Fungal populations in subcrown internodes and crowns of oat crops in Saskatchewan

Discoloration of subcrown internodes (SIs) and crowns/lower culms (CLCs) of 87 oat crops across Saskatchewan in 1998-1999 and of SIs in 31 oat crops in eastern Saskatchewan (Black Soil Zone) in 2000-2001 was evaluated. Fungi in discolored tissue were isolated, identified and quantified, and the percentage of fields from which each fungus was isolated at least once (occurrence) and their relative percentage isolation levels were determined. In the 1998-1999 survey, discoloration severity varied more between years than among soil zones. Fusarium was the most common genus present, and F. culmorum the most common species. This was followed by F. equiseti, Microdochium bolleyi, Cochliobolus sativus, and F. avenaceum. Levels of C. sativus were lower in oat than those reported for wheat and barley in parallel province-wide surveys. Percentage isolation of F. culmorum was higher in the Brown than in the Black/Dark Gray Soil Zone, whereas the percentage occurrence of F. avenaceum was highest in the Black/Dark Gray Soil Zone. In 2000-2001, in eastern Saskatchewan, M. bolleyi, F. avenaceum, C. sativus, F. equiseti, Alternaria spp., and Pyrenophora avenae were the most common fungi isolated from discolored oat SIs. Similar to reports from wheat and barley, F. graminearum was isolated from SIs in eastern Saskatchewan at low levels. For the most part, neither previous crop nor tillage system affected fungal levels in SIs. P. avenae levels increased when the previous crop was another oat rather than wheat or barley. We conclude that oat could maintain or increase inoculum levels of Fusarium pathogens that cause damage to cereal crops in Saskatchewan. This is supported by results from a crop residue study in eastern Saskatchewan that showed that F. avenaceum, F. culmorum and F. graminearum occurred at similar or higher levels in oat fields than in fields of wheat or barley.