Identification of resistance gene analogs linked to a powdery mildew resistance locus in grapevine

Oligonucleotide primers, designed to conserved regions of nucleotide binding site (NBS) motifs within previously cloned pathogen resistance genes, were used to amplify resistance gene analogs (RGAs) from grapevine. Twenty eight unique grapevine RGA sequences were identified and subdivided into 22 groups on the basis of nucleic acid sequence-identity of approximately 70% or greater. Representatives from each group were used in a bulked segregant analysis strategy to screen for restriction fragment length polymorphisms linked to the powdery mildew resistance locus, Run1, introgressed into Vitis vinifera L. from the wild grape species Muscadinia rotundifolia. Three RGA markers were found to be tightly linked to the Run1 locus. Of these markers, two (GLP1–12 and MHD145) cosegregated with the resistance phenotype in 167 progeny tested, whereas the third marker (MHD98) was mapped to a position 2.4 cM from the Run1 locus. The results demonstrate the usefulness of RGA sequences, when used in combination with bulked segregant analysis, to rapidly generate markers tightly linked to resistance loci in crop species. Received: 2 May 2001 / Accepted: 3 August 2001     

Identification of a QTL decreasing yield in barley linked to Mlo powdery mildew resistance

A molecular marker map, including Mlo mildew resistance, of the spring barley cross Derkado (Mlo-resistant) × B83-12/21/5 (Mlo-susceptible) was scanned for yield QTLs to determine whether the association of Mlo resistance with reduced yield was due to linkage or pleiotropy. Over the mapped portion of the genome of the cross, the QTL with the greatest effect upon yield was located within a 22 cM region between mlo and the simple sequence repeat HVM67 on chromosome 4(4H). The association of Mlo resistance with lower yield was therefore due to a repulsion linkage. Analysis of yield component characters revealed QTL alleles for reduced grain number and earlier heading date in the same region, also associated with Mlo resistance. Genotyping of a range of cultivars and sources of Mlo resistance with the HVM67 simple sequence repeat showed that the Derkado HVM67 allele was rare as it was found only in one other cultivar and four land-races or sources of disease resistance. Grannenlose Zweizeilige, the source, and Salome, the carrier of Mlo resistance in Derkado, have the same HVM67 genotype, although Salome was a mixture of two genotypes. The entire mlo-HVM67 chromosomal segment from Grannenlose Zweizeilige is therefore thought to have been transmitted to Derkado, possibly through joint selection for Mlo resistance and early heading. L92, synonym EP79, was another source of Mlo resistance with the same HVM67 allele as Derkado but recombination must have occurred during the breeding of Atem as it possesses a different HVM67 allele which is present in all the other Mlo sources and cultivars surveyed. Abbreviations: GN, grains per main stem ear; HD, heading date; MSTGW, thousand grain weight derived from GN and MSY; MSY, yield of grain on the main stem; PY, yield of grain from the whole plot; sCIM, simplified compound interval mapping; SIM, simple interval mapping; SPY, single plant yield; S-SAP, sequence-specific amplification polymorphism; TGW, thousand grain weight derived from bulk of plot seed; TN, number of fertile stems per plant.     

Identification of QTLs for resistance to powdery mildew and SSR markers diagnostic for powdery mildew resistance genes in melon (Cucumis melo L.)

Powdery mildew caused by Podosphaera xanthii is an important foliar disease in melon. To find molecular markers for marker-assisted selection, we constructed a genetic linkage map of melon based on a population of 93 recombinant inbred lines derived from crosses between highly resistant AR 5 and susceptible ‘Earl’s Favourite (Harukei 3)’. The map spans 877 cM and consists of 167 markers, comprising 157 simple sequence repeats (SSRs), 7 sequence characterized amplified region/cleavage amplified polymorphic sequence markers and 3 phenotypic markers segregating into 20 linkage groups. Among them, 37 SSRs and 6 other markers were common to previous maps. Quantitative trait locus (QTL) analysis identified two loci for resistance to powdery mildew. The effects of these QTLs varied depending on strain and plant stage. The percentage of phenotypic variance explained for resistance to the pxA strain was similar between QTLs (R ² = 22–28%). For resistance to pxB strain, the QTL on linkage group (LG) XII was responsible for much more of the variance (41–46%) than that on LG IIA (12–13%). The QTL on LG IIA was located between two SSR markers. Using an independent population, we demonstrated the effectiveness of these markers. This is the first report of universal and effective markers linked to a gene for powdery mildew resistance in melon.     

