Light Leaf Spot (Pyrenopeziza brassicae) of Oilseed Rape (Brassica napus) and Other Brassica Crops

Light leaf spot (LLS), caused by the fungal pathogen Pyrenopeziza brassicae, is a damaging disease of oilseed rape and other Brassica crops. The pathogen survives on crop debris from the previous cropping season and produces apothecia containing ascospores to infect crops in the next season. P. brassicae penetrates leaf cuticles directly and grows in the subcuticular space without symptoms until white acervuli break through the leaf surface. The main symptoms of LLS are white P. brassicae acervuli (asexual fruiting bodies), often arranged in circles. P. brassicae also causes other symptoms, including necrotic black flecking, leaf distortion, stunting and green islands. The pathogen can infect all parts of Brassica plants leading to yield losses, with leaf infection causing premature defoliation and reducing photosynthetic capacity while pod infection causes premature ripening and seed shedding. Identification of the pathogen is based on symptoms and DNA-based technology. P. brassicae has a complex life cycle, involving both rain-splash dispersed asexual conidia and wind-dispersed sexual ascospores. LLS is a polycyclic disease; after initial leaf infection, conidia and ascospores of P. brassicae produced on infected plant tissues cause secondary infections. Effective control of LLS relies on an integrated approach, combining resistant cultivars, fungicide applications and agronomic practices.