Relative tolerances of wild and cultivated barleys to infection by Blumeria graminis f.sp. hordei (Syn. Erysiphe graminis f.sp. hordei). I. The effects of infection on growth and development

The two lines of wild barley, B19909 and I-17-40 and the cultivated barley, cv. Prisma used in this investigation were found to be the most susceptible to infection of 25 wild and four cultivated barley lines when exposed to the local population of Blumeria graminis f.sp. hordei. All three lines were susceptible during the early stages of growth but expressed some level of adult plant resistance although this level of resistance was significantly higher in line I-17-40 than in either of the other two.The relative tolerances of the lines to the mildew were determined by comparing the effects of infection on their growth and development in growth cabinet experiments. Mildew developed more slowly on line I-17-40 than on the other two lines and by the third week after inoculation, when mildew cover on B19909 and cv. Prisma had reached about 27%, only about 15% of the green leaf area of line I-17-40 was covered. Mildew continued to increase on line B19909 and cv. Prisma so that 6 weeks after inoculation it covered 40% of their leaf-blades. On line I-17-40 30% of the green leaf area was colonised by 4 weeks after inoculation but because of adult plant resistance coupled with the loss of the earlier infected leaves through senescence mildew cover then reduced falling to 15% by 6 weeks. Although total mildew biomass, measured as conidial production was higher on line B19909 than on cv. Prisma all its growth parameters were reduced less indicating that it was the more tolerant line. Conidial production on the lower susceptible leaves of line I-17-40 was slightly lower than on cv. Prisma yet the reaction of these leaves to infection was the same on both lines indicating that tissues of I-17-40 were slightly less tolerant than those of the cultivated barley. However, during the later stages of growth when its upper leaves expressed high levels of ‘adult plant resistance’ dry matter production in this line increased to levels higher even than in the controls. This capacity for compensatory photosynthesis ensured that by the end of growth few differences in any of the measured growth parameters between infected and uninfected plants of line I-17-40 were significant.The greater tolerance of line B19909 over the other two lines and of cv. Prisma over line I-17-40 during the early stages of growth appears to be due to a lower sensitivity to infection of those processes which regulate dry matter accumulation and its distribution around the plant.     

Nucleoside/nucleotide pools in wheat leaves naturally infected with Erysiphe graminis. I. Changes in the flag leaf

Nucleoside and nucleotide contents of the flag leaves of wheat plants, naturally infected with the powdery mildew fungus Erysiphe graminis were analysed in a field experiment. Fungicide treated plants were used as controls. Only low levels of infection occurred during the experiment (1% to 4% of the leaf area), but they resulted in higher leaf dry weight, and lower levels of chlorophyll, inorganic phosphate and NADP compared with the control plants. Although the total adenine nucleotide pools were the same in the flag leaves of infected and control plants, the energy charge values were slightly larger in the infected flag leaves. The total nucleoside content was higher in the infected flag leaves than the control; while the adenosine pool decreased, that of uridine increased strongly. Although the level of UDP-glucose was similar in the flag leaves of infected and control plants only decreasing slightly with time, UDP-N-acetylglucosamine, a precursor for fungal chitin biosynthesis, showed very different behaviour. The amounts of UDP-N-acetylglucosamine were very low in the control plants but increased greatly in the infected flag leaves to very high values (900nmol g⁻¹ d.wt) obviously reflecting exploitation of the hosts metabolism by the fungus for precursors for chitin biosynthesis. The size of the uridine pools was also correlated with the degree of infection and probably reflected recycling of the UDP moiety.     

Relative tolerances of wild and cultivated barley to infection by Blumeria graminis f.sp. hordei (Syn. Erysiphe graminis f.sp. hordei). II—the effects of infection on photosynthesis and respiration

The relative levels of tolerance of two wild barley lines (Hordeum spontaneum), B19909 and I-17-40, and one cultivated barley (Hordeum vulgare), cv. Prisma, to Blumeria graminis f.sp. hordei were determined by comparing the effects of different levels of infection on the photosynthesis and respiration rates of the third leaf. Infection caused the early onset of senescence in all three lines, and in particular in cv. Prisma, and was accompanied by decreases in gross and net photosynthesis rates, increases in respiration rates, and loss of chlorophyll. The onset of senescence occurred at approximately the same time in infected leaves of the two wild lines, but once triggered, photosynthesis rates and chlorophyll levels declined more rapidly in I-17-40 than in B19909. A burst of respiratory activity accompanied the onset of senescence, and this was greatest in cv. Prisma. Conidial production was higher in B19909, indicating a higher level of tolerance in this line.     

