Resistance to powdery mildew in selections from Moroccan barley landraces

Seventy-five barley landraces from Morocco were tested for resistance to powdery mildew and a number of different resistance genes were detected. Thirty-five isolates of Blumeria graminis f. sp. hordei and the Pallas isoline differential set were used. Isolates used in the experiment had virulences corresponding to all major resistance genes used in Europe. Forty-four of the tested landraces showed resistant reactions. From each of these landraces, one to five resistant plants were selected and 92 single plant lines were created. Six lines selected from 3landraces were assumed to carry the mlo gene but they were discarded after microscopic investigation. Seventeen lines were tested in the seedling stage with 17isolates and another 69 lines were tested with 23 differential isolates. These lines showed 71 reaction spectra to isolates of powdery mildew. Eight lines (9%), 255-3-3, 282-3-4, 286-1-1, 294-2-3,294-2-4, 295-1-2, 308-1-2 and 327-2-1, selected from 7 landraces showed resistance to all isolates. Seventy-eight lines (90%) showed a resistant infection type 2with more than 50% of the isolates used. In most of the selected lines (86%) unknown genes, alone or in combination with known specific resistance genes, were detected. Four different resistance alleles (Mlat, Mla6, Mla14 and Mla1) were postulated to be present in the tested lines. The most common was Mlat, which was postulated in 35 (41%) lines. The use of newly identified sources of powdery mildew resistance in barley breeding is discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Genetic analysis of powdery-mildew (Erysiphe graminis f.sp. hordei) resistance derived from wild barley (Hordeum vulgare ssp. spontaneum)

The inheritance of resistance to powdery mildew was investigated in 20 accessions of Hordeum spontaneum and in 20 F₄ lines derived from crosses between the variety ‘Aramir’ and 13 accessions of H. spontaneum. Two resistance genes were detected in 17 accessions, and three resistance genes in one accession. In two accessions, only one resistance gene was present. The 20 breeding lines showed a large variation in infection type and infection level. The genetic relationship between the resistance genes detected was investigated in the seven most resistant F₄ lines. These F₄ lines were divided into three groups which carried different resistance genes. In two lines, the detected resistance gene was shown to be race-specific.     

Two unnecessary powdery mildew resistance genes in a synthetic rye population are neutral on fitness

A synthetic winter rye population was produced with two race-specific powdery mildew resistance genes, one dominant (Rm1) and the other (rm2) recessive, each at a frequency of about 0.50. The population was advanced by open-pollination in an isolated plot under mildew-free conditions for eight years. Samples of generations Syn-0 through Syn-7 were inoculated in the laboratory with two mildew isolates, one avirulent to either resistance gene, the other virulent to Rm1 and avirulent to rm2, to discriminate resistant and susceptible phenotypes. From the proportions of resistant plants, frequencies of Rm1 and rm2 were calculated and the fitness of carriers of resistance alleles was estimated in relation to carriers of susceptibility alleles at the two loci using continuous models and linear regression analyses. Frequencies of the two resistance genes oscillated only weakly over the eight generations. Coefficients of selection against Rm1-and rm2rm2 genotypes were –0.04 and –0.02, respectively, and not significantly different from zero. Thus the two resistance genes were selectively neutral. It is concluded that pyramiding of major powdery mildew resistance genes in rye varieties should not reduce their yield potential in the absence of mildew.     

