Normal germling development by Erysiphe graminis on cereal leaves freed of epicuticular wax

Experiments were conducted to test the hypothesis that recognition of the physical structure of epicuticular leaf waxes by Erysiphe graminis may be important to the development of normal germlings and the formation of functional appressoria. Comparisons of germination rates and characteristics of germling development by E. graminis f.sp. avenae , and in one experiment by f.sp. hordei , were made between intact cereal leaves and leaves from which the epicuticular waxes had been stripped away.
Overall, fungal development was very similar on intact and wax-free leaves: although germination rates were slightly, but significantly, lower, and lengths of appressorial germ tubes slightly greater, on stripped than intact leaves, a very similar proportion of germlings formed apparently normal appressoria in both cases. This was true for f.sp. avenae on first- and fifth-formed leaves of susceptible and adult plant resistant oats, and on barley and wheat first leaves, and for f.sp. hordei on first leaves of barley, oat and wheat. The appressoria formed on stripped leaves not only appeared normal, but also formed haustoria with at least the same frequency as on intact leaves; in several experiments, a higher proportion formed haustoria in stripped than intact leaves. Wax removal did not affect the adult plant resistance of oat cv. Maldwyn, which limits haustorium formation by appressoria, indicating that epicuticular wax was not involved in this resistance. It is concluded that the physical structure of epicuticular wax is not involved in the recognition processes leading to normal germling development.     

Local and systemic effects of oxylipins on powdery mildew infection in barley

Treatment of the first leaves of barley seedlings with the oxylipin colneleic acid, or the two trihydroxy oxylipins 9,12,13-trihydroxy-11(E)-octadecenoic acid and 9,12,13-trihydroxy-10(E)-octadecenoic acid, reduced infection of that leaf by the powdery mildew fungus Blumeria graminis Speer f sp hordei Marchal. When applied to first leaves, etheroleic acid and colneleic acid, as well as the trihydroxy oxylipin 9,12,13-trihydroxy-10(E),15(Z)-octadecadienoic acid, also reduced mildew infection in second leaves. In all cases where local and systemic effects against mildew were observed, activity of the defence-related enzyme phenylalanine ammonia lyase (PAL) was increased, but only following challenge inoculation with powdery mildew. Peroxidase activity was not affected by oxylipin treatment or mildew inoculation. Whether the effects observed were due to the oxylipins or to breakdown products is not known, since no information is available on the stability of these particular oxylipins on leaf surfaces. Nevertheless, these data represent the first report of systemic effects against pathogen infection following pre-treatment with oxylipins.     

Effects of impacting rain drops on the growth and development of powdery mildew fungi

The effects of rain on different stages of powdery mildew development were investigated quantitatively for Erysiphe graminis on barley, Erysiphe pisi on pea and Sphaerotheca pannosa on rose. Water drops 4 mm in diameter released from a height of 2·5 m onto target leaves reduced the numbers of conidia on the impacted surfaces and inhibited subsequent mildew development, the effects declining as the interval between inoculation and impaction increased. Simulated rainfall applied after inoculation reduced the numbers of conidia on leaves and inhibited mildew development, the effect declining as the interval between inoculation and treatment lengthened. Simulated rainfall applied to infected plants reduced their capacity to inoculate other plants, the effect declining as the interval between treatment and use as inoculum lengthened. Controlled exposure of infected peas and roses to natural rain reduced the numbers of conidia on leaves and inhibited subsequent mildew development, especially on upper leaf surfaces.     

