Fungicidal Activities of Methanolic Plant Extracts on Mycelia Growth of Fusarium oxysporum Associated With Sweet Orange (Citrus sinensis (Linnaeus) Osbeck)

Abstract

Post-harvest degradation is a major challenge of sweet orange (Citrus sinensis) production worldwide. The deterioration in the fruit quality from bloom to harvesting stage is greatly caused by microbial infection. The present study was therefore, carried out to identify and control in vitro, the deteriorating fungus responsible for fruit rot disease of sweet orange during storage. Samples of spoilt orange fruits were collected fortnightly from the market. Fusarium oxysporum was isolated and identified from infected sweet orange fruits. Methanoic extracts of Vernonia amygdalina, Hyptis suaveolens and Zingiber officinale were used as biological agents against fungal isolates. Phytochemicals analysis revealed the presence of flavonoids, alkaloid, steroid, saponin, tannin, phenol and terpene in these extracts. All the extracts inhibited mycelia growth of F. oxysporum. The potency of all the extracts increased with increasing concentration in the order, 25mg/ml < 50mg/ml < 75mg/ml. In vitro studies of these extracts revealed that the highest percentage growth inhibition (89.6%, 72.6% and 48.9%) in Z. officinale, V. amygdalina and H. suaveolens respectively were obtained  at 75mg/ml.  Also, Z. officinale gave the highest percentage growth inhibition of F. oxysporum pathogen  (75.1%, 87.0% and 89.6%  at various concentrations of 25,50 and 75mg/ml respectively) compared to control, followed by V. amygdalina (22.8%, 36.2% and 72.6%) while extracts of H. suaveolens caused relatively lower inhibitory effect on mycelia growth. These results revealed that the leaf extract from Z. officinale was the best of the extracts studied, as an antifungal agent of the postharvest rot pathogen of sweet orange fruit. Therefore, it is recommended that further studies should be carried out to test the in vivo efficacy of these plant extracts in store houses since these plants are readily available, the extracts are easy to prepare and not expensive compared to conventional fungicides.