Natural occurrence of ampelomyces intracellular mycoparasites in mycelia of powdery mildew fungi

This is the first extensive investigation that quantifies natural mycoparasitic relationships in the phyllosphere. The presence of Ampelomyces spp. was quantified in naturally occurring powdery mildew fungi collected in Hungary and Romania between 1992 and 1995. A total of 570 samples was studied representing 27 species (nine genera) of the Erysiphaceae infecting 41 host plant genera. The incidence of Ampelomyces spp., determined as the proportion of samples in which intracellular pycnidia were present, varied between 4.3 and 68.8% in the host fungal genera studied. The intensity of mycoparasitism, defined as a percentage of the powdery mildew mycelia parasitized by Ampelomyces , ranged from 0.15 to 65%. Both the incidence and the intensity of mycoparasitism showed the lowest values in Blumeria graminis (DC.) Speer collected from wild and cultivated monocotyledons, while the highest values were found in Arthrocladiella mougeotii (Lév.) Vassilkov infecting Lycium halimifolium Mill. plants. The paper reports for the first time the natural occurrence of Ampelomyces in Sawadaea bicornis (Wallr.:Fr.) Homma on maple.     

Antifungal activity of two alkaloids of Zephyranthes citrina and their field efficacy against powdery mildew (Erysiphe cichoracearum) of balsam

The anti-fungal activity of two alkaloids isolated from bulbs of Zephyranthes citrina was observed against 10 fungi, viz, Aternaria solani, A. triticina, Curvularia lunata, C. maculuns, Cercospora malvacearum, Erysiphe sp., Fusarium udum, Helminthosporium pisi, H. speciferum and Ustilago cynodontis. Different concentrations (200, 400, 600, 800, 1000 µg/ml of alkaloids (A and B) were used. Spore germination was inhibited at 600, 800, 1000 µg/ml. B alkaloid was used against Erysiphe cichoracearum causing powdery mildew in balsam (Impatiens balsamina) in the field as pre- and post-inoculation treatments at 1000, 1500, 2000 µg/ml doses. The extract was effective in both pre- and post-inoculation treatments. Foliar application of this alkaloid resulted in inducing synthesis of phenolic acid in the leaves of balsam. Maximum phenolics were detected in the leaves treated with 1500 µg/ml in both pre- and post-inoculation treatments. The increase in the production of phenolics in treated leaves of balsam can be correlated with the induction of resistance in treated plants against powdery mildew. The significant efficacy of the alkaloid under field conditions opens the possibility of its use by farmers for also controlling other diseases.     

Phylogenetic analysis and predicted secondary structures of the rDNA internal transcribed spacers of the powdery mildew fungi (Erysiphaceae)

The nucleotide sequences of the internal transcribed spacer (ITS) regions of the ribosomal DNA including the 5.8S rRNA gene and the 5′ end of the 28S rRNA gene have been determined for 19 species in 10 genera of the powdery mildew fungi in order to analyze their phylogenetic relationship. These fungi were divided into two large groups based on the nucleotide length of the ITS regions, and this grouping was in line with that based on the morphological characters of the anamorphic stage rather than the teleomorphic stage. Although the variable ITS sequences were often ambiguously aligned, conserved sites were also found. Thus, a neighbor-joining tree was constructed using the nucleotide sequence data of the conserved sites of the ITS regions, the 5.8S rRNA gene, and the 5′ end of the 28S rRNA gene. The phylogenetic tree displayed the presence of four groups in the powdery mildews, which were distinguished by their morphology and/or host ranges. In the ITS2 region, the presence of a common secondary structure having four hairpin domains was suggested, in spite of the highly variable nucleotide sequences of this region. The predicted secondary structure was supported by the compensatory mutations as well as compensatory conserved sequences and high G+C content in the predicted stem regions. Contribution No. 142 from the Laboratory of Plant Pathology, Mie University.     

