Screening of endophytic actinomycetes for their herbicidal activity.
Endophytic actinomycetes were isolated from 6 different plants collected from Uttarakhand, India. Actinomycetes isolates were screened for their herbicidal activity against Parthenium hysterophorus, Ageratum conyzoides and Bidens biternata. These isolates belong to the seven different genera. None of the isolate showed herbicidal activity on SCN agar plates. Therefore, direct fermentation method was used for the phytotoxin production in the submerged culture to study the herbicidal activity against different test weeds. The significant differences were observed in the production of phytoxin in SCN and GS medium. In the case of Ageratum conyzoides (billygoat weed), the culture filtrate of Nocardiodes sp. 1, Nocardiodes sp.2 and Actinomadura sp. showed 60% reduction in seed germination. However, culture filtrate of endophytic actinomycetes was ineffective on seed of Bidens biternata in the pre-emergence condition. In Parthenium hysterophorus, the highest seed germination reduction was observed with the culture filtrate (in SCN) of Nocardiodes sp.1 (80%). While in GS medium, maximum inhibition was observed in culture filtrate of Saccharopolyspora sp. (80%). The culture filtrates exhibited phytotoxic activity towards the germinated seedlings of Ageratum conyzoides, Bidens biternata, and Parthenium hysterophorus showing effects like leaf curling, wilting and burning. In post-emergence condition, reduction in shoot-root length was observed with the culture filtrate of Actinomadura sp.1, Nocardiodes sp.1, Streptomyces sp.1, Saccharopolyspora sp. and Microbispora sp. These findings suggest that endophytic actinomycetes are rich source of herbicidal metabolites. Further studies are required to isolate, purify and structure elucidation of the metabolites.