Abstract
The root system is critical for the survival of nearly all land plants and a key target for improving abiotic stress tolerance, nutrient accumulation, and yield in crop species. Although many methods of root phenotyping exist, within field studies, one of the most popular methods is the extraction and measurement of the upper portion of the root system, known as the root crown, followed by trait quantification based on manual measurements or 2D imaging. However, 2D techniques are inherently limited by the information available from single points of view. Here, we used X-ray computed tomography to generate highly accurate 3D models of maize root crowns and created computational pipelines capable of measuring 71 features from each sample. This approach improves estimates of the genetic contribution to root system architecture and is refined enough to detect various changes in global root system architecture over developmental time as well as more subtle changes in root distributions as a result of environmental differences. We demonstrate that root pulling force, a high-throughput method of root extraction that provides an estimate of root mass, is associated with multiple 3D traits from our pipeline. Our combined methodology can therefore be used to calibrate and interpret root pulling force measurements across a range of experimental contexts or scaled up as a stand-alone approach in large genetic studies of root system architecture.
Highlights
In maize, the entirety of primary, seminal, lateral, crown, and brace roots together form a complex architecture which controls the plant’s ability to effectively acquire water, scavenge nutrients, and resist lodging [1]
In its simplest form, root phenotyping of crop species such as maize or rice can be performed by manual measurement of a limited set of amenable traits, such as root mass, length, width, or the growing angle, either in soil or soil-free conditions
At the designated time point(s) for sampling, root crowns were excavated by root pulling force
Summary
The entirety of primary, seminal, lateral, crown, and brace roots together form a complex architecture which controls the plant’s ability to effectively acquire water, scavenge nutrients, and resist lodging [1]. In its simplest form, root phenotyping of crop species such as maize or rice can be performed by manual measurement of a limited set of amenable traits, such as root mass, length, width, or the growing angle, either in soil or soil-free conditions. Known genes controlling quantitative root system architecture traits in rice were identified using such measurements, including PSTOL1 [9], DRO1 [10], and a recent DRO1 homolog [11]. Root pulling force (RPF) has been useful as a field assay because of its simplicity; it has the greatest potential for large-scale phenotyping and has been applied to both monocots and dicots [16,17,18,19,20,21]. While RPF is generally correlated with greater root biomass and branching, more nuanced interpretations and its association with recently tractable architectural measurements have yet to be established, and the relationship between
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