The relative tolerances of wild and cultivated oats to infection byErysiphe graminisf.sp.avenae: I. The effects of infection on vegetative growth and yield

The effects of infection by the powdery mildew fungusErysiphe graminisf.spavenaewere studied in one line of wild oat (Avena fatua), and two cultivars, Lustre and Peniarth, of cultivated oat (A. sativa) to determine if the wild oat was more tolerant of infection than the two cultivated oats. Seven weeks after inoculation, when the plants were 10-weeks-old with fully expanded flag leaves, the fungus had colonized approx. 40% of the leaf surfaces of wild oat and cv. Lustre but only about 30% of the leaf surfaces of cv. Peniarth. The lower leaves of cv. Peniarth were at least as susceptible, if not more so, than those of the other two lines but the upper leaves, including the flag leaf, were much more resistant. Although cv. Peniarth supported the production of about half the number of mildew conidia as the wild oat and cv. Lustre its total dry weight and grain yield were reduced to the greatest extent. The wild oat was clearly much more tolerant of mildew infection than cv. Peniarth and slightly more tolerant than cv. Lustre. The greater tolerances of the wild oat and cv. Lustre compared to cv. Peniarth appeared to be due to the lower sensitivities of their metabolism to the activities of the mildew fungus.     

Infection of ryegrass by three rust fungi (Puccinia coronata, P. graminis and P. loliina) and some effects of temperature on the establishment of the disease and sporulation

Experiments were conducted to examine the processes leading up to the infection of Lolium temulentum by crown rust ( Puccinia coronata ), stem rust ( P. graminis ) and brown rust ( P. loliina ), and the effects of temperature on these processes and sporulation. Uredia of all three rusts were produced freely if the adaxial leaf surface was inoculated, but did not form following inoculation of the abaxial surface. Light and scanning electron microscopy revealed abnormal growth of germlings on the abaxial surface which had amorphous sheet-like epicuticular waxes and very few stomata. On the adaxial leaf surface germ tubes of all the rusts orientated at right angles to the long axis of the leaf. However, the directional growth of germ tubes was often disrupted when they contacted the surface of bulliform cells at the base of leaf grooves. For P. loliina the optimum temperatures for urediospore germination and sub-stomatal vesicle formation were 12–16°C, and 8–20°C for appressorium formation. The optimum temperatures, for the same stages of fungal development, for P. coronata and P. graminis were higher. Urediospore production of P. loliina was higher at 10°C than at 25°C, but was similar at both temperatures for P. coronata .     

Evaluation of the systemic activity of simeconazole in comparison with that of other DMI fungicides

The systemic activity of simeconazole (RS-2-(4-fluorophenyl)-1-(1H-1,2,4-triazol-1-yl)-3-trimethylsilylpropan-2-ol) in plants was compared with those of eight other sterol demethylation inhibitor (DMI) fungicides. Simeconazole prevented the infection of Blumeria graminis (DC) Speer f sp hordei Marchal on barley leaves within a radius of several centimeters from the edge of local treatment on the leaves when the compound was separated from the leaves by glass coverslips. This reveals that simeconazole has prominent vapour-phase activity. Simeconazole showed excellent curative activity against barley powdery mildew when treated 1-3 days after inoculation. Furthermore, this indicates that simeconazole has notable translaminar activity because, when the compound was applied onto either the adaxial or abaxial leaf surface, it showed excellent efficacy against powdery mildew on the opposite side of the leaf surface of barley and cucumber. Simeconazole also showed excellent efficacy against barley powdery mildew by soil drench 24h after inoculation. This suggests that simeconazole was absorbed very quickly into the barley plant after treatment. The permeability of the compound through cuticular membranes prepared from tomato fruits was about 20% at 22 h after the treatment and was much superior to that of the other DMI fungicides tested.     

