Single-gene resolution of diversity-driven overyielding in plant genotype mixtures

In plant communities, diversity often increases productivity and functioning, but the specific underlying drivers are difficult to identify. Most ecological theories attribute positive diversity effects to complementary niches occupied by different species or genotypes. However, the specific nature of niche complementarity often remains unclear, including how it is expressed in terms of trait differences between plants. Here, we use a gene-centred approach to study positive diversity effects in mixtures of natural Arabidopsis thaliana genotypes. Using two orthogonal genetic mapping approaches, we find that between-plant allelic differences at the AtSUC8 locus are strongly associated with mixture overyielding. AtSUC8 encodes a proton-sucrose symporter and is expressed in root tissues. Genetic variation in AtSUC8 affects the biochemical activities of protein variants and natural variation at this locus is associated with different sensitivities of root growth to changes in substrate pH. We thus speculate that - in the particular case studied here - evolutionary divergence along an edaphic gradient resulted in the niche complementarity between genotypes that now drives overyielding in mixtures. Identifying genes important for ecosystem functioning may ultimately allow linking ecological processes to evolutionary drivers, help identify traits underlying positive diversity effects, and facilitate the development of high-performance crop variety mixtures

Costs and benefits of multiple resistance to insecticides for Culex quinquefasciatus mosquitoes

<p>Abstract</p> <p>Background</p> <p>The evolutionary dynamics of xenobiotic resistance depends on how resistance mutations influence the fitness of their bearers, both in the presence and absence of xenobiotic selection pressure. In cases of multiple resistance, these dynamics will also depend on how individual resistance mutations interact with one another, and on the xenobiotics applied against them. We compared <it>Culex quinquefasciatus </it>mosquitoes harbouring two resistance alleles <it>ace-1</it>^{<it>R </it>}and <it>Kdr</it>^{<it>R </it>}(conferring resistance to carbamate and pyrethroid insecticides, respectively) to mosquitoes bearing only one of the alleles, or neither allele. Comparisons were made in environments where both, only one, or neither type of insecticide was present.</p> <p>Results</p> <p>Each resistance allele was associated with fitness costs (survival to adulthood) in an insecticide-free environment, with the costs of <it>ace-1</it>^{<it>R </it>}being greater than for <it>Kdr</it>^<it>R</it>. However, there was a notable interaction in that the costs of harbouring both alleles were significantly less than for harbouring <it>ace-1</it>^{<it>R </it>}alone. The two insecticides combined in an additive, synergistic and antagonistic manner depending on a mosquito's resistance status, but were not predictable based on the presence/absence of either, or both mutations.</p> <p>Conclusion</p> <p>Insecticide resistance mutations interacted to positively or negatively influence a mosquito's fitness, both in the presence or absence of insecticides. In particular, the presence of the <it>Kdr</it>^{<it>R </it>}mutation compensated for the costs of the <it>ace-1</it>^{<it>R </it>}mutation in an insecticide-free environment, suggesting the strength of selection in untreated areas would be less against mosquitoes resistant to both insecticides than for those resistant to carbamates alone. Additional interactions suggest the dynamics of resistance will be difficult to predict in populations where multiple resistance mutations are present or that are subject to treatment by different xenobiotics.</p

Mixtures of Spatial Spline Regressions

We present an extension of the functional data analysis framework for univariate functions to the analysis of surfaces: functions of two variables. The spatial spline regression (SSR) approach developed can be used to model surfaces that are sampled over a rectangular domain. Furthermore, combining SSR with linear mixed effects models (LMM) allows for the analysis of populations of surfaces, and combining the joint SSR-LMM method with finite mixture models allows for the analysis of populations of surfaces with sub-family structures. Through the mixtures of spatial splines regressions (MSSR) approach developed, we present methodologies for clustering surfaces into sub-families, and for performing surface-based discriminant analysis. The effectiveness of our methodologies, as well as the modeling capabilities of the SSR model are assessed through an application to handwritten character recognition

Genotype by environment interaction for grain yield in spring barley using additive main effects and multiplicative interaction model

Monoculture and use of disease resistant varieties on large scale usually leads to selection of new pathogen races able to overcome the resistance. The use of variety mixtures can significantly improve the control of the disease and provides stable yield among different environments. The objective of this study was to assess genotype by environment interaction for grain yield in spring barley genotypes grown in two places different in terms of soil and meteorological conditions by the additive main effects and multiplicative interaction model. The study comprised 25 spring barley genotypes (five cultivars: Basza, Blask, Skarb, Rubinek and Antek, and 20, two- and three-component mixtures), analyzed in eight environments (compilations of two locations and four years) through field trials arranged in a randomized complete block design, with three replicates. Grain yield of the tested genotypes varied from 32.88 to 74.31 dt/ha throughout the eight environments, with an average of 54.69 dt/ha. In the variance analysis, 68.80% of the total grain yield variation was explained by environment, 6.20% by differences between genotypes, and 7.76% by genotype by environment interaction. Grain yield is highly influenced by environmental factors

