Chlorophyll Fluorescence Imaging of the Chlorophyll Fluorescence Induction Phenomenon for Plant Health Monitoring

Chlorophyll fluorescence imaging is useful as a non-destructive method for evaluating photosynthetic function of plants. A dynamic change in chlorophyll fluorescence intensity, known as the chlorophyll fluorescence induction phenomenon, can be observed by illuminating a dark-adapted green leaf with a stable intensity excitation light. The time course of the chlorophyll fluorescence intensity during this phenomenon, presented as an induction curve, varies depending on the health of the plant. Imaging of the chlorophyll fluorescence induction phenomenon may be used to monitor the health status of plants. In this review, we introduce studies on our chlorophyll fluorescence imaging system for plant health monitoring of tomato crops grown in a greenhouse. We first developed a prototype of the imaging system to confirm performance on detection of artificially induced light stress in a single leaf and whole plant. Based on the successful detection of photosynthetic dysfunction caused by light stress using the prototype, we applied our chlorophyll fluorescence imaging system to measurements of the chlorophyll fluorescence induction curves of tomato crops grown in a semi-commercial greenhouse. Upon comparing the induction curves of 20 tomato crops planted on a north-south lane in the greenhouse, we found two plants with unique induction curve patterns. One of these two plants showed visible symptoms of physiological dysfunction 7 days after measurement. Thus, our chlorophyll fluorescence imaging system appears to be a useful tool for plant health monitoring in horticultural production.