Medicinal plants for suppressing soil-borne plant diseases

Abstract

The possibility of controlling common scab of potato with Geranium pratense, root of which show an antimicrobial activity, was investigated. Application of dried root powder or powdered methanol extract from G. pratense roots to the soil tended to decrease the area with scab lesions on tubers sampled from the soil with a high inoculum level. Mixed-cropping of potato with G. pratense also decreased the incidence of the disease in the soil with a low inoculum level. We isolated an antimicrobial substance against the pathogen, Streptomyces scabies, from a methanol extract of G. pratense roots and identified it as geraniin by MS and 1H- and 13C-NMR. Geraniin accounted for as much as 15% of the root dry weight based on quantitative analysis by HPLC, and its antimicrobial activity corresponded to 1.25% of that of streptomycin based on the paper disk method. These findings suggest that G. pratense could be used as organic amendment or companion crop for the control of common scab of potato.