High-throughput phenotyping (HTP) is one of the main strategies to accelerate genetic gain in wheat breeding programs. Through the efficient screening of large populations, HTP approaches not only assist conventional breeding in the selection of germplasm based on heritable traits such as plant height, phenology and disease resistance, but also enables the exploitation of more complex integrative traits –with relatively lower heritability –for complementary strategies such as physiological breeding, calibration of genomic selection models, screening of genetic resources and gene discovery.

The Global Wheat Program at CIMMYT has adopted Unmanned Aerial Vehicles as the main platform for HTP. UAVs have several advantages over other platforms, including a comparatively low investment, a good tradeoff between resolution and the area that is covered, and versatility in terms of in-season irrigation, planting methods, etc. Moreover, our research has demonstrated that UAV-based phenotyping improves heritability and prediction power of several traits compared to ground-based platforms. Aerial measurements of canopy temperature (CT) have been successfully used to predict yield and photosynthetic capacity, especially under abiotic stress (i.e. drought and heat). Furthermore, we have demonstrated a close relationship between CT and root biomass for the same environments, opening new opportunities for root phenotyping. Spectroscopy also lends itself to UAV‑based HTP. Spectral indices related to pigment composition and the vegetation structure have been used for the estimation of traits associated to photosynthesis, radiation use efficiency and photo-protection, whereas indices related to water content can be used for the estimation of in-season biomass and water status.

Phenotypic data collected from UAVs have many uses within the pipelines of wheat breeding and pre-breeding at CIMMYT. For example, aerial NDVI and CT are being used for improving models of genomic selection in bread wheat, while also being used in the selection of parents for strategic crosses in physiological pre‑breeding. Ongoing research projects in wheat physiology are using aerial phenotypic data to prove conceptual models of source-sink balance and biomass accumulation throughout the cycle, as well as for improving the understanding of the effect of photosynthesis regulatory mechanisms on yield. The adaptation of wheat lines to drought and heat environments has also been evaluated using UAV‑based phenotyping, representing an important component of the commitment of CIMMYT for developing new lines adapted to the conditions in Mexico and other countries around the globe. Finally, aerial phenotypic data has been used to explore the genetic basis of relevant physiological traits.