Rapid phenotyping of different maize varieties under drought stress by using thermal images Giuseppe Romano*, Shamaila Zia*, Wolfram Spreer*, Jill Cairns**, Jose Luis Araus***, Joachim Müller* *Institute of Agricultural Engineering in the Tropics and Subtropics, Universität Hohenheim, Stuttgart 70599, Germany **Global Maize Program, International Maize and Wheat Improvement Center (CIMMYT), D.F., Mexico *** University of Barcelona, Department of Plant Biology, Spain Corresponding author: Giuseppe Romano, Garbenstrasse 9, 70599 Stuttgart, Tel.:+4971145923112; fax: +4971145923298, Email: giuseppe.romano@uni-hohenheim.de Abstract: The development of maize genotypes with high yields under drought is of pivotal relevance for the International Maize and Wheat Improvement Centre (CIMMYT). Thermal images of the canopy of different 92 maize genotypes were acquired in the time interval between anthesis and blister stage with each picture containing five plots of different genotypes. Mean temperature differences of more than 2°C between different genotypes under water stress were then detected using thermal images. Genotypes better adapted to drought exhibiting lower temperatures. A canopy thermal image is a potential promising method to accelerate the screening process and thereby enhance phenotyping for drought adaptation in maize. Keywords: Maize genotypes, water stress, thermal images, canopy temperature, 1. INTRODUCTION The development of maize genotypes with high and stable yields under water stress is vitally important for CIMMYT (International Maize and Wheat Improvement Center) (Bolanos et al. 1996). Different techniques such as soil moisture measurements, leaf water potential and stomatal conductance have already been applied to monitor the water status of plants. However, these measurements are often time consuming, labor intensive and require a number of repetitions to achieve reliable results (Rebetzke et al. 2001). Furthermore, these methods have not yet been automated, something which would allow researchers to quickly distinguish between different crop varieties and treatments. As an alternative, leaf temperature detection by infrared thermometers has been used to detect water stress - which results in stomata closure and an increase in temperature through decreased adiabatic cooling. It is a fast and non-destructive way to identify plant water status; however, this approach is only able to provide information for a small area around each measurement point (Evans et al. 2000) and the heterogeneity of the maize canopy usually prevents proper measurement of the canopy as a whole. In contrast, infrared thermography allows to study whole canopies in an affordable manner; therefore, by placing a thermal camera at an appropriate distance it is possible to obtain information over a large area, incorporating canopies which contain a variety of genotypes at the same time (Jones and Leinonen, 2003). Recently, a number of studies have investigated the suitability of using thermal imaging to detect stress, both in the field and in greenhouses (Cohen et al. 2005). For example, (Grant et al. 2006) found temperature differences in vineyards under two different treatments and recommended the application of thermal imaging for irrigation scheduling. However, further studies need to be carried out in order to assess the potential of using thermal imaging for different crops and for different locations with varying environmental conditions (Alchanatis et al. 2010). Even though, (Jones et al. 2009) suggested the use of thermal imaging for selection in plant breeding, so far the use in phenotyping has not been investigated. However, this is not trivial since for a given irrigation regime the range of genotypic variability in canopy temperature is probably lower than differences in canopy temperature due to by contrasting irrigation 22B02