Efficacy of three botanicals on postharvest fungal contaminants of melon (Citrullus colocynthis) kernels

Abstract

Melon (Citrullus colocynthis L.) is an important crop used mainly for soups in Nigeria. Egusi: as it is commonly called in Nigeria is contaminated by many fungal pathogens which reduce quality of seeds during storage. Use of botanicals can be a safe method to manage fungal contamination instead of chemicals which pose a threat to human health. Therefore, efficacy of Piper guineense, Xylopia aethiopica and Ocimum gratissimum on fungi in shelled Egusi seed kernels (EK) were evaluated. One market in each of six South-western Nigerian states where Egusi is sold was purposively selected in 2012 and 2013. Egusi kernels (1⁄2kg, n = 162) were purchased from selected traders for fungi isolation, identification and incidence (%) determination. Clean EK treated with botanical powder (10, 20 and 40 g kg^–1) were inoculated with Aspergillus flavus, A. niger, A. tamarii, Rhizopus sp., Penicillium aurantiogriseum, P. citrinum and Fusarium solani bi-weekly for 14-week storage period to evaluate growth reduction (%). Control was inoculated with sterile distilled water. Aspergillus flavus, A. niger, A. tamarii, Penicillium citrinum, P. aurantiogriseum, Fusarium solani and Rhizopus sp. were frequently encountered in EK. Aspergillus (32.4±1.6%) was the most predominant fungus followed by Rhizopus (21.5±2.0%) in all States. Piper guineense (40 g kg^–1), X. aethiopica (20 g kg^–1) and O. gratissimum (10 g kg^–1) powders significantly reduced aflatoxin contamination by 42.5%, 56.5% and 45.0%, respectively; fungi growths were progressively reduced by P. guineense (5.5-90.0%), X. aethiopica (6.7-100.0%) and O. gratissimum (7.4 66.7%) up to 12 weeks of storage. Egusi kernels were highly infected with postharvest fungi especially Aspergillus species. Xylopia aethiopica at 20 g kg^–1, O. gratissimum (40.0%) and P. guineense (40.0%) reduced fungi growth on Egusi considerably and therefore could be used as a safe management option to mitigate storage fungi contamination in Egusi kernels.