A simple approach to assess common root rot severity incidence data in wheat

Abstract

Common root rot (CRR) of wheat, caused by Cochliobolus sativus, produces discoloration of the subcrown internodes (SCIs) and is directly related to yield losses. It is critical to clearly define and standardize the CRR assessment methods to avoid subjectivity and variability between assessors. Therefore, in this study, a comparison between the incidence (I; proportion of diseased SCIs) and the severity (S; proportion of SCI showing CRR symptoms) was investigated to explore the possibility of simplifying disease rating. Assessments were made visually at multiple sample sites in artificially- and naturally-inoculated research and production fields for three growing seasons. Significant differences (P = 0.001) in mean I and S values were found among cultivars, with values being consistently higher in the susceptible ones. However, CRR severity increased linearly as incidence increased in both Triticum durum and T. aestivum wheat. Their slopes and intercepts of the I–S relationship were consistent over the three growing seasons. This result may be considered a significant contribution for CRR assessment in wheat breeding programs.