Search for novel genes for resistance to powdery mildew (Sphaerotheca fuliginae) in cucumber (Cucumis sativus)

Summary The current powdery mildew (Sphaerotheca fuligninea) resistant cucumber varieties suffer from leaf chlorosis during autumn, winter and early spring cultivation in the Netherlands. Therefore screening was carried out for novel powdery mildew resistance genes. From 177 accessions, derived from different sources, 108 accessions proved to be partially resistant to S. fuliginea. Crosses were made with 53 resistant accessions to distinguish the presence of novel genes. It is likely that the accessions C. sativus 2145, C. sativus LV 41, PI 188807, Vladivostokij, White and Yellow 1 have one or more recessive powdery mildew resistance genes, different from powdery mildew resistance genes of the line NPI, which was used for variety breeding. Powdery mildew resistance tests with S. fuliginea give similar results in different regions of the world.Abbreviations pmr powdery mildew resistance     

粗山羊草抗小麦白粉病基因遗传多样性的研究

粗山羊草(Ae.tauschii(Coss.)Schmal.)是普通小麦(T.aestivum L.)抗性改良的宝贵遗传资源。本研究对来自伊朗、前苏联等8个国家和地区的78份粗山羊草进行了小麦白粉病(powderymildew)混合菌种苗期接种鉴定,表现免疫或近免疫的有45份,占57.69％;用一套白粉病菌菌株(共16个)对原产地不同的11份粗山羊草分别进行苗期接种鉴定,结果表明除Y168表现感染外,其它10份材料表现出各自不同的抗性反应,只有来自伊朗的Y219、Y221、Y225和来自的苏联的Ae37能抗所有16个菌株,而没有感染的毒性菌株,说明它们可能含有新的不同于15个已知Pm基因的抗性基因。利用完全双列杂交对原产地不同的5份粗山羊草进行了苗期抗白粉病基因的遗传分析,出现3种不同的抗性基因类型,来自伊朗的3份材料表现单显性(PmA)或双显性(PmA、PmB)2种类型,而来自前苏联的2份材料表现出不同于前两种类型的另一种单显性(PmB)类型。从而为增加普通小麦抗白粉病基因的遗传多样性奠定了基础。     

Transfer of disease resistance genes from Triticum araraticum to common wheat

The wild tetraploid wheat species Tr$$ (Zhuk) Zhuk Var. araratieum is a source of pest resistance genes for T$$ aesti$$ L. Our objectives were to describe the breeding behaviour of T.arartuititm when backcrossed to common wheat and transfer resistance to leaf rust (caused by Pu$$) and powdery mildew (caused by Blumeria $$wheat. Crosses were made between five wheat genotypes and $$ accessions. Fertifity and chromosome numbers of BC$$_; plants were determined. Resistance to leaf rust was transferred toBC₂ -derived families from 10 different T’ararati$$an accessions. Leaf rust resistance genes in nine T. araratieum accessions can be assigned to at least four loci. Leaf rust resistance transferred from three accessions was inherited in the hexaploid derivatives as a single. $$ gene in each case. Resistance to powdery mildew was also detected in the T. araratie$$ backcross derivatives. Fertile hexaploid derivatives expressing T’araratieum-derived resistance genes can be recovered after two backcrosses to wheat cultivars.     

Resistance to powdery mildew in a doubled haploid barley population and its association with marker loci

The genetic basis of resistance to powdery mildew (Erysiphe graminis DC. f.sp. hordei Marchal) was analyzed using doubled haploid barley (Hordeum vulgare L.) lines from the cross Harrington/TR306. Based on infection types observed after inoculation with defined single-conidium isolates, the lines were classified into four groups. The observed phenotypic ratio fit a two-locus model. The two putative loci were mapped relative to molecular markers. One coincided with the previously mapped dMlg locus on chromosome 4. Based on the observed infection types, Harrington carries the Mlg resistance allele, and TR306 carries a second locus on chromosome 7 (5H); this was tentatively designated Ml(TR). It is the first reported race-specific powdery mildew resistance gene located on that chromosome. These two loci were also detected by simple interval mapping of disease severity data from naturally infected field plots. Composite interval mapping with the first two resistance loci as co-factors detected an additional locus on chromosome 6, with a minor effect on resistance. Finally, superimposing the race-specific classification onto the field data provided evidence for a minor-effect locus on chromosome 7 (5H). The Mlg locus had the largest effect, the Ml(TR) locus had an intermediate effect and the other two loci had very small effects. This study demonstrates the effectiveness of an integrated approach to identifying and mapping resistance loci using classification data from inoculated experiments and quantitative data from field experiments. This revised version was published online in July 2006 with corrections to the Cover Date.     

