Maturation of ascospores of A-group and B-group Leptosphaeria maculans (stem canker) on winter oilseed rape debris

Ascospores of both A-group and B-group L. maculans matured faster at 15-20degreesC than at 5-10degreesC. At 5-10degreesC, maturation of B-group ascospores was slower than that of A-group ascospores but there was no difference at 15-20degreesC. A-group pseudothecia were mainly produced on the surface of stem bases and B-group pseudothecia were mainly produced under the epidermis of upper stems. At Rothamsted in 2000/2001 and 2001/2002, ascospores matured earlier on stem bases than on upper stems. Ascospores matured and were released earlier in 2001 than 2000 and were then released from autumn to spring. Seasonal differences in first maturation of ascospores were related to differences in summer rainfall. The first phoma leaf spotting appeared in untreated plots of winter oilseed rape 8-15 days after the first release of ascospores