PARASITISM OF OOSPORES OF PYTHIUM SPP BY STRAINS OF ACTINOPLANES SPP

Strains of Actinoplanes spp. were evaluated for their in vitro parasit ism of oospores of Pythium aphanidermatum, Pythium arrhenomanes, Pythi um irregulare, Pythium myriotylum, and Pythium ultimum. Oospores of Py thium arrhenomanes, Pythium irregulare, and Pythium myriotylum were id entified for the first time as hosts of Actinoplanes spp. Newly record ed parasites of oospores of Pythium spp. were Actinoplanes azureus, Ac tinoplanes brasiliensis, Actinoplanes caeruleus, Actinoplanes ferrugin eus, Actinoplanes ianthinogenes, Actinoplanes italicus, Actinoplanes m inutisporangius, Actinoplanes rectilineatus, Actinoplanes teichomyceti cus, Actinoplanes utahensis, Actinoplanes violaceous, Actinoplanes yun nahenis, plus 15 strains of Actinoplanes yet to be speciated. Parasiti zed oospores had disorganized cytoplasms and hyphae of Actinoplanes sp . emerging from them. Infection of oospores in vitro varied from 0 to > 90%. Strains also were very active parasites of oospores in sterile soils. When added to nonsterile soils, several strains increased (p = 0.05) the level of oospore parasitism compared with nonsupplemented so ils. Strains of Actinoplanes spp. exhibited a host specificity for spe cies of Pythium in vitro and in soil. Sporulation of Actinoplanes sp. from infected oospores incubated on soil was frequent and more abundan t than that observed in vitro.