Identification of a Pm4 Allele as a Powdery Mildew Resistance Gene in Wheat Line Xiaomaomai

The wheat powdery mildew resistance gene Pm4 also confers resistance to wheat blast

Wheat blast, caused by the fungus Magnaporthe oryzae, threatens global cereal production since its emergence in Brazil in 1985 and recently spread to Bangladesh and Zambia. Here we demonstrate that the AVR-Rmg8 effector, common in wheat-infecting isolates, is recognized by the gene Pm4, previously shown to confer resistance to specific races of Blumeria graminis f. sp. tritici, the cause of powdery mildew of wheat. We show that Pm4 alleles differ in their recognition of different AVR-Rmg8 alleles, and some confer resistance only in seedling leaves but not spikes, making it important to select for those alleles that function in both tissues. This study has identified a gene recognizing an important virulence factor present in wheat blast isolates in Bangladesh and Zambia and represents an important first step towards developing durably resistant wheat cultivars for these regions.

QTL Mapping of Adult Plant Resistance to Powdery Mildew in Chinese Wheat Landrace Baidatou

Wheat powdery mildew, caused by the biotrophic fungus Blumeria graminis f. sp. tritici (Bgt), is one of the most devastating diseases affecting wheat throughout the world. Breeding and growing resistant wheat cultivars is one of the most economic and effective methods to control the disease, and as such, identifying and mapping the new and effective resistance genes is critical. Baidatou, a Chinese wheat landrace, shows excellent field resistance to powdery mildew. To identify the resistance gene(s) in Baidatou, 170 F7:8 recombinant inbred lines (RILs) derived from the cross Mingxian 169/Baidatou were evaluated for powdery mildew response at the adult-plant stage in the experimental fields in Yangling (YL) of Shaanxi Province and Tianshui (TS) in Gansu Province in 2019, 2020, and 2021. The relative area under disease progress curve (rAUDPC) of Mingxian 169/Baidatou F7:8 RILs indicated that the resistance of Baidatou to powdery mildew was controlled by quantitative trait loci (QTLs). Based on bulk segregation analysis combined with the 660K single nucleotide polymorphism (SNP) array and genotyping by target sequencing (16K SNP) of the entire RIL population, two QTLs, QPmbdt.nwafu-2AS and QPmbdt.nwafu-3AS, were identified, and these accounted for up to 44.5% of the phenotypic variation. One of the QTLs was located on the 3.32 cM genetic interval on wheat chromosome 2AS between the kompetitive allele-specific PCR markers AX-111012288 and AX_174233809, and another was located on the 9.6 cM genetic interval on chromosome 3AS between the SNP markers 3A_684044820 and 3A_686681822. These markers could be useful for successful breeding of powdery mildew resistance in wheat.

Field response and molecular screening of European wheat germplasm against powdery mildew at the Himalayan region of Pakistan

Wheat powdery mildew possesses a significant threat to wheat crops not only on a global scale but also in the northern region of Pakistan. Recognizing the need for effective measures, the exploration and utilization of exotic germplasm take on critical importance. To address this, a series of trials were made to investigate the response of 30 European (EU) lines, in addition to the local checks (Siran, Atta-Habib (AH) and Ghanimat-e-IBGE) against wheat powdery mildew at the Himalayan region of Pakistan. The study involved field testing from 2018 to 2022 across multiple locations, resulting in 38 different environments (location × year). In addition to field evaluations, molecular genotyping was also performed. The disease was absent on the tested lines during 2018, 2019, and 2020 whereas it ranged from 0 to 100% at Chitral location during 2021, where 100% was observed only for one EU wheat line "Matrix." The disease prevailed only at Gilgit location (0-60% for EU wheat line "F236") and at Nagar location (0-10% for EU wheat lines Substance and Nelson) during the disease season of 2022. Most of the EU wheat lines showed very low ACI values, due to an overall low disease pressure. Matrix showed the maximum ACI (1.54) followed by Ritter (1.25) and Bli_autrichion (0.87), whereas the minimum (0.1) was for Substance, JB_Asano, and KWS_Loft followed by Canon (0.19), all exhibiting partial resistance. The molecular marker-based screening revealed that Pm38 was the most prevalent and detected in 100% of wheat lines followed by Pm39 (60%) and Pm8 (30%). Six wheat lines (20%) possessed all three Pm genes (Pm8, Pm38, and Pm39) concurrently. The variability observed in this study can be utilized in future breeding efforts aimed at developing resistant wheat varieties.