Differences in early callose deposition during adapted and non-adapted powdery mildew infection of resistant Arabidopsis lines

The deposition of callose, a (1,3)-β-glucan cell wall polymer, can play an essential role in the defense response to invading pathogens. We could recently show that Arabidopsis thaliana lines with an overexpression of the callose synthase gene PMR4 gained complete penetration resistance to the adapted powdery mildew Golovinomyces cichoracearum and the non-adapted powdery mildew Blumeria graminis f. sp hordei. The penetration resistance is based on the transport of the callose synthase PMR4 to the site of attempted fungal penetration and the subsequent formation of enlarged callose deposits. The deposits differed in their total diameter comparing both types of powdery mildew infection. In this study, further characterization of these callose deposits revealed that size differences were especially pronounced in the core region of the deposits. This suggests that specific, pathogen-dependent factors exist, which might regulate callose synthase transport to the core region of forming deposits.     

Identification of quantitative trait loci for resistance to powdery mildew in a Spanish barley landrace

The Spanish landrace-derived inbred line SBCC97, together with other lines from the Spanish Barley Core Collection, displays high resistance to powdery mildew, caused by the fungus Blumeria graminis f. sp. hordei. The objective of this study was to map quantitative trait loci (QTLs) for resistance to powdery mildew in a recombinant inbred line population derived from a cross between SBCC97 and the susceptible cultivar ‘Plaisant’. Phenotypic analysis was performed using four B. graminis isolates, and genetic maps were constructed with mainly simple sequence repeat (SSR) markers, following a sequential genotyping strategy. Two major QTLs with large effects were identified on chromosome 7H, and they accounted for up to 45% of the total phenotypic variance. The alleles for resistance at each QTL were contributed by the Spanish parent SBCC97. One locus was mapped to the short arm of chromosome 7HS, and was flanked by the resistance gene analogue (RGA) marker S9202 and the SSR GBM1060. This corresponded to the same chromosomal region in which a major race-specific resistance gene from Hordeum vulgare ssp. spontaneum, designated as mlt, had been identified previously. The second QTL was linked tightly to marker EBmac0755, and it shared its chromosomal location with the qualitative resistance gene Mlf, which has only been described previously in the wild ancestor H. spontaneum. This is the first report of these two QTLs occurring together in cultivated barley, and it paves the way for their use in barley breeding programs that are designed to transfer resistance alleles into elite cultivars.     

Abscisic acid negatively regulates post-penetration resistance of Arabidopsis to the biotrophic powdery mildew fungus

Pytohormone abscisic acid(ABA) plays important roles in defense responses.Nonetheless,how ABA regulates plant resistance to biotrophic fungi remains largely unknown.Arabidopsis ABA-deficient mutants,aba2-1 and aba3-1,displayed enhanced resistance to the biotrophic powdery mildew fungus Golovinomyces cichoracearum.Moreover,exogenously administered ABA increased the susceptibility of Arabidopsis to G.cichoracearum.Arabidopsis ABA perception components mutants,abil-1 and abi2-1,also displayed similar phenotypes to ABA-deficient mutants in resistance to G.cichoracearum.However,the resistance to G.cichoracearum is not changed in downstream ABA signaling transduction mutants,abi3-1,abi4-1,and abi5-1.Microscopic examination revealed that hyphal growth and conidiophore production of G.cichoracearum were compromised in the ABA deficient mutants,even though pre-penetration and penetration growth of the fungus were not affected.In addition,salicylic acid(SA) and MPK3 are found to be involved in ABA-regulated resistance to G.cichoracearum.Our work demonstrates that ABA negatively regulates post-penetration resistance of Arabidopsis to powdery mildew fungus G.cichoracearum,probably through antagonizing the function of SA.     

