INFLUENCE OF CROP SUCCESSION ON FOOT AND ROOT DISEASES OF WHEAT

The consequences of different crop successions on foot and root diseas es were analysed on a subsequent winter wheat crop managed identically , regardless of crop succession. At flowering, tillers and roots were assessed for eyespot (Pseudocercosporella herpotrichoides), take-all ( Gaeumannomyces graminis var tritici) and sharp eyespot (Rhizoctonia ce realis). As a consequence, we can propose a simple model of the effect of the preceding crop and the I before that on the 3 diseases. This m odel is based on a crop classification into 3 groups: host, amplifying crop and non-host for take-all and sharp eyespot; and 'strong/weak' h ost, amplifying crop and non-host for eyespot. Whereas host crops tend to increase and non-host crops to decrease disease risk, amplifying c rops (maize, ryegrass, etc) can only increase risk if they are associa ted with host crops.