Effects of number of winter wheat crops grown successively on fungal communities on wheat roots

Roots were taken from winter wheat plants sampled in early summer in each of three years. In each year, first, third and continuous (ninth or subsequent) wheat crops were grown on the same site so that epidemics of take-all disease (causal fungus: Gaeumannomyces graminis var. tritici) were in, respectively, pre-build-up, build-up and decline stages. Fungi on pieces from the upper parts of the roots, serially washed 20 times, were identified by growing onto agar media and allowing them to sporulate. Approximately 107 species of 50 genera were identified, including some that were previously unrecorded in Britain or on wheat. There was usually a trend (with statistically significant differences only in one year) for more fungal isolations per root piece with increasing number of successive wheat crops. