Abstract

Three medicinal plants, Aloe vera, Mentha arvensis and Ocimum sanctum were explored for endophytic actinomycetes diversity, plant growth promoting and antimicrobial activity. Endophytic actinomycetes were most commonly recovered from roots (70% of all isolates) followed by stems (17.5%) and leaves (12.5%), respectively. Single genus Streptomyces ranked first (60% of all isolates) followed by Micromonospora (25%), Actinopolyspora (7.5%), and Saccharopolyspora (7.5%). The highest numbers of endophytic actinomycetes were isolated from Ocimum sanctum (45%). Out of 22 isolates tested, 12 showed the ability to solubilize phosphate in the range of 5.4-16.5 mg/100 ml, while 16 isolates produced indole-3 acetic acid (IAA) ranging between 8.3-38.8 µg/ml. Nine isolates produced the amount of hydroxamate- type of siderophore ranging between 5.9-64.9 µg/ml and only four isolates were able to produce catechol-type of siderophore in the range of 11.2-23.1 µg/ml. Of the nine, interestingly, eight endophytic actinomycetes (88.9%) showed a significant antagonistic activity against one or more phytopathogenic fungi indicating their possible role as plant biocontrol agents. An extended infection of root tissues of Ocimum sanctum by Saccharopolyspora O-9 was observed using transmission electron microscope (TEM). 

Key words: Endophytic actinomycetes, antifungal activity, indole-3-acetic acid, medicinal plants, phytopathogenic fungi, siderophores.