Effect of take-all root infections on nitrate uptake in winter wheat

The effect of take-all root lesions on nitrate uptake of wheat was investigated in two experiments under controlled conditions. Plants were supplied with a nutrient solution labelled with ¹⁵N during stem elongation and flowering to assess the distribution of the isotopic tracer in the different plant organs, and particularly in root segments located on both sides of take-all lesions. The ¹⁵N atom percentage excess measured in root segments located below lesions longer than 1 cm was reduced on average by half compared with that in healthy roots and root segments above lesions, reflecting a reduction in nitrogen uptake by these root segments. This reduction probably resulted from the invasion and breakdown of phloem vessels by the fungus hyphae, interrupting energy supply and thus the uptake process. Severely infected plants showed an increase in the uptake rate per unit of efficient root, which appeared to be a compensatory response to reduction of efficient root biomass in order to satisfy shoot nitrogen demand. However, this compensatory response was insufficient to ensure nitrogen accumulation equivalent to that of healthy plants, as reductions in nitrogen accumulated in roots and aerial parts at flowering were up to 56 and 49%, respectively, for plants with more than 50% of the root system below lesions longer than 1 cm.     

Sensitivity of fungi from cereal roots to fluquinconazole and their suppressiveness towards take-all on plants with or without fluquinconazole seed treatment in a controlled environment

The take-all fungus, Gaeumannomyces graminis var. tritici , was highly sensitive to fluquinconazole ( in-vitro EC₅₀ 0·016–0·018 mg L⁻¹), a fungicide developed for use as a seed treatment to control take-all, and to prochloraz (EC₅₀ 0·006 mg L⁻¹). Fungi of other genera that were commonly isolated from cereal roots were sensitive in varying degrees to prochloraz but were relatively insensitive (e.g. Fusarium culmorum , EC₅₀ > 20 mg L⁻¹) or slightly sensitive (e.g. Epicoccum purpurascens , EC₅₀ 0·514 mg L⁻¹) to fluquinconazole. Gaeumannomyces graminis var. graminis and G. cylindrosporus , weak parasites that can protect roots against take-all, and an unnamed Phialophora sp., all closely related to the take-all fungus, were highly or moderately sensitive to fluquinconazole. Alternaria infectoria and E. purpurascens were most consistently effective in suppressing development of take-all on pot-grown wheat plants dual-inoculated with G. graminis var. tritici and the nonpathogen. Take-all was decreased more on dual-inoculated wheat plants grown from seed treated with fluquinconazole or fluquinconazole plus prochloraz than when only an antagonistic fungus ( A. infectoria , E. purpurascens , Fusarium culmorum or Idriella bolleyi ) or a seed treatment was applied. These fungi were less effective in combination with seed treatments on barley. Gaeumannomyces graminis var. graminis and G. cylindrosporus , tested on wheat, suppressed take-all only in the absence of fungicides. It is suggested that the performance of seed treatment containing fluquinconazole against take-all may in some circumstances be enhanced by its partial specificity for the take-all fungus.     

Take-all in autumn-sown wheat, barley, triticale and rye grown with high and low inputs

Winter cultivars of wheat, barley, triticale and rye were grown under two contrasting husbandry systems (low and high inputs) at two locations (Woburn and Rothamsted) known to be infested with the take-all fungus. The sandy loam at Woburn is less fertile than the silty clay loam at Rothamsted. Root infection in these crops was assessed in spring and summer.
Rye was least infected by the take-all fungus, wheat the most infected and barley and triticale had intermediate levels of infection. Barley yields were less affected by take-all than those of wheat or triticale, because barley was at a later growth stage by the time severe infection occurred. Yields of wheat and barley responded most to the high-input husbandry on the less fertile soil at Woburn. On the basis of quantity of grain, triticale would appear to be a good substitute for wheat on the less fertile soil when inputs are low, but not where they are high. At Rothamsted, yields of wheat and triticale were similar in both input systems. There was no strong support, at either site, for the contention that triticale could be a useful substitute for barley where low or high inputs are used. A total of 177 isolates of Gaeumannomyces graminis var. tritici (the causal fungus of take-all) were obtained from infected roots in these experiments and tested for their pathogenicity on wheat and rye seedlings. These tests revealed a range of pathotypes with varying pathogenicities to wheat and rye, but pathogenicities were not correlated with the host plant from which the fungi were isolated.     

