Leptosphaeria maculans/L. biglobosa disease progression in oilseed rape and timing of ascospore release under New Zealand conditions

Leptosphaeria maculans/L. biglobosa disease progression in oilseed rape and the timing of ascospore release from crop debris were studied in ield experiments in 2011 and 2012. A similar pattern of disease progression was observed in both years, with the irst leaf lesions characteristic of L. maculans observed 11.5 weeks after sowing and stem lesions after 25 weeks. Leaf lesions characteristic of L. biglobosa were observed after 17.5 weeks. Leptosphaeria maculans was isolated from non-symptomatic petioles and stems after 16.5 and 22 weeks, respectively, indicating endophytic growth of the pathogen from leaf lesions. Vaseline-coated slides did not trap ascospores in 2011, but in 2012 both Rotorod and Burkard spore samplers trapped ascospores from 29 May to 21 September. Nested PCR with ITS and species-speciic primers detected both L. maculans and L. biglobosa ascospores, with L. maculans being more frequently detected. Peak ascospore numbers were detected in August and associated with periods of high rainfall.