PCR primers useful for nucleotide sequencing of rDNA of the powdery mildew fungi

Four PCR primers that are useful to determine the nucleotide sequences of the rDNA of the powdery mildew fungi were newly designed. These primers provide both enough stability to work on a wide range of powdery mildews and enough specificity to eliminate contaminating DNA by PCR. DNA sequences of the rDNA ITS region were successfully obtained from specimens that were contaminated by other fungi. In addition, sequence results of the 18S and 28S rDNA were dramatically improved by using these primers in most of the specimens examined.     

First record of dill powdery mildew caused by Erysiphe heraclei DC in Egypt

In Egypt, powdery mildew was observed for the first time on dill plants, during annual disease surveys of March–May 2003 and 2005. Typical symptoms of powdery mildew of dill plant (Anethum graveolens L.) were observed in Gharbeia Governorate. Symptoms of powdery mildew became common on leaves, stems inflorescences and fruits as white irregular areas. These symptoms appeared at vegetative and early flowering stages then gradually increased through fruiting and pre-maturity stages. Samples of infected leaflets, stem, inflorescences and fruits were collected for examination by light and scanning electron microscope (SEM). Microscopic examination revealed that conidiophores were short, erect–69 × 6–10 μm in dimension, conidia were observed without conspicuous fibrosin bodies singly, elliposid to ovoid 25–33 × 10–16 μm in dimension, and the length to width ratio of conidia ranged from 1.7 to 2.0 and were produced singly. Cylindrical foot cells (22.0 × 8.0 μm) were followed by one or two shorter cells (12.5 × 7.5 μm). In spring, the sexual stage (cleistothecia) appeared on infected leaves and stems in spherical, gregarious measures 105–117 (111) × 100– 87.5 μm in diameter. Each cleistothecium contained (2–4) round to ovoid asci, 45–55 (50) × 45–25 (35) μm in dimension. The ascus contained (3–4) ellipsoid to ovoid ascospores, 20–17.5 × 15–10 (13.2) μm. Cleistothecia appendages are simple myceloid branched tips measuring 80–200 (140) μm in length and 3–5 (4) μm in diameter. Based on the observations of the morphology of its anamorph and teleomorph stages, the causal agent of dill powdery mildew was identified as Erysiphe heraclei which is reported for the first time in Egypt.     

Antifungal activity of ethanolic extract of Archu (Rheum emodi) on powdery mildew (Erysiphe cichoracearum) and its role in the induction of resistance in balsam (Impatiens balsamania)

Rheum emodi, vernacularly known as Archu, is one of the important high altitude medicinal plants widely distributed in Himalayan regions. Though widely used in Ayurveda for curing various human diseases, its use in plant diseases is limited. Ethanolic extract of Rheum rhizome was assayed against spore germination of Alternaria solani, Heliminthosporium penniseti and Curvularia palliscens. The inhibition of spore germination was concentration dependent. Maximum inhibition was obtained at 4000 and 5000 ppm followed by 3000, 2000 and 1000 ppm. However, the extract was highly effective in the pre-inoculation treatment against powdery mildew (Erysiphe cichoracearum) of balsam (Impatiens balsamania) under field conditions. High performance liquid chromatographic (HPLC) analysis of balsam leaves showed increased synthesis of phenolic acids, which has been correlated with induced resistance in inhibiting the disease intensity of balsam powdery mildew.     

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     

Hyperparasites of the genus shape Ampelomyces on powdery mildew fungi in Serbia

From 1982 to 1996, in Serbia, 229 species of plants infected with powdery mildew were collected. Seventy-five species had hyperparasites of the genus Ampelomyces. Distribution analysis showed that hyperparasitism was greatest on plants from the families Asteraceae, Apiaceae and Fabaceae. Ampelomyces was not found on the family Poaceae. It was reported for the first time on the families Amygdalaceae, Cornaceae, Grossulariaceae, Plantaginaceae, Rhamnaceae and other 37 plant species. Hyperparasites of the genus Ampelomyces were found on 33 different species of fungi that are causal agents of powdery mildews. They are reported for the first time on nine species. Pycnidial size varied in the range 45–106 × 25.5–40.5 μm and conidia from 4.5–10.5 × 2.5–4.8 μm. This revised version was published online in June 2006 with corrections to the Cover Date.     