Characterizing the pathotype structure of barley powdery mildew and effectiveness of resistance genes to this pathogen in Kazakhstan

Background

Powdery mildew of barley is a wind-borne and obligate biotrophic pathogen, which ranks among the most widespread barley pathogens worldwide. However, purposeful research towards studying the structure of the barley powdery mildew populations, of their virulence and of effectiveness of certain resistance genes against the infection was not conducted in Kazakhstan till present time. This paper is the first to describe characteristics of the pathotype structure of Blumeria graminis f.sp. hordei (Bgh) population and effectiveness of resistance genes in two regions of barley cultivation in the republic.

Results

One hundred and seven isolates of Bgh were obtained from seven populations occurring on cultivated barley at two geographically locations in Kazakhstan during 2015 and 2016. Their virulence frequency was determined on 17 differential lines Pallas. All isolates were virulent on the resistance gene Mla8 and avirulent for the resistance genes Mla9, Mla1 + MlaAl2, Mla6 + Mla14, Mla13 + MlRu3, Mla7 + MlNo3, Mla10 + MlDu2, Mla13 + MlRu3 and Mlo-5. The frequencies of isolates overcoming the genes Mla3, Mla22, Mlat Mlg + MlCP and Mla12 + MlEm2 were 0.0–33.33%, and frequencies of isolates overcoming the genes Mlra, Mlk, MlLa and Mlh ranged from 10.0 to 78.6%. Based on reactions of differential lines possessing the genes Mla22, Mlra, Mlk, Mlat, MlLa and Mlh, pathotypes were identified. In total, 23 pathotypes with virulence complexity ranging from 1 to 6 were identified. During both years in all populations of South Kazakhstan and Zhambyl regions pathotypes 24 and 64 mainly prevailed.

Conclusions

Obtained data suggest that low similarity of populations Bgh in Kazakhstan to European, African, Australian and South-East Asian populations. The present study provides a foundation for future studies on the pathogenic variability within of Bgh populations in Kazakhstan and addresses the knowledge gap on the virulence structure of Bgh in Central Asia. Complete effectiveness of the resistance genes, for which no corresponding virulence was found, will allow Kazakhstanean breeders to access many modern barley cultivars that those possessing the resistance effectiveness genes.

     

Mapping resistance to powdery mildew in barley reveals a large-effect nonhost resistance QTL

Key message

Resistance factors against non-adapted powdery mildews were mapped in barley. Some QTLs seem effective only to non-adapted mildews, while others also play a role in defense against the adapted form.The durability and effectiveness of nonhost resistance suggests promising practical applications for crop breeding, relying upon elucidation of key aspects of this type of resistance. We investigated which genetic factors determine the nonhost status of barley (Hordeum vulgare L.) to powdery mildews (Blumeria graminis). We set out to verify whether genes involved in nonhost resistance have a wide effectiveness spectrum, and whether nonhost resistance genes confer resistance to the barley adapted powdery mildew. Two barley lines, SusBgt_SC and SusBgt_DC, with some susceptibility to the wheat powdery mildew B. graminis f.sp. tritici (Bgt) were crossed with cv Vada to generate two mapping populations. Each population was assessed for level of infection against four B. graminis ff.spp, and QTL mapping analyses were performed. Our results demonstrate polygenic inheritance for nonhost resistance, with some QTLs effective only to non-adapted mildews, while others play a role against adapted and non-adapted forms. Histology analyses of nonhost interaction show that most penetration attempts are stopped in association with papillae, and also suggest independent layers of defence at haustorium establishment and conidiophore formation. Nonhost resistance of barley to powdery mildew relies mostly on non-hypersensitive mechanisms. A large-effect nonhost resistance QTL mapped to a 1.4 cM interval is suitable for map-based cloning.

