Detection of aster yellows phytoplasma DNA in seed and seedlings of canola (Brassica napus and B. rapa) and AY strain identification

A study was conducted to identify the strains of aster yellows (AY) disease present in crops of Brassica napus and B. rapa grown near Medstead, Saskatchewan. AY phytoplasma DNA was detected in midrib, stem and root tissues of several symptomless plants as well as plants exhibiting typical AY disease symptoms. Most symptomatic and symptomless, AY-infected plants produced normal-looking and misshapen seeds. However, for both Brassica species, symptomatic plants produced significantly more seeds containing phytoplasma DNA than symptomless, AY-infected plants. Also, significantly more misshapen seeds contained phytoplasma DNA than normal seeds. Phytoplasma DNA belonging to subgroups 16SrI-A and 16SrI-B was detected in symptomatic and symptomless, AY-infected plants and in seed of these plants. The new AY strain sequences were registered in Genbank. The study reports for the first time the detection of AY strains in seedling tissues of both Brassica species. The research also showed that spiral cleaning has the potential to remove seeds that contain phytoplasma DNA in B. napus.