DEVELOPMENT OF CHLOROPHYLL FLUORESCENCE IMAGING ROBOT FOR PRACTICAL USE IN COMMERCIAL GREENHOUSE

The speaking plant approach (SPA) is becoming an indispensable concept to maximize profit of agricultural production in current greenhouses. This concept is defines the optimal plant cultivation conditions should be achieved by monitoring the physiological status of the plants. Chlorophyll fluorescence imaging technique is useful to evaluate the photosynthetic functions of plant without touching. In this study, we developed a chlorophyll fluorescence imaging robot by modifying the chlorophyll fluorescence imaging system developed in our previous study. The primary feature of this robot is the feasible design, automated simple operation and low-cost, for implementation in commercial tomato production greenhouse. A 1.8 m (H) x 0.7 m (W) blue LED panel (λ< 600 nm) illuminates a 1.8 m (H) x 1.0 m (W) area at a distance of 0.5 m from the panel at PPFD of 20-100 µmol m^-2 s^-1. The chlorophyll fluorescence emission of the illuminated plants was captured by a high weather-resistant CCD camera equipped with a long-pass filter (λ> 660 nm). This system images chlorophyll fluorescence induction phenomenon, a dynamic change in chlorophyll fluorescence intensity induced by an excitation light under dark condition and analyses the shape of the induction curve, the time course of the chlorophyll fluorescence intensity during this phenomenon. The shape of the induction curve is characterized with the initial maximum peak (P), the following transient dip (S) and secondary small peak (M). Two parameters such as P/S and M/S, the fluorescence intensities of P or M divided by the fluorescence intensity of S, were calculated to evaluate the shape of the induction curve. These parameters can be used as indices of ability of photosynthetic electron transport. We applied the developed chlorophyll fluorescence imaging robot to grasp a spatial distribution of photosynthetic function of hydroponically-cultivated tomato plants in a semi-commercial greenhouse. The distribution maps of P/S and M/S consisted of 70 measuring points at equally spaced intervals in a 20 m (North-South) x 11 m (East-West) area revealed that there was a heterogeneous distribution of photosynthetic electron transport ability in the greenhouse.