Applying RGB- and Thermal-Based Vegetation Indices from UAVs for High-Throughput Field Phenotyping of Drought Tolerance in Forage Grasses

Tom De Swaef,Isabel Roldán-Ruiz,Joost Baert,Dirk Reheul,Jonas Aper,Kathy Steppe,Peter Lootens,Mathias Cougnon,Wouter H Maes

doi:10.3390/rs13010147

Abstract

The persistence and productivity of forage grasses, important sources for feed production, are threatened by climate change-induced drought. Breeding programs are in search of new drought tolerant forage grass varieties, but those programs still rely on time-consuming and less consistent visual scoring by breeders. In this study, we evaluate whether Unmanned Aerial Vehicle (UAV) based remote sensing can complement or replace this visual breeder score. A field experiment was set up to test the drought tolerance of genotypes from three common forage types of two different species: Festuca arundinacea, diploid Lolium perenne and tetraploid Lolium perenne. Drought stress was imposed by using mobile rainout shelters. UAV flights with RGB and thermal sensors were conducted at five time points during the experiment. Visual-based indices from different colour spaces were selected that were closely correlated to the breeder score. Furthermore, several indices, in particular H and NDLab, from the HSV (Hue Saturation Value) and CIELab (Commission Internationale de l’éclairage) colour space, respectively, displayed a broad-sense heritability that was as high or higher than the visual breeder score, making these indices highly suited for high-throughput field phenotyping applications that can complement or even replace the breeder score. The thermal-based Crop Water Stress Index CWSI provided complementary information to visual-based indices, enabling the analysis of differences in ecophysiological mechanisms for coping with reduced water availability between species and ploidy levels. All species/types displayed variation in drought stress tolerance, which confirms that there is sufficient variation for selection within these groups of grasses. Our results confirmed the better drought tolerance potential of Festuca arundinacea, but also showed which Lolium perenne genotypes are more tolerant.

Highlights

Grasslands cover about 30% of the agricultural area in Europe (EU28) [1] and represent a substantial economic value through feed production
The overall aim of this study is to evaluate the use of Unmanned Aerial Vehicle (UAV)-based remote sensing for complementing or replacing the breeder score and for assessing the drought tolerance of individual genotypes of three forage grass types, belonging to two species: tall fescue (Fa), diploid perennial ryegrass (Lp2) and tetraploid perennial ryegrass (Lp4)
During the second drought period, Volumetric Water Content (VWC) dropped to levels close to the wilting point (0% relative extractable water (REW))

Summary

Introduction

Grasslands cover about 30% of the agricultural area in Europe (EU28) [1] and represent a substantial economic value through feed production. They are crucial for biodiversity and carbon sequestration [2,3,4]. Grassland persistence and productivity is very sensitive to drought [5,6]. 2021, 13, 147 of dry spells in Western Europe as a consequence of climate change substantially impacts the production and carbon sequestration capacity of these grasslands [7,8,9]. It is important that new varieties of forage grasses possess a good drought tolerance as part of the adaptation strategy of the fodder production system to the changing climate [10].

Objectives

Methods

Results

Discussion

Conclusion