Efficacy of Fungicides and Plant Extracts against Fusarium oxysporum f. sp. batatas Incitant of Fusarium Wilt of Sweet Potato (Ipomeae batatas L.)

In vitro experiments were conducted to evaluate the effect of some fungicides and some plant extracts against Fusarium oxysporum f. sp. batatas (Fob). The experiments were conducted in the Plant Pathology Laboratory of the Department of Crop Protection, Bayero University Kano. Three fungicides (Mancozeb, Hexaconazole and Metalaxyl + coprous oxide) and sterile distilled water as control were arranged in a completely randomized design. The treatments were repeated five times. Mancozeb as the most promising fungicide against the fungus was used as a check, other treatments include; 25% aqueous neem leaf extract, 50% aqueous neem leaf extract, 25% aqueous garlic bulb extract, 50% aqueous garlic bulb extract, 25% aqueous callotropis leaf extract, 50% callotropis leaf extract and control. The treatments were arranged in a completely randomized design and repeated thrice. Data on radial growth and percent growth inhibition of the fungus were recorded and subjected to analysis of variance using GenStat 17th Edition. Among the fungicides tested against Fob, Mancozeb significantly had the least radial growth (13mm) and inhibited growth of the pathogen by 71.1% compared to the other fungicides. Bioassay on plant extracts revealed least radial growth of the fungus (36.7mm) and highest percent growth inhibition (43.5%) when 50% aqueous neem leaf extract was used. This differed significantly with the use of 25% aqueous neem leaf extract which caused 39.3 mm radial growth of the fungus and inhibited growth by 38.5%. This was followed by 50% and 25% callotropis leaf extract, respectively with lower fungal growth and higher percent growth inhibition compared to aqueous garlic bulb extract at the different concentrations, exhibiting similar effect on the growth of the fungus and its inhibition. Aqueous neem leaf extract (50%) contained higher phytochemicals than the other botanical extracts at the different concentrations. These phytochemicals are responsible for better suppression of Fob. Application of 50% aqueous neem leaf extract could be further evaluated as potential bio-pesticide to supplement the use of fungicide against Fusarium wilt of sweet potato.