Epidemiology of blackleg (Leptosphaeria maculans) of canola (Brassica napus) in relation to maturation of pseudothecia and discharge of ascospores in western Australia

ABSTRACT The timing of maturation of pseudothecia and discharge of ascospores of the blackleg fungus (Leptosphaeria maculans) is critical in relation to infection early in the cropping season of canola. During 1998 to 2000, development of pseudothecia was investigated on residues of the previous year's canola crop collected from four agroclimatically different locations: Mount Barker (southern high rainfall), Wongan Hills (central medium rainfall), Merredin (central low rainfall), and East Chapman (northern low rainfall) in Western Australia. The pseudothecia matured on residues at different times after harvest in various regions. In general, pseudothecia maturity occurred earlier in the high-rainfall areas than in medium- and low-rainfall areas. An ascospore discharge pattern was investigated from residues of crop from the previous year (6-month-old residues) at three locations-Mount Barker, Wongan Hills, and East Chapman in Western Australia-and from 18-month-old residues that were burnt and raked in the previous year at Mount Barker and East Chapman. Ascospore discharge commenced earlier in high-rainfall (>450 mm) areas (Mount Barker) and late in northern low-rainfall (