Virulence of Gaeumannomyces graminis var. tritici from fields under short-term and long-term wheat cultivation in the Pacific Northwest, U.S.A.

Gaeumannomyces graminis var. tritici was recovered from 63% of 731 winter wheat plants collected randomly from six sites where wheat had been grown in monoculture for the previous 7–22 years. Typical take-all was not evident at the time the plants were collected. The fungus was isolated by a baiting method without regard to the presence of take-all on the plants. Isolates from fields under short-term wheat cultivation (3 years or less after a break crop) were obtained by plating directly from infected roots of plants with typical take-all. Virulent isolates comprised 89 and 99% of those collected from long- and short-term wheat cultivation respectively. There was also only a slight difference in the proportions of virulent isolates among monoascosporic subcultures from the two groups of isolates. There was thus little evidence that, during prolonged wheat cultivation, declining virulence in the population of G. graminis var. tritici could account for the absence of take-all.     

枯草芽胞杆菌YB-05对小麦全蚀病菌胞内酶活的影响

小麦全蚀病菌是影响小麦产量和质量的主要致病菌之一,前期研究表明枯草芽胞杆菌YB-05对小麦全蚀病菌的生长具有抑制作用。本试验拟通过研究该菌对小麦全蚀病菌相关酶系的诱导变化情况,解析其对小麦全蚀病菌的抑制作用机理。本试验以小麦全蚀病菌Gaeumannomyces gramini（Sacc.）Arx et Oliver var. tritici（Sacc.）Walker为靶标菌,加入终浓度为MIC₅₀枯草芽胞杆菌YB-05发酵液,通过显微镜观察菌株YB-05发酵液对小麦全蚀病菌菌丝结构和形态的影响,通过酶活力测定检测菌株YB-05发酵液对小麦全蚀病菌胞内苯丙氨酸解氨酶（PAL）、过氧化物酶（POD）、过氧化氢酶（CAT）、多酚氧化酶（PPO）和超氧化物歧化酶（SOD）防御酶活的影响,同时检测菌株YB-05发酵液在离体/活体条件下对小麦全蚀病菌线粒体复合酶Ⅱ/Ⅲ活力的影响。小麦全蚀病菌经菌株YB-05发酵液处理后,显微镜观察到其菌丝变粗、断裂,顶端膨大,分枝增多;处理8 d后,胞内的PAL、POD、CAT、PPO和SOD活性比对照依次高24.52%、72.67%、81.81%、80.36%和112.48%;离体条件处理,线粒体复合酶Ⅱ和Ⅲ的活性与对照组相比差异不显著,而活体条件处理下差异显著,线粒体复合酶Ⅱ和Ⅲ分别比对照组分别降低43.95%和55.87%。菌株YB-05发酵液通过结合小麦全蚀病菌线粒体复合酶Ⅱ和Ⅲ的相关基因,从而影响该基因的表达,抑制小麦全蚀病菌线粒体复合酶Ⅱ和Ⅲ的活力,影响小麦全蚀病菌的呼吸,进而导致抑制小麦全蚀病菌菌丝畸变,从而影响小麦全蚀病菌的正常生长。     

Yield Trends during Take-all Decline in Spring Barley and Wheat Grown Continuously1

The effects of take-all, nitrogen and cropping sequence on grain yield were compared for spring barley and spring wheat grown in extended monoculture. Initial crops showed least take-all and maximum yields. Yields fell to a minimum more rapidly in wheat than in barley while the take-all intensity increased to a maximum; take-all decline occurred and yields improved from the 4th and 5th years respectively. Without nitrogen, yields were at their lowest level; application of nitrogen increased yields considerably with responses in proportion to the rate applied. At optimum rates, yield losses were 33% for wheat and 11% for barley with maximum disease intensity but only 9% and 3% respectively with take-all decline. Potential maximum yields in the absence of take-all were calculated to be greater with barley than with wheat.     

