Inheritance of resistance to powdery mildew (Erysiphe graminis f. sp. hordei) in eleven primitive barley varieties

The inheritance of the powdery mildew resistance of eleven primitive barley varieties was investigated. crosses with varieties with identified resistance genes revealed that at least three different genes are present in a group of six genotypes from Greece (Hor736, Hor847, Hor878, Hor1159, Hor1379 and Hor1873) and one from Turkey (Hor1188). One dominant gene is common to these seve genotypes and in the Greek accessions a second gene is present. The expression of this second gene was respectively dominant in the crosses with Hor736 and Hor1159, recessive in the crosses with Hor878 and Hor1873, and depended on the employed powdery mildew isolate in the crosses with Hor847 and Hor1379. The detected genes differ from the resistance genes of the crossing partners, viz. Ml-al2, Ml-(Ab), Ml-(CP) and Ml-(1402). The accessions from China (Hor824 and Hor4021) each possess two resistance genes which differ from Ml-a12, Ml-(La) and Ml-(CP). The major gene is common to both accessions and is either identical, allelic or closely linked to a gene in the variety Nigrate. The Columbian accession Hor1894 possesses one resistance gene linked to a resistance gene in Nigrate but this gene differs from the Ml-a locus. The variety Palestine (Hor3997) possesses two resistance genes of which one is allelic or closely linked to Ml-(at).     

Diallel analysis of partial resistance to powdery mildew caused by Erysiphe graminis f. sp. hordei in spring barley (Hordeum vulgare L.)

Summary Six spring barley genotypes with growth stage dependent expression of partial resistance to powdery mildew were crossed following a half diallel scheme. Data for percentage infected leaf area at different growth stages from the F1 and F2 generation and the F2 offspring were analyzed. The absence of a contrast between parents and offspring indicated that dominance effects were not important at the young growth stages. Diallel analysis showed that general combining ability effects (GCA) were important at all growth stages. Although significant, specific combining ability effects were of minor importance. The cross between the most resistant parents with the largest, negative GCA resulted in the most resistant progeny.     

Characterisation of new oat germplasm for resistance to powdery mildew

Summary Wild oat accessions from the Institute of Plant Genetics and Crop Plant Research (IPK) Gatersleben were selected as potential sources of resistance to powdery mildew (Erysiphe graminis f.sp. avenae). The Avena strigosa accessions AVE 128, AVE 488 and AVE 264, along with A. occidentalis accession CAV 3889 showed high levels of mildew resistance in tests at early and late growth stages over two years; the latter is a particularly useful source because it is a hexaploid species. Moderate levels of resistance were also found in A. fatua accession AVE 1981, AVE 2032 and A.sterilis accession AVE 1373 but this could be due to the later maturity of these genotypes.     

Detection of tolerance of barley cultivars to infection by powdery mildew (Erysiphe graminis f.sp. hordei)

Summary Barley genotypes representing a wide range of resistance expressions and origins, from major resistance genes in modern cultivars to field resistances in landraces, were assessed for tolerance to disease under glasshouse and field conditions. A few genotypes were picked out as showing less yield loss than would be expected from the level of mildew infection. Genotypes showing more than the expected yield loss were also found. The potential use of tolerance as a breeding character is discussed.     

Differences in partial resistance of barley to powdery mildew (Erysiphe graminis DC F.SP. hordei Marchal) after chemomutagenesis. II. Reaction of mutants to pathotypes

