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Ignored fungal pathogen sibling – Leptosphaeria biglobosa

Yongju Huang: University of Hertfordshire

<div>In nature, plants are often infected by more than one pathogen and there are many factors affecting their co-existence on their host which lead to changes in their predominance. Phoma stem canker is a damaging disease of oilseed rape (<em>Brassica napus</em>) and Brassica vegetables. This disease is caused by two closely related sibling pathogens, <em>Leptosphaeria maculans</em> and <em>L. biglobosa. </em>Since<em> L. maculans</em> generally causes stem base canker while<em> L. biglobosa</em> causes upper stem lesions, <em>L. maculans</em> is considered more damaging than <em>L. biglobosa</em>. Therefore, previous work has mainly focused on <em>L. maculans</em> and the importance of <em>L. biglobosa</em> in phoma stem canker epidemics has been ignored. However, results of our recent work show that <em>L. biglobosa</em> can cause both damaging upper stem lesions and stem base cankers. Furthermore, <em>L. biglobosa</em> is less sensitive to some triazole fungicides than <em>L. maculans. </em>The need for effective host resistance to control this disease is greater than ever. However, previous breeding for cultivar resistance has targeted only <em>L. maculans</em>; there is no information about cultivar resistance against <em>L. biglobosa</em>. Recent studies have shown that cultivars resistant against <em>L. maculans</em> are often more susceptible to <em>L. biglobosa</em>. For effective control of phoma stem canker, there is a need to target both <em>L. maculans</em> and <em>L. biglobosa. </em> In this talk, the reasons why <em>L. biglobosa</em> has recently increased in importance in phoma stem canker epidemics in the UK will be discussed, using results from field experiments over three seasons and controlled environment experiments.</div>