Effect of Nitrogen and Powdery Mildew on the Yield Formation of Two Winter Barley Cultivars1

In field experiments the effect of powdery mildew on the yield formation of two barley cultivars ‘Catinka’ (partially resistant) and ‘Tapir’ (susceptible) was investigated in relation to three levels of nitrogen fertilization (40, 90, 150 kg N/ha). Nitrogen increased especially the single ear yield of cv.‘Catinka’, whereas cv.‘Tapir’ showed symptoms of N oversupply. Infection density of Erysiphe graminis hordei also increased with increased nitrogen supply, although it decreased transiently, at the highest N level for cv.‘Tapir’. In general, cv.‘Catinka’ was less tolerant to infections with E. graminis than cv.‘Tapir’, but yield response of both cultivars to powdery mildew (17, 11 and 8 % and 12, 16, and 12 % yield losses for cv.,‘Catinka’ and ‘Tapir’. respectively) showed cultivar × nitrogen interrelationships. Starch and protein contents of grains indicated differences in the intensity of detrimental effects caused by powdery mildew limiting the formation of carbohydrates and/or the translocation processes. Regression analysis demonstrated a closer correlation of yield losses with the photosynthetically active leaf area (r =+0.96 and +0.93 for ‘Catinka’ and ‘Tapir’) than with disease intensity (r =−0.32 and −0.85). Theinte,rpretation of disease/yield loss relations and the detrimental effect of powdery mildew are discussed with reference to plant resistance, remaining green leaf area, the availability of nutrients, to ‘sink and source’ conditions and to the occurrence of,additional environmental stresses.     

The Effect of Downy and Powdery Mildew on Grapevine (Vitis vinifera L.) Leaf Gas Exchange

The impact of powdery (Uncinula necator) and downy mildew (Plasmopara viticola) on grapevine leaf gas exchange was analysed. Gas exchange measurements (assimilation A, transpiration E, stomatal conductance g_s, intercellular concentration of CO₂C_i) were made on three different leaf materials: (i) healthy tissue of diseased leaves, (ii) infected tissue of diseased leaves, (iii) healthy tissue of healthy leaves (control treatment). Using the same source of leaf tissue, photosynthetic pigment concentration (chlorophyll a, b) and fluorescence levels (minimal fluorescence F₀, maximal fluorescence F_m and the optimal quantum yield [F_m ? F₀]/F_m) were determined to explain the mechanism of action of the two diseases on leaf assimilation. The results indicated that powdery and downy mildew reduced the assimilation rates, not only through a reduction in green leaf area (visual lesions), but also through an influence on gas exchange of the remaining green leaf tissues, determining a ‘virtual lesion’. The ratios between virtual and visual lesions were higher in powdery mildewed leaves than in the downy mildewed leaves. The photosynthetic fluorescence level (F_v/F_m) was affected by neither of the two pathogens. The reduction in intercellular concentration of CO₂ and photosynthetic pigment may explain the lower assimilation rates in the healthy tissues of powdery and downy mildewed leaves respectively.     

Identification and mapping of two powdery mildew resistance genes in <Emphasis Type="Italic">Triticum boeoticum</Emphasis> L.

Powdery mildew (PM) caused by Blumeria graminis f. sp. tritici (Bgt), is one of the important foliar diseases of wheat that can cause serious yield losses. Breeding for cultivars with diverse resources of resistance is the most promising approach for combating this disease. The diploid A genome progenitor species of wheat are an important resource for new variability for disease resistance genes. An accession of Triticum boeoticum (A^bA^b) showed resistance against a number of Bgt isolates, when tested using detached leaf segments. Inheritance studies in a recombinant inbred line population (RIL), developed from crosses of PM resistant T. boeoticum acc. pau5088 with a PM susceptible T. monococcum acc. pau14087, indicated the presence of two powdery mildew resistance genes in T. boeoticum acc. pau5088. Analysis of powdery mildew infection and molecular marker data of the RIL population revealed that both powdery mildew resistance genes are located on the long arm of chromosome 7A. Mapping was conducted using an integrated linkage map of 7A consisting of SSR, RFLP, STS, and DArT markers. These powdery mildew resistance genes are tentatively designated as PmTb7A.1 and PmTb7A.2. The PmTb7A.2 is closely linked to STS markers MAG2185 and MAG1759 derived from RFLP probes which are linked to powdery mildew resistance gene Pm1. This indicated that PmTb7A.2 might be allelic to Pm1. The PmTb7A.1, flanked by a DArT marker wPt4553 and an SSR marker Xcfa2019 in a 4.3 cM interval, maps proximal to PmT7A.2. PmTb7A.1 is putatively a new powdery mildew resistance gene. The powdery mildew resistance genes from T. boeoticum are currently being transferred to cultivated wheat background through marker-assisted backcrossing, using T. durum as bridging species.     

