SAPROPHYTIC BEHAVIOUR OF SOME CEREAL ROOT-ROT FUNGI

In southern New South Wales the resumption of ley land for wheat growing has been accompanied by an increase in take-all (Ophiobolus graminis) and Fusarium root rot (Fusarium culmorum). No such increase has been observed in foot and root rots of wheat caused by Helminthosporium sativum and Curvularia ramosa. It is shown experimentally that these differences are related to the relative capacity of the causal fungi to persist in wheat straw buried in each of two unsterilized soils which, because of past cultural treatments, differed in their organic carbon and total nitrogen content. While the saprophytic survival of O. graminis and F. culmorum was promoted by high soil fertility that of H. sativum was markedly depressed. The survival of C. ramsa was little affected by soil fertility. F. culmorum, H. sativum and C. ramosa each remained viable under the soil conditions best suited to their survival in one-third to one-half of the test straws for 2 years but O. graminis was not recovered after the 52nd week of sampling.