No abstract

No abstract

No abstract

No abstract

A range of metal ions and the oxoanion W04" were toxic to zoospores of Phytophthora nicotianae parasitica in the order: Ag+ >> Cu++ > W04?-> Ni+ > Co++ > Zn'. The LDS0 for Ag', 0.11 ,UM (11.4 ppb), compared with 1.84 ,UM (1 17 ppb) for Cu". Silver was similarly toxic to a range of pathogens including Pythium aphanidermatum, Thielaviopsis basicola and Fusarium oxysporum f.spp. Most zoospores of Phytophthora spp. were killed by Ag+ in the range 46 -460 nM (5 -50 ppb), bursting at the higher concentrations. A small sub-population of most propagules exhibited greater tolerance to silver than the whole. In 0.93 ,UM (100 ppb) Ag+ 1.4% of P. nicotianae parasitica zoospores survived but were all killed at 500 ppb. A population of P. cryptogea (1.9%) surviving 0.47 ,UM (50 ppb) were killed at 0.93 PM (100 ppb). Zoospore cysts and germlings showed the same sensitivity to silver. Oospores were mostly killed over the range 0.23 -0.93 ,UM (25 -100 ppb) Ag', some surviving up to the lethal concentration of 9.26 ,UM (1000 ppb). Mycelium of P. cryptogea was generally less sensitive, with some growth occurring at 9.26 PM (100 ppb).Zoosporangiogenesis was unaffected over the range 0.47 -4.65 ,UM (50 -500 ppb). Toxicity increased with increased pH over the range 5.0 -6.5.Ionic silver was lost from solution during a microscope slide bioassay by binding to the glass surface. In the presence of chloride ions, colloidal AgCl formed which was equally toxic to P. cryptogea. Silver and AgCl were further lost from solution by colloidal agglomeration -Ostwald ripeningand by AgCl adsorption to glass. Silver, < 90 nM (10 ppb) Ag' as AgN03 and particles of silver chloride were both strongly attractive to zoospores of P. cryptogea. Spores burst or failed to germinate on entering lethal concentrations. The results are discussed in the context of the use of silver salts to control Phytophthora rootrot pathogens and the importance of ion availability in in oitro toxicity assays. Horsfall J C. 1956. Principles of firtigicidal action. Waltham. Massachusetts: Chronica Botanica Co. Huot T. Bouchardat G. 1899. Sur I'emploi des sels mercuriques et du nitrate d'argent en viticulture. Jain $1 li. 1977. Hundbook of e x y m e irihibitors. UK: Wiley. Kennedy B W. Erwin D C. 1961. Some factors influencing sporangium formation of a Phytophthora species isolated from lucerne in certain salt solutions. Transactions of the British Mycological Society Kennedy R, Pegs G F. 1990. Phytophthora cryptogen root rot of tomato in rockwool nutrient culture. 11. Effect of root zone temperature on infection sporulation and symptom development. Annuls of Applied Biology 117537-55 1. Khew K L. Zentmyer G A. 1973. Chemotactic response of zoospores of five species of Phvtophtliora. Krause G A. 1929. Neice Wege sirr Wussersterilisierirrig. Munich: J F Bergmann. Menyonga J M, Tsao P H. 1966. Production of zoospore suspensions of Pliyoplitlioru pnrasiticir. Miller L P, McCallan S E A. 1957. Toxic action of metal ions to fungus spores. Agricitltitral and Food Miller L P, McCallan S ...