Identifying Soft Red Winter Wheat Cultivars Tolerant to Barley yellow dwarf virus.

Barley yellow dwarf virus (BYDV) is a serious disease of soft red winter wheat. Although there has been interest in tolerant cultivars, identification and development has been slow due to a lack of precision in rating plants for response to BYDV. Visual ratings of symptoms are commonly used to evaluate cultivars, but these ratings have proven to be inconsistent. The objectives of this research were to assess BYDV visual symptom ratings of wheat cultivars under field conditions, to measure disease-related yield reductions in these cultivars, to determine if a relationship exists between BYDV visual symptoms and yield reductions, and to determine BYDV cultivar tolerance. A split-plot design with insecticide treatment (main plot) and 11 cultivars (subplots) was employed over 4 years. The overall relationship between symptom ratings and BYDV yield reductions was weak (R = 0.40) and not consistent across years or cultivars. A consistency of performance analysis showed cultivars clustered into five distinct tolerance classes. Under conditions of high BYDV infestation, visual symptom ratings could be cautiously used to identify highly tolerant cultivars. The most reliable method for rating cultivar tolerance was a direct measure of disease-induced yield reduction across multiple environments.