A new species of Pythium from Wisconsin and Florida isolated from carrots

Pythium sulcatum n. sp. was isolated from carrots with browned and forked roots grown in muck soils from Wisconsin and Florida. It is primarily distinguished by small oogonia and oospores and by antheridia which are variable in shape and frequently adorned with single or multiple transverse furrows and folds, for which the species is named. Zoospores are rarely produced; vesicles always arise from filamentous sporangia indistinguishable from vegetative hyphae. Vegetative hyphal bodies vary in shape and are outnumbered by sexual bodies on most media. Radial growth rates of P. sulcatum on potato dextrose agar are slower than those of P. irregulare, P. paroecandrum, and P. sylvaticum over a wide temperature range, and P. sulcatum may easily be distinguished from these species on that basis.