QTL Mapping Reveals Both All-Stage and Adult-Plant Resistance to Powdery Mildew in Chinese Elite Wheat Cultivars

Powdery mildew caused by Blumeria graminis f. sp. tritici is a threat to wheat production in China. Mapping quantitative trait loci (QTL) for resistance to powdery mildew and developing breeder-friendly markers are important initial steps in breeding resistant cultivars. An all-stage resistance gene and several QTL were identified using a population of 254 recombinant inbred lines developed from a Jingdong 8/Aikang 58 cross. The population was evaluated for powdery mildew resistance across six field environments over three consecutive growing seasons utilizing two different mixtures of B. graminis f. sp. tritici isolates, named #Bgt-HB and #Bgt-BJ. Using genotypic data obtained from the Wheat TraitBreed 50K single-nucleotide polymorphism array, seven stable QTL were identified on chromosome arms 1DL, 2AL, 2DS, 4DL, 5AL, 6BL.1, and 6BL.2. The QTL on 2AL conferred all-stage resistance to B. graminis f. sp. tritici race E20 in greenhouse tests and explained up to 52% of the phenotypic variance in field trials but was resistant only against #Bgt-HB. The gene involved in this QTL was predicted to be Pm4a based on genome location and gene sequence. QPmja.caas-1DL, QPmja.caas-4DL, and QPmja.caas-6BL.1 were identified as potentially new QTL for powdery mildew resistance. QPmja.caas-2DS and QPmja.caas-6BL.1 were effective against both B. graminis f. sp. tritici mixtures, indicating their probable broad-spectrum resistance. A Kompetitive allele-specific PCR marker closely linked to QPmja.caas-2DS was developed and validated in a panel of 286 wheat cultivars. Because both Jingdong 8 and Aikang 58 have been leading cultivars and breeding parents, the QTL and marker reported represent valuable resources for wheat researchers and breeders.

Identification of a Novel Pm65 Allele Conferring a Wide Spectrum of Resistance to Powdery Mildew in Wheat Accession PI 351817

Powdery mildew is caused by the highly adaptive biotrophic fungus Blumeria graminis f. sp. tritici infecting wheat worldwide. Novel powdery mildew resistance genes are urgently needed that can be used rapidly in wheat cultivar development with minimal disruption of trait advances elsewhere. PI 351817 is a German cultivar exhibiting a wide spectrum of resistance to B. graminis f. sp. tritici isolates collected from different wheat-growing regions of the United States. Evaluation of an F2 population and 237 F2:3 lines derived from OK1059060-2C14 × PI 351817 for responses to B. graminis f. sp. tritici isolate OKS(14)-B-3-1 identified a single dominant gene, designated Pm351817, for powdery mildew resistance in PI 351817. Using bulked segregant analysis (BSA) and simple sequence repeat (SSR) markers, Pm351817 was mapped in the terminal region of the long arm of chromosome 2A. Deep sequencing of the genotyping-by-sequencing libraries of the two parental lines identified a set of single-nucleotide polymorphism (SNP) markers in the 2AL candidate gene region. Those SNP markers was subsequently converted to Kompetitive allele-specific PCR (KASP) markers for genotyping the mapping population. Linkage analysis delimited Pm351817 to a 634-kb interval between Stars-KASP656 (771,207,512 bp) and Stars-KASP662 (771,841,609 bp) on 2AL, based on the Chinese Spring reference sequence IWGSC RefSeq v 2.1. Tests of allelism indicated that Pm351817 is located at the Pm65 locus. Pm351817 shows resistance to all B. graminis f. sp. tritici isolates used in this study and can be used to enhance powdery mildew resistance in the United States. KASP markers flanking Pm351817 can be used to select Pm351817 in wheat breeding programs after further tests for polymorphism.

Fighting wheat powdery mildew: from genes to fields

KEY MESSAGE

Host resistance conferred by Pm genes provides an effective strategy to control powdery mildew. The study of Pm genes helps modern breeding develop toward more intelligent and customized. Powdery mildew of wheat is one of the most destructive diseases seriously threatening the crop yield and quality worldwide. The genetic research on powdery mildew (Pm) resistance has entered a new era. Many Pm genes from wheat and its wild and domesticated relatives have been mined and cloned. Meanwhile, modern breeding strategies based on high-throughput sequencing and genome editing are emerging and developing toward more intelligent and customized. This review highlights mining and cloning of Pm genes, molecular mechanism studies on the resistance and avirulence genes, and prospects for genomic-assisted breeding for powdery mildew resistance in wheat.

Genetic basis of resistance against powdery mildew in the wheat cultivar "Tabasco"

European winter wheat cultivar "Tabasco" was reported to have resistance to powdery mildew disease caused by Blumeria graminis f. sp. tritici (Bgt) in China. In previous studies, Tabasco was reported to have the resistance gene designated as Pm48 on the short arm of chromosome 5D when a mapping population was phenotyped with pathogen isolate Bgt19 collected in China and was genotyped with simple sequence repeat (SSR) markers. In this study, single-nucleotide polymorphism (SNP) chips were used to rapidly determine the resistance gene by mapping a new F2 population that was developed from Tabasco and a susceptible cultivar "Ningmaizi119" and inoculated with pathogen isolate NCF-D-1-1 that was collected in the USA. The segregation of resistance in the population was found to link with Pm2 which was identified in Tabasco. Therefore, it was concluded that the previously reported Pm48 on chromosome arm 5DS in Tabasco should be the Pm2 gene on the same chromosome. The Pm2 was also found in European cultivars "Mattis" and "Claire" but not in any of the accessions from diploid wheat Aegilops tauschii or modern cultivars such as "Gallagher," "Smith's Gold," and "OK Corral" being used in the Great Plains in the USA. A KASP marker was developed to track the resistance allele Pm2 in wheat breeding.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11032-023-01402-3.

