Review Seeing is believing: imaging techniques to monitor plant health

Historically, early stress-induced changes in plants have been mainly detected after destructive sampling followed by biochemical and molecular determinations. Imaging techniques that allow immediate detection of stress-situations, before visual symptoms appear and adverse effects become established, are emerging as promising tools for crop yield management. Such monitoring approaches can also be applied to screen plant populations for mutants with increased stress tolerance. At the laboratory scale, different imaging methods can be tested and one or a combination best suited for crop surveillance chosen. The system of choice can be applied under controlled laboratory conditions to guide selective sampling for the molecular characterisation of rapid stress-induced changes. Such an approach permits to isolate presymptomatically induced genes, or to obtain a panoramic view of early gene expression using gene-arrays when plants undergo physiological changes undetected by the human eye. Using this knowledge, plants can be engineered to be more stress resistant, and tested for field performance by the same methodologies. In ongoing efforts of genome characterisation, genes of unknown function are revealed at an ever-accelerating pace. By monitoring changes in phenotypic characteristics of transgenic plants expressing those genes, imagin