The response of resistant and susceptible plants to diclofop-methyl

Wild oat (Avena fatua L.) plants sprayed at the 2-or 3-leaf stages of growth with diclotop-methyl developed chlorosis over the entire leaf blade of all leaves. The leaves became necfrotic ⁷days after spraying Shool growth was inhibited. In wheat (Triticum aesicum L cv.Waldron) discrete chlorotic areas developed only where the herbicide convicted the 2nd or 3rd leaf with no visible injury so new growth uf'ter treutment. Growth inhibition of susceptible oat (Avena sativa L. cv. Garry) was sensitive to placement of diclutop-methyl near the upica and meristematic sites of the plant. Chlorosis and necrosis were independent of herbicide placement. Selective herbicide placement induced chlorosis only or both chlorosis and growth inhibition Root growth in wild oat and barley (Hordeum rulgare L. cv. Dickson) was strongly inhibited by 1–0 μM diclofop-methyl. Wild oat shoots were killed when seedlings were root-treated with 10 μM diclofop-melhyl. The 100 μM rool treatment killed barley shoots but only stunted the growth of wheat shoots by approximately 50%. In root-ireated wheat plants the shoots were turgid and developed a light purple colour, whereas in foliar-treated plants the shoots developed discrete chlorotic areas.     

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.     

Joint action of Cochliobolus lunatus and atrazine on Echinochloa crus-galli (L.) Beauv.

The potential of the endemic fungus Cochliobolus lunatus as a biological control agent against Echinochloa crus-galli was investigated. Under appropriate conditions the fungus produced leaf necrosis on E. crus-galli resulting in death of young seedlings. However, plants with more than two leaves mostly recovered after some time. Bean, barley, maize, oat, rye, tomato and wheat were highly resistant to the fungus. In experiments in a climate room or in a glasshouse E. crus-galli with more than two leaves could effectively be controlled by C. lunatus in combination with a sub-lethal dosage of atrazine as low as 2.5 mg m^?2 due to a positive interaction between fungus and herbicide.     

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     

Combined effects of salt stress and cucurbit downy mildew (Pseudoperospora cubensis Berk. and Curt. Rostov.) infection on growth,physiological traits and antioxidant activity in cucumber (Cucumis sativus L.) seedlings

Abiotic and biotic stresses both decrease quality and quantity of cultivated plants. We compared responses of Cucumis sativus L. cvs Sardes and Beith alpha which were treated with 50 or 100 mM NaCl and/or infected by Pseudoperospora cubensis Berk. and Curt. Rostov.. Both cultivars were affected remarkably when fungus infection was combined with salt stress however; cv Sardes was found out to be relatively tolerant with sustainable growth performance, better leaf water status and lower lipid peroxidation levels under this condition. This relative tolerance could be related to the fine tuning of the activities of the antioxidative enzymes and proline levels.     

Interaction between diclofop-methyl and 2,4-D in wild oat (Avena fatua L.) and cultivated oat (Avena sativa L.), and fate of diclofop-methyl in cultivated oat

Influence of 2,4-D on toxicity of diclofop-methyl to Avena sativa (cv. Selma) and Arena fatua at 2·5 leaf stage has been evaluated under controlled conditions. Effects of 2,4-D on the fate of diclofop-methyl in cultivated oat have also been studied. Mixture with 2,4-D reduced the toxicity of diclofop-methyl to both species. When applied immediately after diclofop-methyl treatment, 2,4-D still reduced herbicide toxicity to wild oat. This reduction was smaller in cultivated oat. and was only observed at higher phytotoxicity. No interaction was observed when a 10-day period separated the two applications. In mixture, 2,4-D enhanced diclofop-methyl penetration and diclofop acid conjugation in cultivated oat, and it slightly increased conjugation when applied separately. None of these effects clearly explain the reduction of diclofop-methyl toxicity by 2, 4-D in cultivated oat. Other processes are possibly involved and could be connected with the site of action of diclofop-methyl.     

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.     