The adult plant rust resistance loci Lr34/Yr18 and Lr46/Yr29 are important determinants of partial resistance to powdery mildew in bread wheat line Saar

Powdery mildew, caused by Blumeria graminis f. sp. tritici is a major disease of wheat (Triticum aestivum L.) that can be controlled by resistance breeding. The CIMMYT bread wheat line Saar is known for its good level of partial and race non-specific resistance, and the aim of this study was to map QTLs for resistance to powdery mildew in a population of 113 recombinant inbred lines from a cross between Saar and the susceptible line Avocet. The population was tested over 2 years in field trials at two locations in southeastern Norway and once in Beijing, China. SSR markers were screened for association with powdery mildew resistance in a bulked segregant analysis, and linkage maps were created based on selected SSR markers and supplemented with DArT genotyping. The most important QTLs for powdery mildew resistance derived from Saar were located on chromosomes 7DS and 1BL and corresponded to the adult plant rust resistance loci Lr34/Yr18 and Lr46/Yr29. A major QTL was also located on 4BL with resistance contributed by Avocet. Additional QTLs were detected at 3AS and 5AL in the Norwegian testing environments and at 5BS in Beijing. The population was also tested for leaf rust (caused by Puccinia triticina) and stripe rust (caused by P. striiformis f. sp. tritici) resistance and leaf tip necrosis in Mexico. QTLs for these traits were detected on 7DS and 1BL at the same positions as the QTLs for powdery mildew resistance, and confirmed the presence of Lr34/Yr18 and Lr46/Yr29 in Saar. The powdery mildew resistance gene at the Lr34/Yr18 locus has recently been named Pm38. The powdery mildew resistance gene at the Lr46/Yr29 locus is designated as Pm39.     

Leaf growth characteristics of Vitis vinifera and prediction of final lamina length for studies of powdery mildew

Total functional leaf area is a key factor in determining crop yield. A nonlinear mixed‐effects model was employed to estimate growth responses for individual leaves using repeated measures of lamina length ≥30 mm, in the absence of disease. Resulting growth curves make allowances for, and allow assessment of, leaf to leaf variability. The major source of variability in leaf growth was identified as differences in thermal time required to reach half final lamina length. Juvenile leaves of Vitis vinifera are susceptible to infection by the powdery mildew fungus (Erysiphe necator) which impairs leaf function. The model was used to predict unobserved final lamina length for a subset of leaves inoculated with E. necator immediately after observations ceased. The severity of infection by E. necator varies among infected leaves. A previous study identified which of the inoculated leaves developed symptoms of severe powdery mildew. Maximum severity of infection was found to occur when individual leaves were at 85.3–97.9% of predicted final lamina length.     

