Epidemiological investigations into root and collar rot of rape, caused by Phoma lingam.
Infection by P. lingam (Leptosphaeria maculans) occurred at the base of the stalk. Under high inoculum potential (rape monoculture or artificial inoculation), the fungus was isolated more frequently at the level of insertion of the lower leaves than at soil level. The fungus spectrum and frequency of fungi isolated changed during the course of the growing period. L. maculans and Fusarium tabacinum increased and were isolated in large numbers, Alternaria spp. and P. eupyrena were found less at the beginning and end of the season, and other spp., the pathogenic importance of some of which was not clear, were isolated less frequently or at low levels. Ascospore discharge was initiated by rainfall or high RH. More spores were discharged at wind speeds of 2-3 m/s, which tended to occur during the afternoon and evening, than at other wind speeds. The low level of leaf infection in rape grown in rotations in the GFR is ascribed to factors including: the short period of ascospore discharge; the low temp. in Nov. and Dec.; and the practice of deep ploughing early in the autum for wheat sowing, which decreased inoculum potential as shown by spore trap results.