A phylogenetically distinct lineage of associated with chlorotic leaf spot of Brassicaceae in North America.

Light leaf spot, caused by the ascomycete , is an established disease of Brassicaceae in the United Kingdom (UK), continental Europe, and Oceania (OC, including New Zealand and Australia). The disease was reported in North America (NA) for the first time in 2014 on spp. in the Willamette Valley of western Oregon, followed by detection in cover crops and on weeds in northwestern Washington in 2016. Preliminary DNA sequence data and field observations suggest that isolates of the pathogen present in NA might be distinct from those in the UK, continental Europe, and OC. Comparisons of isolates from these regions using genetic (multilocus sequence analysis, gene sequences, and rep-PCR DNA fingerprinting), pathogenic ( inoculation studies), biological (sexual compatibility), and morphological (colony and conidial morphology) analyses demonstrated two genetically distinct evolutionary lineages. Lineage 1 comprised isolates from the UK, continental Europe, and OC, and included the type specimen. Lineage 2 contained the NA isolates associated with recent disease outbreaks in the Pacific Northwest region of the USA. Symptoms caused by isolates of the two lineages on and differed, and therefore "chlorotic leaf spot" is proposed for the disease caused by Lineage 2 isolates of . Isolates of the two lineages differed in genetic diversity as well as sensitivity to the fungicides carbendazim and prothioconazole.