Increased yield and yield stability in variety mixtures of spring barley

In the DARCOF II BAR-OF project, six variety mixtures are studied in organic as well as conventional growing systems in the period 2002 to 2005. The focus has been on competitive ability of the component varieties in addition to their disease resistance. This study is included in a European Network on sustainable low-input cereal production focusing on varietal characteristics and crop diversity (SUSVAR - COST 860), initiated in 2004. The following is based on papers presented at two SUSVAR workshops

Composition of variety mixtures in barley and wheat

Breeding within the last 50 years has focused on developing genetic uniform crops/varieties for farmers to be able to produce homogeneous products to be sold. Therefore, especially for selfing crops like wheat and barley where nearly all plants in a field are genetical identical, specific tools have to be applied to ensure genetic diversity. Among these tools is the use of variety mixtures. Principles for composing variety mixtures are to a large extent based on disease resistance characteristics and this is insufficient to predict the performance of the mixtures. Biological principles for interactions between varieties will be of relevance not only to organic farming but also to conventional agriculture where variety mixtures have been used for many years to a varying degree. To improve the performance of mixtures especially under organic conditions we need more information on the ability of different varieties to complement and compensate for each other under a range of different conditions (specific and general mixing ability)

Assessment of disease in low-input cereal cropping systems and variety trials

Disease assessment is the basis for describing disease resistance characteristics of commercial varieties in national variety lists for all crops where disease is considered a problem. It is well known that ‘disease’ in a specific situation depends on a whole range of interacting hosts, pathogens and environmental conditions. However, the biological complexity conflicts with the wish to express disease resistance characteristics of a variety as a single score per disease. This problem will be illustrated by basic dynamics of growth and senescence of both host and pathogen over time. Disease expressed in terms of absolute diseased leaf area, disease relative to total leaf area or green leaf area will be discussed in general. Two particular problems in low-input systems will be discussed, i.e. increased variability in nutritional status in field plots, which may influence the balance between abiotic and biotic stresses (diseases) and interact with disease on individual varieties, as well as the influence of weeds and diverse crops (variety mixtures and composite cross populations). The presence of disease in organic and low-input cropping systems may be underestimated because abiotic stresses, which enhance a general senescence of leaves, may obscure disease assessment, in particular disease on leaves. Weeds may interact by harbouring disease showing similar symptoms as on the target crop, or by ‘diluting’ disease by additional healthy green leaf area of the ‘crop’ like in a variety mixture. Other general topics such as differences between host/pathogen systems, timing of assessment, assessment scale, and interpretation and analysis of data are also discussed

Simultaneous epidemic development of scald and net blotch on single leaf layers of a spring barley crop

Background and objectives Two pathogens growing on the same leaf compete for the same resources, i.e. space and plant nutrients. This may lead to density dependent disease development. The pathogens may also influence each other directly such that the influence of one on the other is more complex than a simple function of the area of the other pathogen. Different interaction types are, for example, competition, mutualism and exploitation. The importance of such interactions for epidemics of simultaneously occurring pathogens has received little attention. The objective of this study is to investigate the simultaneous epidemic development of Rhynchosporium secalis (causing scald) and Drechslera teres (causing net blotch) on spring barley under field conditions. Materials and methods The field trial was performed with artificial inoculation of R. secalis and D. teres on three spring barley varieties differing in their susceptibility towards the pathogens. The pathogens were inoculated in three combinations: only one was inoculated, they were inoculated together, the second pathogen was inoculated 26 days after the first. A non-inoculated treatment was included. The trial had three replications. Nine plants were harvested from each plot five times during the season. Leaves were dried and disease severity and senescence observed. Only leaves with < 50 % senescence were included in the analysis. Whole-plant disease severity over time was calculated as average of disease severity on leaves weighted by leaf area. Disease development per leaf layer was evaluated by fitting an exponential model to severity data over time for each leaf layer per variety, treatment and replicate. Association between scald and net blotch severity on individual leaves was analysed using Kendall’s tau. Results and discussion Net blotch developed on all leaf layers and reached whole-plant disease severities up to 15%. Scald did not develop on upper leaf layers and whole-plant severity was less than 2%. Disease severity curves at whole-plant level showed no effect of inoculating the other pathogen. The analysis of the growth rate of each disease per leaf layer showed a significant effect of variety and leaf layer within variety but no effect of treatment. However, we observed significant negative associations between the diseases on individual leaves for several combinations of leaf layer and variety. These results show that the individual leaf approach can provide new information and underline the importance of considering interactions between pathogens in the field. Acknowledgement This work was funded by the DARCOF II project BAR-O

Sustainability assessment of wheat production using Emergy

Sustainability of crop production has to be given high priority when global biomass resources are limited. Here emergy evaluation is applied in order to assess sustainability of crop production exemplified by winter wheat. Emergy evaluation takes into account all inputs involved in a production system (i.e. renewable and non-renewable, local and imported) and transforms them into a common measure of direct and indirect solar energy requirement. The evaluation of winter wheat production is conducted by comparing conventional and organic management on two soil types using Danish reference conditions. The resource use efficiency of wheat production per kg biomass is higher using conventional management practices. This is due to high yield based on large use of non-renewable resources. The environmental loading ratio from organic management practices is about a third of the conventional implying that the organic management can be considered more sustainable

European perspectives of organic plant breeding and seed production in a genomics era.

