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Phenotyping spring barley for drought tolerance
Klem, Karel ; Findurová, Hana ; Panzarová, K. ; Pytela, J. ; Trtílek, M. ; Holub, Petr
Drought tolerance is a complex of traits that vary depending on the type, severity, and timing of drought. Therefore, a relatively comprehensive assessment of the morphological and physiological phenotypic response to drought is necessary. This methodology focuses on the development of procedures and evaluation of the complex phenotypic response of spring barley genotypes to drought using non-invasively measured parameters based on red-green-blue (RGB) imaging, thermal infrared imaging, and chlorophyll fluorescence imaging measured within an automated phenotyping platform. The development of the methodology was based on an experiment in which the dynamic changes in the response of six barley genotypes, representing a wide range of drought tolerance (from a very sensitive to a very tolerant genotype), to continuous drying until the point of wilting and subsequent re-watering were monitored. Three critical time points during drought and re-watering were identified, key for detecting drought tolerance: i) reaching 50% of available soil water, ii) reaching wilting point, iii) full plant recovery after re-watering. However, the different imaging-based parameters monitored showed potential for assessing drought sensitivity at different time points from the onset of drying or recovery. The correlation with relative yield response increased progressively for the side projected leaf area (SPA) and reached a maximum at the point of complete recovery after re-watering. The actual quantum yield of photosystem II (ΦPSII) showed the highest correlation with relative grain yield around the wilting point. In contrast, the relative difference of leaf temperature to ambient air temperature (Tdiff) showed a high correlation with yield response to drought earlier, as early as at the point of reaching 50% of the level of soil water available to plants. The highest correlations with relative yield response were obtained for RGB colour analysis at the wilting point and after recovery, especially for the relative proportion of khaki, beige, dark green, and olive-green hues. Multiple regression with parameters providing a Pearson correlation coefficient R > 0.5 slightly improved the estimation of the relative yield response to drought, but mainly provided a significant improvement in the estimation of absolute grain yield under drought stress, with an estimation accuracy of around 90% in both cases. This methodology shows that the use of a combination of phenotyping methods in characterising different morphological and physiological traits not only allows the assessment of drought tolerance (based on relative yield response to drought), which is crucial for the selection of genetic resources for subsequent breeding, but also allows the testing of the yield performance of new genotypes under drought stress.
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