Simulation of yield reduction by leaf rust in winter wheat,applied to the analysis of genetic variation in partial resistance

Differences in yield reduction among seven winter wheat genotypes due to leaf rust, as observed in a field experiment, were analysed using a simulation model. In this model, the effects of the disease on crop growth and yield were described on the basis of light interception, photosynthesis, respiration and assimilate partitioning. The model properly described the observed yield difference between the genotypes, both in the absence and in the presence of leaf rust. According to the model, 66% of total yield reduction was due to an accelerated decrease in green leaf area and 18% was due to light capture by dead leaf tissue at the top of the canopy. Genetic variation in yield reduction was, therefore, mainly explained by variation in leaf senescence. Leaf rust did not affect the photosynthetic rate of the remaining green leaf area. Opportunities of selection for individual damage components were assessed from their simulated effect on grain yield, together with their estimated genetic and environmental variance.Samenvatting Verschillen tussen zeven wintertarwegenotypen in opbrengstderving door bruine roest, zoals waargenomen in een veldexperiment, werden geanalyseerd met een simulatiemodel. In dit model werd het effect van de ziekte op gewasgroei en opbrengst beschreven op basis van lichtinterceptie, fotosynthese, ademhaling en assimilatenverdeling. Het model gaf een goede beschrijving van de waargenomen opbrengstverschillen tussen de genotypen, zowel bij aanwezigheid als bij afwezigheid van bruine roest. Van de totale opbrengstreductie werd, volgens modelberekeningen, 66% veroorzaakt door versnelde afname van groen bladoppervlak en 18% door het wegvangen van licht door dood bladweefsel boven in het gewas. De genetische variatie in opbrengstreductie werd zodoende vooral verklaard uit de waargenomen verschillen in bladveroudering tussen de genotypen. De fotosynthese per eenheid resterend groen bladoppervlak werd niet beïnvloed door bruine roest. Respectieven voor selectie op afzonderlijke schadecomponenten werden geëvalueerd op basis van hun gesimuleerde effect op korrelopbrengst, in combinatie met hun genetische en toevalsvariatie.     

Adult-plant resistance to yellow rust in wild emmer wheat

Seventy-six entries of wild emmer, susceptible to a culture of yellow rust, race 39E134, in the seedling stage at a low temperature-profile, were tested with the same culture for field resistance at two locations in the Netherlands. While most entries were susceptible also in the adult-plant stage, 15 showed an intermediate or resistant infection-type in Flevoland and 18 at Wageningen. In subsequent seedling tests at low and high temperature-profiles, including 20 entries which at either of the two locations had displayed field resistance, 16 entries were shown to possess temperature-sensitive genes, whereas four appeared to have true host stage-bound adult-plant resistance.Samenvatting Voor dit onderzoek werden 76 herkomsten van wilde emmer tarwe (Triticum dicoccoides Körn.) geselecteerd op basis van vatbaarheid voor gele roest (Puccinia striiformis Westend f. sp.tritici) in het kiemplantstadium. In een veldtoets met hetzelfde gele roest isolaat (fysio 39E134) werd de reaktie in het volwassenplantstadium bepaald. Deze toets werd in Wageningen in een plastic kas uitgevoerd en in Flevoland in een geïsoleerd veld.In Flevoland vertoonden 15 herkomsten een intermediaire of resistente reaktie, in Wageningen werd dit bij 18 herkomsten waargenomen. Om na te gaan of de waargenomen veldresistentie mogelijk berust op temperatuurgevoelige genen, werd de resistentie vergeleken bij hoge en lage temperatuur. Van de 20 herkomsten, die resistentie vertoonden in de veldtoets in Wageningen of in Flevoland, bleken er 16 temperatuurgevoelige resistentiegenen te hebben. Vier herkomsten lijken echte, stadium afhankelijke, volwassenplantresistentie te vertonen.     

