ABSTRACT

A field trial was conducted at the Research Farms of Michael Okpara University of Agriculture, Umudike, South Eastern Nigeria to evaluate the potential effect of Zingiber officinales rhizomes, Carica papaya seeds and Moringa oleifera leaves on the control of bacterial leaf spot of sweet potato (Ipomoea batatas Lam) in a Randomized Complete Block Design (RCBD) experiment. This study was carried out to isolate, identify and prevent the microorganisms responsible for the leaf spot disease of sweet potato. The experimental design was Randomized Complete Block Design (RCBD) with three replicates, three treatment extracts and three varieties. The sweet potato vines (Umuspo 1, Umuspo 2 and Umuspo 3) were sourced from National Root Crops Research Institute Umudike. Five replicate samples of diseased leaves of sweet potato were obtained randomly from the field. Nutrient agar was used for the isolation and identification of bacteria and fungi respectively. The bacterial populations were estimated after 24hours of incubation while the fungi were observed after 5 days of incubation. The organisms were identified using standard morphological and biochemical tests. The genera of the bacteria isolated and their percentage occurrence include: Pseudomonas (100%), Erwinia (80%), Staphylococcus (40%), Bacillus (20%). Results obtained from the field experiment showed that all the plant parts assessed reduced disease incidence and severity drastically at 5% probability when compared with the untreated control. In this study, extracts of C. papaya seed had the best performance in terms of vine length, number of leaves, stem diameter and number of branches in all the sweet potato varieties, particularly in the result of the combined analysis of extracts used in all the varieties at 4 weeks after treatment. Vine length (144.23cm), number of leaves (270.11), stem diameter (3.54cm) are compared favourably with extracts of Z. officinales on tuber yield at harvest (3.14kg) and M. oleifera in reducing incidence of bacterial leaf spot (16.66%), as well as severity of spots (2.87) (P ≤ 0.05), from the results obtained it means that the extracts of Z. officinales, C. papaya and Moringa oleifera have the potentials to serve as ecofriendly and cheap biopesticides in the management of bacterial leaf spot disease of sweet potato.