Take-all of wheat

Take-all, caused by the soilborne fungus Gaeumannomyces graminis var. tritici, is arguably the most-studied root disease of any crop, yet remains the most important root disease of wheat worldwide. S. D. Garrett launched the study of root diseases and soilborne pathogens as an independent field of science starting in the middle of the 20th century, inspired by and based in large part on his research on take-all during the first half of the 20th century. Because there has been neither a source of host plant resistance nor an effective and economical fungicide for use against this disease, the focus for nearly a century has been on cultural and biological controls. In spite of the intensive and extensive works towards these controls, with mostly site-or soil-specific success, the only broadly and consistently effective controls require either crop rotation (break crops), or the converse, wheat monoculture to induce take-all decline. Take-all decline has become the model system for research on biological control of plant pathogens in the rhizosphere and provided the first proof to the scientific world after decades of debate that antibiotics are both produced in soils and play a role in the ecology of soil microorganisms. On the other hand, even the best yields following take-all decline are rarely equal to those achieved with crop rotation. Because of this, the continuing trends globally to shorten rather than lengthen the rotations in wheat-based cropping systems, and the growing use of direct-seed (no-till) trashy systems to reduce costs and protect soil and water resources, new methods to control take-all are needed more than ever. With high resolution maps of the genomes of cereals and other grasses now available, including a complete sequence of the rice genome, and the interesting differences as well as striking similarities among the genomes of cereals and related grasses, gene transfer to wheat from oats, rice, maize and other grass species resistant to G. graminis var. tritici should be pursued.     

基于无人机数字图像与高光谱数据融合的小麦全蚀病等级的快速分类技术

小麦全蚀病是检疫性的土传病害,对小麦生产危害极大,对其发生的监测是治理的根本。遥感技术可实时、宏观地监测病害发生发展,尤其是将光谱信息与高分辨率数字图像进行融合,可直观、精准地对病害识别和分类。本文基于计算机视觉技术,通过光谱数据与高分辨率数字图像结合的方法,对小麦全蚀病等级进行快速分类。首先,通过ASD非成像光谱仪获取小麦全蚀病的光谱信息,提取全蚀病特征光谱,建立光谱比。其次,利用无人机获取的实时田间数码图像,对其颜色特征进行重量化。最后,利用基于支持向量机的决策树分类对图像视场中的不同全蚀病等级进行分类。结果表明,4个全蚀病等级的分类精度均大于86%(Kappa0.81),平均运算时间小于30s。通过与实地调查的小麦全蚀病的白穗率等级做比对,验证分类结果的准确性,结果表明该方法基本可以实现对小麦全蚀病等级的实时监测。     

不同根区温度对冬小麦生长发育及养分吸收的影响

以Hoagland营养液为介质,采用自制的恒温培养系统研究了不同根区温度对冬小麦生长发育以及N、P、K养分吸收的影响。结果表明:小麦冬前至返青期低温处理明显抑制根系发育,根长、根体积、根系生物量、叶面积、地上部生物量、养分累积量均比常温处理显著降低,其中越冬前低温处理对地上部的影响大于对根系的影响,而返青期低温处理对根系的影响大于地上部;越冬前和越冬期高温促进了根系生长,但地上部生物量和养分累积量呈降低趋势,返青期高温抑制了根长和根体积的增加,但有促进地上部生长的作用。     

Enhanced field control of wheat take-all using cold tolerant isolates of Gaeumannomyces graminis var. graminis and Phialophora sp. (lobed hyphopodia)