The reliability of leaf bioassays for predicting disease resistance on fruit: a case study on grapevine resistance to downy and powdery mildew

This study was designed to assess the reliability of grapevine leaf bioassays for predicting disease resistance on fruit in the field. The efficacy of various grapevine quantitative trait loci (QTLs) for conferring resistance to downy and powdery mildew was evaluated in bioassays and in a 2‐year field experiment for downy mildew. The resistance genes studied were inherited from Muscadinia rotundifolia (Rpv1 and Run1) and from American Vitis species through cv. Regent (QTLRgP and QTLRgD). In bioassays, genotypes carrying Run1 blocked powdery mildew development at early stages. Genotypes combining Run1 with QTLRgP displayed no greater level of resistance. For downy mildew, genotypes carrying Rpv1 and/or QTLRgD were more resistant than the susceptible cv. Merlot, and showed a high level of leaf resistance in the field (<10% severity). Disease levels on bunches were much higher than those on leaves, with a high variability between Rpv1 genotypes (1–48%). A Bayesian decision theory framework predicted that an OIV‐452 threshold of 5 in leaf bioassays allowed accurate selection of grapevine genotypes (P = 0·83) with satisfactory disease severity on bunches. Therefore, this study validates that the use of early bioassays on leaves, as currently performed by grapevine breeders, ensures a satisfactory level of resistance to downy mildew of bunches in the field.     

苹果炭疽叶枯病病原Glomerella cingulata及其侵染过程

为明确苹果炭疽叶枯病病原菌围小丛壳Glomerella cingulata的侵染致病特征,在分离获得该病原菌的基础上,采用形态学观察、ITS序列分析和致病性测定对其进行了鉴定,并利用光学和扫描电子显微镜对病原菌在嘎啦苹果叶片上的侵染过程进行了研究.结果表明,在陕西咸阳地区分离获得的9株病原菌均为围小丛壳G.cingulata.25 ℃下接种9 h后,分生孢子中间产生隔膜,双胞化,并萌发产生芽管和附着胞;24 h后分生孢子的2个细胞均可萌发并形成芽管及附着胞,部分芽管顶端可产生次级分生孢子;48 h后次级分生孢子萌发形成附着胞;72 h后,附着胞下形成的侵染钉可直接入侵寄主,在表皮细胞内形成初生菌丝和次生菌丝,此时叶片表面已出现褐色斑点.接种7 d后叶片病斑处出现分生孢子盘和子囊壳.表明陕西省近年出现的苹果炭疽叶枯病病原菌为围小丛壳G.cingulata,该病菌在嘎啦叶片上的一些特殊侵染行为可能是导致该病害易在短时间内暴发的重要原因.     

The role of the abaxial leaf surface waxes of Lolium spp. in resistance to Erysiphe graminis

Field and glasshouse observations of Lolium spp. grasses indicated that the lower, abaxial, leaf surface was rarely infected by powdery mildew ( Erysiphe graminis ) even when the upper, adaxial, surface was densely colonized. Experiments showed that conidia of two strains of E. graminis , one from Lolium and one from Avena , germinated equally well on both surfaces of Lolium and Avena leaves, but that the subsequent growth and development of germlings was impaired on the lower surface of Lolium leaves, so that most formed only multiple short germ tubes or an abnormal long tube, and only c. 25% or fewer formed infection structures. This contributes to the apparent resistance of the lower Lolium leaf surface to powdery mildew and may help to explain why the disease is relatively unimportant in UK ryegrass crops, since infection structures develop at a high frequency on only 50% of the leaf area, i.e. the upper surface. Scanning electron microscopy showed that the epicuticular waxes on the lower Lolium leaf surface form amorphous sheets. This contrasts with the crystalline plate waxes seen on the upper surface of Lolium leaves and on both surfaces of oat leaves. However, when the lower Lolium leaf surface was washed with chloroform to remove epicuticular wax, normal germling and infection structure development was obtained on the wax-free surface. This suggests that the sheet waxes prevent the pathogen gaining access to features of the cuticular membrane which trigger normal germling development.     

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.     

