Effects of ammonium and nitrate nutrition or take‐all disease of wheat in pots

Abstract

SUMMARYPlant debris, naturaiiy infested with the take‐all fungus (Ophiobolus graminis), was washed from soil and added to a leached sandy loam, deficient in nitrate nitrogen (NO3‐N) and magnesium. Nutrient solutions containing potassium and phosphorus, with and without magnesium, were added to the amended soil unsupplemented, or with either NO3‐N, ammonium nitrogen (NH4+‐N), or both. Nitrification of NH4+‐N was inhibited by 2–chloro‐6–(trichloromethy1)‐pyridine (N‐Serve). After 38 days at 19°C, fewer plants had take‐all with N (75 or 100 mg/kg soil) than without and root systems were most discoloured and had most diseased axes when nutrients were not added. Plants given NH4+‐N developed less take‐all when magnesium was present. A comparison of forms of N in the presence of added magnesium showed that take‐all was least with a mixture of both forms of N, intermediate with NO3‐N alone and worst with NH4+‐N alone. The most extensive lesions on individual root axes occurred on plants given NH4+‐N. It is suggested that take‐all will be least when the amounts and ratio of NH4+‐N and NO3‐N are optimum for the growth of the host.