Crop rotations with and without legumes: a review

Leguminosen sind im ökologischen Landbau aufgrund ihrer Fähigkeit zur Luftstickstofffixierung unverzichtbar für die Stickstoffversorgung der Ackerkulturen und die Proteinversorgung der Nutztiere. Im konventionellen Anbau bieten Leguminosen die Möglichkeit, die häufig getreideintensiven Fruchtfolgen aufzulockern. Eine der wichtigsten Wirkungen dieses Break-crop-Effekts ist das Durchbrechen des Lebenszyklus von fruchtartenspezifischen Pathogenen und der damit verbundenen Einsparung von Pflanzenschutzmitteln. Die vorliegende Übersichtsarbeit stellt den derzeitigen Stand des Wissens zu Fruchtfolgen mit und ohne Leguminosen zusammen. Dabei werden ackerbauliche, ökologische und ökonomische Wirkungen des Anbaus groß- und kleinkörnig Leguminosenarten als Haupt- oder Zwischenfrüchte bzw. Unter­saaten oder als Komponenten in Gemengen dar­gestellt und bewertet. Der Schwerpunkt liegt dabei auf relevanten Publikationen in wissenschaftlichen Journalen sowie Praxis- und Forschungsberichten der Jahre 2010 – 2020 die in Deutschland oder vergleichbaren klimatischen Bedingungen durchgeführt wurden. Abschließend wird daraus der notwendige Forschungsbedarf für die Themenbereiche Pflanzenbau (konventionell und ökologisch), Pflanzenschutz, Ökonomie, Ökologie und Klimaschutz abgeleitet.In organic farming, legumes are indispensable for the nitro­gen supply of arable crops and the protein supply of livestock due to their ability to fix atmospheric nitrogen. In conventional farming, legumes offer the potential to break the often cereal-intensive crop rotations. One of the most important consequences of the break-crop effect is the interruption of the life cycle of crop-specific pathogens and the associated savings of pesticides. This review summarizes the current state of knowledge on crop rotations with and without legumes. It presents and evaluates the agronomic, ecological and economic effects of the cultivation of large- and small-seeded legume species as main or catch crops, when undersown in other crops, or used as components in mixtures. The focus is on relevant publications in scientific journals as well as practice and research reports published between 2010 and 2020 which were carried out in Germany or under comparable climatic conditions. Finally, essential research needs in the areas of crop production (conventional and organic), crop protection, economics, ecology, and climate protection are identified

Genome-wide Association Mapping and Prediction of Adult Stage Septoria tritici Blotch Infection in European Winter Wheat via High-Density Marker Arrays

blotch (STB) caused by the fungus is a devastating foliar disease of wheat ( L.) that can lead to substantial yield losses. Quantitative genetic resistance has been proposed as a durable strategy for STB control. In this study, we dissected the genetic basis of STB infection in 371 European wheat varieties based on 35k and 90k single nucleotide polymorphism marker arrays. The phenotypic data analyses suggested that large genetic variance exists for STB infection with a broad-sense heritability of 0.78. Genome-wide association studies (GWAS) propose the highly quantitative nature of STB infection with potential associations on chromosomes 1A, 1B, 2D, 4A, 5A, 6A, 6D, 7A, and 7B. Increased marker density in GWAS by combining markers from both arrays helped to detect additional markers explaining increased genotypic variance. Linkage disequilibrium analyses revealed genes with a possible role in disease resistance. The potential of genomic prediction (GP) assessed via two models accounting for additive effects and additive plus epistatic interactions among the loci suggested the possibility of genomic selection for improved STB resistance. Genomic prediction results also indicated that the higher-order epistatic interactions are not abundant and that both marker platforms are equally suitable for GP of STB infection. Our results provide further understanding of the quantitative genetic nature of STB infection, serve as a resource for marker-assisted breeding, and highlight the potential of genomic selection for improved STB resistance

Genome-wide association studies and prediction of tan spot (Pyrenophoratritici-repentis) infection in European winter wheat via different marker platforms

Tan spot, caused by the fungus Pyrenophoratritici-repentis (Ptr), is a severe foliar disease of wheat (Triticumaestivum L.). Improving genetic resistance is a durable strategy to reduce Ptr-related losses. Here, we dissected Ptr-infection’s genetic basis in 372 European wheat varieties via single sequence repeats (SSR) in addition to 35k and 90k single nucleotide polymorphism (SNP) marker platforms. In our phenotypic data analyses, Ptr infection showed a significant genotypic variance and a significant negative correlation with plant height. Genome-wide association studies revealed a highly quantitative nature of Ptr infection and identified two quantitative trait loci (QTL), viz., QTs.ipk-7A and QTs.ipk-7B, which imparted 21.23 and 5.84% of the genotypic variance, respectively. Besides, the Rht-D1 gene showed a strong allelic influence on the resistance scores. Due to the complex genetic nature of the Ptr infection, the potential of genome-wide prediction (GP) was assessed via three different genetic models on individual and combined marker platforms. The GP results indicated that the marker density and marker platforms do not considerably impact prediction accuracy (~40–42%) and that higher-order epistatic interactions may not be highly pervasive. Our results provide a further understanding of Ptr-infection’s genetic nature, serve as a resource for marker-assisted breeding, and highlight the potential of genome-wide selection for improved Ptr resistance

