Plant Physiology Root Research Methods

bt-root-research_clip_image002Much has been reported on the potential of roots to improve crop yield and resilience under drought. However, most studies on roots have used time consuming methods to assess rooting differences, limiting their use in breeding, and providing “static” data about roots that did not help resolve the exact role of roots. Even our work on roots in chickpea has used such root extraction methods, using plants grown for about 35 days in 1.2 m length and 16 cm diameter. Although this has yielded very good information and even QTLs for rooting traits, these “static” measurements of root growth cannot capture the highly dynamic growth of roots, which is largely influenced by environmental factors, in particular water deficits. An underlying assumption of these studies is that roots would contribute to higher water uptake and then to higher yield. Yet, the relation between rooting and water uptake remains understudied and controversial. In what drought scenarios, soils, and crops can roots contribute to water uptake and yield remains an open question. Our underlying hypothesis is that water uptake is crucial during key stages like reproduction and grain filling, and small differences in water uptake at these stages could lead to large yield differences. We assume that these differences could not be captured from measurements in rooting differences.

bt-root_reasearch-bSo, we needed methods for direct, precise, and dynamic measurement of water uptake, along with yield, and in field-like situation. For that, at ICRISAT we have developed a lysimetric system to allow the direct measurement of water uptake in-vivo, in a large scale lysimetric facility (over 3000 cylinders of 1.2 m legth and 20 cm diameter and 1500 cylinders with 2.0 m length and 25 cm diameter). Soil depth and volume available to each plant has been designed according to usual sowing densities and is then comparable to field conditions. In the first picture, we can see the cylinder design, with a collar attachment allowing its lifting for weighing. In the second picture, we can see that the weighing

procedure, carried out with a hanging scale, requires minimum labor and effort (cylinder is lifted with a block chain hoist), which improves the throughput (600 tubes can be weighed in one day). The soil surface of the cylinders is covered with plastic beads to prevent soil evaporation, so that cylinder weight differences measure plant transpiration. The cylinder size allows the assessment of yield under a range of stress conditions, and then allows testing the contribution of different traits to yield under various water regimes. The system shown in the pictures is the one used in P2 facilities to analyze the effect of a water deficit on water uptake response of rd29::DREB1A transgenic groundnut events. The following picture shows a large-scale facility that has been developed to measure water uptake on a large range of germplasm of ICRISAT’s mandate crops (groundnut and sorghum in the picture), where it can be seen that the crop is cultivated as a canopy.

With such system, large mapping populations or reference germplasm sets (300-400 entries) can be assessed into several treatments and replications, making it highly valuable for breeding purposes. The combination of that system to screen for genotypic differences in water extraction, infrared leaf temperatures as a proxy for water uptake, and simulation modeling to predict the climatic conditions and crops in which roots can bring yield benefit are the basic anchors of our root research efforts.

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For further information, contact: Vincent Vadez

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