Drought and heat stress tolerance screening in wheat using computed tomography

Abstract

Background: Improving abiotic stress tolerance in wheat requires large scale screening of yield components such as seed weight, seed number and single seed weight, all of which is very laborious, and a detailed analysis of seed morphology is time-consuming and visually often impossible. Computed tomography offers the opportunity for much faster and more accurate assessment of yield components. Results: An X-ray computed tomographic analysis was carried out on 203 very diverse wheat accessions which have been exposed to either drought or combined drought and heat stress. Results demonstrated that our computed tomography pipeline was capable of evaluating grain set with an accuracy of 95-99%. Most accessions exposed to combined drought and heat stress developed smaller, shrivelled seeds with an increased seed surface. As expected, seed weight and seed number per ear as well as single seed size were significantly reduced under combined drought and heat compared to drought alone. Seed weight along the ear was significantly reduced at the top and bottom of the wheat spike. Conclusions: We were able to establish a pipeline with a higher throughput with scanning times of 7 min per ear and accuracy than previous pipelines predicting a set of agronomical important seed traits and to visualize even more complex traits such as seed deformations. The pipeline presented here could be scaled up to use for high throughput, high resolution phenotyping of tens of thousands of heads, greatly accelerating breeding efforts to improve abiotic stress tolerance.

Determination of Wheat Spike and Spikelet Architecture and Grain Traits Using X-ray Computed Tomography Imaging

“…1a). The discrepancy between the 'virtual' grain number and the manually counted grain number was probably caused by small grains that were lteredout during image analysis or erroneously omitted during manually counting, which has been discussed by Hughes et al (2017) and Schmidt et al (2020). The total grain volume of each spike was positively correlated with their mass (r 2 =0.979, Fig.…”

“…Together with the determination of wheat spike and grain traits (Fig. 3) (Hughes et al, 2019(Hughes et al, , 2017Le et al, 2019;Schmidt et al, 2020;Strange et al, 2015), a comprehensive range of morphometric traits of wheat spikes and spikelets can be rapidly obtained using X-ray CT imaging. This provides the opportunity to link detailed wheat spike and spikelet traits to agronomic practices and genetic studies supporting future breeding programmes (Rawson, 1970;Wolde et al, 2019).…”

“…One previous weakness of X-ray CT imaging for studies of this kind has been the long scanning time, which makes measurement of large number of samples, often important for work of this kind, impossible. For example, it took around 30 -40 min to scan one wheat spike in several previous studies (Hughes et al, 2019(Hughes et al, , 2017Le et al, 2019;Schmidt et al, 2020), with the spatial resolution between 15 -68.8 μm. In this study, we improved on the scanning e ciency through two approaches.…”

“…Using the X-ray CT imaging technique, Hughes et al (2019) found the grains of domesticated wheat and barley had different morphometric parameters (length, width and depth) from their wild relatives. Schmidt et al (2020) found wheat grain size and number were reduced under heat and drought stress. Despite the successful use of X-ray CT imaging in the phenotyping of wheat spikes and grains, no success has been achieved to extract speci cally the spikelet information, which requires consideration of the spatial arrangement of the grains.…”

“…Recently, X-ray CT imaging was used to non-destructively study wheat spike and grain traits (Hughes et al, 2019(Hughes et al, , 2017Le et al, 2019;Schmidt et al, 2020;Strange et al, 2015). The morphometric traits of spike and grain, such as grain number, size, length, width and depth, can be extracted from their 3D images using the developed pipeline (Hughes et al, 2017;Schmidt et al, 2020). Using the X-ray CT imaging technique, Hughes et al (2019) found the grains of domesticated wheat and barley had different morphometric parameters (length, width and depth) from their wild relatives.…”