Effects of foliar- and root-applied silicon on the enhancement of induced resistance to powdery mildew in Cucumis sativus

Two cucumber ( Cucumis sativus ) cultivars differing in their resistance to powdery mildew, Ningfeng No. 3 (susceptible) and Jinchun No. 4 (resistant), were used to study the effects of foliar- and root-applied silicon on resistance to infection by Podosphaera xanthii (syn. Sphaerotheca fuliginea ) and the production of pathogenesis-related proteins (PRs). The results indicated that inoculation with P. xanthii significantly suppressed subsequent infection by powdery mildew compared with noninoculation, regardless of Si application. Root-applied Si significantly suppressed powdery mildew, the disease index being lower in Si-supplied than in Si-deprived plants, regardless of inoculation treatment. The resistant cultivar had a more constant lower disease index than the susceptible cultivar, irrespective of inoculation or Si treatment. Moreover, with root-applied Si, activities of PRs (for example peroxidase, polyphenoloxidase and chitinase) were significantly enhanced in inoculated lower leaves or noninoculated upper leaves in inoculated plants of both cultivars. Root-applied Si significantly decreased the activity of phenylalanine ammonia-lyase in inoculated leaves, but increased it in noninoculated upper leaves. However, Si treatment failed to change significantly the activity of PRs in plants without fungal attack. Compared to the control (no Si), foliar-applied Si had no effects either on the suppression of subsequent infection by P. xanthii or on the activity of PRs, irrespective of inoculation. Based on the findings in this study and previous reports, it was concluded that foliar-applied Si can effectively control infections by P. xanthii only via the physical barrier of Si deposited on leaf surfaces, and/or osmotic effect of the silicate applied, but cannot enhance systemic acquired resistance induced by inoculation, while continuously root-applied Si can enhance defence resistance in response to infection by P. xanthii in cucumber.     

Investigations on the role of cuticular wax in resistance to powdery mildew in grapevine

Cuticular wax on the plant epidermis inhibits or enhances prepenetration events of powdery mildew (Erysiphe necator Schwein). We examined the role of cuticular leaf and berry waxes as a resistance mechanism in four grapevine genotypes (Italia?×?Mercan-174, Gürcü, Isabella, Özer Karas?) resistant to powdery mildew after natural infection and inoculation. To understand cuticular wax properties, we determined the amount of wax and antifungal effects of thin layer chromatography (TLC) fractions from cuticular leaf and berry waxes, then assessed the chemical composition of fractions with different antifungal activities using gas chromatography/mass spectrometry (GC/MS). Susceptible genotypes Cabernet Sauvignon and Italia were used for comparison. Resistant and sensitive genotypes did not differ significantly in the total amount of wax on leaves and berries; however, 27 fatty acids, 26 alkanes, 6 terpenes, 4 indole derivatives and 4 ketones, and 3 amides, 3 phenols and 3 steroids were detected in fractions with high antifungal activity (≥75% inhibition of germination) in leaf and/or berry cuticular waxes of resistant genotypes only. These compounds may be evaluated as markers for powdery mildew resistance during genotype selection in a grapevine breeding program.     

Aromatic Substances Inhibiting Wheat Powdery Mildew Produced by a Fungus Detected with a New Screening Method for Phylloplane Fungi

Microorganisms isolated from wheat leaf surfaces were screened for inhibition of wheat powdery mildew. A new screening method, in which wheat leaves were inoculated with Blumeria graminis f. sp. tritici and incubated with the cultured microorganisms under non-contact conditions, was developed in the present study. Using this method, 10 phylloplane fungi that inhibited wheat powdery mildew were selected from 408 microorganisms isolated from wheat leaf surfaces. Among these 10 strains, a fungus designated as Kyu-W63 had an especially strong inhibitory effect. Kyu-W63 produced white colonies without spores when cultivated on PDA. Kyu-W63 had a strong aromatic odor when being cultured. Wheat powdery mildew was suppressed even though a membrane filter with a pore size of 0.45 μm was placed between the mycelial colony and wheat leaf segment. However, when activated charcoal was introduced, Kyu-W63 did not inhibit growth of B. graminis. It was presumed that volatile substances were involved in the inhibitory effect of Kyu-W63. GC-MS analysis was used to identify two substances produced by Kyu-W63 with molecular weights of 164 and 166. Kyu-W63 also inhibited the in vitro growth of four plant pathogenic fungi other than B. graminis. Received 19 September 2001/ Accepted in revised form 7 February 2002     

