Response of wheat root pathogens to crop management in eastern Saskatchewan

Abstract

A survey of common root rot in spring wheat (Triticum aestivum L.) and durum wheat (T. turgidum L. var. durum) crops was conducted in eastern Saskatchewan from 1999 to 2001 to investigate the association of agronomic practices with disease and fungal populations, in particular Fusarium species associated with Fusarium head blight (FHB), which is a disease of increasing importance in this region. Spring wheat preceded by summerfallow, or grown after a sequence that included summerfallow and a cereal crop, had increased levels of Cochliobolus sativus and lower levels of most Fusarium spp. in discoloured subcrown internodes. Cropping sequences that included at least one noncereal crop in the previous 2 yr resulted in higher percentage isolations of F. avenaceum and F. graminearum than sequences which did not include noncereal crops. Highest levels of F. avenaceum, the most common FHB pathogen in the province, were observed when the previous crop was a pulse. Tillage system effects depended on the previous crop. When wheat was preceded by an oilseed crop, C. sativus decreased as the number of tillage operations decreased, whereas F. avenaceum and M icrodochium bolleyi increased with a reduction in tillage. Associations of fungal isolations with previous glyphosate use were negative for C. sativus and positive for F. avenaceum and M. bolleyi, although these effects varied depending on tillage system. Increased levels of important Fusarium pathogens were thus associated with current trends in production practices, namely continuously cropped diversified rotations and less reliance on mechanical soil tillage. Further investigation into the relative role of tillage intensity and glyphosate use versus cropping sequence on Fusarium populations in underground wheat tissue is needed. Key words: Common root rot, wheat, Cochliobolus sativus, Fusarium, tillage, glyphosate, crop rotation, nitrogen