Antifungal activity of selected pesticidal plants against phaeoisariopsis personata and phytochemical analysis, central Tanzania

Abstract

The late leaf spot (LLS) caused by Phaeoisariopsis personata L., is the most serious fungal disease of groundnut worldwide. The LLS causes considerable damage to groundnuts leading to leaf defoliation and consequently reduces pod yields by more than 50%. Research was carried out to evaluate the antifungal activity of Parthenium hysterophorus, Azadirachta indica and Jatropha curcas against P. personata and analyse the possible compounds exhibiting antifungal properties at the Tanzania Plant Health and Pesticide Authority (TPHPA)-Arusha, Tanzania. The field survey results indicated that the LLS disease of groundnuts prevailed in the central zone of Tanzania with overall disease incidences between (54.65-84.70%) and severities (4.9-7.00). This finding provides alerts to the global plant health regulators suggesting a proper management skill. The evaluation the selected pesticidal plants revealed that all the plant extracts showed antifungal activities against P. personata under in vitro and in vivo (screen-house) conditions. The methanolic leaf extracts of all tested plants offered higher antifungal activities with >75% inhibition of mycelial growth of P. personata compared to control (0% inhibition). Similarly, the application of methanolic leaf extracts of selected plant extracts on groundnuts seedlings grown in pots under screen-house condition at the highest concentration (0.5 mg/ml) exhibited antifungal potentials against P. personata by reducing the disease incidence being 14.30% and severity of 2.22 compared to chloroform (17.44%, 4.07) and ethyl acetate (20.56%, 4.26) leaf extracts. Subsequently groundnut seed yield/plant was greater 45.09 g for crop treated with the most effective plant extract (A. indica at 0.5 mg/ml) as compared to untreated 7.76 g. Furthermore, the phytochemical analysis of the selected pesticidal plants by GC-MS identified important phytocompounds with antifungal properties from the tested plant extracts mainly; hexadecanoic acid ethyl ester, methyl salicylate, phytol, phenol 2,4-bis (1,1-dimethylethyl), n-hexadecanoic acid, hexadecanoic acid methyl ester and hexadecane. The presence of these antifungal phytocompounds in the selected plants is associated with their effect on the P. personata. A further study under field condition is recommended on the tested plants (P. hysterophorus, A. indica and J. curcas) on possibility of developing bio fungicides for the management of groundnut LLS disease in Tanzania.