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Techniques

Quantification by Image Analysis of Subcrown Internode Discoloration in Wheat Caused by Common Root Rot. E. G. Kokko, Agriculture Canada, Research Station, P. O. Box 3000, Main, Lethbridge, Alberta T1J 4B1; R. L. Conner, G. C. Kozub, and B. Lee. Agriculture Canada, Research Station, P. O. Box 3000, Main, Lethbridge, Alberta T1J 4B1. Phytopathology 83:976-981. Accepted for publication 4 May 1993. Copyright 1993 Department of Agriculture, Government of Canada. DOI: 10.1094/Phyto-83-976.

Common root rot of wheat, caused by Cochliobolus sativus, produces a brown to black discoloration of the subcrown internodes (SCIs). The degree of discoloration is a measure of root rot severity and is directly related to yield losses. The rating system commonly used to assess the degree of discoloration is subjective, vulnerable to inconsistencies, and limited in quantification to only four categories. This study describes an image-analysis method that reliably quantifies discoloration of SCIs. Quantification is objective, highly precise, quick, and usable with any image analyzer. Image-analysis quantifications were compared with the four-category, subjective rating system for greenhouse collections of SCIs of wheat.