RED-EDGE INDICES TO DIAGNOSE ORANGE SPOTTING DISEASE OF OIL PALM IN MALAYSIA

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Research areas:
Year:
2017
Type of Publication:
Article
Keywords:
Orange spotting, Hyperspectral remote sensing, Red-edge indices
Authors:
Kamlesh Golhani, Ganesan Vadamalai Siva K Balasundram
Abstract:
The use of hyperspectral remote sensing techniques for plant disease diagnosis is gaining much prominence due to its non-destructive feature. The steep gradient in reflectance between visible and near-infrared region is known as the red-edge, which is located between 680 and 780 nm. Red-edge is a stress diagnostic indicator that provides for non-destructive diagnosis of plant disease. This paper investigates the potential of two selected red-edge wavebands (680 nm and 754 nm) in diagnosing Orange Spotting (OS) disease of oil palm. OS is a fast emerging disease in Malaysian oil palm plantations. Coconut cadang-cadang viroid (CCCVd) is the causal agent of OS disease. Four well-known red-edge indices namely Ratio Vegetation Index (RVI), Red Edge Position (REP), Normalized Difference Red Edge Index (NDREI) and Chlorophyll Index-Red Edge (CI-RE) were evaluated using selected wavebands. A spectroradiometer (Model: ASD FieldSpecĀ® HandHeld 2), which operates in the spectral range of 325-1075 nm, was deployed to measure leaf reflectance of fifteen inoculated and five healthy oil palm seedlings grown under glasshouse conditions. A highly effective CCCVd variant, OP246, was used to inoculate the seedlings. Reflectance was measured at 15, 30, 45 and 60 days after inoculation. This work was aimed at investigation of variations on red-edge indices within the specific intervals of inoculation. Red-edge indices were calculated from inoculated and healthy seedlings and analyzed using two-way analysis of variance. Mean differences are interpreted at 0.05 significance level using the Bonferroni test. Results will be discussed further.
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