Use of Botanicals Against Citrus Canker (Xanthomonas axonopodis pv. citri) Affecting Lime (Citrus aurantifolia Swingle) in Sudan

Abstract

Aqueous extracts (2%) of three plants; roselle (Hibiscus subdariffa Linn.), cinnamon (Cinnamomum verum J. Presl.) and clove (Syzygium aromaticum Linn.) were assessed for control of citrus canker disease in lime (Citrus aurantifolia Swingle) caused by Xanthomonas axonopodis pv. citri (Xac) under in vitro and in vivo conditions. Mancozeb fungicide (1.5%) was used as a positive control. In the first experiment, the effect of these three plant extracts was investigated in vitro through inhibition zone technique. Results indicated that roselle and cinnamon extracts caused significantly less inhibitory effect (38.5% and 25%, respectively) on canker severity compared to the fungicide Mancozeb (control), but they were significantly (P ≥ 0.05) more efficacious than clove extract. Clove extract showed little or no in vitro inhibitory activity. In the second experiment conducted in a greenhouse with natural infection of Xac on lime seedlings, aqueous extracts (2%) of roselle, cinnamon and clove significantly (P ≥ 0.05) exhibited an inhibitory effect against the disease severity with a decline from 40.4 to 45.2%. Roselle extract was the most effective for control of citrus canker (45.2%) followed by cinnamon and clove which recorded only 40.4% disease control after three weeks compared to the control treatment.