EVALUATION OF ANTIBACTERIAL ACTIVITY OF SOME PLANT EXTRACTS AGAINST PECTOBACTERIUM CAROTOVORA SUBSP. CAROTOVORA

Abstract

Bacterial soft rot of sweet potatoes tubers, induced by Pectobacterium spp. (previously called Erwinia spp.), results in substantial reduction in quality and thereby reduces its market value and consequently low income for potato growers. Out of 45 bacterial isolates from infected sweet potato tubers collected from Gombe, Billiri and Kashere town, Gombe State Nigeria, thirty-eight (38) were pathogenic on potato tubers. The six isolates selected as test organisms revealed the same results in morphological and biochemical tests hence, identified as Pectobacterium carotovora subsp. carotovora (previously called Erwinia carotovora subsp. carotovora). Antibacterial potential of aqueous extracts of Allium sativum L., Zingiber officinale, Capsicum annum var. chinense, Capsicum annum var. Cayenne and Allium cepa were examined at 25, 50 and 75% concentrations against the growth and survival of Pectobacterium isolates. The treatments consisted of five plant extracts with 3 concentrations each. Streptomycin (0.2%) served as positive control while sterile distilled water served as negative control. The experiment was laid out in a completely randomized design (CRD) with three replicates. All the plant extracts were most effective at 75% concentration. Isolates Pcc-1 and Pcc-2 were most susceptible at 75% concentration. The extracts exhibited their highest potency at 72 hours after incubation (HAI). All the extracts significantly reduced the growth of potato soft rot organisms. It was also found out that the higher the concentration and incubation period, the greater the effect of the extracts on the test isolates.