Variation in adult plant resistance to powdery mildew in spring oats under field and laboratory conditions

Ten oat genotypes were assessed for adult plant resistance (APR) to powdery mildew ( Erysiphe graminis f.sp. avenae ) in small field plots and on detached leaf segments in the laboratory using glasshouse-grown plants. Significant genotype differences were observed in the field and on leaf segments for latent period, infection frequency and spore production, components used to assess APR. The genotype OM1711, which was selected because it expressed a higher level of mildew resistance than its most resistant parent, cv. Maldwyn, showed this transgressive resistance in both field and laboratory tests. By contrast, the genotype OM1387, also selected for high mildew resistance, only showed this enhancement in the field. It is concluded that quantitative assessment of mildew in detached leaves is not sufficiently precise to be used alone in selecting segregants for high levels of APR, and that field data are also needed.     

Components of spore production in apple powdery mildew (Podosphaera leucotricha)

The morphology of powdery mildew ( Podosphaera leucotricha) colonies of known age was studied on six apple cultivars inoculated in a glasshouse. Colonies were observed first on the older leaves. Mean disease incidence ranged from about 20% for cv. Laxton's Superb to about 45% for cv. Crispin. Conidiophore density (number of conidiophores/mm² colony) was higher on younger than on older leaves, higher on the upper than on the lower leaf surface, and decreased with the age of the colony. The number of hyphal interceptions on a line transect was higher on the upper surface but the ratio of conidiophore density to hyphal interceptions was greater on the lower surface and did not differ with colony age or cultivar. The number of conidia/conidiophore was higher on the younger leaves and on the upper surfaces and was at a maximum 7-12 days after the first sign of the colony. The number of conidia/mm² colony was higher on lower surfaces, especially of the younger leaves. There was generally an associated variation between cultivars in components of spore production.     

Potassium phosphate induces systemic protection in barley to powdery mildew infection

In laboratory tests, treatment of the first leaves of barley (Hordeum vulgare L cv Golden Promise) with potassium phosphate led to significant reduction in infection of the second leaves with the powdery mildew fungus Blumeria graminis f sp hordei Marchal, with a 25 mM treatment giving 89% reduction in infection. Although the optimal interval between phosphate treatment of the first leaves and mildew inoculation of the second leaves was 2 days, significant protection was still obtained if the interval was increased to 12 days. Protection against powdery mildew infection was not as effective when the potassium phosphate was applied as a seed treatment or root drench. Phosphate treatment of the first leaves led to significant increases in activities of phenylalanine ammonia lyase (PAL), peroxidase and lipoxygenase in second leaves. Enzyme activities, especially PAL and peroxidase, were increased further when second leaves of phosphate-treated plants were inoculated with powdery mildew. Phosphate treatment of the first leaves did not adversely affect plant growth and, in a field trial, 25 mM potassium phosphate provided 70% control of mildew and gave a small increase in grain yield.     

Threshold values for chemical control of powdery mildew (Erysiphe cruciferarum) on Brussels sprouts

To establish control thresholds for chemical control of powdery mildew (Erysiphe cruciferarum) on Brussels sprouts, mildew intensity on leaves and buds was observed on the cultivars Lunet, Tardis and Asgard during three years in unsprayed plots. Mildew infection on the leaves was observed from late August onwards, increasing to moderate or high levels. In one year light infestation of the buds was observed, but no reduction in quality occurred. These preliminary results indicate, that from late August onwards the following levels of leaf injury by powdery mildew can be tolerated: T=5+0.42^*(Julian date — 235), in which T is the tolerable leaf injury in percentage leaf area covered. When sampling the crop to assess powdery mildew infection, care must be taken that leaves are sampled from all stem positions, as top leaves tend to be much less infected.     

