人工合成抗纹枯病小麦新种质的鉴定

小麦纹枯病是影响我国小麦生产的主要土传病害。培育、推广抗纹枯病小麦品种是防治该病害最经济、有效的方法。普通小麦中抗源匮乏,严重制约抗纹枯病小麦育种的进展。为发掘人工合成小麦中纹枯病新抗源,本试验通过人工接种、抗病鉴定方法,在江苏省和北京市两地,对来源于国际玉米小麦改良中心的102份人工合成六倍体小麦品系,进行4年的纹枯病抗性的多环境鉴定。结果表明,人工合成小麦品系间对小麦纹枯病抗性存在差异,在其中进行小麦纹枯病抗源的筛选是有效的。与普通小麦品种扬麦158、扬麦12相比,这102份人工合成小麦的大部分对纹枯病的抗性表现抗或中抗水平,其中一些品系在多年多点鉴定中表现稳定抗性,如ZC93、ZC111、ZC112、ZC123、ZC172、ZC206和ZC221表现为抗病水平,病情指数低于目前最好的普通小麦抗源,可作为抗纹枯病小麦育种的新抗源。     

玉米秸秆还田配施生防放线菌S024对麦田土壤微生物及小麦纹枯病的影响

采用大田人工接种的方法,研究了玉米秸秆不同还田量以及玉米秸秆还田与生防放线菌S024同时施用对麦田土壤微生物、小麦纹枯病和小麦产量的影响。结果表明:玉米秸秆还田能够显著增加土壤细菌和放线菌数量;秸秆还田同时施用生防菌,拔节期土壤放线菌数量与不还田(对照)相比,平均增加50%,土壤中小麦纹枯病菌的数量与对照相比减少了20%。秸秆还田处理在拔节期对小麦纹枯病有较好的防病效果,其中生防菌+秸秆加倍还田(9000kg.hm-2)处理的防病效果最好,病情指数减退率达57.4%。玉米秸秆还田对小麦有一定增产作用,其中生防菌+秸秆加倍还田处理增产幅度最大,增产23.1%。     

Effect of previous crops on the incidence of eyespot on winter wheat

Surveys of winter wheat from 1939 to 1946 show that eyespot (Cercosporella herpotrichoides Fron.) occurs throughout Britain and that its incidence depends largely on previous cropping and on weather. Examination of 551 crops on land whose cropping for the previous 4 years was known showed that the incidence rose steadily with increasing numbers of preceding wheat and barley crops: where neither crop had been taken for 4 years the proportion of crops with more than 70% infected straws was 2%, rising to 45% where three or four such crops had been taken and the average straws infected rose from 6 to 55%.
The percentage infection to be expected in various groups of crops was calculated from previous cropping; it was compared with the actual infection and so used to assess the importance of other factors in determining the incidence of eyespot. High spring rainfall, early sowing and a dense plant increased incidence and low spring rainfall, late sowing and a thin plant reduced it.
Eyespot was not usually severe on newly ploughed grassland until the third or fourth crop of wheat, but under very wet conditions it was sometimes severe in the second crop.
Oats is much less susceptible than wheat or barley, but some crops were found with a third of their straws infected.
A brief survey of winter wheat in Holland suggested possible causes for the rise and fall of eyespot in recent years and for its present lower incidence there as compared with East Anglia.     

Effects of eyespot on the yield of winter wheat

In two experiments, on Julia and Zephyr spring barley, evidence was obtained that the development of powdery mildew in sprayed plots depended very much on their proximity to unsprayed crop. The effective period of control achieved with one spray was greater where plots were well separated from unsprayed crop than where they were surrounded by or very close to unsprayed crop. There is probably a risk that small plot experiments may not only underestimate the potential effectiveness of fungicides in agricultural practice, but also give misleading information on optimal spray timing.     

Influence of direct-drilling of winter wheat on incidence of take-all and eyespot

Winter wheat drilled directly into stubble or pasture treated with paraquat to kill the vegetation has been found to be less severely attacked by take-all (Ophiobolus graminis (Sacc.) Sacc.) and eyespot (Cercosporella herpotrichoides Fron) than wheat drilled after cultivation. The reduction of take-all is associated, not with a direct effect of the chemical, but with factors, resulting from the technique, which limit the rate of spread of the fungus in the undisturbed soil.     

