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

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.