Behaviour of famoxadone deposits on grape leaves

Famoxadone is a new fungicide developed for the control of crop diseases, including grape downy mildew (Plasmopara viticola). The majority (>90%) of the spray deposit from a famoxadone 500 g kg⁻¹ water‐dispersible granule formation on a grape leaf were found on the leaf surface or associated with epicuticular waxes. A significant fraction of this deposit could not be removed by a water wash, suggesting strong binding to the waxes. Nearly 100% of the spray deposit was still recovered after 12 days of exposure to a dry environment, confirming the good residual properties of the substance. Thirty per cent of the applied active ingredient was lost after exposure to a wet environment, probably via hydrolysis or wash‐off. Studies with radiolabelled famoxadone formulated as a suspension concentrate indicated that redistribution occurred both in dry conditions, via diffusion in the cuticular waxes, and in wet conditions via dissolution in water followed by re‐deposition. No systemic movement of famoxadone was observed within the treated plant. Grape plants treated with famoxadone alone or in mixture with cymoxanil and subjected to up to 50 mm of artificial rain remained well protected against downy mildew infections. Good rain‐fastness was observed even 2 h after fungicide application. Despite low water solubility, famoxadone spray residues on grape leaves were reactivated in surface water sufficiently quickly to prevent infection by P viticola. © 2000 Society of Chemical Industry     

The C28 aldehyde octacosanal is a morphogenetically active component involved in host plant recognition and infection structure differentiation in the wheat stem rust fungus

Using Langmuir–Schäfer technology, a very thin, homogeneous coating of glass surfaces with leaf epicuticular waxes was achieved, allowing the establishment of a bio-assay for morphogenetically active, hydrophobic surface components triggering infection structure differentiation in a rust fungus. A chloroform extract of wheat leaf epicuticular wax coated onto a flat glass surface induced the formation of appressoria, substomatal vesicles, and infection hyphae in about 50% of the germ tubes of Puccinia graminis f.sp. tritici. No induction was seen on a glass surface coated with an inert wax which confered the same hydrophobicity to the surface as the leaf wax. The chemical composition of the leaf epicuticular wax extract was analysed, and the active ingredient was shown to be the C28-aldehyde, octacosanal. The importance of multiple recognition of a ‘host associated surface pattern’ (HASP) integrating both physical and chemical signaling cues for the crucial differentiation of an appressorium upon recognition of a host stoma is discussed.     

不同机制杀菌剂对小麦白粉病的敏感性及与三唑酮的交互抗性

为明确三唑酮和氟环唑、吡唑醚菌酯、啶酰菌胺、嘧菌环胺、乙嘧酚5种不同作用机制的杀菌剂对小麦白粉病的敏感性及交互抗性,采用田间小区试验和室内喷雾离体叶段法测定了不同杀菌剂对小麦白粉病的防治效果。结果表明,5种不同作用机制杀菌剂对小麦白粉病的防治效果可达90%以上,而三唑酮最高的防治效果仅为72.17%;小麦白粉病菌群体对氟环唑、吡唑醚菌酯、啶酰菌胺、嘧菌环胺、乙嘧酚的敏感性EC50分别在0.087~1.901、0.058~1.402、0.186~3.014、0.222~6.005、0.006~1.742μg/mL之间,5种不同作用机制杀菌剂的敏感性均呈连续单峰曲线,可作为小麦白粉病菌对5种不同作用机制杀菌剂的敏感基线。研究表明,三唑酮与氟环唑、吡唑醚菌酯、啶酰菌胺、嘧菌环胺、乙嘧酚之间不存在交互抗性。     

Effect of potassium silicate on epidemic components of powdery mildew on melon

The effects of silicon (Si) supplied in the form of potassium silicate (PS) were evaluated on epidemic components of powdery mildew of melon under greenhouse conditions. The PS was applied to the roots or to leaves. In the first experiment, epidemic components were evaluated after inoculation with Podosphaera xanthii. In the second experiment, the disease progress rate was evaluated on plants subjected to natural infection. The area under the disease progress curve was reduced by 65% and 73% in the foliar and root treatments, respectively, compared to control plants, as a consequence of reductions in infection efficiency, colony expansion rate, colony area, conidial production and disease progress rate. However, root application of PS was more effective than foliar application in reducing most of the epidemic components, except for infection efficiency. This can be explained by the high Si concentration in leaf tissues with root application, in contrast to the foliar treatment where Si was only deposited on the external leaf surfaces. The effects of PS reported in this study demonstrated that powdery mildew of melon can be controlled, and that the best results can be achieved when PS is supplied to the roots.     

