CHARACTERIZATION OF ACTINOMYCETES ANTAGONISTIC TO PHYTOPHTHORA-FRAGARIAE VAR. RUBI, THE CAUSAL AGENT OF RASPBERRY ROOT-ROT

Eleven actinomycete strains that were previously shown to protect rasp berry (Rubus strigosus) plants against Phytophthora infection were cha racterized. All were shown to belong to the genus Streptomyces. Two st rains (EF-34 and EF-76) grew at 4, 15 and 30 degrees C on V8 agar betw een pHs 5 to 9. Seven strains including EF-34 and EF-76 had both the a bility to hydrolyze Phytophthora cell walls and to inhibit Phytophthor a growth at 15 degrees C between pHs 5 to 9. All actinomycetes inhibit ed the growth of P. fragariae var. rubi and of Pythium ultimum. The gr owth of other fungal species and of Gram-negative bacteria was inhibit ed only in the presence of three strains (EF-14, EF-72, and Ef-76). Th e eleven antagonistic actinomycetes were classified into four groups w ith regard to their resistance to various pesticides used to protect r aspberry crops. Strain EF-76 was further characterized. This strain wa s identified as Streptomyces hygroscopicus var. geldanus, and it was s hown to produce geldanamycin, a known antibiotic.