A SIMPLE NONDESTRUCTIVE TECHNIQUE FOR HEALTHY AND DISEASED LEAF-AREA ASSESSMENT OF POTATO PLANTS

A method for assessing the leaf area of potato plants was based on the number of leaves coinciding with imaginary vertical lines descending from a horizontal grid of points above the plant or crop canopy. Leave s seen through each vertically aligned pair of holes in a perforated d ouble table, covering the midpoint of the exposed area, were counted a nd moved aside one by one, until the ground was seen. For both green a nd diseased surfaces the leaf area, or its horizontal component, was c alculated as the product of sum of records and the grid cell size. Tes ted against a destructive method, the technique worked equally well fo r healthy and diseased leaf area of potato plants infected by Phytopht hora infestans. The theoretic estimate of the standard error for a sin gle measurement was derived as the geometric mean of the leaf area and the grid cell size. The method is also suitable for LAI of crop stand s.