International Symposium on Evolutionary Breeding in Cereals

Evolutionary plant breeding has a long history, but has so far not become part of mainstream breeding research, nor has it been implemented in practice to any substantial degree. However, over the last decade, research in evolutionary plant breeding has markedly intensified. For example, there are currently major research projects on-going in this area, including the EU funded project SOLIBAM, the Wheat Breeding LINK project in the UK, and the Danish Biobreed project. Also, a new 3-year international research project called COBRA on this topic is due to start in March 2013. Funded by the CORE Organic 2 Eranet the project brings together over 40 partner organizations from 18 European countries. In addition, interest in evolutionary plant breeding is growing among farmers, breeders and policy makers. In fact, there are currently encouraging developments in the imminent revision of seed legislation in Europe that could lead to more room for evolutionary plant breeding approaches in the future. This renewed interest in evolutionary plant breeding is partly due to the recognition that mainstream plant breeding is limited in terms of its engagement with end users, i.e. farmers and growers. More urgently however, effects of climate change on agricultural production have become more noticeable and there is also a growing awareness of increasing resource constraints; together, these will create more stressful growing conditions for agricultural crops. With this background, it is now being recognized that crops need to be able to cope with more variable, contrasting, fluctuating, and generally more unpredictable growing conditions. To be able to deal with this large and increasing environmental variability, plant breeding needs to become more decentralized and diversified. Evolutionary plant breeding offers great potential in this respect. The contributions collated from this symposium explore this potential as well as the limitations of evolutionary plant breeding. While they only show a part of the on-going research activities in Europe, we hope that these proceedings provide inspiration both for further research and for implementation in practice

Germplasm and Cultivar Development

Cool-season forage grasses have evolved, and continue to evolve, in natural ecosystems subject to environmental factors both in the presence and absence of human influences. The literature often lacks facts describing the evolution and domestication of forage grasses. Furthermore, the literature on this subject mainly deals with evolution of species in the broad scope, i.e., on a scale of hundreds of thousands or millions or years. Thus, some of our conclusions are necessarily speculative and are highly subject to the nature of the research that has been reported. We describe the forces of selection that act upon cool-season forage grasses and attempt to place each in historical perspective and in relation to each other. Because most economically important cool-season forage grasses are perennial, our principal focus will be on perennial species. There has been very little effort to quantify economic values of selection criteria or to empirically compare different breeding procedures in cool-season forage grasses. We attempt to summarize and compare some of the more important and thoroughly reported approaches used since the advent of formal breeding strategies in the late nineteenth and early twentieth centuries. These selection criteria and breeding procedures are as varied as the individual researchers who developed them. Examples are cited to illustrate principles and phenomena of historical or practical importance. More details of the agriculturally important species are discussed in the later chapters of this book. Space limitations prevent us from developing a thorough review, but we cite earlier reviews that thoroughly cover the first few decades of formal cool-season forage grass breeding. We also have summarized the limited amount of research on cool-season forage grasses where attempts have been made to use new technologies for hybridization, tissue culture, and genetic markers. Many of these techniques were first developed using other species and later adapted to cool-season forage grasses. Many are still undergoing rapid development and modification to allow more efficient use in breeding programs. Together they have had little practical impact on cool-season forage grass cultivars, but appear to offer considerable promise for creating new genetic variability and more efficient breeding procedures

Germplasm and Cultivar Development

Cool-season forage grasses have evolved, and continue to evolve, in natural ecosystems subject to environmental factors both in the presence and absence of human influences. The literature often lacks facts describing the evolution and domestication of forage grasses. Furthermore, the literature on this subject mainly deals with evolution of species in the broad scope, i.e., on a scale of hundreds of thousands or millions or years. Thus, some of our conclusions are necessarily speculative and are highly subject to the nature of the research that has been reported. We describe the forces of selection that act upon cool-season forage grasses and attempt to place each in historical perspective and in relation to each other. Because most economically important cool-season forage grasses are perennial, our principal focus will be on perennial species. There has been very little effort to quantify economic values of selection criteria or to empirically compare different breeding procedures in cool-season forage grasses. We attempt to summarize and compare some of the more important and thoroughly reported approaches used since the advent of formal breeding strategies in the late nineteenth and early twentieth centuries. These selection criteria and breeding procedures are as varied as the individual researchers who developed them. Examples are cited to illustrate principles and phenomena of historical or practical importance. More details of the agriculturally important species are discussed in the later chapters of this book. Space limitations prevent us from developing a thorough review, but we cite earlier reviews that thoroughly cover the first few decades of formal cool-season forage grass breeding. We also have summarized the limited amount of research on cool-season forage grasses where attempts have been made to use new technologies for hybridization, tissue culture, and genetic markers. Many of these techniques were first developed using other species and later adapted to cool-season forage grasses. Many are still undergoing rapid development and modification to allow more efficient use in breeding programs. Together they have had little practical impact on cool-season forage grass cultivars, but appear to offer considerable promise for creating new genetic variability and more efficient breeding procedures