Abstract
Actinomycetes were isolated by the use of normal standard isolation techniques (streptomycetes), polyvalent Streptomyces phages and dry heat techniques (non-streptomycetes), respectively. In addition to the standard in vitro antagonism tests on agar, a novel technique was developed to screen isolates on the surface of intact mature carrots in the presence of Pythium coloratum a causal agent of cavity spot disease of carrots. From over two hundred actinomycete isolates only seven were found to be strongly antagonistic against P. coloratum. These were identified as Streptomyces janthinus, S. cinerochromogenes, Actinoplanes philippinensis, Streptoverticillium netropsis, Micromonospora carbonaceae, Actinomadura rubra, and Streptosporangium albidum. In glasshouse trials these actinomycetes significantly reduced the incidence of cavity spot disease in soil infected with P. coloratum.