Aerial high‐throughput phenotyping enabling indirect selection for grain yield at the early‐generation seed‐limited stages in breeding programs

Breeding programs for wheat and other crops require one or more generations of seed increase before replicated yield trials can be sown. Extensive phenotyping at this stage is challenging due to the small plot sizes and large numbers of lines under evaluation, and therefore breeders typically rely on visual selection to promote lines to yield trials. Aerial high‐throughput phenotyping (HTP) enables the rapid acquisition of traits that may be useful for selection among early‐generation lines. With the objective of assessing the potential for aerial measurements recorded on seed increase plots to improve indirect selection for grain yield, two sets of 1,008 early‐generation bread wheat (Triticum aestivum L.) breeding lines were sown both as replicated yield trials and as small, unreplicated plots at the International Maize and Wheat Improvement Center during two breeding cycles. Normalize difference vegetation indices (NDVI) collected with an unmanned aerial vehicle in the small plots were observed to be heritable and moderately correlated with grain yield assessed in yield trials. Furthermore, NDVI was more predictive of grain yield than univariate genomic selection, with still higher overall predictive abilities from multi‐trait approaches. A related experiment showed that selection based on NDVI would have outperformed visual selection, though this approach would have driven a directional response in phenology due to confounding between phenology, NDVI, and yield. A restricted selection index was proposed to address this issue. These results provide a promising outlook for the use of aerial HTP to improve selection at the early‐generation seed‐limited stages of breeding programs.