Summary Seedlings of 45 barley mutants with partial resistance in the field and their parental cultivars Asse, Bomi, and Vada were exposed to six local and two foreign races of powdery mildew, in climatically controlled cabinets. Infectability, pustule size, infection grade, and infection type were estimated. No mutant did demonstrate strong race-specific reactions although some race-specific interactions of moderate grade could be detected. The results of infection of mutants with single races confirmed the quantitative character of their change in resistance determined in the earlier field assessments. The 20 investigated mutants with increased resistance expressed a lower level of disease with each of the used races. Out of the 10 mutants with higher susceptibility in the field, 4 mutants again exhibited higher degrees of infection over all the different races, while the remaining 6 mutants were not distinguishable from the original cultivar under the given growing conditions. Out of the tested 14 developmentally resistant mutants, only the 5 genotypes with different seedling reaction could be analyzed for race-specificity in this study. In all the above cases as the result of one gene mutation, quantitative shifts in level of infection were recorded over all the 8 races.Qualitative estimates of infection type were supported by data on the frequency of chlorotic or necrotic lesions and green islands on the infected leaves. But quantitative methods of assessment, e.g. infection frequency and pustule size, were more effective in studying partial resistance of the mutants. Infection grade, estimated visually 14 days after inoculation, was in agreement with the quantitative parameters accurately measured 7 days after inoculation. Therefore, its careful use can be recommended to speed the screening by narrowing down the materials. Differences in virulence level of the races were observed and their influence on race-specificity studies was discussed.     

Hordeum chilense resistance to powdery mildew and its potential use in cereal breeding

Summary Hordeum chilense is a wild barley with high crossability with Triticum, Hordeum and Secale. Its amphiploid with wheat, tritordeum, has potential as a new crop. H. chilense is highly resistant to the powdery mildew diseases of both wheat and barley. Whereas tritordeum is resistant to barley powdery mildew, its reaction to wheat powdery mildew is similar to that of its wheat parent. However H. chilense contributes to a reduced density of mildew colonies. This quantitative resistance of tritordeum is diluted at higher ploidy levels.     

Genetic analysis of adult plant resistance to powdery mildew in pea (Pisum sativum L.)

Summary An analysis of adult plant resistance of powdery mildew in 15 F₁, F₂ and F₃ populations of pea derived from crossing 15 diverse and susceptible lines with one resistant line revealed that resistance to powdery mildew is controlled by duplicate recessive genes. The genes were designated as er₁ and er₂.Disease reaction showed independent segregation with three known markers in the resistant parent, namely, af (afila, chromosome 1), st (stipule reduced, chromosome 3) and tl (clavicula, chromosome 7).Contribution form the Department of Genetics and Plant Breeding Banaras Hindu University, Varanasi-221005, India.     

Partial resistance to Erysiphe graminis hordei in old European barley varieties

Summary A collection of 133 genotypes consisting mainly of old European barleys and land varieties was assessed for level of partial resistance to barley mildew at the adult plant stage. Identification of any known resistance factors conferring hypersensitive reactions to the mildew races present at various frequencies in N.W. Europe was ensured through seedling tests with an appropriate AO mildew isolate.Thirty-nine varieties with relatively high levels of adult (partial) resistance and lacking known race-specific resistance genes were tested over a period of three years in field disease nurseries. At least thirteen varieties showed significantly less percentage leaf area infected than the control variety Proctor. These constitute a useful reserve of non-hypersensitive resistance, probably under the control of genes with mainly additive effects. In combination, these genes give enhanced levels of resistance, which could be of a more stable nature.     

Spectrum of resistance conferred by ML-O powdery mildew resistance genes in barley

Summary Ten barley mutants and five Ethiopian barley lines representing 11 independently arisen powdery mildew resistance genes in the ml-o locus were tested at the seedling stage to cultures of the powdery mildew fungus from Europe, Israel, USA. Canada, and Japan. They were resistant with infection type 0/(4) in all tests. They were also resistant to field populations of the pathogen when scored in disease nurseries at more than 78 locations in 29 countries in Europe, the Near East, North and South America. New Zealand, and Japan. This indicates that the 11 genes confer the same, world-wide spectrum of powdery mildew resistance. They have no effect on several other barley diseases such as stripe rust and leaf rust.Part of the research reported here was carried out under IAEA Research Agreement No 1043 and Research Contract No 139-74-1 BIO DK with the European Atomic Energy Community.     

