Survival of A-group and B-group Leptosphaeria maculans (phoma stem canker) ascospores in air and mycelium on oilseed rape stem debris

Mycelium of Leptosphaeria maculans survived on oilseed rape stem base debris buried in sand for 2, 4, 6, 8, 10 or 12 months and produced pseudothecia after subsequent exposure on the surface of the ground under natural conditions for 2-4 months, but did not survive on upper stem debris buried for 2 months. Only A-group L. maculans ascospores were produced on the stem base debris which had been buried; no B-group ascospores were produced. Mycelium of L. maculans survived on both stem base and upper stem debris exposed on the sand surface for 2, 4, 6, 8, 10 or 12 months and pseudothecia with viable ascospores were observed at the time of sampling. Both A-group L. maculans (predominant on stem bases) and B-group L. maculans (predominant on upper stems) ascospores were produced on unburied stem base and upper stem debris. Thus B-group L. maculans survived longer on unburied debris than on buried debris. A-group ascospores which were exposed in dry air in darkness at 5-20degreesC survived longer than B-group ascospores; 10-37% of A-group ascospores, compared with 2-31% of B-group ascospores, survived after 35 days.