Field techniques for assessing the reaction of winter wheat cultivars to Septoria nodorum

Abstract

SUMMARYMethods of assessing the reaction of winter wheat cultivars to Septoria nodorum were compared in nine field trials. Plots were inoculated either by scattering naturally infected wheat debris or by spraying with a suspension of conidia at different growth stages, and were subsequently kept damp by several methods. Disease development was monitored by assessing the percentage cover of different organs by lesions, or by measuring the maximum height of lesions above ground. Major differences between cultivars were evident with all methods of inoculation and assessment, but time of assessment was critical for best differentiation. Inoculation with conidia soon after ear emergence, followed by assessment of lesions on flag leaves and ears, was a simple and effective method.Yield loss due to disease was measured by making comparisons either between inoculated and uninoculated plots, with various degrees of separation, or between inoculated plots with and without fungicidal treatment: the first of these methods was more effective in maintaining a disease differential. Yield loss was positively correlated with severity of disease and there was little evidence that cultivars differed in tolerance of disease. Disease was measured more easily and with less error than yield loss.