     

Characterizing the pathotype structure of barley powdery mildew and effectiveness of resistance genes to this pathogen in Kazakhstan

Background

Alike to Reduced height-1 (Rht-1) genes in wheat and the semi dwarfing (sd-1) gene in rice, the sdw1/denso locus involved in the metabolism of the GA, was designated as the ‘Green Revolution’ gene in barley. The recent molecular characterization of the candidate gene HvGA20ox2 for sdw1/denso locus allows to estimate the impact of the functional polymorphism of this gene on the variation of agronomically important traits in barley.

Results

We investigated the effect of the 7-bp deletion in exon 1 of HvGA20ox2 gene (sdw1.d mutation) on the variation of yield-related and malting quality traits in the population of DHLs derived from cross of medium tall barley Morex and semi-dwarf barley Barke. Segregation of plant height, flowering time, thousand grain weight, grain protein content and grain starch was evaluated in two diverse environments separated from one another by 15° of latitude. The 7-bp deletion in HvGA20ox2 gene reduced plant height by approximately 13 cm and delayed flowering time by 3–5 days in the barley segregating DHLs population independently on environmental cue. On other hand, the sdw1.d mutation did not affect significantly either grain quality traits (protein and starch content) or thousand grain weight.

Conclusions

The beneficial effect of the sdw1.d allele could be associated in barley with lodging resistance and extended period of vegetative growth allowing to accumulate additional biomass that supports higher yield in certain environments. However, no direct effect of the sdw1.d mutation on thousand grain weight or grain quality traits in barley was detected.

     

The Arabidopsis genes RPW8.1 and RPW8.2 confer induced resistance to powdery mildew diseases in tobacco

Plant disease resistance (R) gene products recognize pathogen avirulence (Avr) gene products and induce defense responses. It is not known if an R gene can function in different plant families, however. The Arabidopsis thaliana R genes RPW8.1 and RPW8.2 confer resistance to the powdery mildew pathogens Erysiphe orontii, E. cichoracearum, and Oidium lycopersici, which also infect plants from other families. We produced transgenic Nicotiana tabacum, N. benthamiana, and Lycopersicon esculentum plants containing RPW8.1 and RPW8.2. Transgenic N. tabacum plants had increased resistance to E. orontii and O. lycopersici, transgenic N. benthamiana plants had increased resistance to E. cichoracearum, but transgenic L. esculentum plants remained susceptible to these pathogens. The defense responses induced in transgenic N. tabacum and N. benthamiana were similar to those mediated by RPW8.1 and RPW8.2 in Arabidopsis. Apparently, RPW8.1 and RPW8.2 could be used to control powdery mildew diseases of plants from other families.     

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.     

Inheritance of partial resistance to powdery mildew in spring wheat

Summary Four spring wheat (Triticum aestivum L.) cultivars exhibiting partial resistance to powdery mildew induced by Erysiphe graminis f.sp. tritici were crossed to a common susceptible cultivar to study the inheritance of resistance. The genetic parameters contributing to resistance were estimated by generation means analyses. Additive gene action was the most important genetic component of variation among generation means in all four crosses. Additive by additive effects were significant in one cross and both additive by additive and additive by dominance effects were significant in another. Dominance effects were not significant. The F2/F3 correlations in three crosses ranged from 0.27 to 0.43. Three additional crosses among resistant cultivars were employed to study the effectiveness of selection in improving resistance. By selecting the most resistant plants from the F2 and evaluating the progenies in the F4, increases in resistance ranging from 21% to 31% were obtained. In all crosses, there was transgressive segregation in both directions indicating that the genes conferring resistance to these cultivars differ and exhibit additive effects.     