Germination and appressorium formation of wheat leaf rust on susceptible,partially resistant and resistant wheat seedlings and on seedlings of other Gramineae

Germination and appressorium formation of wheat leaf rust urediospores were studied in two experiments. No consistent differences could be detected between 11 genotypes of wheat (Triticum aestivum), two of barley, one ofTriticum dicoccum, one ofT. dicoccoides, one ofT. boeoticum and one ofAegilops squarrosa. Host genotypes and non-hosts gave similar results, suggesting that the phases before penetration of the host leaf are not affected by the resistance mechanisms operating in hosts and non-host genotypes.Samenvatting Kieming en de vorming van appressoria is bestudeerd in twee experimenten. Er zijn geen systematische verschillen waargenomen tussen 11 genotypen van tarwe, twee van gerst, een vanTriticum dicoccum, een vanT. dicoccoides, een vanT. boeoticum en een vanAegilops squarrosa. Waard en niet-waard genotypen gaven overeenkomstige resultaten, dit suggereert dat de fasen voor penetratie van het gastheerblad niet beïnvloed worden door de resistentiemechanismen werkzaam in waard en niet-waard.     

模拟酸雨对小麦条锈病流行学组分的影响

为明确酸雨对小麦条锈病菌孢子萌发及病害流行学组分的影响,采用不同酸度的模拟酸雨(p H值分别为2.5、3.5、4.5和5.6)处理小麦条锈病菌Puccinia striiformis f.sp.tritici生理小种CYR32和CYR33的夏孢子,并将不同酸度模拟酸雨处理后的夏孢子接种小麦感病品种铭贤169,采用组分分析法研究酸雨对病害发展过程的影响。结果表明,随着模拟酸雨酸度的增强,生理小种CYR32和CYR33的夏孢子萌发率均显著降低,萌发24 h后对照组生理小种CYR32和CYR33的夏孢子萌发率分别为93.7%和79.8%,在p H 3.5模拟酸雨处理后萌发率仅为13.1%和8.6%。温室内接种试验结果显示,不同酸度模拟酸雨对生理小种CYR32和CYR33的侵染概率、潜育期和病情指数均有显著影响,对生理小种CYR32和CYR33病斑扩展率影响不显著;与对照相比,p H 3.5模拟酸雨处理后生理小种CYR32和CYR33的侵染概率分别下降79.9%和79.8%。结果表明强酸雨(p H 3.5)显著延长小麦条锈菌潜育期,减少病斑产孢量,降低病情指数和病害进展曲线下面积。     

Effects of powdery mildew and weather on winter wheat yield. 1. Variation of weather between years

A vital question to upgrade disease management systems is whether damage functions, established in years with specific weather conditions, can be applied also in other years. A simulation approach was used to explore effects of weather on yield and damage. Two existing models of wheat and a third, a combination of both, were used to compute yield, first in absence of mildew. In a second paper, effects of mildew will be reported. Yields simulated for different years were not significantly correlated with yields harvested, adjusted for their increase over years, in the Netherlands. Differences in performance between the models could be attributed to the method of simulating development and growth early in the cropping season.Samenvatting Om systemen voor geleide bestrijding van ziekten te verbeteren, werd de vraag gesteld of schaderelaties, vastgesteld in jaren met specifieke weersomstandigheden, ook gebruikt kunnen worden in andere jaren. Twee bestaande modellen van tarwe en een combinatie van beide, werden gebruikt om het effect van weer op opbrengst te berekenen, eerst bij afwezigheid van meeldauw. De berekende opbrengsten in verschillende jaren toonden geen samenhang met de behaalde opbrengsten, gecorrigeerd voor een jaarlijkse toename, in Nederland. Verschillen tussen de modellen konden worden toegeschreven aan de wijze waarop de groei en ontwikkeling van tarwe vroeg in het seizoen wordt berekend.     

Genetic relationship between the adult plant resistance gene Lr12 and the complementary gene Lr31 for seedling resistance to leaf rust in common wheat

A resistant phenotype similar to that conferred in wheat by the complementary genes Lr27  +  Lr31 was produced in the progeny of intercrosses of cultivars carrying Lr27 and a line possessing Lr12 . This confirms that Lr12 is either completely linked with Lr31 or is the same gene. On the basis of these findings and that Lr31 is located on chromosome 4BS, it is concluded that Lr12 must also be located on 4BS. Adult-plant genetic tests confirm that the Australian wheat cultivar Timgalen carries Lr12 , and stocks with Lr12 alone were established from this cultivar.     