公主岭霉素对草莓的防病诱抗和促生效应

为明确公主岭霉素在草莓生产中的防病诱抗效应,于大田采用五点取样法调查公主岭霉素对草莓白粉病的防控效果及对植株生长性状的影响,并于室内采用生测法测定其对草莓叶片防御酶活性和根际土壤酶活性的影响。结果显示,以公主岭霉素水浸提液100倍稀释液进行灌根并协同叶面喷雾对草莓白粉病的预防效果为71.90%;单独叶面喷雾对草莓白粉病的治疗效果为69.90%;灌根协同叶面喷雾预防与叶面喷雾治疗的综合防控处理对草莓白粉病的防治效果可达85.37%。公主岭霉素水浸提液100倍稀释液灌根后草莓幼苗的株高、叶柄长、叶长、叶宽、叶数、径冠等方面均优于清水对照;叶面喷施可提升叶片中多酚氧化酶和超氧化物歧化酶的活性,喷雾后1 d内即较清水对照显著提高;5 d后过氧化氢酶活性显著高于清水对照。灌根后根际土壤中蔗糖酶的活性在用药后15 d内均显著高于清水对照。表明合理施用公主岭霉素可实现对草莓白粉病的有效防控,并诱导提升草莓植株的抗病性,改善草莓生长环境,促进其生长。     

Wax matters: absence of very‐long‐chain aldehydes from the leaf cuticular wax of the glossy11 mutant of maize compromises the prepenetration processes of Blumeria graminis

Conidial germination and differentiation, the so‐called prepenetration processes, of the barley powdery mildew fungus (Blumeria graminis f.sp. hordei) are triggered in vitro by very‐long‐chain aldehydes, minor constituents of barley leaf wax. However, until now it has not been demonstrated that these cuticle‐derived molecules also play a significant role in the initiation and promotion of the fungal prepenetration processes in vivo, on the surface of a living plant leaf. In the maize (Zea mays) wax mutant glossy11, which is completely devoid of cuticular very‐long‐chain aldehydes, germination and appressorial differentiation of B. graminis were strongly impeded. Spraying the mutant leaf surface with aldehyde‐containing wild‐type wax or pure n‐hexacosanal (C₂₆‐aldehyde) fully restored fungal prepenetration, whereas maize wild‐type leaf surfaces coated with n‐docosanoic acid exhibited reduced conidial germination rates of 23%, and only 5% of the conidia differentiated infection structures. In vitro studies were performed to further corroborate the extensive prevention of fungal germination and differentiation in response to artificial surfaces coated with aldehyde‐deficient maize wax. Because of its phenotype affecting the B. graminis prepenetration processes, the glossy11 mutation of maize may become a valuable molecular target and genetic tool that could provide a means of developing basal powdery mildew resistance in the globally important crops wheat and barley.     

Non-enzymatic conjugation of fenoxaprop-ethyl with glutathione and cysteine in several grass species

Laboratory studies have shown that the amounts of glutathione (GSH) and cysteine are higher in grass species that are moderately tolerant, such as wheat (Triticum aestivum L., cv. Fredrick), and moderately susceptible, such as barley (Hor deum vitlgare L., cv. Legér) and triticale (cv. OAC Trillium), to fenoxaprop-ethyl (FE) than in species that are very susceptible to the her bicide, such as oat (Avena saliva L., cv. OAC Woodstock), wild oat (Avena fatua L.), yellow foxtail (Setaria glanca (L.) Bcauv.), large crab grass (Digitaria sanguinalis (L.) Scop.) and bar nyard grass (Echinochloa crus-galli (L.) P.B.). The safener, fenchlorazole-ethyl (FCE) was found to increase and decrease, respectively, the amounts of GSH and cysteine in the moderately tolerant and moderately susceptible species but had no effect on the susceptible species. It is sug gested that in the moderately tolerant and moderately susceptible species, especially following FCE treatment, more GSH is available to detoxify the herbicide. Glutathione-S-tranferase activity (GST) for FE was found to be very low in all of the species tested. In vitro experiments at physio-logical pH. demonstrated that FE may conjugate with GSH nonenzymatically. Therefore, it is suggested that nonenzymatic conjugation of fenoxaprop-ethyl with glutathione may be an important mechanism for tolerance of some grasses to this herbicide.     

The effect of film-forming anti-transpirants on leaf rust and powdery mildew incidence on wheat

Various film-forming anti-transpirants effectively controlled leaf rust and powdery mildew on wheat in the field. Two applications of anti-transpirant emulsions applied after flag leaf emergence were sufficient to suppress leaf rust and powdery mildew on wheat leaves. When applied before, but not after, inoculation anti-transpirant polymers also reduced leaf rust on seedling plants in a growth room experiment.