Abstract
In assaying soil samples from 25 locations (four∼nine samples/Prefecture) in Kyushu Island for Pythium species by a trapping isolation method with cucumber and lupine seeds as baiting substrates, one∼seven taxa/sample were isolated from 24 samples, but no Pythium was isolated from one sample. A total of 433 isolates were identified into 16 taxa including H-Zs, a provisional Pythium group with zoospore formation from hypha-like sporangia, but without sexual organs. Among these fungi, 201 isolates of P. sylvaticum obtained from 22 locations were the most dominant, followed by P. ultimum and P. aphanidermatum. In inoculation experiments of 36 isolates of 16 taxa by the soil-over-agar culture inoculation method, 10 isolates including three each of P. sylvaticum and P. ultimum caused less than 60% of cucumber seeds unemerged, and after emergence, nine including two each of P. aphanidermatum, P. sylvaticum, and P. ultimum caused more than 40% of the seedlings collapsed or diseased. Emergence rates of komatsuna seeds appeared not to be influenced by any Pythium species tested, but after emergence, four isolates of P. sylvaticum, three of P. ultimum and one of P. irregulare caused more than 40% of the seedlings collapsed or diseased. Others were mildly pathogenic or nonpathogenic to both seedlings, but damage rates were below 30%.
