Plant breeding and drought in C3 cereals: what should we breed for?

The dynamics of pigment concentrations are diagnostic of a range of plant physiological properties and processes. This paper appraises the developing technologies and analytical methods for quantifying pigments non-destructively and repeatedly across a range of spatial scales using hyperspectral remote sensing. Progress in deriving predictive relationships between various characteristics and transforms of hyperspectral reflectance data are evaluated and the roles of leaf and canopy radiative transfer models are reviewed. Requirements are identified for more extensive intercomparisons of different approaches and for further work on the strategies for interpreting canopy scale data. The paper examines the prospects for extending research to the wider range of pigments in addition to chlorophyll, testing emerging methods of hyperspectral analysis and exploring the fusion of hyperspectral and LIDAR remote sensing. In spite of these opportunities for further development and the refinement of techniques, current evidence of an expanding range of applications in the ecophysiological, environmental, agricultural, and forestry sciences highlights the growing value of hyperspectral remote sensing of plant pigments.

Hyperspectral remote sensing of plant pigments.

Better understanding of root system structure and function is critical to crop improvement in water-limited environments. The aims of this study were to examine root system characteristics of two wheat genotypes contrasting in tolerance to water limitation and to assess the functional implications on adaptation to water-limited environments of any differences found. The drought tolerant barley variety, Mackay, was also included to allow inter-species comparison. Single plants were grown in large, soil-filled root-observation chambers. Root growth was monitored by digital imaging and water extraction was measured. Root architecture differed markedly among the genotypes. The drought-tolerant wheat (cv. SeriM82) had a compact root system, while roots of barley cv. Mackay occupied the largest soil volume. Relative to the standard wheat variety (Hartog), SeriM82 had a more uniform rooting pattern and greater root length at depth. Despite the more compact root architecture of SeriM82, total water extracted did not differ between wheat genotypes. To quantify the value of these adaptive traits, a simulation analysis was conducted with the cropping system model APSIM, for a wide range of environments in southern Queensland, Australia. The analysis indicated a mean relative yield benefit of 14.5% in water-deficit seasons. Each additional millimetre of water extracted during grain filling generated an extra 55 kg ha-1 of grain yield. The functional implications of root traits on temporal patterns and total amount of water capture, and their importance in crop adaptation to specific water-limited environments, are discussed.

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The role of root architectural traits in adaptation of wheat to water-limited environments

A rising human population and changing patterns of land use mean that world food production rates will need to be increased by at least 50% by 2050, a massive rise in harvestable yield per hectare of the major crops such as rice (Oryza sativa) and wheat (Triticum aestivum). Combinations of breeding for improved morphology-related traits such as harvest index and increased inputs of water and fertilizer, which have sustained yield increases since the 1960s, will be neither sufficient nor sustainable. An important limiting factor will be the capacity to produce sufficient biomass during favourable growing periods. Here we analyse this problem in the context of increasing the efficiency of conversion of solar energy into biomass, that is, leaf and canopy photosynthesis. Focussing on crops carrying out C3 photosynthesis, we analyse the evidence for 'losses' in the process of conversion of solar energy into crop biomass and we explore novel mechanisms of improving biomass production rates, which have arisen from recent research into the fundamental primary processes of photosynthesis and carbohydrate metabolism. We show that there are several lines of evidence that these processes are not fully optimized for maximum yield. We put forward the hypothesis that the chloroplast itself should be given greater prominence as a sensor, processor and integrator of highly variable environmental signals to allow a more efficient transduction of energy supply into biomass production.

Agriculture and the new challenges for photosynthesis research.

This review focuses on recent advances in some key areas of wheat physiology, namely phasic development, determination of potential yield and water-limited potential yield, tolerance to some other abiotic stresses (aluminium, salt, heat shock), and simulation modelling. Applications of the new knowledge to breeding and crop agronomy are emphasized. The linking of relatively simple traits like time to flowering, and aluminium and salt tolerance, in each case to a small number of genes, is being greatly facilitated by the development of molecular gene markers, and there is some progress on the functional basis of these links, and likely application in breeding. However with more complex crop features like potential yield, progress at the gene level is negligible, and even that at the level of the physiology of seemingly important component traits (e.g., grain number, grain weight, soil water extraction, sensitivity to water shortage at meiosis) is patchy and generally slow although a few more heritable traits (e.g. carbon isotope discrimination, coleoptile length) are seeing application. This is despite the advent of smart tools for molecular analysis and for phenotyping, and the move to study genetic variation in soundly-constituted populations. Exploring the functional genomics of traits has a poor record of application; while trait validation in breeding appears underinvested. Simulation modeling is helping to unravel G × E interaction for yield, and is beginning to explore genetic variation in traits in this context, but adequate validation is often lacking. Simulation modelling to project agronomic options over time is, however, more successful, and has become an essential tool, probably because less uncertainty surrounds the influence of variable water and climate on the performance of a given cultivar. It is the ever-increasing complexity we are seeing with genetic variation which remains the greatest challenge for modelling, molecular biology, and indeed physiology, as they all seek to progress yield at a rate greater than empirical breeding is achieving.

