IN-VIVO PHOTOACOUSTIC-SPECTROSCOPY OF LEAVES INFECTED BY FUNGAL AND VIRAL DISEASES

The PA spectra of fungal and viral infected leaves were recorded at a modulation frequency of 17 Hz. The leaves of sugar cane (Saccharum off icinarum L.), severely infected with a sheath blight, and the leaves o f a mung bean (Vigna radiata L.), infected with yellow mosaic virus, e xhibit a higher PA signal than the untreated, healthy leaves of same c ultivars at all wavelengths examined. The ratio of photoacoustic signa ls obtained from diseased and healthy leaves in the UV region was high er, as compared to that in the visible region. In fungal infections, t he higher PA signal was attributed to non-radiative de-excitation (hea t emission). In case of viral infection, the signal appears affected b y both O-2 evolution and heat emission. The PA spectra of leaves show that the heat emission due to non-radiative de-excitation exceeds the O-2 evolution. Additionally, the PA spectroscopy proved capable of dif ferentiating between the healthy C-3 and C-4 leaves.