Cold tolerant isolates of Gaeumannomyces graminis var. graminis ( Ggg ) and Phialophora sp. (lobed hyphopodia), which produced at least comparable growth rates at 5°C to those of pathogenic G. graminis var. tritici ( Ggt ), were shown to control take-all disease in wheat effectively in 2 years of field experiments in New South Wales, Australia. The addition of oat inoculum of these fungi at the rate of 60 kg/ha to the seeding furrow significantly ( P  ≤ 0.05) reduced disease and increased grain yields by 33–45% compared to the Ggt alone treatment. The use of 30 kg/ha of oat inoculum also significantly ( P  ≤ 0.05) reduced disease and increased grain yields by 21–44%. These high levels of take-all control were obtained consistently from four field experiments on three different soil types with different pHs. A treatment inoculated with Ggg alone showed no disease symptoms and produced grain yields similar to that of untreated wheat. This fungus is, therefore, non-pathogenic to wheat. At high rates of inoculation of Ggg and Phialophora sp. (lobed hyphopodia), 65–80% of tillering wheat plants (GS 32) had root systems colonized by these fungi. In contrast, two Pseudomonas spp. and an isolate each of Ggg and Phialophora sp. (lobed hyphopodia), which did not grow at 5°C, were ineffective in controlling take-all. Take-all assessments during heading (GS 61-83) were highly correlated ( R ²=0.6047, P ≤0.0005) with the relative yield increase or decrease of inoculated treatments compared to the Ggt alone treatment. The use of a Ggg isolate (90/3B) and a Phialophora sp. (lobed hyphopodia) isolate (KY) for take-all control has been patented. These fungi are being developed for commercial use.     

Variation in the effects of take-all disease on grain yield and quality of winter cereals in field experiments

Relationships between take-all intensity and grain yield and quality were determined in field experiments on cereal crops using regression analyses, usually based on single-point disease assessments made during anthesis or grain-filling. Different amounts of take-all were achieved by different methods of applying inoculum artificially (to wheat only) or by using different cropping sequences (in wheat, triticale or barley) or sowing dates (wheat only) in crops with natural inoculum. Regressions of yield or thousand-grain weight on take-all intensity during grain filling were similar to those on accumulated disease (area under the disease progress curve) when these were compared in one of the wheat experiments. Regressions of yield on take-all intensity were more often significant in wheat than in the less susceptible crops, triticale and barley, even when a wide range of disease intensities was present in the latter crops. The regressions usually had most significance when there were plots in the severe disease category. Thousand-grain weight and hectolitre weight usually responded similarly to total grain yield. Decreased yield was often accompanied by a significant increase in the percentage of small grains. When severe take-all was present in wheat, regressions showed that nitrogen uptake was usually impaired. This was sometimes accompanied, however, by increased percentage nitrogen in the grain as a consequence of smaller grain size with decreased endosperm. Significant effects of take-all, both positive and negative, on Hagberg falling number in wheat sometimes occurred. Significant regressions of yield on take-all assessed earlier than usual, ie during booting rather than grain-filling in wheat and triticale and during anthesis/grain-filling rather than ripening in barley, had steeper slopes. This is consistent with observations that severe disease that develops early can be particularly damaging, whilst the crops, especially barley, can later express tolerance by producing additional, healthy roots. The regression parameters, including maximum potential yield (y-axis intercept) and the extrapolated maximum yield loss, also varied according to the different growing conditions, including experimental treatments and other husbandry operations. These differences must be considered when assessing the economic potential of a control measure such as fungicidal seed treatment.     

The classification of isolates of Gaeumannomyces graminis from wheat, rye and oats using restriction fragment length polymorphisms in families of repeated DNA sequences

Isolates of the take-all fungus, Gaeumannomyces graminis var. avenae , which affects oats, wheat and other grasses, and of G.g. var. tritici , which preferentially affects wheat, rye and barley, contain a high proportion of repeated sequences. Total DNA from 57 fungal isolates collected from many locations and different cereal hosts, and scored for virulence on wheat, rye and oats, revealed many restriction fragment length polymorphisms. These RFLP s were observed either by staining the DNA directly, by hybridization to radioactively labelled total fungal DNA , or by hybridization with labelled wheat ribosomal DNA . With only a few exceptions, the isolates with the same preferred cereal hosts showed more similar patterns of restriction fragments than isolates that had different pathogenicity properties on cereal hosts, irrespective of the geographical origins of the isolates. This was even the case for R isolates of G.g. var. tritici that were virulent on wheat and rye compared with N isolates that were virulent only on wheat. Isolates were identified by hybridizing DNA from infected root samples with ³²P-labelled total fungal DNA . The restriction fragment polymorphisms involving families of repeated sequence can therefore be used as a predictive assay for host preference of an isolate, and have probably arisen by host selection of fungal lineages. The variation between isolates in different pathogenicity groups suggests that there is little gene flow between isolates that can infect different hosts, even though they can coexist in the same field.     

