Consumption of aphid honeydew,a wheat yield reduction factor,by phyllosphere yeasts under field conditions

Aphid honeydew on wheat leaves can affect host physiology directly and can stimulate infection by necrotrophic pathogens. The role of naturally occurring saprophytes on wheat flag leaves in removing aphid honeydew was examined in five field experiments at different locations in the Netherlands in 1987 and 1988. Aphid populations, saprophyte populations and aphid honeydew were measured weekly. Diseases were monitored at 1–4 week intervals.In the control treatment, sprayed with water, the naturally occurring saprophytes consumed the honeydew almost completely, except in one experiment in which the aphid population increased very rapidly. In the treatments in which the saprophytes were reduced by the broad-spectrum fungicide maneb in 1987 and with maneb alternated with anilazin in 1988, honeydew accumulated. The observed honeydew consumption by the naturally occurring saprophytic population is ascribed mainly to pink and white yeasts (Sporobolomyces spp. andCryptococcus spp., respectively).Additional treatments showed, that in the presence of the naturally occurring saprophytes the yield loss per aphid-infestation-day was lower than when the saprophytes were inhibited by fungicides, showing that yeasts can reduce the detrimental effect of aphid honeydew in wheat.     

The Effect of Fungicides on the Microbial Balance in the Phyllosphere1

The sensitivity to fungicides of saprophytic fungi colonizing cereal leaves (mainly ←pink→ yeasts, Sporobolomyces spp.; ← white → yeasts, Cryptococcus spp.; Aureobasidium pullulans and Cladosporium spp.) is discussed. Fungicides like dithiocarbamates, captafol, benzimidazoles and tridemorph reduce the saprophytic microflora, while others have little or no effect. The fungicides are mostly effective for 2–3 weeks after the treatment. When evaluating the consequences of a disturbance of the microbial balance we should realize that the saprophytes are able to antagonize a number of necrotrophic pathogens of cereal leaves and ears (Cochliobolus sativus, Septoria nodorum, Fusarium culmorum, Pseudocercosporella herpotrichoides, Colletotrichum graminicola). This antagonism is based on nutrient competition, which reduces the superficial development of the pathogen before penetration, resulting in a reduction of infection of about 50 % or more. This interaction seems particularly important when saprophytes compete successfully for extraneous nutrients from pollen grains or aphid honeydew, which will otherwise stimulate infection.     

Damage effects of cereal aphids in wheat

Laboratory and field studies on aphid damage in wheat are described. Both direct and indirect effects of aphids on the behaviour of the crop were studied. In the laboratory a clear effect of honeydew and yeasts on photosynthesis was found. This effect could not be demonstrated under field conditions, since even at yield loss levels of 700 kg ha^–1 the size of this effect may be undetectable with crop enclosures reaching an accuracy of 10%. The effect of honeydew on ageing, measured in the laboratory trials was also found in the field and may form a major cause of the yield losses found in the field. Yield losses under field conditions reached 700 kg ha^–1 and were for 72% due to direct sucking damage of the 35 aphids, found maximally per culm, and direct and indirect honeydew effects. Saprophytic and possibly also some necrotrophic fungi caused 28% of the yield losses. The exact contribution of each of the damage factors was not revealed but it was demonstrated that direct and indirect effects contribute to the final yield losses.Samenvatting Laboratorium- en veldproeven over de schade door bladluizen in tarwe worden beschreven. Een analyse van de directe en indirecte effecten van bladluizen op de groei van het gewas werd verricht. In het laboratorium werd een duidelijk effect van honingdauw en gisten op de fotosynthese gevonden. Dit effect kon niet worden gedemonstreerd in het veld, hetgeen waarschijnlijk wordt veroorzaakt door de orde van grootte van dit effect dat valt binnen de meetfout van de gewasfotosyntheseapparatuur.Het effect van honingdauw op veroudering, dat in het laboratorium werd vastgesteld, kon ook worden aangetoond in het veld en is waarschijnlijk een van de hoofdoorzaken van de oogstverliezen. Deze oogstverliezen in het veld bedroegen 700 kg ha^–1 bij een maximale dichtheid van 35 bladluizen per halm en werden voor 72% veroorzaakt door direct zuigsschade en honingdauweffecten. Van de totale schade werd 28% veroorzaakt door saprofytische en wellicht ook door enige necrotrofe schimmels. De precieze bijdrage van ieder van de schadefactoren tot de schade werd niet vastgesteld, maar de wijze waarop directe en indirecte effecten hun bijdrage leverden aan de uiteindelijke oogstverliezen werd zichtbaar gemaakt.     

