Phytopathology· 2025Q1
An Improved Grading System for Measuring Plant Diseases
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- 2025year
Short summary
A novel plant disease grading system is proposed, deviating from equal percentage values to align with the human eye's logarithmic perception of disease severity.
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Key points
- Traditional disease grading assigns equal percentage values, which does not match human visual perception.
- The new system uses a logarithmic scale with 50% disease as a midpoint, reflecting how the eye distinguishes diseased vs. healthy tissue.
- Grades are defined with doubling factors on either side of the 50% midpoint (e.g., 25-50%, 50-75%).
- A calibration curve using a semi-logarithmic plot is used to convert grades to percentage disease.
AI-generated from the title and abstract; the full text is not read.
Abstract
Heretofore, in recording severity of plant diseases by grading, the grades have been assigned equal values in percentage. According to the Weber-Fechner law, the human eye distinguishes according to the logarithm of the light intensity. Hence, the grades should be based on equal ability to distinguish, not on equal disease. Below 50 percent, the eye sees the amount of diseased tissue. Above 50 percent, it sees the amount of disease-free tissue. A new scoring system is based on 50 percent as a midpoint. The grades differ by a factor of two in either direction as follows: 1 = 0, 2 = 0 to 3, 3 = 3 to 6, to 12, 5 = 12 to 25, 6 = 25 to 50, 7 = 50 to 75, 8 = 75 to 87, 9 = 87 to 94, 10 = 94 to 97, 11 = 97 to 100, 12 = 100. Several plants (20 or more) at random are graded. Mean grade = grade readings + number of readings. A calibration curve is set up with grade numbers on the X-axis and percentage disease on a special semi-log. Y-axis with one and one-half phases from either end up to 50 percent. The grid has the aspect of arithmetic-probability paper. This scheme has been very useful in fungicide research, varietal resistance, etc. It should be useful in plant disease surveying.
The authors' abstract, as published at the source. Phytopathology, 2025 · DOI ↗
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Field: Analytical Chemistry
Analytical ChemistryChemistry