Identification of Resistance Genes Against Powdery Mildew in Four Accessions of Hordeum Vulgare SSP. Spontaneum

Summary Four newly detected accessions of wild barley (Hordeum vulgare ssp. spontaneum) resistant to powdery mildew caused by Blumeria graminis f. sp. hordei were studied with the aim of finding the number of genes/loci conferring the resistance of individual accessions, the type of inheritance of the genes and their relationships to the Mla locus. F₂ populations after crosses between the winter variety ‘Tiffany’ and four wild barley accessions and use of microsatellite DNA markers were focused on the identification of individual resistance genes/loci by means of their chromosomal locations. In PI466495, one locus conferring powdery mildew resistance was identified in highly significant linkage with the marker Bmac0213. This location is consistent with the known locus Mla on chromosome 1HS. In the other three accessions the resistance was determined by two independent loci. In PI466197, PI466297 and PI466461, one locus was identified on chromosome 1HS and three new loci were revealed on chromosomes 2HS (highly significant linkage with Bmac0134), 7HS (highly significant linkage with Bmag0021) and 7HL (significant linkage with EBmac0755). Our prospective aim is identification of further linked DNA markers and the exact location of the resistance genes on the barley chromosomes.     

Identification of a novel recessive gene for resistance to powdery mildew (Blumeria graminis f. sp. hordei) in barley (Hordeum vulgare)

One of the most important diseases of barley (Hordeum vulgare) is powdery mildew, caused by Blumeria graminis f. sp. hordei. Spring barley line 173-1-2 was selected from a Moroccan landrace and revealed broad-spectrum resistance to powdery mildew. The objective of this study was to map and characterize the gene for seedling powdery mildew resistance in this line. After crossing with the susceptible cultivar ‘Manchuria’, genetic analysis of F₂ and F₃ families at the seedling stage revealed powdery mildew resistance in line 173-1-2 conditioned by a single recessive gene. Molecular analysis of non-segregating homozygous resistant and homozygous susceptible F₂ plants conducted on the DArTseq platform (Diversity Arrays Technology Pty Ltd) identified significant markers which were converted to allele-specific PCR markers and tested among 94 F₂ individuals. The new resistance gene was mapped on the long arm of chromosome 6H. No other powdery mildew recessive resistance gene has been located on 6H so far. Therefore, we concluded that the 173-1-2 barley line carries a novel recessive resistance gene designated as mlmr.     

Powdery Mildew Resistance Genes in 127 Northwest European Spring Barley Varieties

One hundred and twenty-seven spring barley varieties grown in Denmark since 1979 were characterized for resistance genes using 30 powdery mildew isolates. The resistance genes are traced in the pedigrees to verify the results. Eleven named genes, 12 tentatively named genes/resistances and six unknown resistances were found. Resistance in many varieties was based on combinations of either known genes or of known and new factors. The following five new or relatively new resistance genes more or less effective against the present powdery mildew populations were detected: the ‘Mlo’ resistance conferred by the recessive mlo gene with the characteristic infection type 0/(4), ‘Ricardo’ and ‘Turkish’ sources having gene Mla3 in common and ‘Turkish’ with Ml(Tu2) in addition. In three varieties the new resistance Ml(IM9) was found in combination with different Mia alleles. Variety ‘Jarek’ has two new unidentified resistances.     

