was crossed directly with the susceptible hard white wheat line KS05HW14 (2n?=?6x?=?AABBDD) followed by backcrossing to develop a population of 96 BC₂F₄ introgression lines (ILs). Genotyping-by-sequencing was used to develop a genome-wide genetic map that was anchored to the Ae. tauschii reference genome. A detached-leaf Bgt assay was used to screen BC₂F_4:6 ILs, and resistance was found to segregate as a single locus (χ?=?2.0, P value?=?0.157). The resistance gene, referred to as Pm58, mapped to chromosome 2DS. Pm58 was evaluated under field conditions in replicated trials in 2015 and 2016. In both years, a single QTL spanning the Pm58 locus was identified that reduced powdery mildew severity and explained 21% of field variation (P value?<?0.01). KASP? assays were developed from closely linked GBS-SNP markers, a refined genetic map was developed, and four markers that cosegregate with Pm58 were identified. This novel source of powdery mildew-resistance and closely linked genetic markers will support efforts to develop wheat varieties with powdery mildew resistance.

     

Identification and mapping of <Emphasis Type="Italic">MLIW30</Emphasis>, a novel powdery mildew resistance gene derived from wild emmer wheat

Powdery mildew, caused by Blumeria graminis f.sp. tritici (Bgt), is a destructive foliar disease of common wheat in areas with cool or maritime climates. Wild emmer wheat, Triticum turgidum ssp. dicoccoides, the progenitor of both domesticated tetraploid durum wheat and hexaploid bread wheat, harbors abundant genetic diversity related to resistance to powdery mildew that can be utilized for wheat improvement. An F₂ segregating population was obtained from a cross between resistant bread wheat line 2L6 and susceptible cultivar Liaochun 10, after which genetic analysis of F₂ and F₂-derived F₃ families was performed by inoculating plants with isolate Bgt E09. The results of this experiment demonstrated that powdery mildew resistance in 2L6, which was derived from wild emmer wheat accession IW30, was controlled by a single dominant gene, temporarily designated MLIW30. Nineteen SSR markers and two STS markers linked with MLIW30 were acquired by applying bulked segregant analysis. Finally, MLIW30 was located to the long arm of chromosome 4A and found to be flanked by simple sequence repeat markers XB1g2000.2 and XB1g2020.2 at 0.1 cM. Because no powdery mildew resistance gene in or derived from wild emmer wheat has been reported in wheat chromosome 4A, MLIW30 might be a novel Pm gene.     

Identification and mapping of a new powdery mildew resistance allele in the Chinese wheat landrace Hongyoumai

Powdery mildew (Pm) caused by Blumeria graminis f. sp. tritici (Bgt) is one of the world’s major wheat diseases and results in large grain yield losses. Discovery and utilization of Pm resistance genes constitute the most common strategy for wheat Pm control. Hongyoumai, a wheat landrace from Henan Province in China, has excellent resistance to infection by Bgt. In order to identify the basis of such Pm resistance, a segregating population was submitted to genetic analysis, which showed that Pm resistance in Hongyoumai was conferred by a single recessive resistance gene. This gene was temporarily named pmHYM. Molecular marker analysis, chromosomal location, resistance spectrum analysis, and an allelism test showed that pmHYM was located on the long arm of chromosome 7B (7BL), most likely representing a new recessive resistance gene allelic with Pm5e and mlXBD. By using 90-kb single-nucleotide polymorphism sequences (SNP) in the BLASTn analysis against the wheat 7BL genome sequence, 12 new simple sequence repeat (SSR) markers linked with pmHYM were developed to map pmHYM co-segregating with the marker Xmp1207 and between markers Xmp925 and Xmp1158, at genetic distances of 2.8 and 2.7 cM, respectively. In addition, physical mapping of the markers linked with pmHYM using Chinese Spring deletion lines indicated a location in the 0.86–1.00 bin of 7BL.     

