Root disease and fungal populations in organic crops under different tillage-cropping systems

There has been a steady expansion in organic production in the Canadian Prairies because of higher consumer demand. Thus, increasing the sustainability of organic systems would be important. An organic trial was conducted in the semi-arid Prairies (2010-2015) with two tillage intensities (low vs. high) in a simplified [spring wheat (Triticum aestivum L.)-forage pea (Pisum sativum L.) green manure (GM)] and a diversified (spring wheat-oilseed-pulse-GM) rotation. In 2013-2015, the impact of these systems on root rot was examined on spring wheat, pulses, and GM crops. Several Fusarium spp. were more abundant in GM and pulses than spring wheat, suggesting that they could be a source of inoculum, especially of F. avenaceum (Fr.:Fr.) Sacc. (teleomorph Gibberella avenacea Cook), for Fusarium diseases in cereals including Fusarium head blight. Under different environments, tillage-rotation systems had an impact on root disease and fungal populations, some of which have biocontrol capabilities. There was no difference among systems for root rot in forage pea, while the low tillage-diversified rotation had the lowest root rot in spring wheat but was associated with more Fusarium spp. For all crops, most Fusaria were not associated with root rot severity. Cochliobolus sativus (Ito & Kurib.) Drechs. ex Dast. [anamorph Bipolaris sorokiniana (Sacc.) Shoemaker] accounted the most for root rot in spring wheat and was favored by intensive tillage and simplified rotations. The Shannon diversity index (H') of fungal species in spring wheat was higher in the diversified rotation under both tillage intensities than when spring wheat alternated with GM in the simplified rotation, especially under high tillage. In forage pea, H' was higher than in spring wheat, but did not differ among tillage-rotation systems.