Response of mulberry accessions to major foliar diseases in temperate conditions of Jammu and Kashmir,India

Thirty-three indigenous and 24 exotic mulberry accessions belonging to five Morus spp. originated from seven countries distributed in temperate and tropical climates were observed for their response to two major foliar diseases during 2010 and 2011 under temperate conditions of Jammu and Kashmir, India. Leaf spot and powdery mildew severity (Percent Disease Index (PDI)) ranged from 0.00 to 74.90% and 0.00 to 59.85%, respectively. Indigenous and exotic accessions responded similarly to leaf spot, but varied too much to powdery mildew. Irrespective of origin, response in ascending order of PDI for leaf spot is M. multicaulis, M. indica, M. alba, M. kayayama and M. bombycis and for powdery mildew is M. multicaulis, M. kayayama, M. bombycis M. alba and M. indica. Among indigenous accessions, Brentul Kashmir offered highest resistance to both the diseases. Nadigam offered maximum resistance only to leaf spot followed by Himachal local; while Chinarpati followed by Mysore local only for powdery mildew. Among exotic accessions, Ichinose offered maximum resistance to both the diseases followed by Kokusou-21 and Tagowase.     

Transient silencing of VvCSN5 enhances powdery mildew resistance in grapevine (Vitis vinifera)

As one of the most economically important fruit crops in the world, the grapevine (Vitis vinifera) suffers significant yield losses from various pathogens including powdery mildew caused by Erysiphe necator. In contrast, several wild Chinese grapevines, including Vitis pseudoreticulata accession Baihe-35-1, are highly resistant to powdery mildew pathogens. Here, we identified a grapevine gene CSN5 (COP9 signalosome complex subunit 5), designated VvCSN5, that was differentially expressed between the resistant ‘Baihe-35-1’ and susceptible ‘Thompson Seedless’ during powdery mildew isolate Erysiphe necator NAFU1 infection. Moreover, transient silencing of VvCSN5 in ‘Thompson Seedless’ leaves enhanced resistance to En NAFU1. This resistance manifested in cell wall callose deposition at attempted infection sites and hypersensitive response-like cell death of penetrated epidermal cells. Several defense-related marker genes (VvPR1, VvPR3, VvPAD4, and VvRBOHD) had higher basal expression levels in VvCSN5-silenced leaves. In addition, we found the structure and activity of CSN5 promoters in ‘Thompson Seedless’ and ‘Baihe-35-1’ were different, which may have been behind their different resistances to powdery mildew infection. Taken together, these results implied that grapevine CSN5 plays an important role in the response to powdery mildew infection.

     

Screening of mulberry germplasm lines against Powdery mildew,Myrothecium leaf spot and Pseudocercospora leaf spot disease complex

Abstract

Fifty-six indigenous and 29 exotic mulberry varieties were screened against powdery mildew, Myrothecium leaf spot, Pseudocercospora leaf spot for a period of three years under field conditions. The percent disease index (PDI) was recorded during the peak season of the diseases. Out of 85 germplasm lines studied four-germplasm lines viz. Thailand lobed (0.43), M. multicaulis (2.63), Italian (2.83) and M. australis (4.56) were found highly resistant; nine lines were resistant; 43 lines were moderately resistant and 29 were susceptible to the disease complex. Powdery mildew showed significant positive correlation with Pseudocercospora leaf spot. Highly resistant varieties may be utilized for future disease resistance breeding programme to evolve multiple disease resistant mulberry varieties.     

Two Erysiphe species associated with recent outbreak of soybean powdery mildew: results of molecular phylogenetic analysis based on nuclear rDNA sequences

 Serious outbreaks of powdery mildew by a fungus belonging to the mitosporic genus Oidium subgenus Pseudoidium have been reported on soybean (Glycine max) in a wide area of eastern Asia since 1998. The taxonomic and phylogenetic placement of the causal fungus has not yet been determined because of lack of the perfect stage. We found ascomata having mycelioid appendages on a single leaf of soybean infested by powdery mildew. Molecular phylogenetic analysis was conducted based on a total of 14 sequences of the rDNA internal transcribed spacer (ITS) region from 13 soybean and wild soybean (Glycine soja) materials collected in Japan, Korea, Vietnam, and the United States, combined with 47 sequence data obtained from the DNA databases. It was revealed that two Erysiphe species were associated with the outbreak of soybean powdery mildew. There was 16% difference between the two species in genetic divergence of the ITS sequence. One species with perfect stage has an ITS sequence identical to that of Erysiphe glycines on Amphicarpaea and is identified as Erysiphe glycines based on the ITS sequence and morphology of ascomata. The second species, without the perfect stage, is likely to be Erysiphe diffusa (= Microsphaera diffusa), known as the fungus causing soybean powdery mildew in the United States, because the ITS sequences are identical to those from materials collected in the United States. However, we need materials having ascomata of E. diffusa to confirm the species name. Received: March 15, 2002 / Accepted: May 22, 2002     

