Fine mapping of an adult-plant resistance gene to powdery mildew in soybean cultivar Zhonghuang 24

Powdery mildew(PM),caused by the fungus Microsphaera diffusa,causes severe yield losses in soybean[Glycine max(L.)Merr.]under suitable environmental conditions.Identifying resistance genes and developing resistant cultivars may prevent soybean PM damage.In this study,analysis of F_(1),F_(2),and F8:11 recombinant inbred line(RIL)populations derived from the cross between Zhonghuang 24(ZH24)and Huaxia 3(HX3)indicated that adult-plant resistance(APR)to powdery mildew in the soybean cultivar(cv.)ZH24 was controlled by a single dominant locus.A high-density genetic linkage map of the RIL population was used for fine mapping.The APR locus in ZH24 was mapped to a 281-kb genomic region on chromosome 16.Using 283 susceptible plants of another F2 population,the candidate region was finemapped to a 32.8-kb genomic interval flanked by the markers InDel14 and Gm16_428.The interval harbored five genes,including four disease resistance(R)-like genes,according to the Williams 82.a2.v1 reference genome.Quantitative real-time PCR assays of candidate genes revealed that the expression levels of Glyma.16g214300 and Glyma.16g214500 were changed by M.diffusa infection and might be involved in disease defense.Rmd_B13 showed all-stage resistance(ASR)to PM in soybean cv.B13.An allelism test in the F2 segregating population from the cross of ZH24 × B13 suggested that the APR locus Rmd_ZH24 and the ASR locus Rmd_B13 may be allelic or tightly linked.These results provide a reference marker-assisted selection in breeding programs.

Genetics,resistance mechanism,and breeding of powdery mildew resistance in cucumbers(Cucumis sativus L.)

Cucumber is an important vegetable worldwide,and powdery mildew(PM)is a common and serious disease of cucumbers.Breeding disease-resistant cucumber varieties is the most advantageous strategy to control this disease.In recent years,exploration and identification of cucumber PM resistance genes have achieved great advancement,and many genes have been cloned and verified using different methods.However,the resistance mechanism of cucumber PM is still unclear,and many ambiguities need to be elucidated urgently.In this review,we summarized the research advances in PM resistance in cucumbers,including genetic analysis,quantitative trait locus mapping,map-based cloning,transcriptomics,mlo-mediated PM resistance,and mining of noncoding RNAs involved in resistance.Finally,the research directions and the problems that need to be solved in the future were discussed.

Identification and fine mapping of PmNJ3946 for powdery mildew resistance in einkorn wheat

Powdery mildew caused by Blumeria graminis f.sp.tritici(Bgt)is a destructive wheat disease.Although it can be easily overcome by deployment of resistance genes,the resistance is often quickly compromised by pathogen virulence.Thus,exploration and characterization of new resistance genes is always ongoing.Line NJ3946 derived from a cross of einkorn wheat accessions TA2032 and M389 showed resistance to powdery mildew.Inheritance analysis of an F2 population derived from a cross of NJ3946 and M389 suggested that the resistance was conferred by a dominant allele.With polymorphic markers identified through bulked segregant analysis(BSA),this gene was mapped to a novel locus on chromosome 3A,and was designated as PmNJ3946.Bulked segregant RNA-seq analysis(BSR-seq)was conducted to obtain more closely linked markers,which allowed delimitation of the PMNJ3946 locus to a 0.9 cM interval covering a physical distance of less than 1 Mb.PMNJ3946 was flanked by Xwgrc5153 and SNP-derived marker CHS21_3A008915069,and co-segregated with SNP-derived markers CHS21_3A008939814 and CHS21_3A008943175.The PmNJ3946 discovery expands the diversity of powdery mildew resistance genes and is useful for wheat breeding.

