Chlorophyll fluorescence imaging for disease-resistance screening of sugar beet

Both biotic and abiotic stresses cause considerable crop yield losses worldwide (Chrispeels, Sadava Plants, genes, and crop biotechnology 2003; Oerke, Dehne Crop Prot 23:275-285 2004). To speed up screening assays in stress resistance breeding, non-contact techniques such as chlorophyll fluorescence imaging can be advantageously used in the quantification of stress-inflicted damage. In comparison with visual spectrum images, chlorophyll fluorescence imaging reveals cell death with higher contrast and at earlier time-points. This technique has the potential to automatically quantify stress-inflicted damage during screening applications. From a physiological viewpoint, screening stress-responses using attached plant leaves is the ideal approach. However, leaf growth and circadian movements interfere with time-lapse monitoring of leaves, making it necessary to fix the leaves to be studied. From this viewpoint, a method to visualise the evolution of chlorophyll fluorescence from excised leaf pieces kept in closed petri dishes offers clear advantages. In this study, the plant-fungus interaction sugar beet-Cercospora beticola was assessed both in attached leaf and excised leaf strip assays. The attached leaf assay proved to be superior in revealing early, pre-visual symptoms and to better discriminate between the lines with different susceptibility to Cercospora.