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Investigating regional differences in proportions of Leptosphaeria maculans and Leptosphaeria biglobosa in southern England

Asna Javaid: University of Hertfordshire

<div>Phoma stem canker, caused by fungal pathogens <em>Leptosphaeria maculans</em> (Lm) and <em>L. biglobosa </em>(Lb), is responsible for worldwide <em>Brassica napus</em> (oilseed rape) yield losses of over £700M. Previously, it was believed that Lm was more damaging than Lb. Recent work suggests that Lb can cause both upper stem lesions and stem cankers. This work investigated proportions of Lm and Lb in <em>Leptosphaeria</em> populations in airborne ascospores and in lesions on leaves/stems of different <em>B. napus</em> cultivars in a field experiment in the UK. Air samplers were operated at four UK sites from September to March in 2015-2016 and 2016-2017. Quantitative PCR analysis of air samples showed differences between sites and seasons in amounts of Lm and Lb DNA. In 2015-2016 there was more Lm DNA than Lb DNA in air samples at three sites, whereas in 2016-2017 there was more Lb DNA than Lm DNA at three sites. The field experiment was done with six cultivars in 2016-2017. The numbers of Lm and Lb lesions on leaves were assessed in autumn/winter and proportions of Lm and Lb DNA in stem cankers were quantified in summer. Cultivars had different proportions of Lm and Lb on leaves and in stem cankers. Cultivars susceptible to both Lm and Lb had more Lm lesions and greater amounts of Lm DNA in cankers whereas cultivars resistant to Lm had more Lb lesions and greater amounts of Lb DNA in cankers. Therefore, there is a need to breed cultivars with resistance against both Lm and Lb.</div>