Comparative resistance to foliar fungal pathogens in transgenic carrot plants expressing genes encoding for chitinase, β-1,3-glucanase and peroxidise

Genes encoding an acidic wheat class IV chitinase (383), an acidic wheat β 1,3-glucanase (638) and a rice cationic peroxidase (POC1) were introduced into ‘Nantes Coreless’ carrot (Daucus carota) by Agrobacterium-mediated transformation. The genes were introduced singly or in various combinations followed by selection imposed by the herbicide phosphinothricin. Regenerated plantlets were screened for presence and expression of the three transgenes using PCR, Southern and Northern hybridisations. Eighteen transgenic lines expressing a single transgene and 2 lines each co-expressing 638/383 and 383/POC1 were assessed for resistance to the necrotrophic fungal pathogens Botrytis cinerea and Sclerotinia sclerotiorum. Percentage leaf area diseased was measured 4 and 7 days after inoculation (dai) and compared to non-transformed control plants. Six lines expressing β-1,3-glucanase 638 alone had no enhanced resistance to B. cinerea at 4 dai and only slight resistance to S. sclerotiorum; there was no effect at 7 dai. Two out of the six lines expressing 383 alone had enhanced tolerance to both pathogens with a 20–50% reduction in disease development at 7 dai. Two lines co-expressing 638/383 had slight reductions in disease by (10–20%) similar to that of the lines expressing chitinase 383 alone. Highest levels of disease resistance were seen in transgenic lines expressing POC1, alone or in combination with chitinase 383. Disease symptoms were slower to develop and symptoms were reduced by up to 90% for B. cinerea and 70% for S. sclerotiorum. The 383/POC1 co-expressing plants developed disease at levels similar to that of POC1 alone. Petioles of plants over-expressing POC1 had higher levels of lignin accumulation constitutively compared to control plants, which was greatly enhanced following inoculation with S. sclerotiorum. These results indicate that peroxidase over-expression can lead to significant disease reduction against necrotrophic pathogens in transgenic carrot plants.     

Surveys of cereal diseases and pests in the Netherlands. 6. Occurrence of insect pests in winter wheat

Between 1980 and 1986, commercial winter wheat fields at the milky-ripe stage were surveyed for insect pests. Leaf injuring insects were common. On average 42% and 95% of the surveyed fields were injured by leaf miners and the cereal leaf beetle, respectively. On average 14% of the leaves was skeletonised by the cereal leaf beetle and leaf injury tended to be high in seasons after winters with low temperatures. Blossom midges were the most important midges. In the period 1980–1984, the orange and lemon blossom midge infested 71 and 21% of the surveyed fields, respectively, Insecticides were mainly used to control aphids. Despite control, on average 80% of the fields and 22% of the tillers were infested by aphids.     

Effect of fungicides on the complex of <Emphasis Type="Italic">Fusarium</Emphasis> species and saprophytic fungi colonizing wheat kernels

