Summary prepared by Myriam Fernandez

Root and crown rot are important and widespread cereal diseases present in most parts of the world, and among the most damaging diseases of cereal crops in western Canada. Some of the pathogens commonly isolated from affected roots and crowns of wheat, barley, and oat in SK are Fusarium species, also responsible for Fusarium head blight in cereals.

Root and crown rot have been shown to cause significant yield losses. Due to the drier growing conditions experienced over the last decade, these diseases have been increasing in incidence and severity in SK. Durum wheat is in general more susceptible to root/crown rot than common wheat, but none of the currently registered wheat cultivars possess good resistance, therefore control of these diseases must rely on agronomic practices.

The impact of cropping system management on root and crown rot of spring wheat was examined at Scott, SK from 2001 to 2006. The systems approach used in this study tried to reflect the most common practices of organic and conventional producers in this region. It consisted of a factorial combination of three input levels [high, with tillage, fertilizer and pesticides); reduced (RED), with conservation tillage, targeted fertilizer and weed control; and organic (ORG) with tillage and N-fixing legumes]; and three levels of cropping diversity (low diversity with wheat and summerfallow or legume green manure fallow; diversified using annual grain crops; and diversified using annual grain crops and perennial forages). All rotations were six years long.

Subcrown internodes and crowns/lower culms of wheat plants were scored for discolouration, and fungi in discoloured tissue were identified and quantified. Overall, input level had a greater impact on disease levels and fungal frequency than cropping diversity. Discolouration severity was lowest in the RED systems, which was attributed to lower percentage isolation of Cochliobolus sativus, the most common root/crown pathogen. There was a differential effect of input level on Fusarium species. The pathogens F. avenaceum and F. culmorum were most associated with RED and/or least associated with ORG systems, whereas the weak pathogen/saprophyte F. equiseti was most associated with ORG systems.

Thus, ORG management helped to reduce populations of F. avenaceum and F. culmorum, two of the most important Fusarium pathogens in the Canadian Prairies. However, the mechanism(s) responsible for reduced Fusarium infections of roots and crowns in wheat grown under organic management were not determined.

It can also be suggested that input system might also affect infection of cereal spikes and grain. Other studies have reported lower Fusarium spike infection levels and concentration of the mycotoxin deoxynivalenol in organic than nonorganic systems.

This is the first North American study confirming observations from other cereal-growing regions on root and crown pathogen prevalence in organic compared with nonorganic systems. Further research into the mechanism(s) responsible for reduced presence of pathogenic Fusarium species under organic management systems is warranted.