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

• Published in: Plant pathology Vol. 69; no. 3; pp. 518 - 537
• Main Authors: Carmody, Shannon M., King, Kevin M., Ocamb, Cynthia M., Fraaije, Bart A., West, Jon S., du Toit, Lindsey J.
• Format: Journal Article
• Language: English
• Published: England Wiley Subscription Services, Inc 01.04.2020; John Wiley and Sons Inc
• Subjects: Agricultural practices; Brassica; Brassica rapa; Brassicaceae; Carbendazim; chlorotic leaf spot; Cover crops; Deoxyribonucleic acid; DNA; DNA fingerprinting; Evolution; Fungicides; Gene sequencing; Genetic analysis; Genetic diversity; Genetic fingerprinting; Inoculation; Leafspot; light leaf spot; MAT protein; Morphology; Nucleotide sequence; Original; Pacific Northwest USA; phylogenetic lineage; Phylogeny; Pyrenopeziza brassicae; Sequence analysis; Signs and symptoms; Spot; United Kingdom > UK; North America; Europe; Pyrenopeziza brassicae; chlorotic leaf spot; light leaf spot; Brassicaceae; phylogenetic lineage; Pacific Northwest USA
• ISSN: 0032-0862; 1365-3059
• DOI: 10.1111/ppa.13137

Light leaf spot, caused by the ascomycete Pyrenopeziza brassicae, 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 Brassica spp. in the Willamette Valley of western Oregon, followed by detection in Brassica juncea cover crops and on Brassica rapa 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, MAT gene sequences, and rep‐PCR DNA fingerprinting), pathogenic (B. rapa 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 P. brassicae 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 B. rapa and B. juncea differed, and therefore “chlorotic leaf spot” is proposed for the disease caused by Lineage 2 isolates of P. brassicae. Isolates of the two lineages differed in genetic diversity as well as sensitivity to the fungicides carbendazim and prothioconazole. Pyrenopeziza brassicae was first found on Brassica spp. in North America (NA) in 2014. The consolidated species concept showed NA isolates are in a distinct evolutionary lineage compared to isolates from continental Europe and the UK.