Septoria nodorum blotch resistance in Aegilops tauschii and its expression in synthetic amphiploids

A collection of 433 Aegilops tauschii was screened for response to infection with Stagonospora nodorum. Resistance similar or marginally superior to the range observed in spring wheat genotypes was readily identified. Three lines, RL5271, Aus18911, and Aus21712, were resistant to a range of pathogen isolates and were similar in resistance to a highly resistant French line, No.33. Accessions of Ae. tauschii assessed as resistant or susceptible as seedlings had corresponding reactions when tested as adult plants, with resistance being commonly expressed as restricted lesion development. Infection frequency differed between some Ae. tauschii lines. Seedling resistance in synthetic bread wheats was expressed partially or not at all depending on both the tetraploid and the tetraploid/Ae. tauschii combination. Assessment of adult responses among a range of synthetics showed occasional expression of moderate resistance around the level observed among reference bread wheat cultivars of similar maturity. Disease escape associated with late maturity was common. One synthetic wheat, #231, derived from a resistant Ae. tauschii, exhibited low adult disease expression associated with late maturity. This line was resistant in seedling tests and seedling resistance was dominant in F1 hybrids to bread wheat.