The present work focuses on the antagonistic interactions among cultivable actinomycetes isolated from agricultural soil and organic amendments (farmyard manure and municipal solid waste compost). Antagonistic interactions, assayed by the double-layer agar method, were checked among isolates obtained from (i) the same treatment (ii) control soil (unamended) against those from amendments and (iii) each treatment against tow phytopatogenic bacteria (Agrobacterium tumefaciens B6 and C58). A high

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... ppressive interaction ratio (≥ 50%) was registered some either the treatment soil. It was found that amendments application decreased this suppressive interaction ratio between actinomycetales. But, it increases the ratio of the antagonistic actinomycetales from soil against Agrobacterium tumefaciens confirming the role of these organic residues as fertilizers. It was also shown, based on the phylogenetic affiliation of bacteria, that the antagonism can play a significant role in structuring bacterial communities in soil.