LONG-TERM SURVIVAL AND SPORULATION OF LEPTOSPHAERIA MACULANS (BLACKLEG) ON NATURALLY-INFECTED RAPESEED/CANOLA STUBBLE IN SASKATCHEWAN

摘要

In semi-arid Saskatchewan, Canada, peak ascospore discharge by Leptosphaeria maculans from. blackleg-infected rapeseed/canola (Brassica napus and B. rapa) stubble residue generally occurred in the second year following the year of crop growth. Over 90% of the original stubble had disappeared by that time, leaving infected crowns and taproots that deteriorated slowly under the prevailing dry surface soil conditions. Ascospores of L. maculans continued to be discharged from this residue for a further 3-5 years, greatly exceeding the mean 3.3 year length of rotations out of rape followed by producers. Ascospore discharge from stubble residue could be intermittent, occasionally missing entire years. Burial or flooding of infected 19-month-old stubble for 10 days almost entirely eliminated the production of ascospores. Rape stems with severe basal cankers produced L. maculans ascospores earlier and in greater numbers than did stems with extensive superficial lesions taken from the same field.