Phytochemical Screening and Antifungal Efficacy of Closely Related Senna obtusifolia and Senna tora on Some Phytopathogenic Fungi

The antifungal activity of crude methanolic leaf extract of closely related Senna obtusifolia and Senna tora of family Caesalpiniaceae was evaluated by growth inhibition analysis on four phytopathogenic fungi viz. Alternaria helianthii, Pythium aphanidermatum, Fusarium oxysporum and Aspergillus niger. In spite of morphological similarities, the methanolic leaf extracts of these species show qualitative and quantitative differences in their chemical profiles establishing them as two distinct chemo-types. The methanolic extract of both the species contain two or more antifungal compounds that act synergistically, inhibiting fungal growth and reproduction. Senna obtusifolia have shown better antifungal efficacy as compared to its close relative S. tora on all the fungal phytopathogens investigated. Scanning electron microscopy observations reveal that the crude methanolic extract induced shrinkage and distortion of fungal mycelium adversely affecting the development of reproductive structures. These results can be correlated with synergistic or additive effect imposed by two or more antifungal compounds present in the crude extract. Statistical analysis support the characteristic difference in antifungal efficacy of methanolic extract of these species. This difference may be due to different permutations and combinations of antifungal compounds present in the extract of these closely related species.