Fusarium head blight of wheat, often associated with mycotoxin contamination of food and feed is caused by various Fusarium species. The efficacy of fungicide sprays for the control of the disease and mycotoxins varies from being highly effective to even increasing mycotoxin levels. The potential role of antagonistic fungi in this variability was investigated assessing sensitivity of Fusarium species and saprophytic fungi colonizing wheat kernels to fungicides. Saprophytes were tested for their antagonistic activity to the prevalent Fusarium species Fusarium avenaceum, Fusarium culmorum, Fusarium graminearum, and Fusarium poae. Fungal isolates from mature winter wheat kernels were Alternaria alternata, Arthrinium sp., Aspergillus niger, Epicoccum sp., Microdochium spp., Rhizopus oryzae and Trichoderma sp. In dual culture A. niger, R. oryzae and Trichoderma hamatum were more effective in reducing mycelial growth of Fusarium species than Microdochium majus; A. alternata and Epicoccum sp. were ineffective because of slow growth rates. Saprophytic fungi were sensitive to triazoles; however, prothioconazole and tebuconazole had stronger effects on mycelial growth of Fusarium species. ED₅₀ values also indicated significant differences in the sensitivity of Fusarium species to triazoles (range 0.1–1.7 mg l⁻¹). Azoxystrobin and fluoxastrobin were largely ineffective in inhibiting in vitro growth of Fusarium spp.; sensitivity of the other fungi was generally lower, except for M. majus which was highly sensitive. Due to differences in fungicide sensitivity among Fusarium spp. and ear-colonizing fungi antagonistic to Fusarium spp. fungicides are likely to modify the balance within the mycoflora of wheat ears which may also affect the mycotoxin contamination of grain.     

The chemical environment of leaf surfaces with special reference to spore germination of pathogenic fungi

The release of diffusible substances from plant leaves, fungal spores or from pollen into water droplets on the surface of leaves is discussed in relation to (1) direct and indirect effects on spores of pathogens and (2) the effect on the growth of saprophytic micro-organisms. Evidence suggests that competition for nutrients in droplets on leaves may limit germination of spores of some pathogens. Modification of the chemical environment of leaf surfaces by saprophytic micro-organisms is discussed in relation to lytic enzyme and antibiotic production, cuticle degradation, production of growth substances and fixation of nitrogen. Examples are given of the effect on pathogenic fungi of diffusible toxins from leaves and inhibitors associated with surface wax. Treatments of leaves that remove or reduce surface wax can result in a stimulation of spore germination of some pathogenic fungi. The possible occurrence of phytoalexins on leaf surfaces prior to entry of pathogens into leaves is discussed in relation to differences in host-pathogen interaction.     

Influence of aldicarb on root lesion nematodes, leaf disease and root rot in wheat and barley

The effects of aldicarb on populations of root lesion nematodes (primarily Pratylenchus penetrans ) and on grain yields of spring barley and wheat were examined in the field over 3 years, 1981*83. The incidence of barley net blotch ( Pyrenophora teres ), wheat leaf blotch ( Leptosphaeria nodorum ), and common root rot ( Cochliobolus sativus ) was also recorded in 1982 and 1983. Aldicarb treatments reduced the size of root lesion nematode populations in soil and roots in all years, except in the mid-season soil sample in 1983. The severity of leaf disease was decreased only in 1982, but the incidence of root rot was not significantly affected by the nematticide. Although aldicarb increased cereal grain yields by approximately 15% there was no significant relationship between numbers of root lesion nematodes in roots and soil and fungal disease symptoms on barley and wheat.     

小麦对麦长管蚜的耐害性及评估方法

为更有效地将耐害性用于小麦病虫害的绿色防控,该文就小麦对麦长管蚜的耐蚜性及其评估方法进行总结。具有耐蚜性的小麦受到一定数量蚜虫为害时,田间产量损失不明显,或能够通过生理生态途径补偿产量损失。耐蚜性不影响蚜虫的取食及生物学参数,对蚜虫进化压力小,因此田间表现更稳定。耐蚜小麦可以允许田间存在一定数量的蚜虫,这不仅可以减轻防治压力,还可以为天敌提供食物,有利于天敌的保护和利用,更符合有害生物绿色防控理念的核心。然而,目前抗麦长管蚜的小麦抗源鉴选主要是以蚜量为基础的抗生性和不选择性,耐害性被忽视。鉴于麦长管蚜田间蚜量与小麦产量(千粒重)损失率正相关,且峰值蚜量和小麦千粒重受损敏感期在小麦灌浆期重合,因此提出了以耐蚜值(千粒重损失率和灌浆期蚜情指标的比值)为依据计算耐蚜指数来评估小麦耐害性的方法,该方法可弥补抗源鉴选中忽视耐害性的不足,也能克服以田间千粒重损失率为依据评估耐害性时很难实现蚜量统一的不足,同时消除抗生性和不选择性带来的影响。     

