Identification of a new subclade of Leptosphaeria biglobosa on Brassica rapa in Oregon, USA
Z. ZOU (1), X. Zhang (1), T. Paulitz (2), C. Ocamb (3), L. duToit (4), F. Dilantha (1) (1) University of Manitoba, Canada; (2) Washington State University, Pullman, U.S.A.; (3) Oregon State University, U.S.A.; (4) Washington State University, Mount Vernon NWREC, U.S.A.

Stem canker of crucifers including Brassica napus, Brassica juncea, and Brassica rapa is a globally important disease that is caused by an ascomycete species complex comprising of Leptophaeria maculans and L. biglobosa. Six isolates retrieved from B. rapa (Barkant) variety in Willamette Valley, Oregon, USA were characterized as L. biglobosa based on the pathogenicity test, internal transcribed spacer (ITS) size and sequence similarities of ITS, actin and β-tubulin genes. These six L. biglobosa isolates along with other 82 L. biglobosa isolates and six L. maculans isolates were employed to perform parsimony and distance analyses on ITS, actin, and β-tubulin sequences. The results revealed that these six isolates formed a new subclade,  more  similar to L. maculans than L. biglobosa ‘canadensis’,  L. biglobosa ‘brassicae’ and other L. biglobosa subclades. We believe, these isolates belong to a new subclade. They are termed here as L. biglobosa ‘americensis’. Pathogenicity tests revealed L. biglobosa ‘americensis’ isolates failed to cause disease in all the resistant and susceptible B. napus varieties/lines tested but caused severe disease symptoms in most B. rapa lines tested and demonstrated virulence in one B. juncea line (common brown mustard). Moreover, L. biglobosa ‘americensis’ isolates demonstrated more profound mycelia growth than other subclades of L. biglobosa. These findings highlighted that L. biglobosa ‘americensis’ isolates were distinct from other L. biglobosa subclade and formed  a new subclade of L. biglobosa.

Abstract Number: P17-649
Session Type: Poster