Thirty-four endophytic actinomycetes were isolated from the roots of native plants oftheAlgerian Sahara.
Morphological and chemical studies showed that twenty-nine isolates belonged to the Streptomyces
genus and five were non-Streptomyces. All isolates were screened for their in vitro antifungal activity
against Rhizoctonia solani. The six that had the greatest pathogen inhibitory capacities were subsequently
tested for their in vivo biocontrol potential on R. solani damping-off in sterilized and non-sterilized soils,
and for their plant-growth promoting activities on tomato seedlings. In both soils, coating tomato seeds
with antagonistic isolates significantly reduced (P < 0.05)the severity of damping-off oftomato seedlings.
Among the isolates tested, the strains CA-2 and AA-2 exhibited the same disease incidence reduction as
thioperoxydicarbonic diamide, tetramethylthiram (TMTD) and no significant differences (P < 0.05) were
observed. Furthermore, they resulted in a significant increase in the seedling fresh weight, the seedling
length and the root length of the seed-treated seedlings compared to the control. The taxonomic position
based on 16S rDNA sequence analysis and phylogenetic studies indicated that the strains CA-2 and AA-2
were related to Streptomyces mutabilis NBRC 12800T (100% of similarity) and Streptomyces cyaneofuscatus
JCM 4364T (100% of similarity), respectively.