The Relationship of Methyl Jasmonate Enhanced Powdery Mildew Resistance in Wheat and the Expressions of 9 Disease Resistance Related Genes

[Objective] This study was carried out to determine the induction effect of jasmonic acid（JA）on powdery mildew resistance in wheat,the activation effect on the expressions of plant disease resistance related genes,and to investigate the relationship between the induced resistance and the gene expression patterns.[Method] Three powdery mildew susceptible cultivars of ＂Chinese Spring＂,＂Pumai 9＂ and ＂Zhoumai 18＂ typically representing different phenotypes in the field were employed.The powdery mildew was assessed by detached leaf assay,and real time quantitative RT-PCR was used to determine the expression patterns of 9 disease resistance related genes of PR1（PR1.1）,PR2（β,1-3 glucanase）,PR3（chitinase）,PR4（wheatwin1）,PR5（thaumatin-like protein）,PR9（TaPERO,peroxidase）,PR10,TaGLP2a（germin-like）and Ta-JA2（jasmonate-induced protein）in leaf of the three cultivars.[Result] MeJA application enhanced the powdery mildew resistances of ＂Chinese Spring＂,＂Pumai 9＂ and ＂Zhoumai 18＂.The induced powdery mildew resistance could be detected from 12 h to 96 h after MeJA treatment,and the peak value was at 24 h.Though there were differences between the three cultivars,MeJA significantly effect on the expressions of the 8 disease resistance related genes except TaGLP2a,and the peak values were at 12 h,24 h or 48 h after treatments.The strongest activation of MeJA was on PR9 and PR1 that their expressions could reach more than 100 times of the untreated samples.MeJA strongly activated PR2、PR4、PR5、PR3、PR10 and Ta-JA2,their expression could reach 10 to 70 times,and there was almost no activation effect on TaGLP2a.The induced powdery mildew resistance positively correlated with the induced expressions of the 8 disease related genes.[Conclusion] The induced powdery mildew resistance positively correlated with the induced expressions of the disease related genes.Jasmonate signalling plays a role in defence against Blumeria graminis f.sp.tritici.and future manipulation of this pathway may improve powdery mildew resistance in wheat.

Molecular Detection of Resistance Genes to Stripe Rust and Powdery Mildew in Common Wheat Cultivar Yunmai52

Yunmai52, developed by crossing with common wheat-Haynaldia villosa6AL/6VS translocation line 92R149 as a resistant parent in 1992, was a common wheat cultivar approved and released in 2007 in Yunnan Province, China, which is characterized by high resistance to powdery mildew and stripe rust. In this study,an F_2 population derived from a cross K78S/Yunmai52 was constructed to investigate the resistance genes, where K78 S is a wheat male sterile line susceptible to powdery mildew and stripe rust. Phenotypic identification of the parents, F_1 and F_2 populations and chi-square analyses showed that F_1 population was immune to stripe rust and powdery mildew; the segregation ratio of resistance and susceptibility to powdery mildew（χ~2=1.10χ~2_（1,0.05）=3.84） and stripe rust（χ~2=0.15χ~2_（1,0.05）=3.84） fit to a 3：1 ratio in F_2 population, indicating that Yunmai52 harbors a dominant stripe rust resistance gene and a dominant powdery mildew resistance gene. The individuals were further detected with a marker co-segregated with Pm21（SCAR_（1400）） and two markers closely linked with Yr26（XWe173 and Xbarc181）. The results showed that polymorphic bands could be amplified between the parents and between resistance and susceptibility gene pools at the same locus. Randomly 96 individuals of F_2 population were selected for verification. The results showed that the phenotype was significantly correlated with the genotype. The detection accuracy of markers SCAR_（1400）, XWe173 and Xbarc181 was 100%, 97.91% and 92.70%, respectively.Yunmai52 harbored powdery mildew resistance gene Pm21 and stripe rust resistance gene Yr26, which were both derived from 6AL/6VS translocation line 92R149.In addition, the results also demonstrate that Pm21 and Yr26 are two genes conferring durable resistance to powdery mildew and stripe rust in wheat.

Identification of Co-Segregating RAPD Marker Linked to Powdery Mildew Resistance Gene Pm18 in Wheat

The Pm18 gene of wheat confers resistance to the powdery mildew which is one of the mostserious diseases in many regions of the world. In this study, bulked segregant analysis(BSA) was used to develop randomly amplified polymorphic DNA (RAPD) markers linked toPm18 gene. Three hundred and twenty decamer primers were screened and one of them wasidentified as RAPD marker (S411600) linked to Pm18. Using the F2 mapping population fromthe cross Pm18Chancellor, the marker S411600 was shown to co-segregate with the genePm18. This marker can be conveniently used for marker-assisted selection in wheatbreeding programs for the identification or pyramiding of Pm18 with other resistancegenes.