The relationship of leaf wetness duration and disease progress of glume blotch,caused byStagonospora nodorum,in winter wheat to standard weather data

Almost 50% of the variation in leaf wetness duration can be explained by maximum and minimum temperatures, rainfall and hours with relative humidity above 90% on a daily basis. All of these parameters can be estimated from a standard weather station. If variables related to wind are added the level of explanation increases to 69–76%. Leaf wetness duration explained up to 42% of the rate of disease increase (RDI) forS. nodorum. Leaf wetness duration was accumulated over a 5-day window period and correlated with rate of disease increase after a 7-day lag period. Standard weather variables could explain 20–34% of the disease increase. The relevance of these statistical models to disease prediction is discussed.     

Components of quantitative resistance to leaf rust in wheat cultivars: diversity,variability and specificity

The aim of this study was to investigate the potential diversity and pathogen‐specificity of sources of quantitative resistance to leaf rust caused by Puccinia triticina in French wheat germplasm. From a set of 86 genotypes displaying a range of quantitative resistance levels during field epidemics, eight wheat genotypes were selected and challenged in a greenhouse with three isolates of the pathogen, belonging to different pathotypes. Five components of resistance were assessed: infection efficiency, for which an original methodology was developed, latent period, lesion size, spore production per lesion, and spore production per unit of sporulating tissue. High diversity and variability for all these components were expressed in the host × pathotype combinations investigated; isolate‐specificity was found for all the components. The host genotypes displayed various resistance profiles, based on both the components affected and the isolate‐specificity of the interaction. Their usefulness as sources of quantitative resistance was assessed: line LD7 probably combines diversified mechanisms of resistance, being highly resistant for all the components, but displaying isolate‐specificity for all the components; cv. Apache did not show isolate specificity for any of the components, which could be related to the durability of its quantitative resistance in the field over more than 11 years.     

Surveys of cereal diseases and pests in the Netherlands. 4. Occurrence of powdery mildew and rusts in winter wheat

Results of annual surveys of winter wheat fields from 1974 to 1986 were compiled to describe epidemics of powdery mildew and rusts in relation to weather and cultivar resistance.An average of 29 and 70% of fields were infected by powdery mildew in May and July, respectively. Mildew prevalence in May was positively correlated with average temperature in October and with average temperature over the months December, January, February and March. In addition, it was correlated negatively with the average grade of mildew resistance of the cultivars sown each year. Prevalence of mildew in July did not show consistent correlations with weather characteristics nor with mildew prevalence in May.Yellow rust was usually not detected in May and on average 18% of the fields was infected in July. The occurrence of yellow rust decreased after 1977, when the farmers adopted cultivars resistant or moderately resistant to yellow rust.Brown rust was usually not detected in May, while in July on average 48% of the fields was infected. Brown rust intensity in July was high in years with a high March temperature and high precipitation during April and May.Black rust was rare in the Netherlands, with 3 and 1% of the fields infected in July 1977 and 1981, respectively.     

Measures of disease intensity in powdery mildew (Erysiphe graminis) of winter wheat. 1. Errors in estimating pustule number