For further optimisation of organic agricultural systems, more focus is required on organically produced seeds and the development of better adapted varieties. Organic plant breeding and seed production need to comply with the concept of naturalness as applied in organic agriculture, which not only includes the nonchemical and agro-ecological approaches, but also the integrity of life approach. As organic environments are less controllable and are more variable, breeding should aim at improved yield stability and product quality by being adapted to organic soil fertility as well as sustainable weed, pest and disease management. Also the ability to produce economicacceptable seed yield avoiding seed-borne diseases should be included. On the short term, organic plant production can gain better yield stability by increasing within-crop diversity by the use of mixtures of conventionally bred varieties or crop populations. Because of expected genotype by environment interaction more research is needed to define the best selection environment for selecting organic varieties. To arrive at better adapted varieties for organic farming systems the role of practical participatory plant breeding may be crucial. Although organic farming is clear on excluding the use of genetically modified organisms and their derivates, the use of molecular markers is still under debate. Questions arise with respect to their efficiency in selecting the most important organic traits, such as yield stability, and on the compounds and substances to produce and apply them. A major concern for a GM-free organic agriculture is an increasing contamination with genetically modified organisms in organic production and products, i.e., the problems related to co-existence of GM and non- GM agriculture. This paper discusses some important factors with regard to possible impact of co-existence on organic farming. Perspectives to a global scale of organic plant breeding and seed production are given from a European point of view

Net blotch severity is best assessed at early grain filling with respect to its effect on grain weight of spring barley

Appropriate disease assessment methods and parameters reflecting whole-season disease severity levels in field plots remain important issues in studies related to plant disease epidemiology, disease resistance of crop cultivars, and disease-induced yield losses. Such methods and parameters should be yield-related to ensure relevance. Net blotch severity was determined over time in inoculated and non-inoculated field plots of three spring barley varieties by whole plot assessments and by assessments of individual leaves of single main tillers. Disease severity measures such as the area-under-disease-progress-curve, mean and maximum severity as well as severity levels at specific growth stages (GS) were derived from the data. Their relation to thousand grain weight (TGW) and their inter-correlations were examined by means of general linear model (GLM) and factor analyses (FA), respectively. All parameters of net blotch severity were significantly negatively correlated with TGW. Disease parameters derived from whole-plot assessments gave a slightly better explanation of TGW than parameters derived by assessing single main tillers. Net blotch severity at GS 70 (beginning of grain filling) of whole plot assessments yielded the highest adjusted R-squared (0.43) while the adjusted R-squared values resulting from using the same parameter of assessments of the upper three, four or all leaves of single tillers were between 0.34 and 0.35. Also, the residuals of TGW of GLM’s using disease covariates from whole-plot assessments and variety effects as independent variables exhibited less pattern related to other sources of variation than residuals of the corresponding models that used single-tiller-based disease covariates. FA revealed that all disease parameters were highly inter-correlated and co-varied along the 1 principal component axis. The results indicate that disease assessments at GS 70 are appropriate to reflect whole-season severity levels of net blotch. In this respect, the time consuming single-tiller method is in this respect not superior to the simpler whole-plot method. However, assessing individual leaf layers of single tillers allows to observe the epidemic development and thus to examine the dynamics of epidemics in much greater detail than assessing whole-plots. This showed, for example, how much each leaf layer contributed at any given time to the total disease and revealed that a substantial fraction of the total disease is being removed during the course of an epidemic by senescence of diseased lower leaves. This level of detail in examining the dynamics of epidemics cannot be achieved by the whole-plot method

Predicting spring barley yield from variety-specific yield potential, disease resistance and straw length, and from environment-specific disease loads and weed pressure

Abstract For low-input crop production, well-characterised varieties increase the possibilities of managing diseases and weeds. This analysis aims at developing a framework for analyzing grain yield using external varietal information about disease resistance, weed competitiveness and yield potential and quantifying the impact of susceptibility grouping and straw length scores (as a measure for weed competitiveness) for predicting spring barley grain yield under variable biotic stress levels. The study comprised 52 spring barley varieties and 17 environments, i.e., combinations of location, growing system and year. Individual varieties and their interactions with environments were analysed by factorial regression of grain yield on external variety information combined with observed environmental disease loads and weed pressure. The external information was based on the official Danish VCU testing. The most parsimonious models explained about 50% of the yield variation among varieties including genotypeenvironment interactions. Disease resistance characteristics of varieties, weighted with disease loads of powdery mildew, leaf rust and net blotch, respectively, had a highly significant influence on grain yield. The extend to which increased susceptibility resulted in increased yield losses in environments with high disease loads of the respective diseases was predicted. The effect of externally determined straw length scores, weighted with weed pressure, was weaker although significant for weeds with creeping growth habit. Higher grain yield was thus predicted for taller plants under weed pressure. The results are discussed in relation to the model ramework, impact of the considered traits and use of information from conventional variety testing in organic cropping systems

Sortsblandingers udbyttestabilitet og udbyttepotentiale

Højere udbytte og bedre udbyttestabilitet er ofte fundet i sortsblandinger i vårbyg sammenlignet med målestandarder og komponentsorter, bl.a. i FØJO II projektet BAROF

Vekselvirkning mellem plantesygdomme påvirker sygdomsudviklingen

Sygdomme i planter kan være forårsaget af mange forskellige mikroorganismer, og ofte vil der i en enkelt afgrøde og på én plante være flere arter tilstede samtidigt. På trods af denne erfaring har der været tradition for at forske i sygdomme enkeltvis, og betydningen på det totale sygdomsniveau af vekselvirkninger mellem de enkelte patogener er kun blevet studeret i begrænset omfang. Her beskrives vekselvirkningen mellem sygdommene bladplet og skoldplet på byg i markforsøg