Inheritance of Powdery Mildew Resistance in Cucumber (Cucumis sativus L.) and Development of an AFLP Marker for Resistance Detection

Cucumber powdery mildew is one of the most destructive diseases of cucumber throughout the world. In the present study, inheritance of powdery mildew resistance in three crosses, and linkage of resistance with amplified fragment length polymorphism （AFLP） markers are studied to formulate efficient strategies for breeding cultivars resistant to powdery mildew. The joint analysis of multiple generations and AFLP technique has been applied in this study. The best model is the one with two major genes, additive, dominant, and epistatic effects, plus polygenes with additive, dominant, and epistatic effects （E-l-0 model）. The heritabilities of the major genes varied from 64.26% to 97.82%, and susceptibility was incompletely dominant for the two major genes in the three crosses studied. The additive effects of the two major genes and the dominant effect of the second major gene were high, and the epistatic effect of the additive-dominant between the two major genes was the highest in cross I . In cross II, the absolute value of the additive effect, dominant effect, and potential ratio of the first major gene were far higher than those of the second major gene, and the epistatic effect of the additive-additive was the highest. The genetic parameters of the two major genes in cross III were similar to those in cross II. Correlation and regression analyses showed that marker E25/M63-103 was linked to a susceptible gene controlling powdery mildew resistance. The marker could account for 19.98% of the phenotypic variation. When the marker was tested on a diverse set of 29 cucumber lines, the correlation between phenotype and genotype was not significant, which suggested cultivar specialty of gene expression or different methods of resistance to powdery mildew. The target DNA fragment was 103 bp in length, and only a small part was found to be homologous to DNA in the other species evaluated, which indicated that it was unique to the cucumber genome.

Genetic behavior of Triticum aestivum–Dasypyrum villosum translocation chromosomes T6V#4S·6DL and T6V#2S·6AL carrying powdery mildew resistance

T6V#2S·6AL and T6V#4S·6DL translocation chromosomes developed from the cross of wheat and different Dasypyrum villosum accessions have good powdery mildew （PM） resistance, but their pairing and pyramiding behavior remains unclear. Results in this study indicated that the pairing frequency rate of the two differently originated 6VS chromosomes in their F1 hybrid was 18.9% according to genomic in situ hybridization （GISH）; the PM resistance plants in the F2 generation from the cross between T6V#4S·6DL translocation line Pm97033 and its PM susceptible wheat variety Wan7107 was fewer than expected. However, the ratio of the resistant vs. the susceptible plants of 15：1 in the F2 generation derived from the cross between the two translocation lines of T6V#2S·6AL and T6V#4S·6DL fitted well. Plants segregation ratio （homozygous：heterozygous：lacking） revealed by molecular marker for T6V#4S·6DL or T6V#2S·6AL in their F2 populations fitted the expected values of 1：2：1 well, inferring that the pairing of the two alien chromosome arms facilitates the transmission of T6V#4S·6DL from the F1 to the F2 generation. A quadrivalent was also observed in 21% of pollen mother cells （PMCs） of homozygote plants containing the two pairs of translocated chromosomes. The chromosome pairing between 6V#2S and 6V#4S indicates that it will be possible to obtain recombinants and clarify if the PM resistance determinant on one alien chromosome arm is different from that on the other.

Molecular and Physical Mapping of Powdery Mildew Resistance Genes and QTLs in Wheat: A Review