/pdf/wheat-physiology-a-review-of-recent-developments-oks8rajhf3.pdf

Wheat physiology: a review of recent developments

Photosynthesis of wheat in a warm, irrigated environment: I: Genetic diversity and crop productivity

Photosynthesis of wheat in a warm, irrigated environment II. Traits associated with genetic gains in yield.

Spectral reflectance (SR) indices (NDVI (R900 -R 680/R900 + R680); GNDVI (R780 -R 550/R780 + R550); and water index, WI (R900/R970)); and 6 chlorophyll indices (R740/R720, NDI = R750 − R705/R750 + R705, R780 − R710/R780 − R680 ,R 850 − R710/R850 − R680, mND = R750 -R 705/R750 + R705 -2 R445, and mSR = R750 - R445/R705 -R 445) were measured with a FieldSpec spectroradiometer (Analytical Spectral Devices, Boulder, CO) on bread wheat (Triticum aestivum L.) genotypes adapted to irrigated and drought conditions to establish their relationship with yield in field-grown plots. Bread wheat genotypes from the International Maize and Wheat Improvement Center (CIMMYT) were used for this study in 3 experiments: 8 genotypes in a trial representing historical progress in yield potential, and 3 pairs of near-isolines for Lr19, both of which were grown under well- watered conditions; and the third experiment included 20 drought tolerant advanced genotypes grown under moisture stress. These were grown during the 2000 and 2001 spring cycles in a temperate, high radiation environment in Obreg´ on, NW M´ exico. The 9 SR indices were determined during grain filling along with canopy temperature depression (CTD), flag leaf photosynthetic rate, and chlorophyll estimates using a SPAD meter. The relationship of SR indices with grain yield and biomass fitted best with a linear model. NDVI and GNDVI showed positive relationships with grain yield and biomass under well-irrigated conditions (r = 0.35-0.92), whereas NDVI showed a stronger association with yield under drought conditions (r = 0.54). The 6 chlorophyll indices showed significant association with yield and biomass of wheat genotypes grown under well-irrigated conditions (r = 0.39-0.90). The association between chlorophyll indices and chlorophyll estimates was correlated (r = 0.38-0.92), as was the case for photosynthetic rate (r = 0.36-0.75). WI showed a significant relationship with grain yield in wheat genotypes grown under drought stress conditions (r = 0.60) as well as with grain yield and biomass under well-irrigated conditions (r = 0.52-0.91). The relationship between WI and CTD was significant (P ≤ 0.05) in both environments (r = 0.44-0.84). In conclusion, the SR showed potential for identifying higher-yielding genotypes in a breeding program under dry or irrigated conditions, as well as for estimating some physiological parameters.

Association between canopy reflectance indices and yield and physiological traits in bread wheat under drought and well-irrigated conditions

An increase of grain yield of bread wheat cultivars has been frequently linked to the photosynthesis rate because all the dry matter produced in the plant depends on this process. Genetic variation in photosynthesis rate among genotypes of wheat and other crops is commonly of interest to physiologists and breeders, because it can be used as a direct physiological indicator of high yield. Our studies have demonstrated that genetic variability in flag leaf photosynthesis rate exists among bread wheat genotypes, and grain yield can be associated with photosynthesis in an environment with high radiation levels (>1600 µmoles m-2 s-1). The results also indicate that the photosynthesis rate is highly inheritable from plants F5 to plants F7 , and it can be used for identifying high yielding genotypes.

https://dialnet.unirioja.es/descarga/articulo/5167136.pdf

Algunas consideraciones en la relación entre fotosíntesis y el rendimiento de grano en trigo

Resumen es: Se realizaron aplicaciones de nitrogeno (0, 100 y 200 kg ha-1) en el cultivo del frijol (Phaseolus vulgaris L.) cv. Flor de Durazno para buscar increment...

M Gutiérrez-Rodrı́guez

Papers

Photosynthesis of wheat in a warm, irrigated environment: I: Genetic diversity and crop productivity

Photosynthesis of wheat in a warm, irrigated environment II. Traits associated with genetic gains in yield.

Association between canopy reflectance indices and yield and physiological traits in bread wheat under drought and well-irrigated conditions

Algunas consideraciones en la relación entre fotosíntesis y el rendimiento de grano en trigo

Índices de reflectancia y rendimiento del frijol con aplicaciones de nitrógeno