title: Stress indicators based on airborne thermal imagery for field phenotyping a heterogeneous tree population for response to water constraints.
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.
authors: Montpellier SupAgro, UMR 1334 Amélioration Génétique et Adaptation des Plantes méditerranéennes et tropicales, TA-A-108/03, Avenue Agropolis, 34398 Montpellier Cedex 5, France.
authors: Nicolas
authors: N
authors: Virlet
authors: CIRAD, UMR Territoires, Environnement, Télédétection et Information Spatiale, Station Ligne-Paradis, 7 Chemin de l'IRAT, 97410 Saint-Pierre, France.
authors: Valentine
authors: V
authors: Lebourgeois
authors: INRA, UMR 1334 AGAP, TA-A-108/03, Avenue Agropolis, Avenue Agropolis, 34398 Montpellier Cedex 5, France.
authors: Sébastien
authors: S
authors: Martinez
authors: INRA, UMR 1334 AGAP, TA-A-108/03, Avenue Agropolis, Avenue Agropolis, 34398 Montpellier Cedex 5, France.
authors: Evelyne
authors: E
authors: Costes
authors: IRSTEA, UMR TETIS, Remote Sensing Centre, 500 rue J. F. Breton, 34093 Montpellier Cedex 5, France.
authors: Sylvain
authors: S
authors: Labbé
authors: Montpellier SupAgro, UMR 1334 Amélioration Génétique et Adaptation des Plantes méditerranéennes et tropicales, TA-A-108/03, Avenue Agropolis, 34398 Montpellier Cedex 5, France regnard@supagro.inra.fr.
authors: Jean-Luc
authors: JL
authors: Regnard
mesh_terms: D055864:Droughts; D013696:Temperature; D014197:Trees / Q000502:physiology*
keywords: Drought; Malus × domestica Borkh.,; evapotranspiration; phenomics; remote sensing; surface temperature; temperate fruit species; vegetation index; water deficit index (WDI).