Assessments of pustule number and severity of powdery mildew on winter wheat in the Netherlands were made in commercial fields and in experimental plots. The sample variance (s²) of the number of pustules per leaf (m) was fairly constant over years, varieties, growth stages and leaf postitions, but depended strongly on the average pustule number: . The effect of sample size on the precision of the estimate is discussed and it is concluded that it is difficult to estimate low disease intensities accurately. Estimates are given for the detection level of pustule counts in relation to sample size.Mildew intensity on the lower surface of leaves can be estimated from the intensity on the upper surface. This method reduces the duration of the observation, but introduces an additional error. At low disease intensities and small sample sizes this method is more efficient than sampling mildew on both surfaces of leaves. The common practice of assessments of the upper surface of leaves only may not be the most efficient method.Samenvatting Aantallen puistjes meeldauw per blad werden geteld in praktijkpercelen en veldproeven met wintertarwe. De steekproefvariantie van het aantal puistjes was tamelijk constant in de jaren, rassen, gewasstadia en bladposities, maar was sterk afhankelijk van het gemiddeld aantal puistjes . Het effect van de steekproefgrootte op de nauwkeurigheid van de schatting wordt besproken en het blijkt dat het moeilijk is om lichte aantastingen nauwkeurig te schatten. Er worden schattingen gegeven van de detectiegrens in afhankelijkheid van de steekproefgrootte.Meeldauwaantastingen aan de onderkant van het blad, kunnen worden geschat uit de aantasting op de bovenkant van het blad. Deze methode levert een tijdsbesparing op, maar ook een extra onnauwkeurigheid. Alleen bij lichte aantastingen en kleine steekproeven is deze methode efficiënter dan een directe tweezijdige bemonstering. Het schatten van meeldauw op de bovenkant van bladeren is, hoewel algemeen gebruikelijk, waarschijnlijk niet de meest efficiënte methode.     

Application of pathogen surveys,disease nurseries and varietal resistance characteristics in an IPM approach for the control of wheat yellow rust

The present paper presents the rationale for the use of pathogen surveys, inoculated and non-inoculated disease nurseries and varietal resistance characteristics in an integrated approach to control wheat yellow rust in Denmark. The non-inoculated disease observation plots, which gave valuable information about yellow rust at the year, site and variety level, served as the primary sample source for the pathogen survey revealing pathogen virulence dynamics. This survey was also the main source for isolates of new pathotypes, a prerequisite for the assessment of the resistance characteristics of varieties and breeding lines in inoculated nurseries, and the postulation of race-specific resistance genes. A simple grouping of varieties into four categories with respect to resistance to the current yellow rust population proved robust, and this grouping was used as a determinant in a web-based decision support system for pesticide applications in cereals, Crop Protection On-line (CPO). The interplay between the different research and survey activities in the integrated pest management (IPM) approach demonstrated the need for a coherent and long-term involvement at all stages from plant breeding to the official variety approval system, extension service and research in disease epidemiology and resistance genetics.     

Effects of powdery mildew and weather on winter wheat yield. 2. Effects of mildew epidemics

Wheat yield losses caused by powdery mildew were computed based on effects of the disease on leaf photosynthesis. Powdery mildew was introduced in a crop model of wheat by quantification of five parameters, taking the vertical and horizontal distribution of mildew in the crop into account. The most important parameters were those of the mildew intensity, the distribution of mildew in the crop, and the effect of mildew on assimilation at light saturation. Measured mildew epidemics in field experiments in three different years, were used to compute yield losses. Computed losses were compared to measured losses. On average, computed yield loss approached measured, but measured yield loss was underestimated, especially in early mildew epidemics due to the computation of partitioning and reallocation of assimilates. Other processes which may cause an underestimation are described. The use of crop models as a method to upgrade disease management systems is discussed.Samenvatting Opbrengstderving van wintertarwe werd berekend aan de hand van het effect dat meeldauw heeft op de blad-fotosynthese. Een rekenmodel voor de gewasgroei van tarwe werd uitgebreid met meeldauw. Met inachtneming van de vertikale en horizontale verdeling van meeldauw in het gewas, werd meeldauw in het model gekwantificeerd door vijf parameters. De belangrijkste parameters waren die van de meeldauwintensiteit, de verdeling van meeldauw in het gewas en het effect van meeldauw op de assimilatie bij een overvloed aan licht. Epidemieën van meeldauw, gemeten in veldproeven in drie verschillende jaren, werden gebruikt om opbrengstdervingen te berekenen. Gemiddeld kwam deze redelijk overeen met de in de veldproeven gemeten opbrengstderving. De gemeten opbrengstderving werd echter onderschat, vooral bij vroege epidemieën van meeldauw door de wijze waarop de (her)verdeling van assimilaten wordt berekend. Andere mechanismen, die een onderschatting van opbrengstderving kunnen veroorzaken worden besproken. Of deze modellen als methode gebruikt kunnen worden om systemen voor de geleide bestrijding van ziekten te verbeteren wordt bediscussieerd.     