Wheat powdery mildew （Pro） is a major disease of wheat worldwide. During the past years, numerous studies have been published on molecular mapping of Pm resistance gene（s） in wheat. We summarized the relevant findings of 89 major re- sistance gene mapping studies and 25 quantitative trait loci （QTL） mapping studies. Major Pm resistance genes and QTLs were found on all wheat chromosomes, but the Pm resistance genes/QTLs were not randomly distributed on each chromosome of wheat. The summarized data showed that the A or B genome has more major Pm resistance genes than the D genome and chromosomes 1A, 2A, 2B, 5B, 5D, 6B, 7A and 7B harbor more major Pm resistance genes than the other chromosomes. For adult plant resistance （APR） genes/QTLs, B genome of wheat harbors more APR genes than A and D genomes, and chromo- somes 2A, 4A, 5A, 1B, 2B, 3B, 5B, 6B, 7B, 2D, 5D and 7D harbor more Pm resistance QTLs than the other chromosomes, suggesting that A genome except 1A, 3A and 6A, B genome except 4B, D genome except 1D, 3D, 4D, and 6D play an impor- tant role in wheat combating against powdery mildew. Furthermore, Pm resistance genes are derived from wheat and its rela- tives, which suggested that the resistance sources are diverse and Pm resistance genes are diverse and useful in combating against the powdery mildew isolates. In this review, four APR genes, Pm38/Lr34/Yr18/Sr57, Pm46/Lr67/Yr46/Sr55, Pm？/Lr27/Yr30/ SY2 and Pm39/Lr46/Yr29, are not only resistant to powdery mildew but also effective for rust diseases in the field, indicating that such genes are stable and useful in wheat breeding programmes. The summarized data also provide chromosome locations or linked markers for Pm resistance genes/QTLs. Markers linked to these genes can also be utilized to pyramid diverse Pm resis- tance genes/QTLs more efficiently by marker-assisted selection.

Breeding melon(Cucumis melo)with resistance to powdery mildew and downy mildew

Melon(Cucumis melo L.)production is often restricted by a plethora of pests and diseases,including powdery mildew and downy mildew caused respectively by the fungal species Podosphaera xanthii/Golovinomyces orontii and oomycete species Pseudoperonospora cubensis.Many efforts have been directed on identification of resistant sources by screening(wild)melon germplasm.In the current review,we summarized such efforts from various publications of the last 50 plus years.Resistance to powdery mildew has been identified in 239 melon accessions and downy mildew resistance in 452 accessions of both C.melo and the wild relative species C.figarei.Among the resistance sources,C.melo var.cantalupensis accessions PMR 45,PMR 5,PMR 6,and WMR 29 as well as C.melo var.momordica accessions PI 124111,PI 124112,and PI 414723 have been considered as the most valuable germplasm because multiple resistance genes have been identified from these accessions and are widely used in melon resistance breeding.Further genetic mapping in a number of resistant sources has enabled identification of 25 dominant genes,two recessive genes and seven QTLs conferring powdery mildew resistance,as well as eight dominant genes and 11 QTLs for downy mildew resistances.Based on the reported sequences of associated markers,we anchored physically(many of)these genes and QTLs to chromosomes of the melon cv.DHL92 genome.In addition to presenting a comprehensive overview on powdery mildew and downy mildew resistance in(wild)melon germplasm,we suggest strategies aiming at breeding melon with durable and broad-spectrum resistance to pathogens and pests.

Comparative genetic mapping revealed powdery mildew resistance gene MlWE4 derived from wild emmer is located in same genomic region of Pm36 and Ml3D232 on chromosome 5BL

Powdery mildew, caused by Blumeria graminis f. sp. tritici, is one of the most devastating wheat diseases. Wild emmer wheat（Triticum turgidum ssp. dicoccoides） is a promising source of disease resistance for wheat. A powdery mildew resistance gene conferring resistance to B. graminis f. sp. tritici isolate E09, originating from wild emmer wheat, has been transferred into the hexaploid wheat line WE4 through crossing and backcrossing. Genetic analyses indicated that the powdery mildew resistance was controlled by a single dominant gene, temporarily designated Ml WE4. By mean of comparative genomics and bulked segregant analysis, a genetic linkage map of Ml WE4 was constructed, and Ml WE4 was mapped on the distal region of chromosome arm 5BL. Comparative genetic linkage maps showed that genes Ml WE4, Pm36 and Ml3D232 were co-segregated with markers XBD37670 and XBD37680, indicating they are likely the same gene or alleles in the same locus. The co-segregated markers provide a starting point for chromosome landing and map-based cloning of Ml WE4, Pm36 and Ml3D232.

