A Thesis Submitted in Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Life Sciences of the Nelson Mandela African Institution of Science and Technology
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.