EFFICACY OF BOTANICAL EXTRACTS FROM GARLIC AND NEEM ON CONTROLLING POTATO SOFT ROT PATHOGENS

Abstract

Soft rot of potatoes (Solanum tuberosum L.) caused by Pectobacterium and Dickeya subspecies leads to economic losses in agriculture worldwide including Zimbabwe, where losses range from 20 – 60%. A laboratory experiment was carried out using the potato tuber maceration test to screen the effect of two botanicals extract, neem (Azadirachta indica A. Juss.) leaf and garlic (Allium sativum L.) cloves in controlling soft rot disease caused by bacterial pathogens, namely Pectobacterium carotovorum subspecies carotovorum (Pcc), Pectobacterium atrosepticum (Pa) and Dickeya dadantii (Dd). Preparations of two concentrations [(10 and 25% (w/v)] of the aqueous extracts of garlic and neem plants were used in dip and spray applications. Sterile distilled water was used as a negative control. Three tuber halves were used for each treatment. Five 10 mm filter paper discs (Whatman’s No. 1) pre-soaked in 1 x 10⁶ cfu/mL bacterial cell suspensions of Pcc, Pa and Dd respectively were placed on each tuber half and incubated for 48 h at 25^oC. After 48 h the filter paper discs were removed and the rotting zone diameter was measured. The experiment was a 3x2x2x2+1 factorial laid out in a completely randomised design, each treatment replicated three times. The two botanicals significantly inhibited the growth of two bacteria, Pa and Dd but were ineffective against Pcc. Concentration, method of application and their interactions were not significant in inhibiting the bacteria. Neem and garlic extracts can be used to control Pa and Dd infections.