Disease assessment

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EURORES Eurowheat Fungicide Resistance Network

Currently wheat production in western Europe is reliant on the application of plant protection products throughout the growing season. Fungicides account for approximately 25% of these applications, with septoria tritici blotch, caused by Zymoseptoria tritici the primary target. Unfortunately the evolutionary potential of Z. tritici, coupled with the high specific nature of current fungicide chemistries place the pathogen at a high risk of fungicide resistance development. Over the past decade the consequences of this have been observed at field level. In addition to fungicide resistance, changes in the registration of plant protection products within the EU will impact upon the availability of current and future chemistries. It is therefore imperative that both the potential development of resistance and subsequent spread is minimized. As part of the C-IPM ERA-NET, EUR-RES was established with in the EUROWHEAT platform to provide the basis from which to achieve this goal. Specifically the EURO-RES project aims to A) determine levels of resistance and the dynamics of resistance spread in partner countries B) determine the impacts of fungicide control strategies using the diversity in resistance levels throughout western Europe and C) make publically available the research findings through the EUROWHEAT platform in such a manner that they can be readily utlised by extension services and growers

Multiplex qPCR assay for simultaneous quantification of CYP51‐S524T and SdhC‐H152R substitutions in European populations of Zymoseptoria tritici

Demethylation inhibitor (DMI) and succinate dehydrogenase inhibitor (SDHI) fungicides are currently relied upon for the control of septoria tritici blotch (STB) in European wheat fields. However, multiple mutations have occurred over time in the genes encoding the targeted proteins that have led to a practical loss of fungicide efficacies. Among the different amino acid substitutions in Zymoseptoria tritici associated with resistance to these fungicides, S524T in CYP51 (DMI target) and H152R in SdhC (SDHI target) are regarded as conferring the highest resistance factors to DMI and SDHI, respectively. To facilitate further studies on the monitoring and selection of these substitutions in Z. tritici populations, a multiplex allele-specific quantitative PCR (qPCR) assay allowing for estimation of both allele frequencies in bulk DNA matrices was developed. The assay was then used on complex DNA samples originating from a spore trap network set up in Belgium, Denmark, Sweden, and Ireland in 2017 and 2018, as well as on leaf samples with symptoms. The S524T allele was present in all field samples and its proportion was significantly higher in Ireland than in Belgium, whereas the proportion of H152R was only sporadically present in both countries. The frequency of S524T varied greatly in the airborne inoculum of all four countries; however, the H152R allele was never detected in the airborne inoculum. The method developed in this study can be readily adopted by other laboratories and used for multiple applications including resistance monitoring in field populations of Z. tritici

Whole Genome Association Mapping of <em>Fusarium</em> Head Blight Resistance in European Winter Wheat (<em>Triticum aestivum</em> L.)

<div><p>A total of 358 recent European winter wheat varieties plus 14 spring wheat varieties were evaluated for resistance to <i>Fusarium</i> head blight (FHB) caused by <i>Fusarium graminearum</i> and <i>Fusarium culmorum</i> in four separate environments. The FHB scores based on FHB incidence (Type I resistance)×FHB severity (Type II resistance) indicated a wide phenotypic variation of the varieties with BLUE (best linear unbiased estimation) values ranging from 0.07 to 33.67. Genotyping with 732 microsatellite markers resulted in 782 loci of which 620 were placed on the ITMI map. The resulting average marker distance of 6.8 cM allowed genome wide association mapping employing a mixed model. Though no clear population structure was discovered, a kinship matrix was used for stratification. A total of 794 significant (−log₁₀(p)-value≥3.0) associations between SSR-loci and environment-specific FHB scores or BLUE values were detected, which included 323 SSR alleles. For FHB incidence and FHB severity a total of 861 and 877 individual marker-trait associations (MTA) were detected, respectively. Associations for both traits co-located with FHB score in most cases. Consistent associations detected in three or more environments were found on all chromosomes except chromosome 6B, and with the highest number of MTA on chromosome 5B. The dependence of the number of favourable and unfavourable alleles within a variety to the respective FHB scores indicated an additive effect of favourable and unfavourable alleles, i.e. genotypes with more favourable or less unfavourable alleles tended to show greater resistance to FHB. Assessment of a marker specific for the dwarfing gene <i>Rht-D1</i> resulted in strong effects. The results provide a prerequisite for designing genome wide breeding strategies for FHB resistance.</p> </div