Multispectral image analysis detects differences in drought responses in novel seeded Miscanthus sinensis hybrids

Drought tolerance in Miscanthus sinensis is a desirable trait because of its potential use to develop new varieties, namely intra-specific hybrids, adapted to drought-prone marginal lands. In this study, drought tolerance was evaluated on 8 M. sinensis intra-specific hybrids (GRC1–GRC8). Plants were grown in the growth chamber (14/10 h, 25/20°C, 70% relative air humidity and 300 μmol m−2 s−1 irradiance). Drought was induced by withholding irrigation for 21 days (stress phase) and after re-watering (recovery phase) for 7 days. Nondestructive multispectral 3D images for plant morphology, color, and chlorophyll fluorescence imaging were used to quantify drought-induced changes on a weekly basis for the entire duration of the experiment. Total leaf area (TLA) and digital biomass (DB) responded most rapidly to water deficits (7–14 days), followed by leaf senescence (14–21 days), and finally, a drop in the maximum efficiency of PSII (Fv/Fm; 21 days). Traits measured on the last day of the drought treatment were used to calculate the phenotypic plasticity. Significant differences in drought susceptibility and phenotypic plasticity were found among the studied hybrids. Drought treatment (21 days) reduced DB and TLA on average by 50%, normalized difference vegetation index (NDVI) by 20% and Fv/Fm from 0.79 (in control) to 0.69 in the less drought-susceptible hybrids (GRC4 and GRC5), whereas in drought-sensitive hybrids (GRC2 and GRC3), 21 days of drought reduced DB and TLA on average by 80%, NDVI by 45% and Fv/Fm dropped from 0.79 (in control) to 0.35. The more drought-resilient hybrids showed lower phenotypic plasticity than their more sensitive counterparts, a stay-green strategy enabled through lower biomass accumulation and by extension, reduced water usage. Multispectral imaging and image analysis enabled fast and nondestructive quantification of plant morphological and physiological responses under drought conditions and could be used as an effective screening tool for drought susceptibility.