Fine mapping of powdery mildew resistance gene PmTm4 in wheat using comparative genomics

Powdery mildew,caused by Blumeria graminis f.sp.tritici,is one of the most severe wheat diseases.Mining powdery mildew resistance genes in wheat cultivars and their appliance in breeding program is a promising way to control this disease.Genetic analysis revealed that a single dominant resistance gene named PmTm4 originated from Chinese wheat line Tangmai 4 confers resistance to prevailing isolates of B.graminis f.sp.tritici isolate E09.Detailed comparative genomics analyses helped to develop closely linked markers to PmTm4 and a fine genetic map was constructed using large F2population,in which PmTm4 was located into a 0.66-c M genetic interval.The orthologous subgenome region of PmTm4in Aegilops tauschii was identified,and two resistance gene analogs（RGA）were characterized from the corresponding sequence scaffolds of Ae.tauschii draft assembly.The closely linked markers and identified Ae.tauschii orthologs in the mapping interval provide an entry point for chromosome landing and map-based cloning of PmTm4.

IDENTIFICATION OF RAPD MARKER LINKED TO POWDERY MILDEW RESISTANCE GENE Pm12 IN WHEAT

Powdery mildew is one of the most serious diseases of wheat in China. In this paper,bulked segregant analysis (BSA) was used to search for randomly amplified polymorphic DNA (RAPD) markers linked to the Pm12 gene,which confers resistance to the powdery mildew in wheat. 200 decamer primers were screened and one RAPD marker (S107 1900 ) was identified to be linked to Pm12 in coupling phase,and their genetic distance is 11.98± 4.00cM. This marker can be used for marker-assisted selection in wheat breeding for the identification or pyramiding of Pm12 with other resistance genes.

The Potential Role of Powdery Mildew-Resistance Gene Pm40 in Chinese Wheat-Breeding Programs in the Post-Pro21 Era

Powdery mildew, which is caused by Blumeria graminis f. sp. tritici （Bgt）, is an important leaf disease that affects wheat yield. Powdery mildew-resistance （Pro） gene Pro21 was first transferred into wheat in the 1980s, by translocating the Heuchera villosa chromosome arm 6VS to the wheat chromosome arm 6AL （6VS.6AL）. Recently, new Bgt isolates that are virulent to Pm21 have been identified in some wheat fields, indicating that wheat breeders should be aware of the risk of deploying Pm21, although pathological details regarding these virulent isolates still remain to be discovered. Pm40 was identified and mapped on the wheat chromosome arm 7BS from several wheat lines developed from the progenies of a wild cross between wheat and Thinopyrum intermedium. Pm40 offers a broad spectrum of resistance to Bgt, which suggests that it is likely to provide potentially durable resistance. Cytological methods did not detect any large alien chromosomal segment in the wheat lines carrying Pm40. Lines with Pm40 and promising agronomical traits have been released by several wheat-breeding programs in the past several years. Therefore, we believe that Pm40 will play a role in powdery mildew-resistance wheat breeding after Pm21 resistance is overcome by Bgt isolates. In addition, both Prn21 and Pm40 were derived from alien species, suggesting that the resistance genes derived from alien species are potentially more durable or effective than those identified from wheat.

Characterization of RAPD Markers,and the RFLP Marker Linked to Powdery Mildew Resistance Gene Derived from Different Accessions of H.villosa

The analysis was carried out on performance of the resistance gene from Haynaldia villosa accession of the former Soviet Union to different isolates of Bluemerie graminis. Polymorphisms were revealed between 6D/6V substitution line Pm930640 and its pedigree parents using five RAPD markers of OPAN031700, OPAI01700, OPAL03750, OPAD07480 and OPAG15580 screened out from 120 random 10-mers primers. Three RAPD markers of OPAN03, OPAI01 and OPAL03 were linked with the resistance gene by analysis of F2 population of Chancellor×Pm930640. Analysis of 29 wheat lines including part of lines conferring the known genes from Pm1 to Pm20 respectively, lines conferring resistance gene from two H. villosa accessions and the related wheat parents, were analyzed and the results showed that these markers not only linked to the gene resistant to powdery mildew from H. villosa, but also detected different genetic backgrounds. OPAL03750 can be used as the marker to distinguish the different resistant lines from two H. villosa accessions because it was only observed in the materials from H. villosa of the former Soviet Union. RFLP analysis also showed the polymorphisms between two H. villosa accessions and their derived resistant lines.

