Diversity of actinomycetes antagonistic to plant pathogenic fungi in cave and sea-mud soils of Korea

To isolate actinomycetes antagonistic to plant pathogenic fungi, soil samples were collected from caves and sea-shores in Korea. The 481 actinomycetes were isolated from the soil samples pre-treated by dry-heating at 100 degrees C for Ih. Streptomyces isolates were rich in all the soil samples examined, representing more than 50% of total counts. Nocardioform actinomycetes were isolated at 6-18.8%. They were relatively rich in both cave and sea-mud soils rather than other rare actinomycete genera. Saccharomonospora could be isolated only in 3 cave soil samples from Cheondong, Kosoo, and Nodong, but was not present in all the sea-mud soils examined. Dactylosporangium, Saccharomonospora, and Streptosporangium were very rare in both cave and sea-mud soils. The 311 of 481 actinomycete isolates inhibited the mycelial growth of at least one of the tested fungi. The isolation rates of antagonistic actinomycetes from cave soils ranged from 45.7% to 78%, and those of sea-mud soils were from 59.1% to 66.0%. The 96 of 136 Streptomyces isolates from cave soils, and 93 of 133 isolates from sea-mud soils showed antifungal activity. The proportion of antagonistic;isolates of Nocardioform actinomycetes (13.6%) was lower than that of other genera. Among the actinomycetes from sea-mud soils, Dactylosporangium and Streptosporangium had highest proportions of actinomycete antagonists of 85.7% and 80%, respectively. The isolation rate of Nocardioform antagonist from sea-mud soils was 11.1% similar in the cave soils. Streptomyces strains showed higher antifungal activities against plant pathogenic fungi than did other rare actinomycete antagonists.