Luis Aguirrezábal

Genetic variability for leaf growth rate and duration under water deficit in sunflower: analysis of responses at cell, organ, and plant level

Plants under water deficit reduce leaf growth, thereby reducing transpiration rate at the expense of reduced photosynthesis. The objective of this work was to analyse the response of leaf growth to water deficit in several sunflower genotypes in order to identify and quantitatively describe sources of genetic variability for this trait that could be used to develop crop varieties adapted to specific scenarios. The genetic variability of the response of leaf growth to water deficit was assessed among 18 sunflower (Helianthus annuus L.) inbred lines representing a broad range of genetic diversity. Plants were subjected to long-term, constant-level, water-deficit treatments, and the response to water deficit quantified by means of growth models at cell-, leaf-, and plant-scale. Significant variation among lines was found for the response of leaf expansion rate and of leaf growth duration, with an equal contribution of these responses to the variability in the reduction of leaf area. Increased leaf growth duration under water deficit is usually suggested to be caused by changes in the activity of cell-wall enzymes, but the present results suggest that the duration of epidermal cell division plays a key role in this response. Intrinsic genotypic responses of rate and duration at a cellular scale were linked to genotypic differences in whole-plant leaf area profile to water deficit. The results suggest that rate and duration responses are the result of different physiological mechanisms, and therefore capable of being combined to increase the variability in leaf area response to water deficit.

GlyPh: a low-cost platform for phenotyping plant growth and water use

Breeding drought-tolerant crop varieties with higher water use efficiency could help maintain food supply to a growing population and save valuable water resources. Fast and accurate phenotyping is currently a bottleneck in the process towards attaining this goal, as available plant phenotyping platforms have an excessive cost for many research institutes or breeding companies. Here we describe a simple and low-cost, automatic platform for high-throughput measurement of plant water use and growth and present its utilisation to assess the drought tolerance of two soybean genotypes. The platform allows the evaluation of up to 120 plants growing in individual pots. A cart moving in only one direction carries the measuring and watering devices. Watering and measurement routines allow the simulation of multiple water regimes for each plant individually and indicate the timing of measurement of soil water content and image capture for growth estimation. Water use, growth and water use efficiency were measured in two experiments with different water scenarios. Differences in water use efficiency between genotypes were detected only in some treatments, emphasising the importance of phenotyping platforms to evaluate a genotypes phenotype under a broad range of conditions in order to capture valuable differences, minimising the chance of artefacts and increasing precision of measurements.

Management and Breeding Strategies for the Improvement of Grain and Oil Quality

This chapter focuses on sunflower as an oilseed model and bread wheat as a cereal model. It includes comparisons with other species to emphasize similarities and differences with these model crops. The rationale for the use of these model species is threefold. Research on model species has proven useful in other areas of knowledge, for example, Arabidopsis thaliana and rice as models for dicotyledonous and monocotyledonous plants in genetics, respectively. Grain oil and protein, major storage compounds in sunflower and wheat are important in human and animal diets and increasingly important for nonfood uses. The knowledge of quality aspects in these two species is sufficient to allow for meaningful quantitative models that capture major genetic, environmental, and G × E effects. This chapter comprises three main parts. It briefly reviews the effects of environmental, genetic, and G × E factors on grain oil and protein concentration and composition. Then it outlines the process-based crop models accounting for grain yield in both species and for concentration and composition of oil (sunflower) and protein (wheat). Finally, it uses a combination of modeling and experiments to analyze the relationships between quality traits and yield, and management and breeding strategies for the improvement of grain quality.

Improving grain quality: ecophysiological and modeling tools to develop management and breeding strategies

Abstract Grain quality is a complex character primarily determined by processes at the crop level. This chapter reviews the effects of environment, genotype, and their interactions, on grain oil and protein concentration and composition. The focus is on sunflower as an oilseed model and bread wheat as a cereal model. Sunflower oil composition is analyzed in terms of concentration and composition of fatty acids, tocopherols and phytosterols while, in bread wheat, grain prolamin composition is considered. Process-based crop models accounting for grain yield in both species, and for concentration and composition of oil (sunflower) and protein (wheat) are described. A combination of modeling and experiments allowed analysis of the relationships between quality traits and yield. Finally, we use physiologically-based relationships of yield and oil attributes (sunflower) and yield and protein attributes (wheat) to design management and breeding strategies for grain quality improvement.

Biomass Allocation Patterns Are Linked to Genotypic Differences in Whole-Plant Transpiration Efficiency in Sunflower

Increased transpiration efficiency (the ratio of biomass to water transpired, TE) could lead to increased drought tolerance under some water deficit scenarios. Intrinsic (i.e., leaf-level) TE is usually considered as the primary source of variation in whole-plant TE, but empirical data usually contradict this assumption. Sunflower has a significant variability in TE, but a better knowledge of the effect of leaf and plant-level traits could be helpful to obtain more efficient genotypes for water use. The objective of this study was, therefore, to assess if genotypic variation in whole-plant TE is better related to leaf- or plant-level traits. Three experiments were conducted, aimed at verifying the existence of variability in whole-plant TE and whole-plant and leaf-level traits, and to assess their correlation. Sunflower public inbred lines and a segregating population of recombinant inbred lines were grown under controlled conditions and subjected to well-watered and water-deficit treatments. Significant genotypic variation was found for TE and related traits. These differences in whole-plant transpiration efficiency, both between genotypes and between plants within each genotype, showed no association to leaf-level traits, but were significantly and negatively correlated to biomass allocation to leaves and to the ratio of leaf area to total biomass. These associations are likely of a physiological origin, and not only a consequence of genetic linkage in the studied population. These results suggest that genotypic variation for biomass allocation could be potentially exploited as a source for increased transpiration efficiency in sunflower breeding programmes. It is also suggested that phenotyping for TE in this species should not be restricted to leaf-level measurements, but also include measurements of plant-level traits, especially those related to biomass allocation between photosynthetic and non-photosynthetic organs.