南宁市桑白粉病病原菌种类鉴定

桑白粉病是桑树的重要病害,分为桑里白粉病和桑表白粉病。通过形态特征观察和ITS、D1/D2序列分析,明确桑里白粉病的病原菌为桑生球针壳Phyllactinia moricola;桑表白粉病的病原菌为桑白粉菌Erysiphe mori。桑钩丝壳Uncinula mori是桑白粉菌的异名。     

Quantitative trait Loci mapping for adult-plant resistance to powdery mildew in bread wheat

ABSTRACT Powdery mildew, caused by Blumeria graminis f. sp. tritici, is a major disease to wheat (Triticum aestivum) worldwide. Use of adult-plant resistance (APR) is an effective method to develop wheat cultivars with durable resistance to powdery mildew. In the present study, 432 molecular markers were used to map quantitative trait loci (QTL) for APR to powdery mildew in a doubled haploid (DH) population with 107 lines derived from the cross Fukuho-komugi x Oligoculm. Field trials were conducted in Beijing and Anyang, China during 2003-2004 and 2004-2005 cropping seasons, respectively. The DH lines were planted in a randomized complete block design with three replicates. Artificial inoculation was carried out in Beijing with highly virulent isolate E20 of B. graminis f. sp. tritici and the powdery mildew severity on penultimate leaf was evaluated four times, and the maximum disease severity (MDS) on penultimate leaf was investigated in Anyang under natural inoculation in May 2004 and 2005. The heritability of resistance to powdery mildew for MDS in 2 years and two locations ranged from 0.82 to 0.93, while the heritability for area under the disease progress curve was between 0.84 and 0.91. With the method of composite interval mapping, four QTL for APR to powdery mildew were detected on chromosomes 1AS, 2BL, 4BL, and 7DS, explaining 5.7 to 26.6% of the phenotypic variance. Three QTL on chromosomes 1AS, 2BL, and 7DS were derived from the female, Fukuho-komugi, while the one on chromosome 4BL was from the male, Oligoculm. The QTL on chromosome 1AS showed high genetic effect on powdery mildew resistance, accounting for 19.5 to 26.6% of phenotypic variance across two environments. The QTL on 7DS associated with the locus Lr34/Yr18, flanked by microsatellite Xgwm295.1 and Ltn (leaf tip necrosis). These results will benefit for improving powdery mildew resistance in wheat breeding programs.     

细胞乳突的形成和小麦白粉菌成功侵染的关系

 用一套己知抗白粉病单基因的小麦材料,研究了小麦白粉菌诱发寄主表皮细胞产生的乳突与成功侵染的关系。抗病小麦叶片上,诱发产生乳突的分生孢子占测定分生孢子数的58.8%,感病品种为63.8%。这表明抗性不同的小麦材料接种白粉菌之后,叶表皮细胞内形成乳突的百分率相近,然从在抗病材料和感病材料中形成的乳突阻止病原物发育和成功侵染的作用不相同,在抗病叶片上,诱发产生乳突的分生孢于中有88%停留在压力孢阶段,不继续发育,仅有12%能突破乳突形成吸器,使得侵染成功。与此对照,在感病叶片上只有32%诱发乳突的分生孢子不能穿透乳突,而68%则能突破乳突。成功地与寄主建立寄生关系。我们的研究表明,乳突能否成功地阻止白粉菌侵入可能与乳突形成的迟早有关。