Field testing putative biological controls of take-all: rationale and results1

In seeking biological control of the wheat take-all fungus (Gaeumannomyces graminis var. tritici) by introduced organisms, the demonstration of satisfactory field performance is proving a formidable hurdle. A novel experimental design incorporating small plots, 37 x 31 cm, has been used in UK at Rothamsted and Woburn since 1983 to test different kinds of control for take-all and to explore some of the problems of providing adequate field tests of putative biocontrol agents. Three years of bacterial treatments, using different plots each year, provided no evidence of effective control of the disease. Of the few significant treatment effects, most occurred in spring and were temporary: at Woburn they were mostly decreases in take-all and at Rothamsted mostly decreases in growth of the wheat plant without concomitant changes in take-all.     

水分胁迫持续时间对冬小麦根冠生物量累积的影响

为了解冬小麦根、冠对土壤含水量变化的响应,对不同水分条件下温室盆栽冬小麦作了分析研究。该试验包括七个水分状态,充分供水A处理(75%~100?,FC为田间持水量),中度胁迫B处理(55%~65?)和重度胁迫C处理(35%~45?)以及分蘖期开始中度、重度胁迫到孕穗期复水的BA1、CA1处理和抽穗期复水的BA2、CA2处理。试验结果表明:分蘖期开始的水分胁迫无论何时恢复供水都不影响冬小麦根、冠生长过程的总趋势;但随胁迫程度、胁迫持续时间的增加,胁迫期内根、冠的相对生长率,根、冠总重均降低,但根重占有量增大,且水分供应量的减少和胁迫时间的延长使冬小麦生育周期提前结束;随胁迫的增加,胁迫时间的延续,最大根重减小,但较大根重维持的时间延长;当复水后,各处理对复水存在不同程度的滞后效应和激发补偿生长,导致短期胁迫的根重占有量小于长期胁迫处理,中度胁迫小于重度胁迫,冠重也随之改变。造成此现象的原因:水分胁迫影响植株的功能,但自适应能力的作用促使分配于根系的同化物质增加,改善和提高根系的吸水能力,缓减植株由于缺水造成损失;对于供水超过75?的植株,生育后期的冠重占有量较小,根重较大则归因于生长过程已形成的庞大根系。     

EFFECT OF CHLORTHAL DIMETHYL ON OAT AND FOXTAIL SEEDLING ANATOMY*

Summary. The root and shoot growth of oat (Avena sativa L.) and green foxtail (Setaria viridis (L.) Beauv.) were generally reduced proportionately to the concentration of chlorthal dimethyl applied. Foxtail shoot growth was stimulated by a concentration of 2 ppm. Cells in the shoot and root meristems of treated plants were completely disarranged and considerably hypertrophied. Differentiation was irregular and extended nearer the apices in tissue of treated seedlings than in normal tissue. Histochemical tests showed that the amount of starch, proteins and nucleic acids in seedling tissue decreased with an increase of chlorthal dimethyl concentration, whereas the endosperm of the seeds retained more starch and protein than the controls. The walls of shoot nieristem and root epidermal cells were thickened or altered so as to stain more intensely than corresponding cells in untreated tissue. Effet du diméthyle chlorthal sur l'anatomie des plantules d'avoine et de séaire     

Effects of different cultivated or weed grasses, grown as pure stands or in combination with wheat, on take-all and its suppression in subsequent wheat crops

Grass species were grown in plots, as pure stands or mixed with wheat, after a sequence of wheat crops in which take-all ( Gaeumannomyces graminis var. tritici ) had developed. Annual brome grasses maintained take-all inoculum in the soil as well as wheat (grown as a continuous sequence), and much better than cultivated species with a perennial habit. Take-all developed more in wheat grown after Anisantha sterilis (barren brome) or Bromus secalinus (rye brome), with or without wheat, than in continuous grass-free wheat in the same year, where take-all decline was apparently occurring. It was equally or more severe, however, in wheat grown after Lolium perenne (rye-grass) or Festuca arundinacea (tall fescue), despite these species having left the least inoculum in the soil. It was most severe in plots where these two grasses had been grown as mixtures with wheat. It is postulated that the presence of these grasses inhibited the development of take-all-suppressive microbiota that had developed in the grass-free wheat crops. The effects of the grasses appeared to be temporary, as amounts of take-all in a second subsequent winter wheat test crop were similar after all treatments. These results have important implications for take-all risk in wheat and, perhaps, other cereal crops grown after grass weed-infested cereals or after set-aside or similar 1-year covers containing weeds or sown grasses, especially in combination with cereal volunteers. They also indicate that grasses might be used experimentally in wheat crop sequences for investigating the mechanisms of suppression of, and conduciveness to, take-all.     