Paecilomyces fumosoroseus (Deuteromycotina: Hyphomycetes) as a potential mycoparasite on Sphaerotheca fuliginea (Ascomycotina: Erysiphales)

Hyphomycete Paecilomyces fumosoroseus that is well known as saprophytic and entomopatogenic fungus was investigated for its mycoparasitism on the cucumber powdery mildew pathogen. Mycoparasitism was documented by using standard bioassay and SEM. Effects of mycoparasitism were evaluated in three types of experiments. Paecilomyces fumosoroseus was applied in the form of graded suspensions into a colony of powdery mildew on a leaf segment. Interaction between both fungi was observed as the percentage of colonized area vs. experimental time. In the second experiment, young cucumber plants were sprayed with a suspension of Paecilomyces fumosoroseus 24 h before inoculation of Sphaerotheca fuliginea. Pre-treatment with P. fumosoroseus reduced development and spreading of powdery mildew infection significantly 15 days post-inoculation in contrast to pre-treatments with sulfur fungicide and distilled water. The development of pure culture powdery mildew under determined experimental conditions was observed and compared with treated variants. In the third experiment, mildewed plants were treated with a suspension of P. fumosoroseus. The control treatments with sulfur fungicide and distilled water were tested. Effects of P. fumosoroseus on the dispersion of powdery mildew during a 21-day period were observed.P. fumosoroseus suppressed the development and spread of cucumber powdery mildew significantly during the time of the experiment. The mechanical and physical damages and disruptions of vegetative and fruiting structures of powdery mildew were recorded under light microscopy and S.E.M.Results were concluded in pursuance to differences between the natural behaviour and development of S. fuliginea on cucumber plants treated with P. fumosoroseus and non-treated plants.     

Simultaneous modification of three homoeologs of TaEDR1 by genome editing enhances powdery mildew resistance in wheat

Wheat (Triticum aestivum L.) incurs significant yield losses from powdery mildew, a major fungal disease caused by Blumeria graminis f. sp. tritici (Bgt). enhanced disease resistance1 (EDR1) plays a negative role in the defense response against powdery mildew in Arabidopsis thaliana; however, the edr1 mutant does not show constitutively activated defense responses. This makes EDR1 an ideal target for approaches using new genome‐editing tools to improve resistance to powdery mildew. We cloned TaEDR1 from hexaploid wheat and found high similarity among the three homoeologs of EDR1. Knock‐down of TaEDR1 by virus‐induced gene silencing or RNA interference enhanced resistance to powdery mildew, indicating that TaEDR1 negatively regulates powdery mildew resistance in wheat. We used CRISPR/Cas9 technology to generate Taedr1 wheat plants by simultaneous modification of the three homoeologs of wheat EDR1. No off‐target mutations were detected in the Taedr1 mutant plants. The Taedr1 plants were resistant to powdery mildew and did not show mildew‐induced cell death. Our study represents the successful generation of a potentially valuable trait using genome‐editing technology in wheat and provides germplasm for disease resistance breeding.     

Quantitative trait loci for resistance against powdery mildew in a segregating wheat×spelt population