Characterisation of Pseudomonas chlororaphis subsp. aurantiaca strain Pa40 with the ability to control wheat sharp eyespot disease

This study details the isolation and characterisation of Pseudomonas chlororaphis subsp. aurantiaca strain Pa40, and is the first to examine P. chlororaphis for use in suppression of wheat sharp eyespot on wheat. Pa40 was isolated during an investigation aimed to identify biocontrol agents for Rhizoctonia cerealis. Over 500 bacterial strains were isolated from the rhizosphere of infected wheat and screened for in vitro antibiosis towards R. cerealis and ability to provide biocontrol in planta. Twenty‐six isolates showed highly antagonistic activity towards R. cerealis, in which Pseudomonas spp. and Bacillus spp. were predominant members of the antagonistic community. Strain Pa40 exhibited clear and consistent suppression of wheat sharp eyespot disease in a greenhouse study and suppression was comparable to that of chemical treatment with validamycin A. Pa40 was identified as P. chlororaphis subsp. aurantiaca by the Biolog identification system combined with 16S rDNA, atpD, carA and recA sequence analysis and biochemical and physiological characteristics. To determine broad‐spectrum applicability and the specific mechanisms involved in Pa40's pathogen suppression this strain was tested for antibiosis towards various phytopathogens and assayed for many biocontrol activities and plant‐beneficial traits. Strain Pa40 inhibited the growth of 10 of 13 phytopathogenic fungal strains and six of eight phytopathogenic bacteria tested. This original work characterises HCN, protease and siderophore production in P. chlororaphis. Each of these characteristics likely contributed to Pa40's biocontrol capabilities as well as stimulation of the hypersensitive response in tobacco and the presence of genes involved in the biosynthesis of phenazine, 2‐hydroxylated phenazine and pyrrolnitrin.     

A cell wall invertase modulates resistance to fusarium crown rot and sharp eyespot in common wheat

Fusarium crown rot (FCR) and sharp eyespot (SE) are serious soil-borne diseases in wheat and its relatives that have been reported to cause wheat yield losses in many areas. In this study, the expression of a cell wall invertase gene, TaCWI-B1, was identified to be associated with FCR resistance through a combination of bulk segregant RNA sequencing and genome resequencing in a recombinant inbred line population. Two bi-parental populations were developed to further verify TaCWI-B1 association with FCR resistance. Overexpression lines and ethyl methanesulfonate (EMS) mutants revealed TaCWI-B1 positively regulating FCR resistance. Determination of cell wall thickness and components showed that the TaCWI-B1-overexpression lines exhibited considerably increased thickness and pectin and cellulose contents. Furthermore, we found that TaCWI-B1 directly interacted with an alpha-galactosidase (TaGAL). EMS mutants showed that TaGAL negatively modulated FCR resistance. The expression of TaGAL is negatively correlated with TaCWI-B1 levels, thus may reduce mannan degradation in the cell wall, consequently leading to thickening of the cell wall. Additionally, TaCWI-B1-overexpression lines and TaGAL mutants showed higher resistance to SE; however, TaCWI-B1 mutants were more susceptible to SE than controls. This study provides insights into a FCR and SE resistance gene to combat soil-borne diseases in common wheat.     

Effects of water potential and temperature on the development of eyespot lesions in wheat

Growth of Pseudocercosporella herpotrichoides on potato dextrose agar at water potentials from -0.5 to -6.9 MPa was optimal at 20°C. At 12 and 20°C, six isolates of P. herpotrichoides grew more rapidly at -0.5 to -2 MPa than at -6.9 MPa. Wheat plants inoculated with P. herpotrichoides and grown in columns of soil at either 15 or 20°C developed more severe eyespot lesions under a heavy watering regime than under medium or light watering regimes. P. herpotrichoides penetrated leaf sheaths of inoculated plants grown in compost more rapidly at 10°C night/15°C day temperatures than at 5/10°C; death of leaf sheaths was also more rapid and consequently there were fewer living infected leaf sheaths at 10/15°C than at 5/10°C. Irrigating for 5 wk before harvest increased the severity of eyespot lesions in a 1983 wheat crop.     