Resistance to Powdery Mildew Is Conferred by Different Genetic Loci at the Adult-Plant and Seedling Stages in Winter Wheat Line Tianmin 668

Winter wheat line Tianmin 668 was crossed with susceptible cultivar Jingshuang 16 to develop 216 recombinant inbred lines (RILs) for dissecting its adult-plant resistance (APR) and all-stage resistance (ASR) against powdery mildew. The RIL population was genotyped on a 16K genotyping by target sequencing single-nucleotide polymorphism array and phenotyped in six field trials and in the greenhouse. Three loci-QPmtj.caas-2BL, QPmtj.caas-2AS, and QPmtj.caas-5AL-conferring APR to powdery mildew were detected on chromosomes 2BL, 2AS, and 5AL, respectively, of Tianmin 668. The effect of resistance to powdery mildew for QPmtj.caas-2BL was greater than that of the other two loci. A Kompetitive allele-specific PCR marker specific for QPmtj.caas-2BL was developed and verified on 402 wheat cultivars or breeding lines. Results of virulence and avirulence patterns to 17 Blumeria graminis f. sp. tritici isolates, bulked segregant analysis-RNA-sequencing, and a genetic linkage mapping identified a resistance allele at locus Pm4 in Tianmin 668 based on the seedling phenotypes of the RIL population. The PCR-based DNA sequence alignment and cosegregation of the functional marker with the phenotypes of the RIL population demonstrated that Pm4d was responsible for the ASR to isolate Bgt1 in Tianmin 668. The dissection of genetic loci for APR and ASR may facilitate the application of Tianmin 668 in developing powdery mildew-resistant wheat cultivars.

Harnessing Knowledge from Plant Functional Genomics and Multi-Omics for Genetic Improvement

Plant biology research has currently entered the post-genomics era with the advances in genomic technologies [...].

Fine Mapping and Candidate Gene Analysis of Pm36, a Wild Emmer-Derived Powdery Mildew Resistance Locus in Durum Wheat

Powdery mildew (PM) is an economically important foliar disease of cultivated cereals worldwide. The cultivation of disease-resistant varieties is considered the most efficient, sustainable and economical strategy for disease management. The objectives of the current study were to fine map the chromosomal region harboring the wild emmer PM resistance locus Pm36 and to identify candidate genes by exploiting the improved tetraploid wheat genomic resources. A set of backcross inbred lines (BILs) of durum wheat were genotyped with the SNP 25K chip array and comparison of the PM-resistant and susceptible lines defined a 1.5 cM region (physical interval of 1.08 Mb) harboring Pm36. The genetic map constructed with F_2:3 progenies derived by crossing the PM resistant line 5BIL-42 and the durum parent Latino, restricted to 0.3 cM the genetic distance between Pm36 and the SNP marker IWB22904 (physical distance 0.515 Mb). The distribution of the marker interval including Pm36 in a tetraploid wheat collection indicated that the positive allele was largely present in the domesticated and wild emmer Triticum turgidum spp. dicoccum and ssp. dicoccoides. Ten high-confidence protein coding genes were identified in the Pm36 region of the emmer, durum and bread wheat reference genomes, while three added genes showed no homologous in the emmer genome. The tightly linked markers can be used for marker-assisted selection in wheat breeding programs, and as starting point for the Pm36 map-based cloning.

Pm SN15218 : A Potential New Powdery Mildew Resistance Gene on Wheat Chromosome 2AL

Powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), is a devastating fungal disease that seriously damages the yield and quality of wheat in many regions of the world. Identifying new resistance genes and breeding new resistant varieties are effective methods to control this disease. The breeding line SN15218 shows good resistance against powdery mildew. We, therefore, developed an F2 population and 287 F2:3 families crossed between SN15218 and the powdery mildew susceptible cultivar Huixianhong (HXH). Genetic analysis indicated that a single dominant gene, designated herein Pm SN15218 , conferred resistance to the Bgt isolate E09 in SN15218. Bulked segregant RNA-Seq (BSR-Seq) analysis revealed that Pm SN15218 is located in a ∼25-Mb interval on chromosome 2AL. Using the polymorphism information between SN15218 and HXH, we developed 13 polymerase chain reaction (PCR) markers and mapped this gene to a 0.5-cM genetic interval between the two flanking markers PmM12 and PmM14, corresponding to a 6.01-Mb physical region in the Chinese Spring reference genome. The results of molecular marker analysis, allelic tests of resistance spectrum, and DNA resequencing indicated that Pm SN15218 is distinct from the known resistance gene Pm4b on 2AL.