Competition between vegetative plants of wild oat (Avena fatua L.) and wheat (Triticum aestivum L.)

Competition between wild oat (Avena fatua L.) and wheat (Triticum aestivum L.) was studied in two experiments; a replacement series model and a technique for separation of root and shoot systems. Wild oat and wheat in association resulted in a relative yield total very close to unity showing that the two species were‘crowding for the same space’(or competing for the same resources) and were‘mutually exclusive'. Wild oat was more competitive than wheat, as shown by its aggressivity relative to wheat, relative yields, shoot dry weights and other plant attributes. The greater competitive ability of wild oat was predominantly due to its greater root competitive ability, while the two species had similar shoot competitive ability. Root competition had a much greater effect on the relative performance of the two species than did shoot competition. The effects of root and shoot competition were additive.     

Mechanisms of inhibition of Gaeumannomyces graminis var. tritici by fluorescent pseudomonads

The take-all fungus Gaeumannomyces graminis var. tritici reduced the weight of wheat plants grown in tubes containing sterilized sand and plant nutrient solution. Fluorescent pseudomonads, when added to the tubes, inhibited the take-all fungus and increased plant weight. Iron (as FeNaEDTA) had no effect on the inhibition of the fungus by the pseudomonads. Some of the pseudomonads produced a compound in the wheat rhizosphere with a UV absorption peak at 365 nm, but the inhibition of G. graminis by pseudomonads was not proportional to the UV absorbance of rhizosphere extracts. A yellow crystalline compound, absorbing at 365 nm, was extracted from broth cultures and shown to be toxic to G. graminis under acid conditions. This compound is considered to be phenazine-I-carboxylic acid.     

我国小麦产区间病害发生与损失差异比较研究

为系统全面地掌握我国各产区小麦病害的发生情况,本文重点分析了我国小麦五大产区(华东麦区、华中麦区、华北麦区、西北麦区和西南麦区)小麦锈病、赤霉病、白粉病、纹枯病、黑穗病、根腐病和全蚀病的发生及防控情况。结果表明：我国小麦病害发生危害具有区域性特点,华东和华中麦区小麦纹枯病和赤霉病发病面积较大,且造成产量损失占比远超其余三大产区;华北麦区以白粉病发生最重;西北和西南麦区锈病和白粉病发生最重。我国小麦病害防治效果显著,华东和华中麦区赤霉病、纹枯病的年均挽回损失率均在80%以上;华北麦区年均挽回损失率最高的病害是白粉病(84.43%);西北和西南麦区对锈病年均挽回损失率分别为78.20%和85.26%;黑穗病、根腐病和全蚀病挽回损失率较低。     

Influence of time of emergence of wild oat on competition with wheat

The influence of time of emergence of wild oat (Avena fatua L.) on its competition with wheat (Triticum aestivum L.) was studied, using boxes that allowed separation of root and shoot competition. The relative yield total for mixtures of wild oat and wheat, grown under different forms of competition and with different wild oat sowing times, was very close to unity, indicating that the two species competed fully for limiting resources. Wild oat was more competitive than wheat when the two species were sown simultaneously, due largely to its greater root competitive ability; the two species had similar shoot competitive abilities. When wild oat was sown 3 or 6 weeks later than wheat, wheat was more competitive than wild oat and the production of wild oat panicles was prevented. This was mainly the result of greater root competitive ability of the wheat, although shoot competitive ability was also greater. The effects of root and shoot competition were additive. It is concluded that in order to prevent the return of wild oat seeds to the soil, and hence obtain long-term benefit, it is necessary to control the wild oat seedlings emerging within the first 3 weeks after drilling a wheat crop.