Field assessment of partial resistance to powdery mildew in spring barley

Summary Partial resistance to powdery mildew in spring barley was evaluated in three plot types: large isolation plots, in 1.4 m² plots in chessboard design with guard plots of spring wheat and in single rows. Percentage leaf area covered by powdery mildew was scored four to six times during the season and partial resistance was characterized by the area under the disease progress curve. Varietal differences were revealed in al three plot designs, differences between the most resistant and susceptible genotypes being of a factor five. Differences between varieties decreased with decreasing plot size. The relationship between single scores of amount of powdery mildew on the upper four leaves and the area under the disease progress curve was high in all plot designs during the first two to three weeks after heading, allowing selection for the trait by one or two scorings. Differential ranking of varieties between different plot designs was observed, and is assumed to be due to increasing plot interference with reduced plot size and reduced distance between plots. A reliable selection for partial resistance could be made in large isolation plots and in 1.4 m² plots, but hardly in single rows.     

Differences in resistance of wild Lactuca species to natural infection of lettuce powdery mildew (Erysiphe cichoracearum)

Summary The natural infection of Erysiphe cichoracearum on 29 accessions of five wild Lactuca species (L. serriola, L. saligna. L. virosa, L. aculeata and L. dentata) and on one hybrid of L. serriola x L. sativa has been investigated for two and three years, respectively. No infection was observed on L. serriola (PI 255665), L. saligna (LSA/92/1 and LSA/92/2), L. virosa (LVIR/26 and LVIR/57/1) and L. dentata (PI 234204). The level of susceptibility of the control cultivars of L. sativa was found to be moderate (Fila) to fairly high (Hilde).     

Conservation of powdery mildew resistance genes in three composite cross populations of barley

Summary Barley powdery mildew was used as a model to evaluate the potential of barley composite cross populations for conservation of disease resistance. The objective was to determine if increases in resistance to powdery mildew could be detected over periods of time in composite cross populations developed in California, where the disease might have had a selective influence on the populations, and the same populations grown in Montana, where no selective influence of powdery mildew was expected. Four isolates of Erysiphe graminis f. sp. hordei were used to monitor the frequencies of plants with specific mildew resistances through early, intermediate and late generations of three composite cross populations (CCII, CCV, CCXII) grown at Davis, California, and Bozeman and Moccasin, Montana. Changes in frequencies of plants resistant to the four isolates were observed between generations in all populations from the three locations. Trends in the frequencies of resistance are discussed in relation to selection pressure applied by E. graminis. It is suggested that associations with gene complexes other than resistance to E. graminis might help to explain the increased resistance observed in these studies.This research was funded in part by U.S. Agency for International Development Contract No. AID/DSAN-C-0024. The authors are grateful to Dr A. L. Kahler for seed of the composite cross populations and to Dr J. G. Moseman for the powdery mildew cultures.Cooperative investigations of the Agricultural Research Service, U.S. Department of Agriculture; the Department of Plant Pathology, Montana State University; and The Montana Agricultural Experiment Station. Journal Series Paper No. 1381 of the Montana Agricultural Experiment Station.     

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.     

The oat line Pc54 as a source of resistance to crown rust,stem rust and powdery mildew in Europe

Summary The oat line Pc54 was found to be resistant to powdery mildew under both field and glasshouse conditions. The ratio of resistant to susceptible F₂ and F₂ progeny of a cross between a selection from the Pc54 line (Cc7422) and a susceptible cultivar (Selma) showed that, in addition to carrying the crown rust resistance gene Pc54 and the pg15 gene for stem rust resistance, the mildew resistance of the Pc54 line was conditioned by a single incompletely dominant gene along with additional factors which modified the expression of resistance. Previous results, that there was no linkage between genes Pc54 and Pg15, were confirmed. In addition, there was no evidence of linkage between the mildew resistance gene and gene Pc54. Evaluation of selections from within the Pc54 line showed that the expression of both stem rust and mildew resistance was modified by, or linked to, plant height. The effectiveness of genes Pc54 and Pg15, as measured by virulence frequencies, in central and eastern Europe is described.     

