Reflectance Measurement of Artificially Induced Ultraviolet Radiation Stress on Cotton Leaves

Cotton plants (Gossypium hirsutum L. cv 'McNair 220') at the third true leaf stage were exposed to ultraviolet radiation (UVR) for seven days and compared with controls that received only natural light. Light reflectance was spectrophotometrically measured over the 0.5-2.5 #m waveband on nonexcised leaves immediately after treatment and again seven days later. Spectral measurements were also conducted on plant leaves that received only natural light. Leaves of cotton plants exposed to UVR had less near-infrared reflectance at the 0.85-/~m wavelength than control leaves. This was apparently caused by altered leaf size and structure. The UVR-treated leaves were thinner, smaller in area, and had a different mesophyll structure than control leaves. Results indicate that reflectance measurements at the 0.85-#m wavelength may be usehtl to detect UVR<lamaged cotton plants.