Anti-Alternaria solani Activity of Onion (Allium cepa), Ginger (Zingiber officinale) and Garlic (Allium sativum) In vitro

Plant pathogens cause serious losses in quantity and quality of agricultural products. Use of fungicides is gradually becoming unpopular due to their negative effects on ecosystems, human and animal health, and due to resistance by pathogens to the fungicides. In vitro studies were carried out in order to determine the effects of three plant extracts; onion (Allium cepa), ginger (Zingiber officinale) and garlic (Allium sativum) on the control of Alternaria solani. The experiment was laid in a Completely Randomized Design (CRD) with a 3x3 factorial arrangement plus one control. The first factor was plant extract, with three levels (garlic, onion and ginger) the second was plant extract concentration, with three levels (50%, 75% and 100%). The experiment was carried out in the laboratory at Midlands State University, Zimbabwe, in October 2014. Data on mycelia growth diameter, mycelia inhibition percent and spore germination percent was collected. Results showed that the plant extracts had strong anti-A. solani activity and their effect increased with increase in their concentration. Ginger and garlic had significantly stronger effect on reducing mycelia growth, reducing spore germination and causing high inhibition percentage of A. solani. Ginger was the most effective in controlling A. solani across all concentrations. It can be concluded that the plant extracts (onion, ginger and garlic) can be used as natural fungicides to control pathogenic fungi. It is recommended that further research be done on the plant extracts so as to identify the active compounds which are in the extracts as these are responsible for this fungicidal activity and to carry out more studies to test antifungal activity of these studied plant extracts on other different fungi, at different concentration levels. Further experiments may also be done in the field to determine effects of these plant extracts in controlling diseases caused by A. solani.