Screening of indigenous weed extracts against Fusarium solani with an emphasis to soil fertility-related microbial activities

Use of synthetic chemical fungicides against soil borne plant pathogens is discouraged because of the cost, health and environmental issues. Consequently, research has been initiated to explore antifungal potential of natural products like plant extracts, but most of the investigations neglect the impact of drenching with extracts on soil biological activities, particularly those related to soil fertility. Aqueous leaf extracts of eight weeds, which are mostly reported to have antifungal potential, namely Cannabis sativa (L.), Datura alba (L.), Parthenium hysterophorus (L.), Euphorbia hirta (L.), Solanum nigrum (L.), Calotropis procera (L.), Ricinus communis (L.) and Convolvulus arvensis (L.) were evaluated at 200, 400 and 600 ppm in malt extract broth medium by using food poisoning technique, against a soil borne pathogenic fungus Fusarium solani. After 10 days of incubation, the weed extracts significantly inhibited the growth of F. solani. All the extracts, except E. hirta and C. sativa, at 400 and 600 ppm did not decrease fungus dry weight of F. solani more than that at 200 ppm. The extracts were then tested for their possible harms to soil nitrogen fixation, nitrification and phosphate solubilization. No weed extract showed lethal effects against nitrogen fixer populations in the soil. However, D. alba, S. nigrum and R. communis extracts significantly reduced soil phosphate solubilizing activity, and P. hysterophorus, S. nigrum and R. communis inhibited ammonium oxidation. The antifungal potentials of C. sativa, E. hirta, C. procera and C. arvensis were safer to soil fertility related to biological activities than rest of the weed extracts.