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The incidence and pathogenicity of Alternaria leaf spot associated with canola (Brassica napus) in southern Australia

Hebba Al-lami: School of Agriculture and Environment, Faculty of Science, University of Western Australia

<div><em>Alternaria</em> spp., especially <em>Alternaria brassicae</em>, <em>A. brassicicola</em>, <em>A. raphani</em>, <em>A. alternata</em>, <em>A. japonica </em>and <em>A. tenuissima</em> associated with a range of different disease symptoms in <em>Brassicaceae</em>, including various leaf lesions on cauliflower, broccoli, and oilseed brassicas including canola and mustard. <em>Alternaria </em>spp. can cause serious losses, for example, up to 47% in Indian mustard (<em>Brassica juncea</em>) and >70% in some other <em>Brassica</em> spp. However, as yet, resistance breeding programs in rapeseed-mustard against <em>A. brassicae </em>have had minimal success. <em>Alternaria</em> spp. associated with leaf lesions on canola and associated weedy <em>Brassicaceae</em> in Australia were unknown, studies were undertaken to determine which <em>Alternaria</em> spp. were associated with diseased leaves of canola (<em>B. napus</em>) and wild radish (<em>Raphanus raphanistrum</em>) plants across two cropping seasons. More than 400 <em>Alternaria</em> spp. isolates were collected and are being identified using PCR-based assay by sequencing of the ITS region of the rDNA operon, the gene fragment plasma membrane ATPase and also the ‘Alt a 1’ gene. Fifteen species of <em>Alternaria</em> have now been identified, including <em>A. brassicae</em>, <em>A. alternata </em>and <em>A. infectoria</em>, and thirteen of the different <em>Alternaria</em> spp. were found to be pathogenic on <em>B. napus</em> and <em>B. juncea</em>.</div>