Ascocarp formation and survival and primary inoculum production in Erysiphe (sect. Microsphaera) pulchra in dogwood powdery mildew

Development of powdery mildew Erysiphe (sect. Microsphaera) pulchra in dogwood (Cornus florida) was assessed over a 5‐year period (1996–2000). Variations in the timing of initial infection, disease severity, ascocarp formation, and primary inoculum density were evaluated. Ascocarps formed late in the growing season (September‐November) when relatively low temperatures (< 27°C) persisted for at least 2 weeks, but ascocarp abundance was not influenced by disease severity. Studies conducted in a controlled environment showed that low temperatures triggered ascocarp formation and neither day length nor host plant age affected ascocarp formation. Ascocarps formed within 12–14 days at 18°C/ 10°C (day/night) and 23°C/15°C, but required 25 days at 26°C/18°C; no ascocarps formed at 28°C/ 20°C. Because ascocarps are an important source of primary inoculum for dogwood powdery mildew, ascocarp survival was evaluated in a 2‐year study (1998–2000). 60–80% of mature, dark‐coloured ascocarps survived at ‐10°C and ‐20°C and maintained viable spores for 4 months, but only 4–12% of partially developed, light brown ascocarps survived at ‐10°C and ‐20°C in the first experiment and only 30–40% survived in the second experiment. Immature ascocarp initials (cream‐yellow in colour) withered and disintegrated at all temperatures (24°C/20°C, 4°C, ‐10°C, and ‐20°C). Because ascocarps need time to mature, the timing of ascocarp initiation affects ascocarp maturity and thus winter survival and primary inoculum density. The evaluation of spring inoculum dispersal to spore traps and trap plants in 1999 and 2000 showed that rainfall patterns in early spring influenced primary inoculum and thus the timing of initial infection.     

Resveratrol stimulates phenolic metabolism and PSII efficiency in wheat infected with powdery mildew

The beneficial effects of trans-resveratrol on pathogen-response and its physiological mechanisms were studied in two wheat cultivars differing in the level of resistance against powdery mildew (Blumeria graminis (DC.) Speer). Resveratrol induced phenolics metabolism in a manner that lead to increased phenylalanine ammonia-lyase (PAL) and β-D-glucosidase activity in leaf regions showing no symptoms of pathogen infection. In less-resistant cultivar, similar alterations were additionally observed in regions invaded by the pathogen. Resveratrol also stimulated photosynthetic efficiency during pathogenesis and this effect was more prominent in the resistant cultivar. Regulatory function of resveratrol on wheat growth and development was also observed (stimulation of generative induction). High performance liquid chromatography (HPLC) analysis detected a low amount of compound with retention time corresponding to trans-resveratrol in healthy leaves and increased the content of this compound in infected foliage. The multidirectional properties of resveratrol activity in wheat plants are discussed.     

Resistance that stacks up: engineering rust and mildew disease control in the cereal crops wheat and barley

Staying ahead of the arms race against rust and mildew diseases in cereal crops is essential to maintain and preserve food security. The methodological challenges associated with conventional resistance breeding are major bottlenecks for deploying resistance (R) genes in high-yielding crop varieties. Advancements in our knowledge of plant genomes, structural mechanisms, innovations in bioinformatics, and improved plant transformation techniques have alleviated this bottleneck by permitting rapid gene isolation, functional studies, directed engineering of synthetic resistance and precise genome manipulation in elite crop cultivars. Most cloned cereal R genes encode canonical immune receptors which, on their own, are prone to being overcome through selection for resistance-evading pathogenic strains. However, the increasingly large repertoire of cloned R genes permits multi-gene stacking that, in principle, should provide longer-lasting resistance. This review discusses how these genomics-enabled developments are leading to new breeding and biotechnological opportunities to achieve durable rust and powdery mildew control in cereals.     

