Photoacoustic spectroscopy, a nondestructive method for sensitive analysis of disease in plants

摘要

The Photoacoustic (PA) spectra of wheat leaves infected by brown rust were recorded at modulation frequencies, 18 Hz and 228 Hz, using a 300W Xenon Arc lamp. The PA signals at 6328.8 nm radiation of He-Ne laser were recorded at different modulation frequencies to ascertain depth of penetration of the disease in the infected leaf tissue. For an abaxial surface of the leaf facing the incident radiation, the PA signal from leaves severely infected with brown rust disease is higher than that obtained from healthy leaves. This is in a marked contrast to a situation observed when an adaxial surface faces the incident radiation (the PA signal from severely infected leaves is lower than that from the intact leaf). In case of a horizontal spread of a disease, the tendency towards the stem side of the leaf was observed. Our results also reveal the progress of disease vertically through the leaf.