Molecular Cytogenetic Identification of a New Wheat-Rye 6R Chromosome Disomic Addition Line with Powdery Mildew Resistance

Rye (Secale cereale L.) possesses many valuable genes that can be used for improving disease resistance, yield and environment adaptation of wheat (Triticum aestivum L.). However, the documented resistance stocks derived from rye is faced severe challenge due to the variation of virulent isolates in the pathogen populations. Therefore, it is necessary to develop desirable germplasm and search for novel resistance gene sources against constantly accumulated variation of the virulent isolates. In the present study, a new wheat-rye line designated as WR49-1 was produced through distant hybridization and chromosome engineering protocols between common wheat cultivar Xiaoyan 6 and rye cultivar German White. Using sequential GISH (genomic in situ hybridization), mc-FISH (multicolor fluorescence in situ hybridization), mc-GISH (multicolor GISH) and EST (expressed sequence tag)-based marker analysis, WR49-1 was proved to be a new wheat-rye 6R disomic addition line. As expected, WR49-1 showed high levels of resistance to wheat powdery mildew (Blumeria graminis f. sp. tritici, Bgt) pathogens prevalent in China at the adult growth stage and 19 of 23 Bgt isolates tested at the seedling stage. According to its reaction pattern to different Bgt isolates, WR49-1 may possess new resistance gene(s) for powdery mildew, which differed from the documented powdery mildew gene, including Pm20 on chromosome arm 6RL of rye. Additionally, WR49-1 was cytologically stable, had improved agronomic characteristics and therefore could serve as an important bridge for wheat breeding and chromosome engineering.     

Molecular mapping of powdery mildew resistance gene <Emphasis Type="Italic">PmSGD</Emphasis> in Chinese wheat landrace Shangeda using RNA-seq with bulk segregant analysis

Wheat powdery mildew, caused by the fungal pathogen Blumeria graminis f. sp. tritici (Bgt), is one of the most devastating diseases of wheat in China and causes serious yield losses. Resistance genes are urgently needed by wheat breeding programs to combat this disease. In the present study, genetic analysis of powdery mildew resistance was conducted on segregated F₂ and F_2:3 populations derived from the cross of Shangeda (providing good resistance to powdery mildew) and Chancellor (susceptible to powdery mildew). The results showed that the resistance of Shangeda to E09 was controlled by a single recessive gene, tentatively designated as PmSGD. In addition, RNA sequencing of the parental lines Shangeda and Chancellor and the corresponding bulked pools derived from homozygous resistant or susceptible F_2:3 lines was implemented to identify single-nucleotide polymorphisms (SNPs). The PmSGD gene was estimated to be located in the 240–250-Mb region of chromosome 7B based on the characteristics of putative SNP loci distributed on 21 wheat chromosomes. Among the developed SNP markers, 17 (57%) markers were linked to PmSGD flanked by SNP2-57 and SNP2-46, with genetic distances of 0.4 and 0.8 cM, respectively. The reaction patterns of Shangeda and cultivars (lines) carrying the Pm5e, Pmhym, mlxbd, and PmTm4 genes to 22 Bgt isolates indicated that PmSGD may be allelic or very closely linked to those genes. All of the SNP loci linked to PmSGD were used to test 38 cultivars with known Pm gene(s), and the results suggested that these SNP loci are useful for pyramiding PmSGD by marker-assisted selection.     

Genetic analysis of a novel broad-spectrum powdery mildew resistance gene from the wheat-<Emphasis Type="Italic">Agropyron cristatum</Emphasis> introgression line Pubing 74

Main conclusion

A novel broad-spectrum powdery mildew resistance gene PmPB74 was identified in wheat- Agropyron cristatum introgression line Pubing 74. Development of wheat cultivars with broad-spectrum, durable resistance to powdery mildew has been restricted by lack of superior genetic resources. In this study, a wheat-A. cristatum introgression line Pubing 74, originally selected from a wide cross between the common wheat cultivar Fukuhokomugi (Fukuho) and Agropyron cristatum (L.) Gaertn (2n = 4x = 28; genome PPPP), displayed resistance to powdery mildew at both the seedling and adult stages. The putative alien chromosomal fragment in Pubing 74 was below the detection limit of genomic in situ hybridization (GISH), but evidence for other non-GISH-detectable introgressions was provided by the presence of three STS markers specific to A. cristatum. Genetic analysis indicated that Pubing 74 carried a single dominant gene for powdery mildew resistance, temporarily designated PmPB74. Molecular mapping showed that PmPB74 was located on wheat chromosome arm 5DS, and flanked by markers Xcfd81 and HRM02 at genetic distances of 2.5 and 1.7 cM, respectively. Compared with other lines with powdery mildew resistance gene(s) on wheat chromosome arm 5DS, Pubing 74 was resistant to all 28 Blumeria graminis f. sp tritici (Bgt) isolates from different wheat-producing regions of northern China. Allelism tests indicated that PmPB74 was not allelic to PmPB3558 or Pm2. Our work showed that PmPB74 is a novel gene with broad resistance to powdery mildew, and hence will be helpful in broadening the genetic basis of powdery mildew resistance in wheat.