白粉病菌侵染苦瓜的生理机制

对大顶苦瓜感染白粉病的发病过程和生理机制进行研究。结果发现,感病苦瓜叶片质膜透性与对照相比增加较少,其增加量与病情指数相关性不高;叶绿素a、b、总叶绿素、类胡萝卜素含量随病情加重均下降,接种15d,与对照比分别下降72.6%、68.5%、71.5%和27.1%,其中叶绿素a、b和总叶绿素含量变化与病情指数相关性很高,以叶绿素a含量变化相关性最高;氧化酶活性测定结果表明,感病苦瓜叶片中POD和PPO活性与对照比上升,且随感病时间延长活性增加更多,接种15d,POD和PPO活性较对照增加528.5%和70.4%,两个酶活性变化与病情指数的相关性也很高。     

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.     

Transgenic Pm3 multilines of wheat show increased powdery mildew resistance in the field

Resistance (R) genes protect plants very effectively from disease, but many of them are rapidly overcome when present in widely grown cultivars. To overcome this lack of durability, strategies that increase host resistance diversity have been proposed. Among them is the use of multilines composed of near-isogenic lines (NILs) containing different disease resistance genes. In contrast to classical R-gene introgression by recurrent backcrossing, a transgenic approach allows the development of lines with identical genetic background, differing only in a single R gene. We have used alleles of the resistance locus Pm3 in wheat, conferring race-specific resistance to wheat powdery mildew (Blumeria graminis f. sp. tritici), to develop transgenic wheat lines overexpressing Pm3a, Pm3c, Pm3d, Pm3f or Pm3g. In field experiments, all tested transgenic lines were significantly more resistant than their respective nontransformed sister lines. The resistance level of the transgenic Pm3 lines was determined mainly by the frequency of virulence to the particular Pm3 allele in the powdery mildew population, Pm3 expression levels and most likely also allele-specific properties. We created six two-way multilines by mixing seeds of the parental line Bobwhite and transgenic Pm3a, Pm3b and Pm3d lines. The Pm3 multilines were more resistant than their components when tested in the field. This demonstrates that the difference in a single R gene is sufficient to cause host-diversity effects and that multilines of transgenic Pm3 wheat lines represent a promising strategy for an effective and sustainable use of Pm3 alleles.     

Polyamine metabolism in barley reacting hypersensitively to the powdery mildew fungus Blumeria graminis f. sp. hordei

Polyamine levels and activities of enzymes of polyamine biosynthesis and catabolism were examined in the barley cultivar Delibes (Ml1al + Ml(Ab)) reacting hypersensitively to the powdery mildew fungus, Blumeria graminis f. sp. hordei (race CC220). Levels of free putrescine and spermine and of conjugated forms of putrescine, spermidine and spermine were greatly increased 1–4 d following inoculation of barley with the powdery mildew. These changes in polyamine levels were accompanied by elevated activities of the polyamine biosynthetic enzymes ornithine decarboxylase (ODC), arginine decarboxylase (ADC) and S‐adenosylmethionine decarboxylase (AdoMetDC) and the polyamine catabolic enzymes diamine oxidase (DAO) and polyamine oxidase (PAO). Activities of two enzymes involved in conjugating polyamines to hydroxycinnamic acids, putrescine hydroxycinnamoyl transferase (PHT) and tyramine feruloyl‐CoA transferase (TFT) were also examined and were found to increase significantly 1–4 d after inoculation. The possibility that the increased levels of free spermine, increased polyamine conjugates, and increased DAO and PAO activities are involved in development of the hypersensitive response of Delibes to powdery mildew infection is discussed.