The role of genotypic diversity in stabilizing plant productivity in variable environments

Crop varietal mixtures have the potential to increase yield stability compared to monocultures in highly variable and unpredictable environments, yet knowledge of the specific mechanisms underlying enhanced yield stability has been limited. Field studies are constrained by environmental conditions that cannot be fully controlled and thus reproduced. This thesis tested the suitability of Arabidopsis thaliana as a model system to allow for reproducible experiments on ecological processes operating within crop genetic mixtures. Knowledge of the ecological processes occurring within varietal mixtures may improve the exploitation of mixtures in both conventional and subsistence agriculture. Genotypic diversity among accessions of A. thaliana buffered against abiotic stress, specifically nutrient and heat stress, and increased yield stability through compensation. The role of compensatory interactions in genotypic mixtures was supported by experiments investigating the ability of A. thaliana genotypic diversity to buffer against biotic stress, specifically the oomycete pathogen Hyaloperonospora arabidopsidis and viral pathogen Turnip yellows virus. Findings from research on plant phenotypic traits involved in competition and compensation in A. thaliana, were translated into the crop plant winter barley in field experiments. Mixtures achieved high and stable yields despite being subjected to multiple abiotic and biotic stresses, some of which were not anticipated. Unexpectedly, facilitation was identified as an important ecological process occurring within mixtures. This indicates that crop varietal mixtures have the capacity to stabilise productivity even when environmental conditions and stresses are not predicted in advance

Applications of crop competitive ability in winter oats (Avena sativa L.)

Crop competition is a key component of an integrated approach to weed management. Variation in competitive ability and competitive traits have been identified in many other crop species, however little work has been done on oats. Trials were carried out over four years at one organic site with five husked and three naked oat varieties. Mid-season Leaf Area Index (LAI) and tillering ability were identified as weed suppressive traits using path analysis. Differences in weed tolerance were found among varieties. Trade-offs may exist between competitive traits and yield potential which could be optimised by limiting competitive traits later in the season. Selection of competitive traits with high heritability, whilst minimising yield penalties, could be applied in breeding programmes to develop varieties with greater weed competitive ability

Selecting winter wheat lines from a composite cross population

The extremely diverse genetic variation in wheat Composite Cross Populations (CCP) represents a valuable source of breeding material. Such material could be selected as part of a participatory breeding programme with the potential advantage of selecting adaptation targeted for particular environments. For example, selections could be made aimed at producing lines that would thrive under the wide range of management practices conducted as part of organic and low input farming systems. Ears were selected from a CCP mixed stand under organic field conditions in the UK and Hungary. Selected lines were multiplied as single ear rows and 1m2 plots. The best performing five lines from the two selection sites were trialled in Suffolk, UK, in replicated plots including a commercial control variety (Alchemy) and the original population. Alchemy was chosen due to its good disease resistance and consistent performance at the trial site. Assessments included crop and weed cover, foliar and ear diseases, Leaf Area Index (LAI), crop height, as well as grain and straw yield. The first year of trials has been completed with five of the Hungarian selected lines and trials including locally selected lines are on-going. For the first trial year including only the Hungarian selected lines, there were significant differences among varieties (P<0.001) and Alchemy had the highest average yield. Across all trial entries grain yield was correlated negatively with yellow rust infection on the flag leaf at heading (P<0.001) and with reduced green leaf area during grain ripening (P<0.001). In current trials including locally selected lines, some of the selected lines had significantly lower yellow rust infection than the average of the original CCP and of the control variety Alchemy (P<0.001). There was also greater early ground cover (P<0.005) and (LAI) at tillering (P<0.05) in some lines compared to Alchemy and the original population. Crop cover was also correlated negatively with early weed cover (P<0.05). These observations suggest that it is possible to select lines with enhanced resistance to local disease and the ability to compete with weeds at an early stage. However, because average grain yields and percentage protein content are negatively correlated in this study (P<0.01), this trade-off should not be ignored when selecting lines for specific end uses. This can be avoided by developing mixtures of high performing lines with potentially greater stability than pure-line monocultures. Such mixtures may perform better than the original CCP but with the risk of reduced stability over multiple seasons because of their reduced diversity. Acknowledgements: The work reported here is supported by the EU Core Organic II project COBRA

Applications of crop competitive ability in winter oats (Avena sativa L.)

Crop competition is a key component of an integrated approach to weed management. Variation in competitive ability and competitive traits have been identified in many other crop species, however little work has been done on oats. Trials were carried out over four years at one organic site with five husked and three naked oat varieties. Mid-season Leaf Area Index (LAI) and tillering ability were identified as weed suppressive traits using path analysis. Differences in weed tolerance were found among varieties. Trade-offs may exist between competitive traits and yield potential which could be optimised by limiting competitive traits later in the season. Selection of competitive traits with high heritability, whilst minimising yield penalties, could be applied in breeding programmes to develop varieties with greater weed competitive ability

Increased yield stability of field-grown winter barley (Hordeum vulgare L.) varietal mixtures through ecological processes

Crop variety mixtures have the potential to increase yield stability in highly variable and unpredictable environments, yet knowledge of the specific mechanisms underlying enhanced yield stability has been limited. Ecological processes in genetically diverse crops were investigated by conducting field trials with winter barley varieties (Hordeum vulgare), grown as monocultures or as three-way mixtures in fungicide treated and untreated plots at three sites. Mixtures achieved yields comparable to the best performing monocultures whilst enhancing yield stability despite being subject to multiple predicted and unpredicted abiotic and biotic stresses including brown rust (Puccinia hordei) and lodging. There was compensation through competitive release because the most competitive variety overyielded in mixtures thereby compensating for less competitive varieties. Facilitation was also identified as an important ecological process within mixtures by reducing lodging. This study indicates that crop varietal mixtures have the capacity to stabilise productivity even when environmental conditions and stresses are not predicted in advance. Varietal mixtures provide a means of increasing crop genetic diversity without the need for extensive breeding efforts. They may confer enhanced resilience to environmental stresses and thus be a desirable component of future cropping systems for sustainable arable farming

An online toolbox for cover crops and living mulches

Cover crops and living mulches form an integral component of conservation agriculture promoting soil health and minimising external inputs. The OSCAR Project (Optimising Subsidiary Crop Applications in Rotation) aims to improve practices of conservation agriculture in farming systems across Europe. The principal output of the project is to develop a toolbox to make technical and scientific information publically available to farmers, researchers, and other stakeholders. The continually evolving toolbox is currently available online at www.covercrops.eu and will consist of three facets (1) An interactive user-fed wiki providing information on subsidiary crops species and machinery use with links to published literature. (2) A searchable database on subsidiary crops and technology. This will detail climatic and soil specific plant traits and will form a decision support tool to aid choices of subsidiary crops. (3) A discussion forum will also facilitate the exchange of information between farmers, researchers and stakeholders on conservation agricultural systems across European countries

Calcium Handling Defects and Cardiac Arrhythmia Syndromes

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