Effect of garlic (Allium sativum) extract on fungal spoilage and preservation of onion (Allium cepa) bulbs

Abstract

The study investigated the occurrence and virulence of some fungal pathogens causing rot of onions. Antifungal potentials of garlic extract against these fungi and its effects on shelf life were also studied. Ten percent aqueous garlic extract was used in fungal growth inhibition of artificially inoculated onion bulbs as well as used in fungal growth inhibition of artificially inoculated onion bulbs as well as whole bulb preservation experiments and sterile distilled water served as control in both experiments. Results showed that Aspergillus niger, A. niger, Penicillium and Rhizopus sp occurred in rotting onion bulbs and Aspergillus niger was found to be the most virulent, having a mean rot diameter of 1.94mm, followed by A. flavus (0.42mm), Rhizopus sp (0.15 mm), while Penicillium sp was the least virulent in causing rot in the bulbs, with 0.12 mm. Onion bulbs inoculated with blank agar disc showed no rot symptoms. There were significant differences between the control and treated samples at p<0.05.Garlic extract was effective in inhibiting mycelial growth of all fungal pathogens in the pretreated onion bulbs (Aspergillus niger (2.84 mm),Aspergillus flavus (1.61 mm), Penicillium (0.48 mm) and Rhizopus spp ( 0.54 mm)and were significantly lower than control at p<0.05. Whole onion bulbs (treated and control) remained healthy without any sign of rot until 4 weeks after storage however,mean rot reduction of 58% was observed in onion bulbs treated with 10% garlic extract at 9 weeks after storage. The untreated (control) samples developed rot symptoms after four weeks of storage. Garlic extract could be used to elongate shelf life of onions due to its antifungal and preservative potentials.