Resistance Analysis of Wheat Cultivars against Powdery Mildew in Anhui Province of China

[ Objective ] The paper was to determine the resistance level of the tried and pre-examination wheat cultivars against powdery mildew in Anhui Province of China. [ Method ] By using artificial inoculation and identification method in fields, the resistance of wheat cultivars was identified in consecutive three years from 2010 to 2012. [ Result] The highly susceptible （HS） cultivar accounted for 30%, 42% and 11% of total tested cultivars in the years of 2010, 2011 and 2012, respectively; moderately susceptible （MS） cultivar accounted for 53% of total tested cuhivars in 2010, which accounted for 47% and 57% in 2011 and 2012, respectively; moderately resistant （MR） cuhivar accounted for 17% of total tested cultivars in 2010, which accounted for 11% and 32% in 2011 and 2012, respectively. [ Conclusion] The paper can guide breeding direction, and also provide scientific basis for variety approval.

Identification of Resistance of Powdery Mildew and Stripe Rust of Winter Wheat Strains in Xinjiang

Wheat powdery mildew and stripe rust are the major diseases in wheat producing area in Xinjiang.To obtain wheat germplasm resources and varieties resistant to powdery mildew and rust,36 high-generation stable strains of Xinjiang winter wheat were evaluated using the method of natural inducement from 2018 to 2020.A total of 5 strains with high resistance to powdery mildew,4 strains with slow stripe rust and 1 strain with resistance to powdery mildew and adult plant slow stripe rust were obtained.And the parental combination of disease-resistant varieties was analyzed.These studies will provide theoretical basis for the breeding of resistant wheat varieties in Xinjiang.

A single-nucleotide substitution in the leucinerich-repeat-only gene CsLRR1 confers powdery mildew resistance in cucumber

Dear Editor,A variant with single substitution in the LRR-only protein CsLRR1,which regulates cucumber resistance to powdery mildew through a salicylic-acid-mediated pathway,provides a major source of resistance for cucumber breeding.Cucumber powdery mildew(PM),mainly caused by the biotrophic pathogen Podosphaera xanthii(synonym Podosphaera fusca),poses a serious threat to cucumber crops globally,leading to substantial reductions in fruit yield and quality(Martinez-Cruz et al.,2017).

Genome Analysis in Wheat Breeding for Disease Resistance

A brief review on the development of wheat germplasm with introduced powdery mildew and scab resistance from Haynaldia villosa Sch. and Leymus racemosus Lam., Roegneria ciliaris (Trin.) Nevski as well as R. kamoji C. Koch respectively was made. In the course of germplasm development, genome analysis by means of chromosome banding, genomic in situ hybridization (GISH) or fluorescence in situ hybridization (FISH), molecular markers, particularly restriction fragment length polymorphism (RFLP) coupled with aneuploid analysis was employed for the purpose of improving breeding efficiency. Potential use of such germplasm in wheat breeding practice, basic studies and some related problems were also discussed.

Orthologous genesPm12andPm21from twowild relatives of wheat show evolutionary conservation but divergent powdery mildew resistance

Wheat powdery mildew,caused by Blumeria graminis f.sp.tritici(Bgt),is a devastating disease that threatens wheat production worldwide.Pm12,which originated from Aegilops speltoides,a wild relative of wheat,confers strong resistance to powdery mildew and therefore has potential use in wheat breeding.Using susceptible mutants induced by gamma irradiation,we physically mapped and isolated Pm12 and showed it to be orthologous to Pm21 from Dasypyrum villosum,also a wild relative of wheat.The resistance function of Pm12 was validated via ethyl methanesulfonatemutagenesis,virus-induced gene silencing,and stable genetic transformation.Evolutionary analysis indicates that the Pm12/Pm21 loci in wheat species are relatively conserved but dynamic.Here,we demonstrated that the two orthologous genes,Pm12 and Pm21,possess differential resistance against the same set of Bgt isolates.Overexpression of the coiledcoil domains of both PM12 and PM21 induces cell death in Nicotiana benthamiana leaves.However,their full-length forms display different cell death-inducing activities caused by their distinct intramolecular interactions.Cloning of Pm12 will facilitate its application in wheat breeding programs.This study also gives new insight into two orthologous resistance genes,Pm12 and Pm21,which show different race specificities and intramolecular interaction patterns.