冬小麦抗旱性状遗传力分析

依据Griffing方法I,配制不同类型的复合双列杂交组合,在水地(浇越冬水、返青拔节水、孕穗水和灌浆水)和旱地(雨养)条件下,在不同生育时期测定冬小麦株高、单株穗数、单株粒重、穗粒数、黄叶数、SOD、POD、MDA等农艺、生理生化性状,研究不同组合类型对其杂交后代的抗旱性遗传力及其与抗旱性的关系.结果表明,单株粒重、穗下节长、黄叶数、籽粒饱满度、落黄特性、成穗数、株高等7个性状与抗旱性关系密切且遗传力较强,可作为高产种质杂种后代的早期抗旱性鉴定指标.SOD活性和MDA含量由于广义遗传力和狭义遗传力均较高,可以在杂种后代早期世代进行选择,OA能力和POD活性广义遗传力较高但狭义遗传力低,适宜在杂种后代的晚期世代进行选择.     

Identification of resistance genes to Puccinia striiformis in seedlings of Ethiopian and CIMMYT bread wheat varieties and lines

In a controlled environment, the reaction was observed of 42 bread wheat varieties and lines inoculated with 19 isolates of yellow rust differing in their virulence to 20 differential varieties. Five varieties and lines showed resistance to all isolates. The remaining ones appeared to have the genesYr2, Yr3, Yr4, Yr6, Yr7, Yr9 andYrA, either singly or in combination.Yr9 derived from rye was present in 67% of the varieties and lines.Yr4 is the only effective gene in that material as, in Eastern and Central Africa, yellow rust has virulence to the otherYr genes. Recognition of virulence toYr genes is enhanced by the use of a supplemental set of differential varieties supposedly carrying a single gene.Samenvatting Onder geconditioneerde klimaatsomstandigheden zijn 42 Ethiopische en CIMMYT rassen en lijnen van broodtarwe (Triticum aestivum) in het kiemplantstadium geïnoculeerd met 19 isolaten van gele roest die onderling verschilden in hun pathogeniteit voor 20 differentiërende tarwerassen waarvan de resistantie-achtergrond bekend is. De genom-gen relatie is toegepast om resistentiegenen te identificeren. Vier rassen en lijnen bleken resistent te zijn tegen alle isolaten. Verondersteld wordt dat hun resistentie berust op genen die niet eerder herkend waren of op een combinatie van bekende genen die niet compatibel was met de gebruikte isolaten. In het overige tarwemateriaal kon de aanwezigheid worden aangegeven van de resistentiegenenYr2, Yr3, Yr4, Yr6, Yr7, Yr9 enYrA. Het van rogge afkomstige en door het CIMMYT veel gebruikte resistentiegenYr9 was in 28 rassen en lijnen (67%) aanwezig. In het onderzochte tarwemateriaal isYr4 het enige voor Oost en Centraal Afrika effectieve resistentiegen omdat de daar voorkomende gele roest pathogeniteit bezit voor de overige genen. Het herkennen van pathogeniteit van gele roest voor bepaalde resistentiegenen is verbeterd door het toevoegen van tarwerassen met monogene resistentie aan het internatinale gebruikte tarwesortiment voor de determinatie van gele-roestfysio's.     

Spatiotemporal patterns of oxidative burst and micronecrosis in resistance of wheat to brown rust infection

