Phenotypic and genetic variation in the architectural responses of a C4 grass to drought stress
Improvement of next generation C4 grass feedstocks is a promising avenue towards meeting the challenge of sustainably ensuring global food and fuel security in the face of climate change. C4 grasses are inherently resource use efficient, have a variety of food, fuel, and other industrial product applications, and already play a large role in global agriculture. Ideally biofuel feedstocks should be grown on marginal and potentially drought prone acreage to avoid displacement of food production. Therefore, next generation C4 grass feedstocks must be both highly productive and highly drought tolerance. Plant architecture provides a framework for finding a balance between these targets. Plant architecture is the organization of the plant body and enables the capture of resources, influences the local microenvironment, and ensures reproductive success. Due to its impacts on productivity and the maintenance of productivity in response to environmental stress, tailored modification of plant architecture is a focus of modern breeding efforts. Imaging techniques are widely used in modern crop improvement efforts to accelerate the detection of useful genotype-to-phenotype associations. Here we used Setaria viridis mapping populations as a field-based C4 grass model system for understanding plant architectural responses to drought stress. Various imaging techniques were applied with the intent of capturing aspects of plant architecture within specific nuanced contexts determined by choice of imaging field of view, point of view, and time frame. Imaging within these contexts constrained the physiological, anatomical, and developmental interpretation of the image outputs. First we show that canopy hemispherical imaging combined with light attenuation modeling is an effective means of detecting the same genotype-to-phenotype associations for aboveground biomass as laborious and destructive traditional harvests. However, hemispherical imaging was unable to resolve specific architectural contributions to growth. Next we apply the same hemispherical imaging system to evaluate the canopy light environment at specific times of day to show that leaf rolling serves to temporarily reduce canopy radiation use as part of strategy to limit water use over prolonged periods of drought stress. Finally, image-based measurements of internode elongation and arrangement were combined with a modeled growth function to reveal the positive response of reproductive internodes to water-deficit and the compensatory effect that vegetative internode elongation has on recovering height lost to stress. Furthermore, the resulting phenotypes were correlated with life strategy and local adaptation and explained genotype-to-phenotype associations that were missed by coarser measurements of growth. These results emphasize the power of low-cost digital imaging techniques when placed within effective contexts.
Plant architecture, drought, physiology, quantitative genetics
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign