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Title: Mycoflora of seed of common teasel (Dipsacus fullonum) in Washington State

item Dugan, Frank
item Rector, Brian

Submitted to: Pacific Northwest Fungi
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/24/2007
Publication Date: 9/12/2007
Citation: Dugan, F.M., Rector, B.G. 2007. Mycoflora of seed of common teasel (Dipsacus fullonum) in Washington State. Pacific Northwest Fungi 2 (6):1-10.

Interpretive Summary: Common teasel is extremely prevalent throughout several regions of North America, and is sometimes considered a noxious weed. It is abundant immediately adjacent to the farm of the USDA-ARS Western Regional Plant Introduction Station (WRPIS) in Pullman, WA. The plant is the classic host of the stem and bulb nematode, a pathogen of quarantine significance on garlic and other Allium species, important crops at the WRPIS farm. Potential natural enemies of the weed have been previously listed, but the microbial ecology of teasel seed is insufficiently documented. This survey documents the primary fungal taxa colonizing seed of common teasel and reports highly significant correlations of the most prevalent colonizers with seed health. This research also documents the direct production of an asexual state, Cladosporium herbarum, from the apical cells of sexual fruiting bodies of a highly visible colonizer, Davidiella (Mycosphaerealla) tassiana.

Technical Abstract: Seeds of standing common teasel (Dipsacus fullonum) were harvested in January 2007 in Pullman, Washington, and divided into two categories, symptomatic versus asymptomatic, on the basis of signs of fungal colonization at 10-50X magnification. The most common signs were pseudothecia of Davidiella tassiana. Fungi were recovered from all seeds of both categories when seeds were surface-disinfested and incubated on agar media. Aureobasidium pullulans accounted for 57-72% of fungal isolates from asymptomatic seed, but only 16-26% of isolates from symptomatic seed. Cladosporium spp. and Alternaria spp. exhibited a combined frequency of 54-64% from symptomatic seed, versus 16-35% from asymptomatic seed. Asymptomatic seed germinated at incidences of 44-76% whereas symptomatic seed germinated at incidences of 2-6%. When seeds or germinated seedlings were inoculated with conidial suspensions of representative isolates of Au. pullulans, C. herbarum (anamorph of D. tassiana) or Alternaria sp., and incubated under conditions favorable for germination or growth of teasel, no differences were apparent between treated seed and non-inoculated control seed. The correlation between colonization by Alternaria and Cladosporium species and diminished germination ability probably reflects unidentified, predisposing factors for diminished germination. Immature pseudothecia of D. tassiana were repeatedly observed to germinate directly on the seed by production of fertile conidiophores from the apices of the papillae.