Identification and use of a wild plant with antimicrobial activity against Ralstonia solanacearum, the cause of bacterial wilt of potato

Fresh aerial tissue and roots of 14 wild plants in Okinawa prefecture were investigated for their antimicrobial activity against Ralstonia solanacearum , which causes bacterial wilt of potato. A 70% aqueous ethanol extract of fresh aerial tissue of Geranium carolinianum L. showed strong antimicrobial activity against R. solanacearum . This extract also showed antimicrobial activity against the pathogens causing common scab of potato and soil rot of sweet potato. The antimicrobial substance could be extracted with hot water, and was effective against R. solanacearum in soil. In the field test, a treatment combining incorporation of dried aerial tissue into the soil and solarization was highly effective for control of bacterial wilt of potato. These findings suggest that G. carolinianum L. could be used as a biological agent for the control of bacterial wilt of potato.     

Control of soil rot of sweet potato by the incorporation of the fresh aerial tissue of Geranium carolinianum L. into the soil

In a previous study, we found that a 70% aqueous ethanol extract of the fresh aerial tissue of Geranium carolinianum L. showed antimicrobial activity against the pathogen causing soil rot of sweet potato. As the appropriate time for cultivation of sweet potato and the growing period of G. carolinianum do not overlap in Okinawa Prefecture, Japan, the fresh aerial tissue is available in order to control soil rot of sweet potato. Thus, we examined the control effect of fresh aerial tissue against soil rot of sweet potato. The various trials (a single repetition of 20 m²) were performed in fields that had undergone 8 years of continuous cropping of sweet potato at Okinawa Prefectural Agricultural Experiment Station, Horticultural branch. After harvest, when the disease severity was evaluated by determining the necrotic area of the storage root, the incorporation of fresh aerial tissue (5000 kg 1000 m^-2) into the soil was considered to be highly effective, with a protective value of 75.4. This result shows that G. carolinianum could be used as a biological agent for the control of soil rot of sweet potato.     

THE pH DEPENDENCE OF THE SURFACE CONCENTRATIONS OF CALCIUM AND PHOSPHORUS ON HYDROXYAPATITE IN AQUEOUS solUTIONS

A radioisotope dilution technique was used to measure the surface concentrations of Ca and P on hydroxyapatite equilibrated at pH values ranging from 5.19 to 8.81. The concentrations were rarely equal to those calculated for a stoichiometric surface. In general the molar surface Ca/P increased from a value less than the stoichiometric figure of 1.67 at low pH values to a value greater than 1.67 at high pH values. The solution Ca/P showed the opposite trend with pH. The deviations of the surface concentrations of Ca and P from stoichiometric values were attributed to adsorption and desorption of the elements at the solid surface. The extent of these reactions was influenced by both surface charge and the solution concentration of Ca and P. The relevance of the pH dependence of the surface composition of hydroxyapatite to the interpretation of solubility studies on the solid is discussed.