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.

     

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.

     

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.

     

<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.

     

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.

     

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.     

<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.

     

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.

     

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.

     

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.     

Mapping of novel powdery mildew resistance gene(s) from <Emphasis Type="Italic">Agropyron cristatum</Emphasis> chromosome 2P

Key message

A physical map of Agropyron cristatum 2P chromosome was constructed for the first time and the novel powdery mildew resistance gene(s) from chromosome 2P was(were) also mapped.

Abstract

Agropyron cristatum (L.) Gaertn. (2n = 28, PPPP), a wild relative of common wheat, is highly resistant to powdery mildew. Previous studies showed that wheat-A. cristatum 2P disomic addition line II-9-3 displayed high resistance to powdery mildew, and the resistance was attributable to A. cristatum chromosome 2P. To utilize and physically map the powdery mildew resistance gene(s), 15 wheat-A. cristatum 2P translocation lines and three A. cristatum 2P deletion lines with different chromosomal segment sizes, obtained from II-9-3 using ⁶⁰Co-γ ray irradiation, were characterized using cytogenetic and molecular marker analysis. A. cristatum 2P chromosomal segments in the translocations were translocated to different wheat chromosomes, including 1A, 4A, 5A, 6A, 7A, 1B, 2B, 3B, 7B, 3D, 4D, and 6D. A physical map of the 2P chromosome was constructed with 82 STS markers, consisting of nine bins with 34 markers on 2PS and eight bins with 48 markers on 2PL. The BC₁F₂ populations of seven wheat-A. cristatum 2P translocation lines (2PT-3, 2PT-4, 2PT-5, 2PT-6, 2PT-8, 2PT-9, and 2PT-10) were developed by self-pollination, tested with powdery mildew and genotyped with 2P-specific STS markers. From these results, the gene(s) conferring powdery mildew resistance was(were) located on 2PL bin FL 0.66–0.86 and 19 2P-specific markers were identified in this bin. Moreover, two new powdery mildew-resistant translocation lines (2PT-4 and 2PT-5) with small 2PL chromosome segments were obtained. The newly developed wheat lines with powdery mildew resistance and the closely linked molecular markers will be valuable for wheat disease breeding in the future.

     

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.     

Mapping and validation of a new QTL for adult-plant resistance to powdery mildew in Chinese elite bread wheat line Zhou8425B

Key message

Four QTLs for adult-plant resistance to powdery mildew were mapped in the Zhou8425B/Chinese Spring population, and a new QTL on chromosome 3B was validated in 103 wheat cultivars derived from Zhou8425B.

Abstract

Zhou8425B is an elite wheat (Triticum aestivum L.) line widely used as a parent in Chinese wheat breeding programs. Identification of genes for adult-plant resistance (APR) to powdery mildew in Zhou8425B is of high importance for continued controlling the disease. In the current study, the high-density Illumina iSelect 90K single-nucleotide polymorphism (SNP) array was used to map quantitative trait loci (QTL) for APR to powdery mildew in 244 recombinant inbred lines derived from the cross Zhou8425B/Chinese Spring. Inclusive composite interval mapping identified QTL on chromosomes 1B, 3B, 4B, and 7D, designated as QPm.caas-1BL.1, QPm.caas-3BS, QPm.caas-4BL.2, and QPm.caas-7DS, respectively. Resistance alleles at the QPm.caas-1BL.1, QPm.caas-3BS, and QPm.caas-4BL.2 loci were contributed by Zhou8425B, whereas that at QPm.caas-7DS was from Chinese Spring. QPm.caas-3BS, likely to be a new APR gene for powdery mildew resistance, was detected in all four environments. One SNP marker closely linked to QPm.caas-3BS was transferred into a semi-thermal asymmetric reverse PCR (STARP) marker and tested on 103 commercial wheat cultivars derived from Zhou8425B. Cultivars with the resistance allele at the QPm.caas-3BS locus had averaged maximum disease severity reduced by 5.3%. This STARP marker can be used for marker-assisted selection in improvement of the level of powdery mildew resistance in wheat breeding.

     

<Emphasis Type="Italic">VpUR9</Emphasis>, a novel RING-type ubiquitin ligase gene from <Emphasis Type="Italic">Vitis pseudoreticulata</Emphasis>, is involved in powdery mildew response in transgenic <Emphasis Type="Italic">V. vinifera</Emphasis> plants

Ubiquitination plays important roles in disease resistance in plants. We report the identification and functional characterization of the RING-type ubiquitin ligase gene VpUR9 from Chinese wild Vitis pseudoreticulata accession Baihe-35-1. VpUR9, encodes 164 amino acids and possesses a RING conserved motif. It is homologously cloned from the cDNA library of the high powdery mildew (Erysiphe necator [Schw.] Burr) resistant V. pseudoreticulata accession Baihe-35-1 inoculated with E. necator. The gene is induced in response to powdery mildew and salicylic acid. VpUR9 fused with FLAG-tag controlled by 35S promoter was transformed into 15 regenerated V. vinifera L. cv. Red Globe lines via Agrobacterium tumefaciens-mediated transformation. Twelve of these lines were confirmed by Western blot of FLAG-tag. As a result, the powdery mildew-resistance of Red Globe transformed with VpUR9 was repressed. Furthermore, the expression of some disease-resistant related genes (NPR1, PR1, PR10 and PAL) of the transgenic Red Globe declined compared with wild type grapes when inoculated with powdery mildew or salicylic acid. When treated with jasmonic acid methyl ester, its PR1 gene expression decreased, while the expressions of NPR1, PR10 and PAL all increased, contrasting with the wild type grape.     