Molecular mapping of partial resistance to powdery mildew in winter wheat cultivar Folke

The Swedish winter wheat (Triticum aestivum L.) cultivar Folke has a long record of partial and race non-specific resistance to powdery mildew (caused by Blumeria graminis f. sp. tritici) in the field. The aim of the present study was to map the main genetic factors behind the partial resistance in Folke and identify molecular markers for use in marker-assisted selection. A population of 130 recombinant inbred lines was developed from a cross between Folke and the moderately susceptible spring wheat line T2038. The population was tested for powdery mildew resistance over two years at two locations in Norway and genotyped with DArT and SSR markers. Composite interval mapping detected a total of eight quantitative trait loci (QTL) for powdery mildew resistance; six with resistance from Folke on 2BS, 2DL, 5AL, 5BS and 6BS and two with resistance from T2038 on 5BS and 7AL. None of the loci with resistance from Folke mapped to chromosomal regions with known race-specific resistance genes, which confirmed the race non-specific nature of the resistance in this cultivar. The molecular markers linked to the reported QTL will be useful as a tool for selecting partial and potentially durable resistance to powdery mildew based on the resistance in Folke.     

豌豆抗白粉病资源筛选及分子鉴定

由豌豆白粉菌引起的白粉病是豌豆生产上的重要病害,利用抗病品种是防治该病害最经济有效的方法。本研究在控制条件下苗期接种鉴定了396份豌豆资源对2个不同地理来源的豌豆白粉病菌分离物EPBJ和EPYN的抗性,用4个与豌豆抗白粉病基因er1连锁的SCAR标记对66份免疫或抗病资源进行标记基因型鉴定。结果表明,在鉴定的396份资源中,有101份资源表现免疫或抗病,其中对分离物EPBJ和EPYN免疫的资源分别为59份(14.9%)和60份(15.2%),对2个分离物均免疫的资源有54份(13.6%);在鉴定的82份中国资源中,有8份对2个分离物均表现免疫。分子标记将66份免疫或抗病资源鉴定为13个标记基因型,同一地理来源的抗性资源分属不同的标记基因型,其中8份来自中国云南的抗性资源分属7个标记基因型。研究表明,中国存在有效的豌豆白粉病抗源,抗性资源具有丰富的遗传多样性。     

Mapping QTL involved in adult plant resistance to powdery mildew in the winter wheat line RE714 in two susceptible genetic backgrounds

The objective was to study the genetic basis of adult plant resistance to powdery mildew of the winter wheat line RE714 by quantitative trait loci (QTL) analysis and to investigate the stability of the QTL detected in two different genetic backgrounds. Two DH populations from the crosses between RE714 and the susceptible parents ‘Festin’ and ‘Hardi’ were used. Reaction of the DH lines to powdery mildew was assessed in different environments in Belgium under natural disease infection. Considering both populations and according to the environment tested, one to seven QTL were detected. Among them, residual effects of the race‐specific resistance genes Pm4b and MIRE were found. Two major QTL were very stable (on chromosome 5D and at the MIRE locus), since they were detected in both populations and over all environments tested. The QTL detected varied according to the susceptible parent used, and a residual effect at the Pm4b gene was not observed with the genetic background of ‘Hardi’.     

Discovery,characterization and exploitation of Mlo powdery mildew resistance in barley

Summary Mlo resistance to barley powdery mildew is a relatively new kind of resistance. It was originally described in a powdery mildew resistant barley mutant in 1942 and has been mutagen-induced repeatedly since then. About 1970 it was also recognized in barley landraces collected in Ethiopia in the 1930s. It is unique in that 1) Mlo resistance does not conform to the gene-for-gene system; 2)mlo genes originating from different mutational events map as non-complementing recessive alleles in one locus; 3) all alleles confer the same phenotype, though with small quantitative differences; 4) it is effective against all isolates of the pathogen; and 5) the resistance is caused by rapid formation of large cell wall appositions at the encounter sites preventing penetration by the fungus. Powdery mildew isolates with elevated Mlo aggressiveness have been produced on barley in the laboratory, but have not been found in nature. Mlo resistance is considered very durable. The exploitation of Mlo resistance has been hampered by pleiotropic effects of themlo genes, vix. necrotic leaf spotting and reduced grain yield, but they have been overcome by recent breeding work. During the 1980s Mlo-resistant spring barley varieties have become cultivated extensively in several European countries, in 1990 on about 700,000 ha.     