Effect of powdery mildew (Erysiphe graminis f.sp. hordei) on photosynthesis and grain yield of partially resistant genotypes of spring barley (Hordeum vulgare L.)

The effect of powdery mildew on the photosynthesis and grain yield of partially resistant spring barley was investigated. The effect of powdery mildew on the CO₂ exchange rate (CER) of inoculated and non-inoculated leaves was measured in several glasshouse experiments. Grain yield reduction by powdery mildew was determined in three field experiments. The CER of the inoculated leaves was reduced by infection but that of the non-inoculated leaves was not significantly different from that of the corresponding leaves of the control plants. The reduction in CER of the different genotypes was closely related to the percentage leaf area infected with powdery mildew. The correlation between degree of mildew infection and grain yield reduction varied between r = 0.84 (significant at P = 0.01) and r = 0.41 (not significant). Differences in greenness of the crop were correlated better with grain yield reduction (r = 0.66, P = 0.01) than powdery-mildew infection itself. Low percentages of powdery-mildew infection did not lead to significant reduction in grain yield. Partial resistance to powdery mildew could thus be a valuable attribute of future barley varieties.     

Molecular characterization of a novel powdery mildew resistance gene Pm30 in wheat originating from wild emmer

Powdery mildew caused by Erysiphe graminis f. sp. tritici is one of the most important wheat diseases in many regions of theworld. A powdery mildew resistance gene, originating from wild emmerwheat (Triticum dicoccoides) accession `C20', from Rosh Pinna, Israel,was successfully transferred to hexaploid wheat through crossing andbackcrossing. Genetic analysis indicated that a single dominant genecontrols the powdery mildew resistance at the seedling stage. SegregatingBC₁F₂ progenies of the cross 87-1/C20//2*8866 wereused for bulked segregant analysis (BSA). The PCR approach was used togenerate polymorphic DNA fragments between the resistant and susceptibleDNA pools by use of 10-mer random primers, STS primers, and wheatmicrosatellite primers. Three markers, Xgwm159/430,Xgwm159/460, and Xgwm159/500, were found to be linked tothe resistance gene. After evaluating the polymorphic markers in twosegregating populations, the distance between the markers and the mildewresistance gene was estimated to be 5–6 cM. By means of ChineseSpring nullisomic-tetrasomics and ditelosomics, the polymorphic markersand the resistance gene were assigned to chromosome arm 5BS and werephysically mapped on the gene rich regions of fragment length (FL) 0.41–0.43 by Chinese Spring deletion lines. As no powdery mildew resistancegene has been reported on chromosome arm 5BS, the mildew resistancegene originating from C20 should be a new gene and is designated Pm30.     

Isolation of wheat mutants with increased resistance to powdery mildew from small induced variant populations

Small variant wheat populations created by induced mutagenesis (n = 69) or adventitious regeneration (n = 66) were intensively screened for an altered response (compared to the parent variety ‘Guardian’) to the causal pathogen of powdery mildew in wheat, Blumeria graminis f. sp. tritici. Intensive field screening following natural infection of replicated plots of wheat lines over two years revealed a total of 13 mutants exhibiting significantly greater resistance than ‘Guardian’: eight from induced mutagenesis (11.6%) of the M2 population and five from adventitious regeneration (7.6%). Complete resistance was identified in two lines, (one (M66) developed following induced mutagenesis, and the other (SC240) by adventitious regeneration). The complete resistance in the induced mutant was stable over two generations and was associated with a high frequency of leaf flecking, and consequently a low grain yield. Resistance in SC240 proved to be unstable; SC240 exhibited complete resistance to powdery mildew in the SC₂ and SC₃ generations, but only 20% of the SC₄ plants were completely resistant, while the remainder were indistinguishable in mildew response to ‘Guardian’. The mildew response of all the SC₅ generation of SC240 was not significantly different from ‘Guardian’. Yield analysis of the thirteen mutants with increased resistance in the presence of powdery mildew indicated that eleven exhibitedgrain yields at least as high as that of ‘Guardian’, while the mutant M19 exhibited a yield significantly higher than that of ‘Guardian’. This revised version was published online in July 2006 with corrections to the Cover Date.     