     

Chromosomal Location and Comparative Genomics Analysis of Powdery Mildew Resistance Gene Pm51 in a Putative Wheat-Thinopyrum ponticum Introgression Line

Powdery mildew (PM) is a very destructive disease of wheat (Triticum aestivum L.). Wheat-Thinopyrum ponticum introgression line CH7086 was shown to possess powdery mildew resistance possibly originating from Th. ponticum. Genomic in situ hybridization and molecular characterization of the alien introgression failed to identify alien chromatin. To study the genetics of resistance, CH7086 was crossed with susceptible genotypes. Segregation in F₂ populations and F_2:3 lines tested with Chinese Bgt race E09 under controlled conditions indicated that CH7086 carries a single dominant gene for powdery mildew resistance. Fourteen SSR and EST-PCR markers linked with the locus were identified. The genetic distances between the locus and the two flanking markers were 1.5 and 3.2 cM, respectively. Based on the locations of the markers by nullisomic-tetrasomic and deletion lines of ‘Chinese Spring’, the resistance gene was located in deletion bin 2BL-0.89-1.00. Conserved orthologous marker analysis indicated that the genomic region flanking the resistance gene has a high level of collinearity to that of rice chromosome 4 and Brachypodium chromosome 5. Both resistance specificities and tests of allelism suggested the resistance gene in CH7086 was different from previously reported powdery mildew resistance genes on 2BL, and the gene was provisionally designated PmCH86. Molecular analysis of PmCH86 compared with other genes for resistance to Bgt in the 2BL-0.89-1.00 region suggested that PmCH86 may be a new PM resistance gene, and it was therefore designated as Pm51. The closely linked flanking markers could be useful in exploiting this putative wheat-Thinopyrum translocation line for rapid transfer of Pm51 to wheat breeding programs.     

Evolutionary divergence of the rye <Emphasis Type="Italic">Pm17</Emphasis> and <Emphasis Type="Italic">Pm8</Emphasis> resistance genes reveals ancient diversity

Key message

We have isolated a novel powdery mildew resistance gene in wheat that was originally introgressed from rye. Further analysis revealed evolutionary divergent history of wheat and rye orthologous resistance genes.

Abstract

Wheat production is under constant threat from a number of fungal pathogens, among them is wheat powdery mildew (Blumeria graminis f. sp. tritici). Deployment of resistance genes is the most economical and sustainable method for mildew control. However, domestication and selective breeding have narrowed genetic diversity of modern wheat germplasm, and breeders have relied on wheat relatives for enriching its gene pool through introgression. Translocations where the 1RS chromosome arm was introgressed from rye to wheat have improved yield and resistance against various pathogens. Here, we isolated the Pm17 mildew resistance gene located on the 1RS introgression in wheat cultivar ‘Amigo’ and found that it is an allele or a close paralog of the Pm8 gene isolated earlier from ‘Petkus’ rye. Functional validation using transient and stable transformation confirmed the identity of Pm17. Analysis of Pm17 and Pm8 coding regions revealed an overall identity of 82.9% at the protein level, with the LRR domains being most divergent. Our analysis also showed that the two rye genes are much more diverse compared to the variants encoded by the Pm3 gene in wheat, which is orthologous to Pm17/Pm8 as concluded from highly conserved upstream sequences in all these genes. Thus, the evolutionary history of these orthologous loci differs in the cereal species rye and wheat and demonstrates that orthologous resistance genes can take different routes towards functionally active genes. These findings suggest that the isolation of Pm3/Pm8/Pm17 orthologs from other grass species, additional alleles from the rye germplasm as well as possibly synthetic variants will result in novel resistance genes useful in wheat breeding.