A new powdery mildew resistance gene: Introgression from wild emmer into common wheat and RFLP-based mapping

An Israeli accession (TTD140) of wild emmer, Triticum turgidum var. dicoccoides, was found resistant to several races of powdery mildew. Inoculation of the chromosome-arm substitution lines (CASLs) of TTD140, in the background of the Israeli common wheat cultivar ‘Bethlehem’ (BL), with five isolates of powdery mildew revealed that only the line carrying the short arm of chromosome 2B of wild emmer (CASL 2BS) exhibited complete resistance to four of the five isolates. To map and tag the powdery mildew resistance gene, 41 recombinant substitution lines, derived from a cross between BL and CASL 2BS, were used to construct a linkage map at the gene region. The map, which encompasses 69.5 cM of the distal region of chromosome arm 2BS, contains six RFLP markers, a morphological marker (glaucousness inhibitor, W1 ^I), and the powdery mildew resistance gene. Segregation ratios for resistance in F₂ of BL × CASL 2BS and in the recombinant lines, combined with the susceptability of F₁ progeny to all tested isolates, indicate that resistance is controlled by a single recessive allele. This alleleco-segregated with a polymorphic locus detected by the DNA marker Xwg516, 49.4 cM from the terminal marker Xcdo456. The new powdery mildew resistance gene was designated Pm26. This revised version was published online in July 2006 with corrections to the Cover Date.     

四川豌豆种质资源白粉病抗性及分子鉴定

豌豆白粉病是由白粉菌（Erysiphe pisi D. C.）引起的豌豆最重要的病害之一,控制豌豆白粉病最经济有效且环保的方法是种植抗病品种。在温室条件下对400份豌豆种质资源进行白粉病抗性鉴定,同时利用7个与已知豌豆抗白粉病基因连锁的分子标记进行基因型鉴定。结果表明,在400份资源中,有8份表现免疫,3份表现抗病,5份表现抗感分离,其余384份均为感病;16份抗性资源中有10份来自于四川省中部不同纬度地区,其余6份为国外引进资源;7个分子标记将400份种质资源分为39个标记基因型,其中16份抗性资源分为7个标记基因型。上述抗性资源及其标记基因型可有效应用于豌豆白粉病抗性育种的研究中。     

Screening and identification of resistance to Leptosphaeria maculans (stem canker) in Brassica napus accessions

The occurrence of race-specific resistance genes to the stem canker fungus, Leptosphaeria maculans, was analysed in 453 accessions of B. napus, mainly originating from the Institut für Pflanzengenetik und Kulturpflanzenforschung (IPK) GeneBank. Major resistance genes Rlm1, Rlm2, Rlm4 and the putative RlmBBA gene were investigated using genetically improved strains of the fungus harbouring as few corresponding avirulence genes as possible. In addition, a screening with fully virulent isolates was used to uncover novel resistance sources. Major resistance genes were rarer in frequency and diversity in spring-type cultivars compared to winter types. In the former, 65.7% of the accessions were fully susceptible to all isolates, whereas only 12.2% of the winter types were devoid of at least one R gene. In spring cultivars, the most common R gene, Rlm4 was found in 26.6% of accessions, whereas the other R genes were rare. In winter cultivars, the most common R genes were Rlm2 (more than 45.9–54.0% of the accessions) and Rlm4 (26.4–27.7% of the genotypes). In winter types however, the improvement of the quality of oils, through the generation of single- and double-low genotypes improved the homogeneity of the cvs, whereas it impoverished R gene diversity, including the loss of complete resistance that was harboured by 18.4% of the less advanced accessions, and a reduction in the ratio of accessions harbouring Rlm1. Correlation between the R gene(s) present in the accessions and their field resistance is discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Single-gene resistance to powdery mildew in zucchini squash (Cucurbita pepo)

