Impacts of previous crops on Fusarium foot and root rot, and on yields of durum wheat in North West Tunisia

The impacts of ten previous crop rotations (cereals, legumes and fallow) on Fusarium foot and root rot of durum wheat were investigated for three cropping seasons in a trial established in 2004 in Northwest Tunisia. Fungi isolated from the roots and stem bases were identified using morphological and molecular methods, and were primarily Fusarium culmorum and F. pseudograminearum . Under low rainfall conditions, the previous crop affected F. pseudograminearum incidence on durum wheat roots but not F. culmorum . Compared to continuous cropping of durum wheat, barley as a previous crop increased disease incidence more than fivefold, while legumes and fallow tended to reduce incidence.  Barley as a previous crop increased wheat disease severity by 47%, compared to other rotations. Grain yield was negatively correlated with the incidence of F. culmorum infection, both in roots and stem bases, and fitted an exponential model (R 2 = -0.61 for roots and -0.77 for stem bases, P <0.0001). Fusarium pseudograminearum was also negatively correlated with yield and fitted an exponential model (R 2 = -0.53 on roots and -0.71 on stem bases, P < 0.0001) but was not correlated with severity.