     

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.     

Lr67/Yr46 confers adult plant resistance to stem rust and powdery mildew in wheat

Key message

We demonstrate that Lr67/Yr46 has pleiotropic effect on stem rust and powdery mildew resistance and is associated with leaf tip necrosis. Genes are designated as Sr55, Pm46 and Ltn3 , respectively.

Abstract

Wheat (Triticum aestivum) accession RL6077, known to carry the pleiotropic slow rusting leaf and yellow rust resistance genes Lr67/Yr46 in Thatcher background, displayed significantly lower stem rust (P. graminis tritici; Pgt) and powdery mildew (Blumeria graminis tritici; Bgt) severities in Kenya and in Norway, respectively, compared to its recurrent parent Thatcher. We investigated the resistance of RL6077 to stem rust and powdery mildew using Avocet × RL6077 F₆ recombinant inbred lines (RILs) derived from two photoperiod-insensitive F₃ families segregating for Lr67/Yr46. Greenhouse seedling tests were conducted with Mexican Pgt race RTR. Field evaluations were conducted under artificially initiated stem rust epidemics with Pgt races RTR and TTKST (Ug99 + Sr24) at Ciudad Obregon (Mexico) and Njoro (Kenya) during 2010–2011; and under natural powdery mildew epiphytotic in Norway at Ås and Hamar during 2011 and 2012. In Mexico, a mean reduction of 41 % on stem rust severity was obtained for RILs carrying Lr67/Yr46, compared to RILs that lacked the gene, whereas in Kenya the difference was smaller (16 %) but significant. In Norway, leaf tip necrosis was associated with Lr67/Yr46 and RILs carrying Lr67/Yr46 showed a 20 % reduction in mean powdery mildew severity at both sites across the 2 years of evaluation. Our study demonstrates that Lr67/Yr46 confers partial resistance to stem rust and powdery mildew and is associated with leaf tip necrosis. The corresponding pleiotropic, or tightly linked, genes, designated as Sr55, Pm46, and Ltn3, can be utilized to provide broad-spectrum durable disease resistance in wheat.     

<Emphasis Type="Italic">Pm62</Emphasis>, an adult-plant powdery mildew resistance gene introgressed from <Emphasis Type="Italic">Dasypyrum villosum</Emphasis> chromosome arm 2VL into wheat

Key message

Pm62, a novel adult-plant resistance (APR) gene against powdery mildew, was transferred from D. villosum into common wheat in the form of Robertsonian translocation T2BS.2VL#5.

Abstract

Powdery mildew, which is caused by the fungus Blumeria graminis f. sp. tritici, is a major disease of wheat resulting in substantial yield and quality losses in many wheat production regions of the world. Introgression of resistance from wild species into common wheat has application for controlling this disease. A Triticum durum-Dasypyrum villosum chromosome 2V#5 disomic addition line, N59B-1 (2n?=?30), improved resistance to powdery mildew at the adult-plant stage, which was attributable to chromosome 2V#5. To transfer this resistance into bread wheat, a total of 298 BC₁F₁ plants derived from the crossing between N59B-1 and Chinese Spring were screened by combined genomic in situ hybridization and fluorescent in situ hybridization, 2V-specific marker analysis, and reaction to powdery mildew to confirm that a dominant adult-plant resistance gene, designated as Pm62, was located on chromosome 2VL#5. Subsequently, the 2VL#5 (2D) disomic substitution line (NAU1825) and the homozygous T2BS.2VL#5 Robertsonian translocation line (NAU1823), with normal plant vigor and full fertility, were identified by molecular and cytogenetic analyses of the BC₁F₂ generation. The effects of the T2BS.2VL#5 recombinant chromosome on agronomic traits were also evaluated in the F₂ segregation population. The results suggest that the translocated chromosome may have no distinct effect on plant height, 1000-kernel weight or flowering period, but a slight effect on spike length and seeds per spike. The translocation line NAU1823 has being utilized as a novel germplasm in breeding for powdery mildew resistance, and the effects of the T2BS.2VL#5 recombinant chromosome on yield-related and flour quality characters will be further assessed.

