Antimicrobial property of Distemonanthus, Zanthoxylum, Morinda, and Moringa species on potato (Solanum tuberosum) postharvest bacterial tuber rot

Abstract

Potato (Solanum tuberosum) is a very important crop globally with a high value for human nutrition. Its productivity in Nigeria is  hindered by bacterial rot disease, which is commonly managed with synthetic pesticides despite its detriment to humans and the  environment. This study investigated the antimicrobial potential of four botanicals (Distemonanthus benthamianus, Zanthoxylum  zanthoxyloides (Zz), Morinda lucida, and Moringa oleifera (Mo) in vitro against four postharvest potato tuber rot-causing bacteria. One  hundred rotted tubers were collected from four markets viz: Bodija, Sabo, and Apata, Ibadan (Oyo State), and Garki (Abuja). Three concentrations (500, 1000, and 1500mg/ml) of methanol extract of each of the botanicals were evaluated against the rot bacteria. The  antimicrobial property of the most effective explant in vitro was evaluated in vivo against the rot bacteria. Four bacteria (Erwinia  carotovora (Ec), Clavibacter species, Bacillus subtillis, and Pseudomonas syringe pv. Phaseolicola) were isolated and identified to be  responsible for the potato rot. The severity of rot induced by the bacteria ranged between 39.77 and 46.34%. Distemonanthus  benthamianus extract (at 500- 1500mg/ml) significantly (p<0.05) produced the highest antibacterial property in vitro against the four  bacterial isolates, followed by Zz whereas the other explants showed no bacteriotoxic property except Mo against Ec only at 1500mg/ml.  Distemonanthus benthamianus, next to Erythromycin (antibiotics), produced higher inhibition zones (5.0±0-9.3±3.1mm) on all the  bacteria isolates than all other explants and significantly inhibited rot development in potato in vivo. The high antimicrobial potential of  D. benthamianus against postharvest bacterial tuber rot of potato suggests a safe biopesticide for postharvest potato disease  management