Possibility of disease process monitoring of plants by laser-induced fluorescence method: development and evaluation of LIF measurement systems

Abstract

We applied the laser-induced fluorescence (LIF) method to the monitoring of plant disease caused by environmental changes. An LIF spectrum measurement system and an LIF lifetime measurement system were developed for this purpose. The former one was constructed with a 6 ns, 355-nm Nd: YAG laser and a multiwavelength spectroscopic detection system. The later one was constructed with a 300 fs, 660-nm laser and a streak scope with a time resolution of 25 ps. Morning glory and Zelkova were prepared to investigate disease process monitoring by the LIF measurement system. The LIF spectra of the stressed leaves showed that the spectral intensities at 460 nm and 530 nm rapidly increased for 3 hours and then decreased for 20 hours, while the spectra at 685 nm and 740 nm decreasing constantly. In the LIF lifetime measurement, the chlorophyll fluorescence lifetime of Zelkova leaves was measured at 685 nm and 740 nm. It was found that the lifetime was composed of a fast component of about 100 ps and a slow one of about 600 ps and after UV-B irradiation the lifetime varied sinusoidally among the lifetime of normal leaves. Through these experiments the performance of the systems was checked and their potential for plant disease process monitoring was confirmed.