Identifying High-Throughput Field Phenotyping Platform for Characterizing Drought Stress Response in Maize.

Breeding for the development of drought tolerant maize hybrids is getting increased attention in the face of limiting water supplies and changing weather patterns. Drought tolerance in maize is a highly complex trait, and responses to different drought conditions (timing, duration, and severity) are under the control of different genes and physiological mechanisms. Characterizing plant responses to specific water-stress episodes is necessary, but is highly laborious and time consuming and can be undermined by rainfall events. Unmanned aerial vehicles (UAVs) mounted with sensors hold potential for nondestructive, high-throughput phenotyping of the plant canopy. The objective of this study was to develop and evaluate a UAV platform for capturing canopy reflectance data. The UAV was tested over two years. In year one, a panel of 98 maize topcrosses derived from a set of diverse inbred lines and two commercial testers were grown under well-watered (WW) and water-stressed (WS; 40% WW irrigation rate) conditions.  In year two, five hybrids differing in drought tolerance were grown under four water treatments: dry land, WW, 75% WW rate, and 50% WW rate. During year one, yield was reduced by 40% in the WS block relative to the WW block, with most stress occurring during grain filling. Vegetation images were captured by a multispectral camera mounted to the UAV and reflectance values were extracted for each small plot. Differences were observed among hybrids for vegetative indices such as normalized difference vegetation index (NDVI). Repeatability estimates of NDVI were 0.37 for the WW treatment and 0.60 for the WS treatment. Spectral reflectance data is currently being extracted from images taken during year two. Results gathered to date suggest good potential for UAV-mounted sensors to distinguish hybrids grown under water stress. An important challenge is connecting reflectance data to key physiological properties related to drought tolerance during specific crop stages.