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ABSTRACT
Despite the presence of different variety of chemical fungicides, the search for new antifungal substances against plant pathogens continues because of the negative effect these fungicides has on both the plants and the environment. This study was aimed at assessing the antifungal activities of Ocimum gratissimum leaf extract and AgNP individually and their synergistic combination against selected phytopathogenic fungi. Lasiodiplodia sp, Ceratocystis paradoxaand Phoma sp used in this study were isolated from diseased plants. AgNP was synthesized using Moringa oleifera leaf extract. Antifungal activities of O. gratisssimum aqueous andethanolic extracts and AgNP individually and synergistically were performed using the food poisoning method. From the results, O. gratissimum alone demonstrated lower activities against the pathogens with radial growth inhibition ranging from 85.00±0.00mm (Ceratocystis paradoxa. 50%) to 7.00±0.18mm (Lasiodiplodia sp 25%) this was significantly different from the controls (85.00±0.00mm for Lasiodiplodia sp, 59.60±3.49mm for Ceratocystis paradoxaand 25.00±3.18mm for Phoma sp). For AgNP alone the radial growth inhibition ranging from 85.00±0.00mm (Phoma sp, 25%) to 2.60±0.26mm (Lasiodiplodia sp100%), this was significantly different from the controls. The synergistic combination of O. gratissimum leafextract and AgNP gave a result ranging from 65.84±1.51mm(Phoma sp, 100%) to 5.00±0.00mm (Lasiodiplodia sp 100%), this was significantly different from the controls. The highest percentage mycelial radial growth inhibition for Ocimum gratissimum leaf extract was 91.76% (Lasiodiplodia sp 25%) and the lowest was -206.00% (Phoma sp 50%). The highest percentage mycelial radial growth inhibition forAgNP alone was 96.94% (Lasiodiplodia sp 100%) and the lowest was -240.00% (Phoma sp 50%). The percentage mycelial radial growth inhibition for the synergistic combination of O. gratisssimum leaf extract and AgNP was 94.12 (Lasiodiplodia sp 100%) and the lowest was -123.20% for (phoma sp 75%). The results of this study reveal that O. gratisssimum aqueous andethanolic extracts and AgNP significantly reduced the mycelial radial growth of the tested pathogens (Lasiodiplodia sp and Ceratocystis paradoxa) individually and synergistically, but the inhibition is greater in the synergistic combinations. Meanwhile, the mycelial radial growth was not inhibited in Phoma sp. Further studies should however be conducted to ascertain the effectiveness of these natural fungicides in vivo.
