Sixteen Streptomyces cultures.l.e, four wild type strains. eleven mutanl and
one regenerated protoplast isolate were tested for their abilities to inhibit one o~ more
of three locat isolates of the plant pathogenic fungi, Fusarium sdsni, Rhizo Ionia
solani and Sclerotium ro/fsii. which cause root rot disease. Bacillus subtitles was used to measure the antibacterial antibiotic activity of
Streptomyces strains and mutants. All tested cultures were antibacterial antibiotic
producers except R 1. G2 and Sir. ebus. Mutant R4 was the best antibacterial
producer. The sixteen cultures were tested for their antifungal activity against Fu arium
solani. All of them inhibited F. solani growth after three days of incubation. After seven
days. the antifungal activities of two-strains, Sfr. albus and Str. Gn'seovin'dis wa~ lost.
Antifungal activities of eight mutants increased by increasing incubation ~eriod.
Mutants R2. R4 and G4 were the higher antifungal activity mutants against F. Jolani.
The best producer was R2 mutant, either after three or seven days of incubation.1 Two strains. Sir. albus and Sir. griseoviridis were inactive against Rhizoclonia 1 lani,
after three and seven days of incubation. The activities of seven cultures were
decreased after seven days of incubation. Mutants R2. VT and GR were the higher
antifungal activity after seven days of incubation. G1 mutant was the best antir~ngal
activity against Rhizoctonia solani after three days of incubation. All tested cultures showed antifungal activities against Sclerotium olfsii. Three cultures. R 1. Str. a/bus and Str. griseoviridis, lost their activities after even
days of incubation. Three mutants G1. G2 and G3 isolated from Sir. grise us, were
higher antifungal activities against R. solani. The best antifungal activity was G2 after
three and seven days of incubation. Since, G2 was inactive as antibacterial anti iotic
producer so in some cases, it is advantage to use such mutant as a biocontrol st ain.
On the basis of the above results, S. rolfsii showed to be very sensitive to most vf the
Streptomyces tested cultures. Mutant R2 proved to be the best in its antifungal activity
against two out of the three tested plant pathogenic fungi. GR. which was selected
after protoplast regeneration. has a remarkable antifungal activity. It was one of three
higher antifungal activities against R. solani after seven days of incubation.