Involvement of polyamines, diamine oxidase and polyamine oxidase in resistance of barley to Blumeria graminis f. sp. hordei

Polyamine levels and diamine and polyamine oxidase activities have been investigated in the first leaves of barley (Hordeum vulgare L.) in the absence of or following inoculation with conidia of powdery mildew (Blumeria graminis f. sp. hordei). Two cultivars with varying sensitivity to powdery mildew, viz., Chariot (resistant) and Golden Promise (susceptible) were used. The levels of putrescine, spermidine and spermine were found to be higher in the leaves of Chariot than in the leaves of Golden Promise and, with the exception of spermine, were generally higher in both cultivars after inoculation. In inoculated leaves of Chariot, levels of putrescine and spermidine peaked at 9 days and 12 days, respectively. In controls (uninoculated leaves), the activities of these enzymes, and putrescine and spermidine levels also increased but not to the same extent as in inoculated leaves. With Golden Promise, the levels of putrescine and spermidine in the inoculated leaves changed very little over sampling times but were always higher than in the controls. In this cultivar, there was little difference between inoculated leaves and the controls in diamine oxidase activity which reached a maximum value at 9 days post-inoculation. Activity of the bound form of diamine oxidase was low in both the cultivars. Polyamine oxidase was not detected at 3 days after inoculation in either cultivar but activity at fairly low levels was recorded at later times, usually reaching a maximum value at 9 days. The results suggest that polyamine metabolism and diamine oxidase activity in particular may be involved in the mechanism conferring resistance to barley powdery mildew in Chariot.     

Investigations on resistance of oats to Heterodera avenae: Location of resistance genes

Summary By using 15 available mono/nullisomic lines of Sun II back ground, the Heterodera avenae resistance gene in Nelson (from Avena sativa CI 3444) and Panema (from A. sterilis I. 376) were located on monosome XV. Genes with smaller effects were located on monosomes VIII and X. The absence of these genes derived from Sun II would increase cyst production on plants lacking major resistance genes.     

Molecular mapping of powdery mildew resistance genes in wheat: A review

Powdery mildew, caused by Blumeria graminis f. sp. tritici (syn. Erysiphe graminis f. sp. tritici), is one of the most important diseases of common wheat (Triticum aestivum L.) worldwide. Molecular mapping and cloning of genes for resistance to powdery mildew in hexaploid wheat will facilitate the study of molecular mechanisms underlying resistance to powdery mildew diseases and help understand the structure and function of powdery mildew resistance genes, and permit marker-assisted selection in breeding programs. So far, 48 genes/alleles for resistance to powdery mildew at 32 loci have been identified and located on 16 different chromosomes, of which 21 resistance genes/alleles have been tagged by restriction fragment length polymorphisms (RFLPs), random-amplified polymorphic DNAs (RAPDs), amplified fragment length polymorphisms (AFLPs), sequence characterized amplified regions (SCARs), sequence-tagged sites (STS) or simple sequence repeats (SSRs). Several quantitative trait loci (QTLs) for adult plant resistance (APR) to powdery mildew have been associated with molecular markers. The detailed information on chromosomal location and molecular mapping of these genes has been reviewed. Isolation of powdery mildew resistance genes and development of valid molecular markers for pyramiding resistance genes in breeding programs is also discussed.