Utilization of Nitrogen by Ophiobolus graminis

Abstract

THE survival period of the fungus Ophiobolus graminis, causing the 'take-all' disease of wheat, in infected wheat straw buried in the soil is increased by the application of nitrogen in such forms as calcium nitrate, ammonium nitrate, ammonium sulphate, ammonium carbonate, and dried blood1,2. I have recently suggested2 that these sources of nitrogen are directly utilized by O. graminis, which is thereby enabled to decompose more of the carbohydrate material of the straw, and hence to prolong its existence. Fellows has claimed3, however, that O. graminis is unable to utilize nitrates or ammonium salts, and can assimilate nitrogen only in certain organic forms. His claim is invalidated by the experiments of Padwick4, using a very similar synthetic medium to that employed by Fellows, but with the addition of a growth-promoting factor. In the presence of a growth-promoting extract obtained from carrots, growth of O. graminis was increased four-fold by the addition of 0·15 per cent of nitrogen as sodium nitrate to the medium.