小麦种质抗纹枯病性的鉴定和遗传分析

对2300余份创新种质和引进种质抗纹枯病性进行了自然病地初步鉴定,在此基础上选择一批抗性好的种质进行了人工病圃鉴定,共评选出高抗纹枯病的创新种质14份,引进种质21份。这些种质都兼抗1－3种其它病害,且综合性状较好,其中创新种质最好,为抗纹枯病育种提供了良好的种质材料。还选用7个抗纹枯病性不同的亲本组配成半双列杂交组合。采用Hayman法进行了基因效应分析,结果表明,抗纹枯病性的遗传不符合加性－显性模型。     

蜡样芽孢杆菌B3-7在大田小麦根部的定殖动态及其对小麦纹枯病的防治效果

为了阐明蜡样芽孢杆菌B3-7在大田条件下的生态适应性以及对于小麦纹枯病的生防效果,通过利用绿色荧光蛋白编码基因gfp标记生防菌株B3-7,室内比较了GFP标记菌株和原始出发菌株在菌落形态、生长特性,生物薄膜产生以及在小麦根部定殖等方面的特性,结果发现GFP标记菌株和出发菌株在上述特性方面无明显差别。在此基础上,大田条件下测定了GFP标记菌株在小麦根部的定殖动态和对于小麦纹枯病的生防效果。结果发现,GFP标记菌株在小麦根部能够长期定殖,其存在量在小麦分蘖期最大,每克根重达到105CFU,拔节期后,该细菌数量一直维持在104CFU之上。同时发现,生防菌株能够有效降低小麦纹枯病的严重度和提高罹病小麦的产量。小麦分蘖期、孕穗期和灌浆期生防菌对于小麦纹枯病的防治效果分别达到60%、34%,34%,小麦成熟后产量提高13%—15%。结果表明,B3-7在大田条件下具有较好的生态适应性和防治小麦纹枯病的能力。     

Combined application of Bacillus subtilis NJ-18 with fungicides for control of sharp eyespot of wheat

Antagonistic bacterium, Bacillus subtilis NJ-18, can biologically control several plant diseases. A combined strategy of wheat sharp eyespot control consisting of B. subtilis NJ-18 and fungicides was evaluated. Greenhouse and field tests were conducted to determine the effect of combining the B. subtilis NJ-18 with the fungicides flutolanil and difenoconazole for the control of wheat sharp eyespot caused by Rhizoctonia cerealis Van der Hoeven. The sensitivity of B. subtilis NJ-18 to fungicides flutolanil and difenoconazole was tested. The growth of NJ-18 was unaffected by flutolanil in a broth medium, and the survival of NJ-18 spores on wheat seed was unaffected by difenoconazole. In greenhouse experiments, disease control obtained with a combination of NJ-18 and either fungicide was better than the control obtained with the bacterium or fungicides alone, and some combinations of bacterium plus fungicide demonstrated a small synergistic effect in reducing disease. Similar results were obtained with repeated field experiments. In addition to providing a highly effective disease control, the use of combinations enabled a reduced level of fungicide application. Overall, the results suggest that the combination of B. subtilis strain NJ-18 and flutolanil or difenoconazole represents a promising new tool for the control of sharp eyespot of wheat.     

Effects of soil fumigation on soil nitrogen and on disease incidence in winter wheat

Winter wheat was grown in soil fumigated with D-D, 85% dazomet dust or formalin, and top-dressed with o or 125 kg nitrogen/ha. Six weeks after fumigation, there was much more ammonium nitrogen in fumigated than in unfumigated soil. Nitrate was also more after fumigation with dazomet, but less after D-D and formalin. After 5 months, only D-D plots had less nitrate and more total mineral nitrogen than unfumigated plots. Take-all (Ophiobolus graminis) was less prevalent in the first crop after dazomet or formalin, but was more prevalent in the second crop than after other treatments. Eyespot (Cercosporella herpotrichoides) was decreased only by formalin and only in the first crop after applying it. Fumigation had little effect on the incidence of other diseases recorded or on grain yield, except that yields were light on D-D plots in the first crop after fumigation, when ears were severely deformed.     

