Ratio of rice reflectance for estimating leaf blast severity with a multispectral radiometer

Abstract

Rice reflectance was measured to determine the spectral regions most sensitive to leaf blast infection with a multispectral radiometer. As disease severity increased, reflectance also increased in the 400-500 nm (blue), 570-700 nm (red), and 900-2000 nm regions but decreased in the 500-570 nm and 700-900 nm regions. The increased reflectance in the blue and red regions may be attributed to decreased chlorophyll and carotenoid contents in response to the blast infection. The maximum and minimum reflectance differences occurred at 680 nm and 760 nm for the nondiseased and diseased rice, respectively. The spectral location of maximum sensitivity was 675 nm regardless of disease severity. Rice reflectance ratios were evaluated as indicators of leaf blast severity. Two ratios, R550/R675 (reflectance at 550 nm divided by reflectance at 675 nm), and R570/R675 quantified the significant disease severity. These wavelengths were selected based on the sensitivity minima and maxima. The ratios of nondiseased rice plants varied depending on growth stage. The variation in ratios must be considered when they are used to estimate leaf blast severity.

Effects of Mycosphaerella leaf disease on the spectral reflectance properties of juvenile Eucalyptus globulus foliage

“…The greatest difference between severity classes, not surprisingly, was found in the NIR region, near 760 nm. This is similar to that found by Kobayashi et al. 2003, Stone et al.…”

“…Both these leaf features are grossly affected within the Mycosphaerella lesions. Our results also concur with Kobayashi et al. (2003) and Carter et al.…”

“…(1999) as being sensitive to chlorophyll breakdown but is also influenced by the retention or accumulation of the carotenoid pigments during senescence. Kobayashi et al. 2003 also identified the wavelength 675 nm as being sensitive to the severity of rice blast disease ( Magnaporthe grisea ).…”

“… Malthus and Madeira 1993; Carter et al. 1996; Nilsson and Johnsson 1996; Kobayashi et al. 2001,2003; Stone et al.…”

Temporal chlorophyll fluorescence signals to track changes in optical properties of maturing rice panicles exposed to high night temperature

“…Compared with those on leaves, studies connecting with spectral properties of rice panicles are limited. A number of Vis have been tested in rice panicles from the milky ripening stage to harvest (Chen et al, 2006) and have been identified as indicators of rice panicle blast (Kobayashi et al, 2001), or as a potent parameter for leaf blast detection (Kobayashi et al, 2003). Kobayashi et al (2001) suggested Vis for rice blast detection, which followed a decrease in the absorbtion of photosynthetic pigments and changes in the internal structure of rice panicles during senescence.…”