Absence of detectable yield penalty associated with insensitivity to Pleosporales necrotrophic effectors in wheat grown in the West Australian wheat belt

Genetic disease resistance is widely assumed, and occasionally proven, to cause host yield or fitness penalties due to inappropriate activation of defence response mechanisms or diversion of resources to surplus preformed defences. The study of resistance gene trade‐offs has so far been restricted to biotrophic pathogens. In some Pleosporales necrotrophic interactions, quantitative resistance is positively associated with insensitivity to effectors. Host lines that differ in sensitivity can easily be identified amongst current cultivars and advanced breeding lines. Large wheat cultivar trials were used to test whether lines sensitive or insensitive to three necrotrophic effectors from Pyrenophora tritici‐repentis and Parastagonospora nodorum differed in yield when subjected to natural disease and stress pressures in the West Australian wheat belt. There was no significant yield penalty associated with insensitivity to the fungal effectors ToxA, SnTox1 and SnTox3. Some yield gains were associated with insensitivity and some of these gains could be attributed to increased disease resistance. It is concluded that insensitivity to these effectors does not render such plants more vulnerable to any relevant biotic or abiotic stress present in these trials. These results suggest that the elimination of sensitivity alleles for necrotrophic effectors is a safe and facile strategy for improving disease resistance whilst maintaining or improving other desirable traits.     

Surveys of cereal diseases and pests in the Netherlands. 6. Occurrence of insect pests in winter wheat

Between 1980 and 1986, commercial winter wheat fields at the milky-ripe stage were surveyed for insect pests. Leaf injuring insects were common. On average 42% and 95% of the surveyed fields were injured by leaf miners and the cereal leaf beetle, respectively. On average 14% of the leaves was skeletonised by the cereal leaf beetle and leaf injury tended to be high in seasons after winters with low temperatures. Blossom midges were the most important midges. In the period 1980–1984, the orange and lemon blossom midge infested 71 and 21% of the surveyed fields, respectively, Insecticides were mainly used to control aphids. Despite control, on average 80% of the fields and 22% of the tillers were infested by aphids.     

小麦禾谷缢管蚜发生为害与生态环境研究

八十年代以来,我区麦蚜频繁成灾,减产2—3成的麦田较为普遍,研究证明:成灾的主要原因是优势种群已由麦长管蚜Sitobion avenae(Fabr.)转变为禾谷缢管蚜Rhopalosiphumpadi(L.)。田间调查弄清了禾谷缢管蚜在不同海拔高度的早、中、晚播麦田的不同生育阶段,以及在植株各部位的分布。穗期禾谷缢管蚜发生轻重与3月中旬平均温度呈正相关,与3月下旬雨量呈负相关。由此建立了预测禾谷缢管蚜发生程度的多元回归方程式: Y=0.792 0.205X_1-0.015X_2用这个预测式回测8年田间实测值与预测值极近。     

Comparative Analysis of the Role of Substrate Specificity in Biological Control of Botrytis Elliptica in Lily and B. Cinerea in Cyclamen with Ulocladium Atrum

