Phenotyping drought tolerance and yield performance of barley using a combination of imaging methods

Abstract

Drought resistance represents a complex of traits that are differently employed depending on drought type, severity and timing. Hence, a relatively comprehensive assessment of morphological and physiological phenotypic response to drought is required. We evaluated the dynamic responses of six barley genotypes, representing a wide range of drought tolerance, to continuous drying and re-watering using non-invasively measured parameters based on red-green-blue (RGB), thermal infrared and chlorophyll fluorescence imaging within an automated phenotyping platform. We identified three critical points in drought progress: i) 50% level of available soil water, ii) wilting point, iii) full plant recovery after re-watering. However, the individual monitored parameters showed the potential to evaluate drought sensitivity at different points since the onset of drying. The correlation with relative yield response gradually increased for the side projected leaf area (SPA) and reached the maximum at the point of full recovery. The actual quantum yield of photosystem II (ΦPSII) showed the highest correlation with a relative grain yield around wilting point. In contrast, the relative leaf temperature difference demonstrated a high correlation with yield response earlier, at 50% of available water. The highest correlations with the relative yield response were obtained for the colour RGB analysis at the wilting point and after recovery, particularly for khaki, beige, dark-green and olive-green colours. Multiple regression with parameters providing Pearson’s correlation coefficient R > 0.5 slightly improved the estimation of relative yield response to drought but ensured significant improvement of absolute grain yield estimation under drought stress. This study shows that combining the phenotyping methods representing different morphological and physiological traits allows not only the assessment of drought tolerance (based on relative yield response to drought) which is crucial for selecting the genetic resources for the subsequent breeding process but also allows to test the yield performance of new genotypes under drought stress.