     

A new powdery mildew resistance allele at the Pm4 wheat locus transferred from einkorn (Triticum monococcum)

Powdery mildew is one of the most destructive foliar diseases of wheat. A set of differential Blumeria graminis f.sp. tritici (Bgt) isolates was used to test the powdery mildew response of a Triticum monococcum-derived resistant hexaploid line, Tm27d2. Segregation analysis of 95 F_2:3 lines from a Chinese Spring/Tm27d2 cross revealed that the resistance of Tm27d2 is controlled by a single dominant gene. Using monosomic analysis and a molecular mapping approach, the resistance gene was localized to the terminal end of chromosome 2AL. The linkage map of chromosome 2AL consisted of nine simple sequence repeat markers and one sequence-tagged site (STS) marker (ResPm4) indicative for the Pm4 locus. According to the differential reactions of 19 wheat cultivars/lines with known powdery mildew resistance genes to 13 Bgt isolates, Tm27d2 carried a new resistance specificity. The complete association of the resistance allele with STS marker ResPm4 indicated that it represented a new allele at the Pm4 locus. This new allele was designated Pm4d. The two flanking markers Xgwm526 and Xbarc122 closely linked to Pm4d at genetic distances of 3.4 and 1.0 cM, respectively, are present in chromosome bin 2AL1-0.85-1.00.     

Molecular mapping of a powdery mildew resistance gene in common wheat landrace Baihulu and its allelism with Pm24

Powdery mildew is one of the most devastating diseases of wheat in areas with cool and maritime climates. Chinese wheat landrace Baihulu confers a high level of resistance against a wide range of Blumeria graminis DC f. sp. tritici (Bgt) races, especially those currently prevailing in Shaanxi. The objectives of this study were to determine the chromosome bin location of the mlbhl gene from Baihulu and its allelism with Pm24. To investigate the inheritance of powdery mildew resistance and detect adjacent molecular markers, we constructed a segregating population of 301 F₂ plants and corresponding F_2:3 families derived from Baihulu/Shaanyou 225. Genetic analysis revealed that a single dominant gene was responsible for seedling stage powdery mildew resistance in Baihulu. A genetic map comprising Xgwm106, Xgwm337, Xgwm1675, Xgwm603, Xgwm789, Xbarc229, Xgpw4503, Xcfd72, Xcfd83, Xcfd59, Xcfd19, and mlbhl spanned 28.2?cM on chromosome 1D. Xgwm603/Xgwm789 and Xbarc229 were flanking markers tightly linked to mlbhl at genetic distances of 1.5 and 1.0?cM, respectively. The mlbhl locus was located in chromosome bin 1DS 0.59–1.00 delimited by the SSR markers Xgwm337 and Xbarc229. When tested with a differential array of 23 Bgt isolates Baihulu displayed a response pattern that was clearly distinguishable from that of Chiyacao and varieties or lines possessing documented Pm genes. Allelism analysis indicated that mlbhl is a new gene, either allelic or closely linked with Pm24. The new gene was designated Pm24b.     

普通小麦99-2439中的白粉病抗性遗传

普通冬小麦品系99-2439在郑州连续4年对田间白粉菌(Blumeria graminis sp.tritici)表现高抗,但其抗性基因来源不清.通过染色体C-分带和IRS染色体特异性SCAR标记鉴定,表明它是一个小麦-黑麦(Triticum aestivum-Secale cereale)lBL/1RS异易位系.通过对中国春×99-2439杂交F2代分离群体抗性鉴定和1RS染色体臂检测结果分析,证明该抗病基因不在1RS染色体臂上.用单孢小麦白粉菌分离株对其抗性遗传进行研究,结果表明,99-2439的白粉病抗性由一对小种专化、隐性抗病基因控制.由于携带Pm5a的Hope/8Cc对中国的21个小麦白粉菌分离菌株均高度感病,而99-2439高抗混和白粉菌和5个单孢分离菌株,所以,99-2439所携带的抗白粉病基因不同于Pm5a.