Isolation and screening of phytotoxin producing actinomycetes and determination of phytotoxin effect spectrum of selected strains

Actinomycetes are well-known phytotoxin producing microorganisms. Nowadays the use of microbial herbicides versus traditional chemicals draws a great deal of attention as they do not cause any environmental problems. Actbacterial strains of 40 rhizospheric and phyllospheric samples were isolated. Primary screening was implemented on radish and cress seeds on GAP‌Agar. Then, bioassay of cell‌free broth of strains with more than 70% inhibitory effect on the seed growth was performed using GPM and SCD liquid media. Finally, compounds were extracted by organic solvents. The dry‌weight, production time and effectiveness of the superior isolate products were examined and three superior products were examined for their product effect spectrum by 10 resistant weeds. Among 457 screened isolates, 11 strains showed 70% or more inhibitory effect on GAP ‌medium. In secondary screening, seed growth inhibitions of 11 strains were more than 70% using cell‌free broth. These strains belonged to Streptomyces genus. According to dry weight products, production time and effectiveness PM2-2, TM14-5 and KB2-21 strains were selected for next steps and PM2-2 was the superior strain. Discussion and Streptomyces species are amog the best phytotoxins producers and the only phytotoxins introduced to the market are produced by the members of this genus. The growth inhibition of the most plant seeds examined by the isolated strains in this experiment showed an excellent potential for these phytotoxins. phytotoxins produced by some of the strains in the present study had high inhibitory effect and broad effect spectrum like commercial ones, so they seem to be economical.