The accumulation of H₂O₂ (oxidative burst) and the progress of pathogen development were studied in compatible and incompatible wheat‐brown rust interactions. The accumulation of H₂O₂ was detected in 98·7% of guard cells with appressoria 8 h post inoculation (hpi). The reaction in both susceptible and resistant plants declined 2–3 days post inoculation (dpi). The second phase of the oxidative burst was observed in the mesophyll and/or epidermis. In susceptible plants it began 4–5 dpi and was detected only in the epidermis. In resistant plants the response was observed in the mesophyll. In moderately resistant plants it was induced 1–3 dpi, and the percentage of infection units reached 80–90% 8 dpi. This corresponded with severe necrotic symptoms. In highly resistant plants, the oxidative burst was short and transient. The percentage of infection units with H₂O₂ accumulation reached its highest level (60–70%) 2 dpi, and decreased thereafter. Four days later, the low percentage and weak DAB staining indicated very low H₂O₂ accumulation. The localization and the time‐course changes of the oxidative burst correlated with the profiles of the micronecrotic response, haustorium mother cell formation and pathogen development termination. An early and localized induction of oxidative burst followed by its rapid quenching correlated with high resistance and almost no disease symptoms. The possible correlation of the oxidative burst and pathogen development patterns with the level and durability of resistance conferred by Lr genes are discussed.     

Genetic architecture of adult plant resistance to leaf rust in a wheat association mapping panel

Leaf rust caused by Puccina triticina is one of the most destructive fungal diseases of wheat (Triticum aestivum). Adult plant resistance (APR) is an effective strategy to achieve long‐term protection from the disease. In this study, findings are reported from a genome‐wide association study (GWAS) using a panel of 96 wheat cultivars genotyped with 874 Diversity Arrays Technology (DArT) markers and tested for adult leaf rust response in six field trials. A total of 13 quantitative trait loci (QTL) conferring APR to leaf rust were identified on chromosome arms 1BL, 1DS, 2AS, 2BL, 2DS, 3BS, 3BL, 4AL, 6BS (two), 7DS, 5BL/7BS and 6AL/6BS. Of these, seven QTLs mapped close to known resistance genes and QTLs, while the remaining six are novel and can be used as additional sources of resistance. Accessions with a greater number of combined QTLs for APR showed lower levels of disease severity, demonstrating additive and significant pyramiding effects. All QTLs had stable main effects and they did not exhibit a significant interaction with the experiments. These findings could help to achieve adequate levels of durable resistance through marker‐assisted selection and pyramiding resistance QTLs in local germplasm.     

Genetic diversity of the wheat yellow rust population in Pakistan and its relationship with host resistance

Yellow rust, caused by Puccinia striiformis f.sp. tritici (PST), is an important disease that threatens wheat production in Pakistan. This study was designed to explore the virulence and simple sequence repeat (SSR) diversity of the Pakistani PST population and the ongoing selective pressures of widely grown wheat cultivars. Analyses of 49 isolates sampled from the North‐West Frontier Province of Pakistan led to the identification of 12 distinct pathotypes. The virulence frequencies of v2 (virulent against Yr2), v6, v7, v9, vSU and v27 ranged from 63% to 100%. Virulences v3, v4, v17 and vSD were uncommon, whilst v5, v10, v15, v24, v32 and vSp were not detected. The pathotypes thus described were then classified into 27 distinct genotypes. Bayesian structure analysis clustered these genotypes into five groups (in addition to one hybrid isolate) which represent three distinct lineages of the SSR‐based phylogenetic tree. Of the studied isolates, 80%, represented by three predominant pathotypes (P1–P3), belonged to the same characteristic Pakistani lineage, whilst the other isolates were close to either a Mediterranean lineage or a Northern European lineage. Genetic recombination was detected within P2 isolates. Resistance genes postulated in 40 Pakistani wheat cultivars indicated the high frequency of Yr2, Yr6, Yr7, Yr9, Yr27 and YrSU. Only 11 cultivars were found to be resistant to P1–P3. Migration and varietal diversity factors might contribute to maintaining the currently high genetic diversity in Pakistani PST, and have serious regional implications for wheat improvement programmes.     

底墒和补灌量对冬小麦产量和水分利用的影响

在大型半自动控制防雨池栽条件下,采用裂区设计,以不同底墒(350、450、650 mm)为主处理,生育期补灌量(0、56.3、78.1、100 mm)为副处理,研究了不同土壤底墒和补灌量对冬小麦产量、产量构成和水分利用的影响.结果表明,在不补灌条件下,0～200 cm土壤有效底墒最大利用率为42.6％～74.2％,其中...