Development and validation of breeder-friendly KASPar markers for <Emphasis Type="Italic">er1</Emphasis>, a powdery mildew resistance gene in pea (<Emphasis Type="Italic">Pisum sativum</Emphasis> L.)

Powdery mildew of pea is caused by Erysiphe pisi DC and is a serious threat to pea (Pisum sativum L.) production throughout much of the world. Development and utilization of genetic resistance to powdery mildew is considered an effective and sustainable strategy to manage this disease. One gene, er1, conferring powdery mildew resistance, was previously cloned and sequenced, and the functional markers for each resistance allele were reported. Allele-specific DNA markers are efficient and powerful tools to facilitate crop improvement and new cultivar development in breeding programs. However, extensive application of these markers is limited by gel-associated obstacles. In this study, eight breeder-friendly kompetitive allele-specific PCR (KASPar) markers were developed to overcome the problems of gel-based markers and increase the efficiency of genotypic screening. In order to identify additional pea germplasm with powdery mildew resistance, these KASPar markers were deployed and used to genotype a pea collection derived from the USDA pea single-plant (PSP) collection. Simultaneously, a phenotypic screening and a genotypic validation using the corresponding gel-based functional markers were conducted on the PSP collection. One pea accession, PI 142775, was identified by both phenotyping and genotyping to carry the allele er1-1 for powdery mildew resistance, indicating that the KASPar assay is an efficient and robust tool for breeding for powdery mildew resistance.     

A microsatellite sequence in the fifth intron provides a broad-spectrum SSR marker for multiple alleles of the <Emphasis Type="Italic">er1</Emphasis>/<Emphasis Type="Italic">PsMLO1</Emphasis> powdery mildew resistance gene in <Emphasis Type="Italic">Pisum sativum</Emphasis> L.

Powdery mildew caused by the biotrophic ascomycete fungus Erysiphe pisi Syd. is one the most devastating diseases of peas (Pisum sativum L.) with enormous impact in seed production. The most efficient genetic resistance to this disease, so far identified, is conferred by the naturally occurring or experimentally induced by chemical mutagenesis recessive state of the locus er1. Genetically mapped over 2 decades ago, this gene was recently identified as a homolog of the barley (Hordeum sativum L.) powdery mildew resistance gene MLO, and renamed as PsMLO1. The broad wide resistance conferred by the er1/PsMLO1 locus was found to be a consequence of the loss of function of the encoded PsMLO1 protein. After the publication of the expressed sequence of this gene by another research group, we published the genomic sequences of this gene which harbors a relatively long (TA) microsatellite sequence (SSR) in the fifth intron. SSR markers based on this highly polymorphic microsatellite can be used for marker-assisted selection in multiple pea powdery mildew resistance breeding programs involving the er1/PsMLO1 resistance, except in the rare circumstances where the progenitor lines are monomorphic for the microsatellite sequence.     

Adult plant stripe rust resistance gene <Emphasis Type="Italic">Yr71</Emphasis> maps close to <Emphasis Type="Italic">Lr24</Emphasis> in chromosome 3D of common wheat

Australian cultivar Sunco carries three adult plant stripe rust resistance genes. One of these genes corresponded to Yr18 in chromosome 7DS; the second, YrCK, was mapped on chromosome 2D. Here, we describe the characterization of the third adult plant resistance (APR) gene from Sunco. Sunco/2*Avocet S-derived lines SA65 (resistant) and SA67 (susceptible) were crossed and a recombinant inbred line F₆ population was generated. Monogenic segregation among SA65/SA67-derived RIL population was demonstrated and the resistance locus was designated YrSA3. Selective genotyping using an iSelect 90 K Infinium SNP array and SSR markers located YrSA3 on chromosome 3D. Development of KASP markers for SNP loci showing association with YrSA3 allowed construction of a genetic map harboring the resistance gene. Ten KASP markers (KASP_8306, KASP_9142, KASP_10438, KASP_16434, KASP_17207, KASP_20836, KASP_23518, KASP_23615, KASP_57983 and KASP_63653), one SSR marker (gwm114b) and Lr24/Sr24 were mapped 1.8 cM distal to YrSA3. Comparison of marker data indicated that the previously named seedling stripe rust resistance gene Yr45 was located proximal to YrSA3, and therefore the latter was formally designated Yr71. Two recombinants carrying Lr24/Sr24 and Yr71 in combination were identified for use as donor sources in wheat breeding programs. The robustness of gwm114b, KASP_16434, KASP_17207 and KASP_20836 for marker-assisted selection of these genes was demonstrated through tests on 74 Australian wheat cultivars.