2.6. In-Vitro Assay of Plant Extracts against Pyricularia grisea
The fungitoxic effect of different plant extracts in-vitro were studied by inoculating PDA with 14-day-old pure
cultures of P. grisea [19]. Small mycelia segments (5 mm) were made using a sterile 5 mm diameter cork borer.
Each mycelial segment was then transferred singly onto the centre of each PDAPE Petri dishes at 1%, 5%, 10%
and 25% concentrations (v/v). The PDA Petri dishes without plant extracts were used as negative control and
PDA mixed with Apron Star® 42 WS contained 20% Thiamethoxam, 20% Metalaxyl-M and 2% Difenoconazole,
trade names Cruiser and Actara were included as positive controls. The experiments were laid out in a split plot
in a randomized complete block design with rice blast as main plot and plant extracts as a subplots with 50
treatments (12 plant extracts with 4 different concentrations and 2 controls: Apron Star® 42 WS and distilled
water). The inoculated Petri dishes were sealed with masking tape and incubated at 28˚C - 32˚C for five days in
alternating cycles of 12 hours light and darkness to induce growth of P. grisea. Radial growth of P. grisea was
then recorded after every three days for up to 21 days after inoculation by measuring mycelial growth diameters
along two diagonal lines previously drawn on the reverse side of each Petri dish to serve as a reference, using a
30 cm plastic ruler to determine the effectiveness of plant extracts. Calculation of percent inhibition of fungal
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growth was estimated based on Ogbeborand Adekunle [26] methods as follows: Percentage mycelial inhibition
= 100 (Mycelial growth diameter in control—Mycelial growth diameter in treatment)/Mycelial growth diameter
in control. The treatments that showed high percentage control in in-vitro by reducing P. grisea growth were selected and the experiments were repeated twice.