Abstract
Plant height (PH) is an essential trait in the screening of most crops. While in crops such as wheat, medium stature helps reduce lodging, tall plants are preferred to increase total above-ground biomass. PH is an easy trait to measure manually, although it can be labor-intense depending on the number of plots. There is an increasing demand for alternative approaches to estimate PH in a higher throughput mode. Crop surface models (CSMs) derived from dense point clouds generated via aerial imagery could be used to estimate PH. This study evaluates PH estimation at different phenological stages using plot-level information from aerial imaging-derived 3D CSM in wheat inbred lines during two consecutive years. Multi-temporal and high spatial resolution images were collected by fixed-wing (PlatFW) and multi-rotor (PlatMR) unmanned aerial vehicle (UAV) platforms over two wheat populations (50 and 150 lines). The PH was measured and compared at four growth stages (GS) using ground-truth measurements (PHground) and UAV-based estimates (PHaerial). The CSMs generated from the aerial imagery were validated using ground control points (GCPs) as fixed reference targets at different heights. The results show that PH estimations using PlatFW were consistent with those obtained from PlatMR, showing some slight differences due to image processing settings. The GCPs heights derived from CSM showed a high correlation and low error compared to their actual heights (R2 ≥ 0.90, RMSE ≤ 4 cm). The coefficient of determination (R2) between PHground and PHaerial at different GS ranged from 0.35 to 0.88, and the root mean square error (RMSE) from 0.39 to 4.02 cm for both platforms. In general, similar and higher heritability was obtained using PHaerial across different GS and years and ranged according to the variability, and environmental error of the PHground observed (0.06–0.97). Finally, we also observed high Spearman rank correlations (0.47–0.91) and R2 (0.63–0.95) of PHaerial adjusted and predicted values against PHground values. This study provides an example of the use of UAV-based high-resolution RGB imagery to obtain time-series estimates of PH, scalable to tens-of-thousands of plots, and thus suitable to be applied in plant wheat breeding trials.
Highlights
Wheat (Triticum sp.) is among the leading food crops, and it is grown in a range of environments and geographical areas
The median value and standard deviations (SD) for groundtruth plant height (PH) measured at E+40 showed some discrepancies across cycles and trials, possibly attributable to the different genotypes used in each high biomass association panel (HiBAP) panel, the year effect and differences in emergence dates
The present study aimed to prove the applicability of aerial photogrammetry to estimate PH in the wheat breeding context
Summary
Wheat (Triticum sp.) is among the leading food crops, and it is grown in a range of environments and geographical areas. Wheat has become the most important source of dietary protein and the second most important source of calories (carbohydrates) for humans (Shewry et al, 2016). Wheat breeding for plant height (PH) has been historically used to reduce lodging and improve grain yield and quality (Reynolds et al, 2020). The identification and introduction of major dwarfing or semi-dwarfing genes were significant advancements in the wheat breeding work led by Norman Borlaug that enabled grain yield increase in most environments and contributed to the “Green Revolution” (Reynolds and Borlaug, 2006; Würschum et al, 2015). PH contributes to biomass production, as it is associated with increased photosynthesis due to a better light interception and distribution through the canopy in taller plants (Song et al, 2013)
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