 Powdery mildew is one of the major diseases of wheat in regions with a maritime or semi-continental climate and can strongly affect grain yield. The attempt to control powdery mildew with major resistance genes (Pm genes) has not provided a durable resistance. Breeding for quantitative resistance to powdery mildew is more promising, but is difficult to select on a phenotypic basis. In this study, we mapped and characterised quantitative trait loci (QTLs) for adult-plant powdery mildew resistance in a segregating population of 226 recombinant inbred lines derived from the cross of the Swiss wheat variety Forno with the Swiss spelt variety Oberkulmer. Forno possibly contains the Pm5 gene and showed good adult-plant resistance in the field. Oberkulmer does not have any known Pm gene and showed a moderate susceptible reaction. Powdery mildew resistance was assessed in field trials at two locations in 1995 and at three locations in 1996. The high heritability (h²=0.97) for powdery mildew resistance suggests that the environmental influence did not affect the resistance phenotype to a great extent. QTL analysis was based on a genetic map containing 182 loci with 23 linkage groups (2469 cM). With the method of composite interval mapping 18 QTLs for powdery mildew resistance were detected, explaining 77% of the phenotypic variance in a simultaneous fit. Two QTLs with major effects were consistent over all five environments. One of them corresponds to the Pm5 locus derived from Forno on chromosome 7B. The other QTL on 5A, was derived from the spelt variety Oberkulmer and did not correspond to any known Pm gene. In addition, five QTLs were consistent over three environments, and six QTLs over two environments. The QTL at the Pm5 locus showed a large effect, although virulent races for Pm5 were present in the mixture of isolates. Molecular markers linked with QTLs for adult-plant resistance offer the possibility of simultaneous marker-assisted selection for major and minor genes. Received: 22 September 1998 / Accepted: 26 October 1998     

<Emphasis Type="Italic">MlAG12</Emphasis>: a <Emphasis Type="Italic">Triticum timopheevii</Emphasis>-derived powdery mildew resistance gene in common wheat on chromosome 7AL

Wheat powdery mildew is an economically important disease in cool and humid environments. Powdery mildew causes yield losses as high as 48% through a reduction in tiller survival, kernels per head, and kernel size. Race-specific host resistance is the most consistent, environmentally friendly and, economical method of control. The wheat (Triticum aestivum L.) germplasm line NC06BGTAG12 possesses genetic resistance to powdery mildew introgressed from the AAGG tetraploid genome Triticum timopheevii subsp. armeniacum. Phenotypic evaluation of F₃ families derived from the cross NC06BGTAG12/‘Jagger’ and phenotypic evaluation of an F₂ population from the cross NC06BGTAG12/‘Saluda’ indicated that resistance to the ‘Yuma’ isolate of powdery mildew was controlled by a single dominant gene in NC06BGTAG12. Bulk segregant analysis (BSA) revealed simple sequence repeat (SSR) markers specific for chromosome 7AL segregating with the resistance gene. The SSR markers Xwmc273 and Xwmc346 mapped 8.3 cM distal and 6.6 cM proximal, respectively, in NC06BGTAG12/Jagger. The multiallelic Pm1 locus maps to this region of chromosome 7AL. No susceptible phenotypes were observed in an evaluation of 967 F₂ individuals in the cross NC06BGTAG12/‘Axminster’ (Pm1a) which indicated that the NC06BGTAG12 resistance gene was allelic or in close linkage with the Pm1 locus. A detached leaf test with ten differential powdery mildew isolates indicated the resistance in NC06BGTAG12 was different from all designated alleles at the Pm1 locus. Further linkage and allelism tests with five other temporarily designated genes in this very complex region will be required before giving a permanent designation to this gene. At this time the gene is given the temporary gene designation MlAG12.     

Powdery Mildew Caused by an Erysiphe sp. on Korean Ginseng

In August and September 2014, Korean ginseng (Panax ginseng) plants showing symptoms of powdery mildew infection were found in a polyethylene film‐covered greenhouse in Suwon, Korea. The mildew was initially observed to occur in circular to irregular white colonies, which subsequently developed into abundant mycelial growths on both leaf surfaces. No chasmothecia were observed. Based on its morphological characteristics, the fungus was determined to be a species of Erysiphe. Phylogenetic analysis of the sequence of the internal transcribed spacer region of the ribosomal DNA obtained from the isolate placed the powdery mildew fungus in the genus Erysiphe. Here, we describe this Erysiphe sp. found growing on Korean ginseng using both illustrations and molecular data. A comparison of the Korean isolate and three previous records of powdery mildews known to grow on Panax plants is also provided. This is the first report of powdery mildew on Korean ginseng in Korea.     

