Two phytotoxic azaphilone derivatives from Chaetomium globosum, a fungal endophyte isolated from Amaranthus viridis leaves.

A fungal endophyte isolated from the leaves of the allelopathic plant Amaranthus viridis of the family Amaranthaceae was identified as Chaetomium globosum through molecular means using internal transcribed spacer (ITS) region of rDNA gene. This is the first report of the isolation of C. globosum from Amaranthaceae. Chromatographic separation of the EtOAc extract of the fungal fermentation in potato dextrose broth yielded two known chlorine-containing azaphilone derivatives, chaetomugilin D (1) and chaetomugilin J (2). Compounds 1 and 2 were found to show phytotoxic activity in the lettuce (Lactuca sativa) seed germination bioassay. The IC50 values of 1 and 2 for root growth inhibition were 24.2 and 22.6 ppm, respectively, while IC50 values for shoot growth inhibition were 27.8 and 21.9 ppm, respectively. Phytotoxic activities of the chaetomugilin group of compounds have been reported for the first time, although their antifungal, antimicrobial and cytotoxic activities are known.

Allelopathic activity studies of Mikania scandens.

Preliminary investigation of a number of plant extracts for allelopathic activity using seed germination inhibition bioassay showed a promising activity of the water extract of the aerial parts of Mikania scandens. Activity-guided fractionation of the M. scandens extract led to the isolation of the highly allelopathic active compound mikanolide, with minimum inhibitory concentration of 0.083 µM mL(-1). As M. scandens is a highly abundant invasive plant in Sri Lanka and other South Asian countries, this plant could be developed as an environment friendly natural herbicide, either in crude form as shredded plant material or as pure mikanolide, which is the major constituent (∼0.02%) in the plant.