Biocontrol of Damping-Off Disease Caused by Rhizoctonia Solani in Some Medicinal Plants Using Local Strain of Streptomyces Pactum

A number of 187 Streptomyces isolates were isolated from different Egyptian soil samples and screened for their antifungal activities (mm inhibition zone) by agar diffusion method, only 5 isolates representing 2.67% produced antifungal metabolites. Starch nitrate agar was the most suitable medium for growth and production of antifungal metabolites by different Streptomyces isolates. In addition, Streptomyces isolate S131 was the most efficient isolate in antifungal activities (mm) which was identified as a strain of Streptomyces pactum. S131 .Furthermore, the most sensitive test organism for antifungal metabolites produced by S. pactum strain S131was Aspergillus niger followed by Fusarium oxysporum, Candida albicans, Aspergillus flavus, Fusarium moniliforme, Rhizoctonia solani and Pythium sp which resulted 20, 17, 16, 15,15, 14 and 13 mm of inhibition zone around agar (6 mm) culture disks of Streptomyces pactum- S131, respectively. Application of cultural filtrate in biocontrol against damping-off caused by Rhizoctonia solani in fennel and coriander seedlings were studied, the results revealed that there were significantly differences among all soil treatments in the percentage of total survival fennel plants from damping-off disease. The maximum percentage of total survival fennel plants from damping-off disease was recorded at uninfested soil treatment followed by soil infested with R. solani + rhizolex, soil infested with R. solani + culture filtrate and soil infested with R. solani, which resulted 82.35, 69.41, 55.50 and 22.28%, respectively. In addition, there were no significantly differences between uninfested soil and soil infested with R. solani + rhizolex in the percentage of total survival coriander plants from damping-off disease, which gave 91.67 and 90.67%, respectively. But there were significantly differences between soil infested with R. solani + culture filtrate of Streptomyces pactum strain S131 and soil infested with R. solani only in the percentage of total survival coriander plants from damping-off disease, which gave 58.34 and 11.09%, respectively.