Pflanzenpathologie und Pflanzenschutz

Phoma lingam

Reklassifizierung der Teleomorphe von Phoma lingam

Stem canker of oilseed rape is caused by an ascomycetous fungus, whose anamorph is Phoma lingam. As already shown in detail, huge variability was found within the anamorph. All phenotypic and genetic gathered data suggest that Phoma lingam is a species complex.

The classical definition of a species tells that indivuduals of a species may produce fertile offspring. A- and B-type NA-1 isolates fullfil these requirements in a more or less validated manner. Those isolates can be successfully mated on petri-dishes in a intraspecific manner. Interspecific crosses never have been shown neither by our or other groups who established the method of in vitro crossing. This observation may also, beside the numerous pheno-and genotypic traits, aid to the conclusion that A-and B-NA1 type isolates belong to different species.

The differentiation of A- and B-type isolates was consequently suggested by Shoemaker and Brun (2001), who described morphological differences of the sexual fruiting bodies (pseudothecia) of these two types. The authors described a pronounced neck under the ostiolum of pseudothecia of B-type isolates. Similar results were seen in our group after studying in-vitro crosses on tooth picks. We attributed these properties for a long time to artificial conditions. Nevertheless, both observations clearly describe morphologic differences of the teleomorphs. Although there are no morphologic traits to dinstinguish the A and B-type anamorphs, we clearly support the taxonomic differentiation of these types. Shoemaker and Brun suggested the nomen novuum Leptosphaeria biglobosa for B-NA1 isolates. The perfect stage of A-type isolates will still be Leptosphaeria maculans.

Further differences between A- und B-typ NA-1 isolates became obvious during studies performed in the context of environmental requirements of these fungi (Huang et al 2001). It was shown, that ascospores of A-type isolates preferently germinate from intersitial cells and showed a pronounced branching of the mycelium. In contrast ascospores of B-type NA-1 isolates preferently germinanted from terminal cells and showed a craned and poorly branched mycelium.

Selected publications:
  • Huang YK , Toscano-Underwood C , Fitt BDL , Todd AD , West JS , Koopmann B, Balesdent MH (2001). Effects of temperature on germination and hyphal growth from ascospores of A-group and B-group Leptosphaeria maculans (phoma stem canker of oilseed rape). Annals of Applied Biology 139, 193–207.
  • Shoemaker RA , H Brun (2001). The teleomorph of the weakly aggressive segregate of Leptosphaeria maculans. Canadian Journal of Botany 79 pp 412-419.