Stress indicators based on airborne thermal imagery for field phenotyping a heterogeneous tree population for response to water constraints.

Nicolas Virlet,Sébastien Martinez,Valentine Lebourgeois,Evelyne Costes,J.-L Regnard,S Labbe

doi:10.1093/jxb/eru309

Abstract

As field phenotyping of plant response to water constraints constitutes a bottleneck for breeding programmes, airborne thermal imagery can contribute to assessing the water status of a wide range of individuals simultaneously. However, the presence of mixed soil-plant pixels in heterogeneous plant cover complicates the interpretation of canopy temperature. Moran's Water Deficit Index (WDI = 1-ETact/ETmax), which was designed to overcome this difficulty, was compared with surface minus air temperature (T s-T a) as a water stress indicator. As parameterization of the theoretical equations for WDI computation is difficult, particularly when applied to genotypes with large architectural variability, a simplified procedure based on quantile regression was proposed to delineate the Vegetation Index-Temperature (VIT) scatterplot. The sensitivity of WDI to variations in wet and dry references was assessed by applying more or less stringent quantile levels. The different stress indicators tested on a series of airborne multispectral images (RGB, near-infrared, and thermal infrared) of a population of 122 apple hybrids, under two irrigation regimes, significantly discriminated the tree water statuses. For each acquisition date, the statistical method efficiently delineated the VIT scatterplot, while the limits obtained using the theoretical approach overlapped it, leading to inconsistent WDI values. Once water constraint was established, the different stress indicators were linearly correlated to the stem water potential among a tree subset. T s-T a showed a strong sensitivity to evaporative demand, which limited its relevancy for temporal comparisons. Finally, the statistical approach of WDI appeared the most suitable for high-throughput phenotyping.

Highlights

According to current climate change models for the 21st century, increases in average temperatures are expected, with longer or more frequent episodes of extreme temperatures and drought, notably in the Mediterranean basin (IPCC, 2007; Giorgi and Lionello, 2008)
Such studies are rarely performed for woody perennials, some studies on genetic determinism of traits related to water use and drought tolerance improvement have been undertaken for forest trees [e.g. in Populus, Dillen et al (2008) and Monclus et al (2009); in Quercus, Brendel et al (2008) and Roussel et al (2009)]
For date 3, a number of the average values of normalized difference vegetation index (NDVI) and Ts–Ta for the well watered (WW) trees were located outside the left border of the theoretical envelope, leading to out-of-range water deficit index (WDI) values

Summary

Introduction

According to current climate change models for the 21st century, increases in average temperatures are expected, with longer or more frequent episodes of extreme temperatures and drought, notably in the Mediterranean basin (IPCC, 2007; Giorgi and Lionello, 2008). Breeding programmes focused on these targets are currently being developed for the cereal crops that are of major importance for food purposes, such as wheat, rice, and maize (Braun et al, 2010; Fischer et al, 2011; Masuka et al, 2012). Such studies are rarely performed for woody perennials, some studies on genetic determinism of traits related to water use and drought tolerance improvement have been undertaken for forest trees [e.g. in Populus, Dillen et al (2008) and Monclus et al (2009); in Quercus, Brendel et al (2008) and Roussel et al (2009)]. For these species, water resource research to date has focused on irrigation scheduling and crop management rather than on plant breeding for better use of water (Naor, 2006; Wang and Gartung, 2010)

Methods

Results

Discussion

Conclusion