DIFFERENTIAL (HOST‐SPECIFIC) ACCUMULATION OF ZOOSPORES OF PYTHIUM ON ROOTS OF GRAMINACEOUS AND NON‐GRAMINACEOUS PLANTS

Abstract

Zoospores of Pythium graminicola Subramanian and P. arrhenomanes Drechs., which characteristically infect the Gramineae, differed from spores of P. aphanidermatum (Edson) Fitzp. and P. ultimum Trow, which have wide host ranges, by accumulating to a greater degree on roots of graminaceous as compared with non-graminaceous plants. These differential responses occurred with wild plants collected from field sites or grown in a glasshouse, but not with cultivated cereals and dicotyldedonous plants (Antirrhinum majus L. and Lycopersicon esculentum Mill.) grown in a glasshouse. Differential responses involved mainly encystment and accumulation of encysted spores, rather than taxis. Root mucigel was implicated in zoospore accumulation. Host-differences in this respect did not occur with damaged roots; treatment of roots with methylene blue or periodate (but not alcian blue or Calcofluor) prevented or reduced zoospore encystment without markedly affecting accumulation of motile zoospores.