Using aerated compost tea in comparison with a chemical pesticide for controlling rose powdery mildew

Rose powdery mildew (Sphaerotheca pannosa var. rosae) is one of the most common foliar diseases of roses worldwide. Application of chemical products on the plant or in the soil kills a range of the beneficial micro-organisms thereby disturbing ecosystem. Compost tea helps to restore and increase the populations of those beneficial micro-organisms. The objective of the present study was to evaluate the comparison of biopesticide (compost tea) and a chemical pesticide. The experiment was performed in three treatments, which were compost tea, fungicide (Topaz) and no treatment in three replications. After foliar applications of biopesticide and fungicide, the control percentage was estimated based on the number of infected flowers with powdery mildew. The results indicated that there was a significant difference between these treatments on rose in controlling powdery mildew (F?=?23.25, p?=?0.0015, df?=?2), at a probability level of 1% (p???0.01). So, that control percentage of compost tea treatment was the most.     

Studies of the incidence, severity and distribution of false rust (Synchytrium psophocarpi), leaf spot (Pseudocercospora psophocarpi) and powdery mildew (Oidium sp.) on winged bean (Psophocarpus tetragonolobus) in Papua New Guinea

The incidence, severity and distribution of false rust, (Synchytrium psophocarpi), leaf spot (Pseudocercospora psophocarpi) and powdery mildew (Oidium sp.) on winged beans (Psophocarpus tetragonolobus) were evaluated on pure lines and mixed stands grown in Papua New Guinea between 1976 and 1978. Almost all of the 148 pure lines were susceptible to false rust and leaf spot and the incidence of these diseases increased with plant age. Standard area diagrams were superior to disease keys in evaluating disease severity. Levels of false rust on 10 promising agronomic lines differed according to the locality where the lines were grown. Two Thai lines showed resistance to false rust but P. scandens was immune to false rust and leaf spot. Surveys of 51 sites containing mixed stands of winged beans in the Eastern Highlands, Western Highlands, East New Britain, East Sepik, Madang and Morobe Provinces of Papua New Guinea indicated that leaf spot and false rust were present in both the wet and dry seasons and the apparent absence of disease was probably due to time and size of samples. The diseases appeared to be present in all the traditional winged bean growing areas of Papua New Guinea. It was difficult to obtain evidence of differences in palatability of tissues infected with false rust. The value of surveys and disease assessment in relation to evaluation of crop losses of winged bean caused by these pathogens and selection for resistance is discussed.     

First record of <Emphasis Type="Italic">Erysiphe magnifica</Emphasis> on lotus,a host outside the Magnoliales

The powdery mildew Erysiphe magnifica (Erysiphales, Ascomycota) has been recorded for the first time on lotus (Nelumbo nucifera) based on a collection from the Botanical Garden in Frankfurt am Main, Germany. This powdery mildew previously known only from Magnolia species was identified by a combination of light and scanning electron microscopic investigation of ascomata and the Oidium stage, and comparison of ITS DNA sequences. This finding is discussed with respect to the narrow host specificity concept used in Erysiphales taxonomy, the effect of lotus leaf surface on fungal infection, and the extending geographical distribution of powdery mildews.     

Evidence for Resistance-inducing Compounds in Conidia of Erysiphe graminis f.sp. hordei

Preparations of Erysiphe graminis f.sp. hordei conidia were spray-applied to the first leaf of barley plants which were subsequently challenge inoculated with virulent powdery mildew. The powdery mildew reducing effect of the preparations was assessed by scoring the outcome of the challenge inoculation. Homogenates of ungerminated conidia, germinated conidia, and methanol-water extracts of germinated conidia reduced the number of powdery mildew colonies. Cell wall fragments from ungerminated conidia, germinated conidia, and conidial germination fluid obtained from conidia germinated in aqueous suspension did not reduce the number of powdery mildew colonies. Microsconical analysis of the infection course following challenge inoculation indicated that the powdery mildew reducing effect is due partly to induced resistance.