Fungitoxic Potentials of Ocimum gratissimum L. and Zingiber offcinale (L.) Roscoe Extracts against fungi associated with postharvest rot of Carica papaya L

Abstract

The fungitoxic potentials of Ocimum gratissimum and Zingiber officinale extracts on fungi associated with rotting Carica papaya were investigated. Rotting and healthy pawpaw fruits of Carica papaya were obtained from Bodija Market, Ibadan, Nigeria. Isolation of fungi from the rotting fruits was carried out using standard procedures. Pure cultures of the isolated fungi were obtained on Acidified Potato Dextrose Agar (APDA). Leaves of Ocimum gratissimum and rhizomes of Zingiber officinale were obtained from the Botanical Garden, University of Ibadan, Nigeria.

Crude extracts (aqueous and methanol) of the plants were obtained using standard procedures. The antimicrobial potentials of the extracts on the isolated fungi in vitro at concentrations of 25%, 50%, 75% and 100% were evaluated. Their interactive effects on the pathogens were also assessed. Cultures with 0% methanol and water served as controls. All experiments were conducted in triplicates. Petri plates were incubated at room temperature for seven days. Radial and diametric growth of the fungi was measured every 24 hours using a metre rule. Data obtained were subjected to analysis using SAS (version 9.2), and means were separated using Duncan Multiple Range Test (DMRT) at p ≤ 0.05.

The isolated fungi were Colletotrichum gloeosporioides, Lasiodiplodia theobromae and Aspergillus flavus. Inhibitory effects of extracts from both plants and both solvents on the isolated pathogens were significantly better than the control. The inhibitory effect of the methanol extracts was greater than that of the aqueous extracts. The inhibitory effect of Ocimum gratissimum extract was also significantly greater than that of Zingiber officinale (p ≤ 0.05). Inhibition at all extract concentrations was significantly better than the control. However, inhibition at 100% and 75% concentrations was higher than at other concentrations. Inhibition obtained with the different treatment combinations was greater than that achieved with individual concentrations.

Generally, inhibition of Lasiodiplodia theobromae was significantly greater than that of Aspergillus flavus, which in turn was significantly greater than that of Colletotrichum gloeosporioides (p ≤ 0.05). Ocimum gratissimum and Zingiber officinale could therefore be said to possess promising fungitoxic potentials. More work is required to ascertain their efficacy under in vivo conditions.