Infection of Brachypodium distachyon with Selected Grass Rust Pathogens

The model temperate grass Brachypodium distachyon is considered a nonhost for wheat rust diseases caused by Puccinia graminis f. sp. tritici, P. triticina, and P. striiformis. Up to 140 Brachypodium accessions were infected with these three rust species, in addition to P. graminis ff. spp. avena and phalaridis. Related B. distachyon lines showed similar cytological nonhost resistance (NHR) phenotypes, and an inverse relationship between P. graminis f. sp. tritici and P. striiformis growth was observed in many lines, with accessions that allowed the most growth of P. graminis f. sp. tritici showing the least P. striiformis development and vice versa. Callose deposition patterns during infection by all three rust species showed similarity to the wheat basal defense response while cell death that resulted in autofluorescence did not appear to be a major component of the defense response. Infection of B. distachyon with P. graminis f. sp. avena and P. graminis f. sp. phalaridis produced much greater colonization, indicating that P. graminis rusts with Poeae hosts show greater ability to infect B. distachyon than those with Triticeae hosts. P. striiformis infection of progeny from two B. distachyon families demonstrated that these NHR phenotypes are highly heritable and appear to be under relatively simple genetic control, making this species a powerful tool for elucidating the molecular basis of NHR to cereal rust pathogens.