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Disease Detection and Losses

A Quantitative Method for Estimating Density of Septoria tritici Pycnidia on Wheat Leaves. Zahir Eyal, Senior Lecturer, Division of Mycology and Plant Pathology, Department of Botany and Department of Statistics, Tel-Aviv University, Israel; Morton B. Brown, Senior Lecturer, Division of Mycology and Plant Pathology, Department of Botany and Department of Statistics, Tel-Aviv University, Israel. Phytopathology 66:11-14. Accepted for publication 23 May 1975. DOI: 10.1094/Phyto-66-11.

Thirty-five-millimeter photographic transparencies of cleared wheat leaves heavily infected with pycnidia of Septoria tritici were scanned with a television beam. The signal which measures the opacity of the transparency was sampled at a dense grid of points and the digitized output was stored in a computer. The processed output was used to estimate the relationship between pycnidial number, pycnidial mean area, and percent coverage. The mean area of the pycnidia is related to pycnidial density; therefore, as the density increases, the size of the pycnidia decreases. The area of the available leaf region, in which each pycnidium is embedded, limits the maximum actual coverage by pycnidia per leaf unit area. The maximal actual coverage of heavily infected leaves was 22.87%. This was rescaled to give coverage of 100%. A diagrammatic scale for estimating pycnidial coverage was based on five grades: 12, 25, 50, 75, and 87 percent pycnidial coverage of wheat leaves.