Changes in leaf spectral properties induced in barley by cereal powdery mildew

Changes in spectral properties induced in barley leaves by cereal mildew were evaluated to identify important regions in the 400–1100 nm spectrum which can be used to detect infected barley leaves. Five spring barley lines grown in greenhouses were inoculated with mildew. During a 20-day period the directional spectral reflectance of the adaxial surface of the first leaf blades was recorded as well as the g d.wt. cm −2 leaf area, % water, and total chlorophyll content of the leaves. 1) The spectral reflectance of control leaves and inoculated resistant leaves was very similar throughout the experiment. 2) No changes in spectral reflectance from inoculated leaves were evident within the first 3 days following inoculation. 3) Six days after inoculation, the susceptible lines showed significantly higher reflectance in the visible (422–712 nm) wavelength region. 4) Ten days after inoculation, the susceptible lines showed significantly higher spectral reflectance between 400 and 1100 nm compared to control plants. 5) The differences in near infrared reflectance between control and infected plants observed were small and occurred several days later than changes in the visible region. 6) The differences in reflectance of blue and red wavebonds between control and inoculated plants were highly correlated to the cholorophyll content of infected leaves, r = 0.89 and 0.95, respectively. 7) Significant changes in spectral relectance of single leaves infected with mildew occur earlier in the visible region of the spectrum (400–706) than in the near infrared part of the spectrum.