28份人工合成小麦对禾谷孢囊线虫、纹枯病、条锈病和叶锈病的抗性

为了发现具有兼抗多种病害的小麦种质,本研究采用田间病圃法和人工接种法,对28份人工合成小麦的禾谷孢囊线虫、纹枯病、条锈病和叶锈病进行了抗性鉴定。人工合成小麦对这些病害表现不同程度的抗性反应。C2和C20对鉴定的4种病害都具有抗性,C5、C10和C25对这些病害都表现感病。8份材料对Heterodera avenae和H. filipjevi两种病原线虫都表现抗性反应型,也有的材料只抗一种线虫。供试材料对纹枯病的抗性表现较好,其中19份材料表现抗性反应型。9份材料对接种的条锈菌小种CY30、CY31、CY32和CY33均表现抗性反应型,5份材料对叶锈菌小种THT和PHT都具抗性。     

A sharp threshold for disease persistence in host metapopulations

A sharp threshold is established that separates disease persistence from the extinction of small disease outbreaks in an S→E→I→R→S type metapopulation model. The travel rates between patches depend on disease prevalence. The threshold is formulated in terms of a basic replacement ratio (disease reproduction number), ?(0), and, equivalently, in terms of the spectral bound of a transmission and travel matrix. Since frequency-dependent (standard) incidence is assumed, the threshold results do not require knowledge of a disease-free equilibrium. As a trade-off, for ?(0)>1, only uniform weak disease persistence is shown in general, while uniform strong persistence is proved for the special case of constant recruitment of susceptibles into the patch populations. For ?(0)<1, Lyapunov's direct stability method shows that small disease outbreaks do not spread much and eventually die out.     

Observations on take-all and eyespot diseases of wheat in Yorkshire

Wheat crops were surveyed in Yorkshire from 1944 to 1946 on farms where crops were reported to be unsatisfactory. Take-all ( Ophiobolus graminis (Sacc.) Sacc.) and eyespot ( Cercosporella herpotrichoides Fron.) were both found to be present; the latter is the most serious trouble on the better wheat lands.
The variation in the incidence of these diseases on selected farms during the three seasons has been compared.
The effect of rotation has been examined; both diseases were found to be encouraged by too frequent cropping with wheat or barley. The incidence of disease in wheat crops following a 1-year seeds ley was found to be influenced by the nurse crop used to undersow the seeds, and also by the time at which the ley was ploughed up. Oats were found to be preferable to either wheat or barley as a nurse crop, and in 1946 late ploughing considerably reduced the amount of eyespot disease present in the following wheat crop.
A 1-year ley is considered to be of too short a duration to ensure the disappearance from the soil of Ophiobolus graminis and Cercosporella herpotrichoides surviving from the previous crop, and a period of 2–3 years is suggested as being desirable.     

Mapping of QTL conferring resistance to sharp eyespot (Rhizoctonia cerealis) in bread wheat at the adult plant growth stage

Key message

Seven sharp eyespot resistance QTL were detected consistently across five environments and delimited to seven DNA marker intervals, respectively, six of which were independent of plant height and heading time.

Abstract

Sharp eyespot, caused mainly by the soil-borne fungus Rhizoctonia cerealis, is one of the important diseases of bread wheat (Triticum aestivum L.). This disease has escalated into a major threat to wheat production in some regions of the world. Wheat resistance to sharp eyespot can be a potential means to reduce the needs for application of fungicides and agricultural inputs. In the present study, the winter wheat lines, Luke and AQ24788-83, both of which possess quantitative resistance to sharp eyespot, were crossed and a population consisting 241 recombinant-inbred lines (RILs) was constructed. These RILs were assessed for sharp eyespot resistance by conducting five field and greenhouse trials during the period from 2008 to 2012, and they were genotyped with 549 simple-sequence repeat DNA markers. Seven quantitative trait loci (QTL) were detected consistently across the five trial environments to be associated with the sharp eyespot resistance. They were mapped on chromosomes 1A, 2B, 3B, 4A, 5D, 6B, and 7B. Four of these QTL are unequivocally novel, while it is possible that the other three might also be novel. Plant height and heading date of the 241 RILs were recorded in the four field trials. All of the seven disease resistance QTL were independent of plant height and heading time except one that was significantly associated with plant heading time. This association might be attributed genetically to a single QTL, or to different but closely linked QTL. In the case of single QTL, pleiotropism might be involved or the sharp eyespot resistance might be conferred in a physical instead of physiological nature.