Biological control of Botrytis spp. by the fungal antagonist Ulocladium atrum is based on their interaction in plant tissue. U. atrum is effective against B. cinerea in commercial cyclamen crops but not effective against B. elliptica in lily crops. Based on the necrotrophic nature of the Botrytis spp. and the saprophytic nature of U. atrum it is hypothesised, and experimentally confirmed, that the interaction between Botrytis spp. and U. atrum, resulting in a biocontrol effect, only takes place in necrotic plant tissue. The role of necrotic tissue in the epidemiology of B. cinerea in cyclamen and B. elliptica in lily was found to be different. Removal of symptomless senescing leaves resulted in a significant reduction of the area under the disease severity progress curve (AUDPC) for B. cinerea in cyclamen but had no effect on the disease severity in lily. U. atrum applications significantly reduced B. cinerea AUDPC values in cyclamen but were less efficient than the removal of senescing leaves. In lily, disease severity was not affected by applications of U. atrum. It is concluded that necrotic cyclamen tissue, not killed by B. cinerea, plays an important role in the onset of disease. Colonisation of this tissue by U. atrum prevents saprophytic colonisation of those leaves by B. cinerea. In contrast, conidia of B. elliptica directly infect healthy lily leaf tissue. U. atrum applications aimed at blocking the infection pathway from a saprophytic base are therefore not effective against B. elliptica. Control options based on competitive interactions in and around B. elliptica lesions resulted in a reduced production of conidia by B. elliptica but proved ineffective against disease development. The potential of U. atrum as a biocontrol agent against Botrytis spp. and possibly against other necrotrophs appears to be determined by the competitive saprophytic ability of the antagonist in mutual substrates of pathogen and antagonist and by the role of these substrates in disease epidemiology.     

生防荧光假单胞菌CPF-10对西瓜根围土壤真菌群落的影响

探讨了生防菌荧光假单胞菌Pseudomonas fluorescens CPF-10对西瓜根围土壤真菌群落结构的影响。采用传统分离培养法,结合变性梯度凝胶电泳(DGGE)分析,研究了施用CPF-10后不同生育期西瓜根围土壤真菌群落结构的变化。结果表明:施入生防菌CPF-10后2周,其对土壤真菌有一定的促进作用;第3～7周时,CPF-10对土壤真菌尤其是部分病原菌有较强的抑制作用;CPF-10对丛枝菌根真菌(AMF)有一定的促进作用,可维持3周左右;收获期后则检测不到CPF-10对土壤真菌群落的影响。生防菌CPF-10对西瓜根围土壤真菌群落产生的短暂影响不会对土壤生态系统构成长期威胁。对比土著真菌及丛枝菌根真菌的DGGE图谱和切胶条带测序结果,发现DGGE技术更适用于分析小范围特定菌属如丛枝菌根真菌的变化。     

Interaction between phyllosphere yeasts, aphid honeydew and fungicide effectiveness in wheat under field conditions

Aphid honeydew can reduce fungicide effectiveness against necrotrophic pathogens of wheat under controlled conditions. In 1988 and 1989, field experiments were carried out at different locations in The Netherlands, to assess the interference of honeydew with fungicide effectiveness under field conditions, and to establish whether honeydew consumption by naturally occurring saprophytes could prevent this effect. Different combinations of chemicals were used to create differences in saprophytic population densities and aphid populations, which were expected to result in differences in the amount of honeydew and other nutrients on the leaves. In two of the experiments, Septoria nodorum was the only necrotrophic pathogen present; in the other two the only necrotroph was S. tritici . On several sampling dates, the effect of the fungicides was significantly enhanced by addition of insecticide, most often when the saprophytes were reduced by maneb/anilazine. This effect of insecticide is ascribed to prevention of interference of honeydew with fungicide activity, and not to a direct effect of insecticide, as insecticide alone had no effect on necrosis. On the basis of the fact that interference of honeydew with fungicide activity was most apparent when saprophytic population densities were reduced, it is concluded that the naturally occurring saprophytes can generally prevent the effect of honeydew. The same interactions are likely to occur between other nutrients and fungicides, and it is therefore argued that the naturally occurring saprophytes should be protected by elimination of harmful chemicals.     

Regional and varietal differences in the risk of wheat seed infection by fungal species associated with fusarium head blight in Italy

The incidence of seed infection by fungal species pertinent to the fusarium head blight complex was monitored from 1999 to 2002 in two soft and three durum wheat cultivars grown across the northern, central and southern production zones of Italy, in order to characterize the species composition at the seed level. The main species recovered were Fusarium graminearum, F. poae and Microdochium nivale. There was a marked influence of production zone on seed infection incidence for both durum and soft wheat cultivars, with incidence of infection generally decreasing from the northern to the southern zone. Incidence of seed infection by different species of Fusarium was twice to four times higher in durum compared with the soft wheat cultivars in the study. There were no significant differences in terms of seed infection incidence between the two soft wheat cultivars, but the durum cultivars differed in their levels of seed infection for some of the pathogens. The results demonstrated that the durum cultivars were more at risk of seed infection by pathogens associated with fusarium head blight, and that wheat grown in northern Italy is at higher risk of seed infection by these species.     

