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

A collection of 433 Aegilops tauschii was screened for response to infectio n with Stagonospora nodorum. Resistance similar or marginally superior to t he range observed in spring wheat genotypes was readily identified. Three l ines, 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 re sistance being commonly expressed as restricted lesion development. Infecti on frequency differed between some Ae. tauschii lines. Seedling resistance in synthetic bread wheats was expressed partially or not at all depending o n both the tetraploid and the tetraploid/Ae. tauschii combination. Assessme nt of adult responses among a range of synthetics showed occasional express ion of moderate resistance around the level observed among reference bread wheat cultivars of similar maturity. Disease escape associated with late ma turity was common. One synthetic wheat, #231, derived from a resistant Ae. tauschii, exhibited low adult disease expression associated with late matur ity. This line was resistant in seedling tests and seedling resistance was dominant in F-1 hybrids to bread wheat.