The effects of the herbicide asulam on the gametophytes of Pteridium aquilinum, Cryptogramma crispa and Dryopteris filix-mas

Fern spores were germinated, grown and exposed to different concentrations of asulam (the active ingredient of Asulox) in liquid culture. Gametophytes of Pteridium aquilinum [L. (Kuhn)] (bracken) were exposed to 100 g l(-1) f or 24 h at the following three stages: germination; during filamentous grow th. and after transition had occurred. This treatment severely inhibited ge rmination and killed photosynthetic gametophytes outright. Gametophytes of all species tested [Pteridium aquilinum, Cryptogramma crispa CL.) Hook and Dryopteris filix-mas (L.) Schott] varied in their responses to lower concen trations. This variation was in terms of the response of the gametophytes a nd the numbers of gametophytes showing each response. Some gametophytes suf fered 100% cell mortality, but in others some cells died and some survived, while the remainder of the gametophytes suffered no cell mortality. The ce lls affected varied from gametophyte to gametophyte at the same dose and th e proportions of gametophytes showing each response changed with concentrat ion, mortality increasing with increasing concentration. Pteridium showed l ower levels of mortality at each concentration than either of the other spe cies. The bioassay system described provides a rapid laboratory-based metho d to screen for Asulox susceptibility of fern gametophytes in comparison wi th Pteridium. (C) 2000 Annals of Botany Company.