枯草芽孢杆菌B1514可湿性粉剂对小麦纹枯病的防效及对土壤微生物区系和小麦产量的影响

为明确枯草芽孢杆菌B1514可湿性粉剂（WP）在小麦纹枯病防治中的应用前景,于2014-2015年在中国河北省文安县、献县、枣强县及辛集市4个实验站进行了田间试验,研究了B1514 WP对小麦纹枯病的防效,采用失重法测定了其对玉米秸秆腐解效果的影响,利用稀释平板法研究了其对土壤微生物区系的影响,并测定了该菌剂对小麦生长及产量的影响。结果表明:越冬期至拔节期,B1514 WP对小麦纹枯病的防效均显著高于B1514片剂,但明显低于戊唑醇湿拌种剂（WS）;成熟期,辛集、献县和枣强试验点B1514 WP处理组平均防效为64.0%,与戊唑醇WS处理差异不显著,比B1514片剂处理组高7.2%,差异达显著水平,而文安试验点B1514 WP处理组防效为65.2%,与B1514片剂差异不显著,但显著低于戊唑醇WS处理组。在成熟期,B1514 WP对玉米秸秆的累积腐解率为64.2%,较空白对照提高38.6%,但与B1514片剂和秸秆腐解剂处理差异不显著。此外,B1514 WP处理显著提高了土壤中可培养细菌数量（92.8%）,降低了真菌数量（48.4%）,但对放线菌数量无显著影响。采用B1514 WP拌种后,小麦株高和分蘖数分别比空白对照提高8%和12%;4个试验点小麦平均产量为7 545 kg/hm2,分别比B1514片剂、戊唑醇WS、秸秆腐解剂处理和空白对照提高6.8%、5.5%、9.3%和10.9%。研究表明,B1514 WP对小麦纹枯病具有很好的防效,并能加速秸秆腐解,增加土壤中细菌数量、降低真菌数量,促进小麦生长并增产。     

Field assessment of the effects of deltamethrin on polyphagous predators in winter wheat

In the south-west of England, cereal aphids can spread barley yellow dwarf virus and reproduce during winter. Ground-living polyphagous predators may be important in controlling these active cereal aphids. This 2-year study investigated the effect of deltamethrin on predator numbers, using pitfall traps. A randomised block design was used in an area of winter wheat (cv. Aquilla) in which deltamethrin-treated and control plots were surrounded by polyethylene barriers. Pitfall catches of polyphagous predators were reduced by about 30% in the treated plots compared with the control plots.     

New Trends in the Chemical Control of Wheat Diseases1

Following a list of the economically most important fungal wheat diseases, recent trends in chemical seed treatment are discussed. Different fungicide mixtures are now available for the replacement of mercurial dressings, but are generally more expensive. The control of fungal diseases by spraying has become more and more common over the past ten years in certain countries. Advantage has been taken of the curative action of the modern systemic chemicals. The major diseases are powdery mildew, rusts, eyespot, glume-and leaf-blotch. The general application of a fungicide programme is restricted by regional wheat prices, and should also be limited to reduce environmental contamination. Knowledge about economic thresholds and correct timing of control are indispensable, and in special cases the development of warning systems is advisable. The role of Cycocel (chlormequat) is also discussed. A danger of fungicide resistance in populations of plant pathogenic fungi has arisen with the introduction of the systemic fungicides (one-site-inhibitors). As yet, however, no economically important case of fungicide resistance within cereal pathogens is known. Factors favouring the stepwise selection of resistant strains under field conditions are discussed in detail, and experimental data are presented on this subject. Other positive or negative side-effects of the modern fungicides are described.