Identification and molecular mapping of a resistance gene to powdery mildew from the synthetic wheat line M53

Powdery mildew disease caused by Blumeria graminis f. sp. tritici (Bgt) is an economically important disease in wheat worldwide. The identification of germplasms resistant to the disease can not only facilitate the breeding of resistant cultivars, but can also broaden the diversity of resistance genes. The Mexican M53 is a synthetic hexaploid wheat line developed at the International Maize and Wheat Improvement Center (CIMMYT) from the cross between Triticum durum and Aegilops tauschii249. Infection of M53 with 15 different pathogen races revealed that the resistance in M53 was race-dependent and effective against the majority of the tested Bgt races, including the race 15 predominant in the Beijing wheat growing area. Inoculation of the parents of M53 with the race 15 demonstrated that M53 and Ae. tauschii249 were resistant, whereas T. durum was susceptible. The inoculation of three segregating F₂ populations developed from the crosses between M53 and three susceptible Chinese wheat cultivars with the race 15 showed that the resistant gene in M53 segregated in a single dominant manner. Amplified fragment length polymorphism (AFLP) and simple sequence repeat (SSR) markers were used to map the gene in a segregating F₂ population consisting of 213 lines developed from the cross Wan7107 × M53. Two closely linked AFLP markers, Apm109 and Apm161, were identified to flank the gene with genetic distances of 1.0 cM and 3.0 cM, respectively. The recognized gene was assigned to the long arm of chromosome 5D as determined by three linked SSR markers, Xwmc289b, Xgwm583, and Xgwm292, and by the physical mapping of Apm109 using Chinese Spring nullisomic–tetrasomic and ditelosomic stocks. The resistance gene identified in M53, temporarily designated as Pm-M53, could be used in local wheat-breeding programs to improve powdery mildew resistance.     

A mutation in a coproporphyrinogen III oxidase gene confers growth inhibition, enhanced powdery mildew resistance and powdery mildew-induced cell death in Arabidopsis

Key message

A gene encoding a coproporphyrinogen III oxidase mediates disease resistance in plants by the salicylic acid pathway.

Abstract

A number of genes that regulate powdery mildew resistance have been identified in Arabidopsis, such as ENHANCED DISEASE RESISTANCE 1 to 3 (EDR1 to 3). To further study the molecular interactions between the powdery mildew pathogen and Arabidopsis, we isolated and characterized a mutant that exhibited enhanced resistance to powdery mildew. The mutant also showed dramatic powdery mildew-induced cell death as well as growth defects and early senescence in the absence of pathogens. We identified the affected gene by map-based cloning and found that the gene encodes a coproporphyrinogen III oxidase, a key enzyme in the tetrapyrrole biosynthesis pathway, previously known as LESION INITIATION 2 (LIN2). Therefore, we designated the mutant lin2-2. Further studies revealed that the lin2-2 mutant also displayed enhanced resistance to Hyaloperonospora arabidopsidis (H.a.) Noco2. Genetic analysis showed that the lin2-2-mediated disease resistance and spontaneous cell death were dependent on PHYTOALEXIN DEFICIENT 4 (PAD4), SALICYLIC ACID INDUCTION-DEFICIENT 2 (SID2), and NONEXPRESSOR OF PATHOGENESIS-RELATED GENES 1 (NPR1), which are all involved in salicylic acid signaling. Furthermore, the relative expression levels of defense-related genes were induced after powdery mildew infection in the lin2-2 mutant. These data indicated that LIN2 plays an important role in cell death control and defense responses in plants.     

Molecular phylogenetic status of korean strain of Podosphaera xanthii, a causal pathogen of powdery mildew on Japanese thistle (Cirsium japonicum) in Korea

Powdery mildew diseases are sensitive to climate change and spread can be favored by increased temperature and low moisture. During 2011 to 2012, a powdery mildew disease by a Podosphaera species was observed on the leaves of Japanese thistle (Cirsium japonicum) in Korea. The initial sign of this disease included scattered superficial white mycelia on leaves. As the disease progressed, abundant necrotic black spots exhibiting chasmothecia were formed on the leaves. rDNA ITS and 28S homologies of the fungus (EML-CSPW1) showed 100% identity values with those regions from many strains of P. xanthii (syn. P. fusca) via NCBI BLASTN search.