Cucurbita pepo (pumpkin, squash,gourd) is an economically important species that is susceptible to the cucurbit powdery mildew fungus, Podosphaera xanthii(syn. Sphaerotheca fuliginea). ‘True French’, an open-pollinated cultivar of the Zucchini Group of C. pepo, was crossed with an unnamed powdery-mildew resistant straight neck-type accession, the resistance of which was apparently derived from an interspecific cross with a resistant wild species of Cucurbita,and resistant plants were selected in the F₂ generation. This was followed by six cycles of backcross-pedigree selection for resistance, and resulted in the development of an accession true-breeding for resistance to powdery mildew and nearly isogenic to ‘True French’. The resistant and susceptible near-isogenics were crossed and seeds of the filial and backcross generations were produced. Plants of the parental accessions and their progenies were grown together in a controlled-environment chamber, exposed to the pathogenic fungus, and scored as resistant, partially resistant, or susceptible 27–33 days after sowing. The results indicated that resistance is conferred by a single incompletely dominant gene, designated Pm-0. This revised version was published online in August 2006 with corrections to the Cover Date.     

Possible New Genes for Resistance to Powdery Mildew, Septoria Glume Blotch and Leaf Rust of Wheat

An Ethiopian wheat collection consisting of 293 tetraploid and hexaploid entries was investigated for resistance to powdery mildew, Septoria glume blotch, and leaf rust with the aim of finding probable new genes for resistance to these diseases. Seedlings were screened with isolates of these diseases in the greenhouse or growth chamber. The material was also scored for field resistance to powdery mildew after the fifth leaf stale. The diversity of the reaction types to powdery mildew and Septoria glume blotch was estimated by the Shannon-Weaver diversity index. Thirty-nine entries (13%) of the collection were resistant to moderately resistant co the mildew isolates, 14S-77 and 46—77, that had: a combined virulence spectrum effective against nine identified genes for resistance to powdery mildew. One hundred and et till TV-tour entries (63 %) of the collection showed field resistance to mildew. One hundred and eighty-one entries (62 %) of the collection were at least moderately resistant in an aggressive isolate of Sartorial nodorum. Resistance to a race of leaf rust was detected in one hundred and sixty-eight entries or 58.% of the collection. Generally, resistance to these diseases is concentrated in Central and Southern Ethiopia. The different reaction types of the resistant entries to these diseases and the high estimates of diversity for reaction types indicated the presence of many different probable new genes and genetic backgrounds for resistance to these diseases.     

Screening of Portuguese cole landraces (Brassica oleracea L.) with Peronospora parasitica and Plasmodiophora brassicae

Summary Forty-four landraces of Portuguese coles (Brassica oleracea L.), representing different morphotypes, were screened at the cotyledon stage for downy mildew resistance, caused by Peronospora parasitica. Two isolates of the pathogen, PHW 630 and PHW 828, were used in the experiment. The mean disease interaction phenotype varied among the landraces. Overall, the Portuguese coles have shown resistance to both isolates, particularly to isolate PHW 828. Some landraces were identified with differential reaction to the two P. parasitica isolates. Some of the Portuguese coles are, therefore, good sources of resistance genes to P. parasitica, and could be used in breeding programs or in the development of a downy mildew host differential set. Among the morphotypes tested, Couve Algarvia (ISA 207), Couve Galega (ISA 243 and 187) and Couve Glória de Portugal (ISA 84) have presented the highest resistance interaction. For the development of host differential sets, the landraces ISA 2 (Penca de Mirandela), ISA 35 (Couve de Valhascos) and ISA 600 (Penca Espanhola) could be further selected for the differentiation of P. parasitica isolates. They are resistant to PHW 828 and susceptible to PHW 643.The same morphotypes and landraces were also screened at the seedling stage for resistance to clubroot, caused by Plasmodiophora brassicae Woron.. Although some variation for resistance could be noticed in some the landraces tested, mainly Galega kale types, none of them presented a sufficient level of resistance as to be directly be useful in breeding for resistance to race 6 of P. brassicae.