Developing Two Spectral Disease Indices for Detection of Wheat Leaf Rust (Pucciniatriticina)

Abstract

Spectral vegetation indices (SVIs) have been widely used to detect different plant diseases. Wheat leaf rust manifests itself as an early symptom with the leaves turning yellow and orange. The sign of advancing disease is the leaf colour changing to brown while the final symptom is when the leaf becomes dry. The goal of this work is to develop spectral disease indices for the detection of leaf rust. The reflectance spectra of the wheat's infected and non-infected leaves at different disease stages were collected using a spectroradiometer. As ground truth, the ratio of the disease-affected area to the total leaf area and the fractions of the different symptoms were extracted using an RGB digital camera. Fractions of the various disease symptoms extracted by the digital camera and the measured reflectance spectra of the infected leaves were used as input to the spectral mixture analysis (SMA). Then, the spectral reflectance of the different disease symptoms were estimated using SMA and the least squares method. The reflectance of different disease symptoms in the 450~1000 nm were studied carefully using the Fisher function. Two spectral disease indices were developed based on the reflectance at the 605, 695 and 455 nm wavelengths. In both indices, the R 2 between the estimated and the observed was as highas 0.94.

Affecting Factors and Recent Improvements of the Photochemical Reflectance Index (PRI) for Remotely Sensing Foliar, Canopy and Ecosystemic Radiation-Use Efficiencies

“…Drought [30,93], temperature stress [87,93], low nitrogen concentration [91,94], iron deficiency [95], high altitude [96], high ultraviolet A/B [97,98] and disease [99][100][101][102] can potentially induce biochemical and physiological changes (e.g., chlorophyllic and carotenoid contents, xanthophyll cycle and NPQ) and inhibit the photochemistry of PSII, thus leading to a decrease in PRI, which was more apparent in young than in mature leaves as cadmium stress increased [103]. Variations in the angle and direction of illumination [104] and instrumental FWHM (full width at half-maximum) [69] can also change the optical properties, which then influence PRI values.…”

Hyperspectral Measurements for Estimating Vertical Infection of Yellow Rust on Winter Wheat Plant

“…Liu et al (2014) proposed a new spectral ratio index in the near infrared (NIR) shoulder region (NSRI), defined by a simple ratio of reflectance at 890 nm to reflectance at 780 nm, for assessing leaf structure deterioration. Ashourloo et al (2014) developed spectral disease indices for the detection of leaf rust using a spectroradiometer. Zhao et al (2014) carried out hyperspectral measurements of severity of stripe rust on individual wheat leaves at the heading stage and grain filling stage.…”

In-field detection and quantification of Septoria tritici blotch in diverse wheat germplasm using spectral-temporal features

“…Hyperspectral remote sensing has shown significant potential for the rapid, non-invasive assessment of crop diseases at different scales, ranging from single leaves (e.g. Ashourloo et al, 2014;Mahlein et al, 2010) to the canopy (e.g. Cao et al, 2013;Yu et al, 2018) to fields and regions (Wakie et al, 2016).…”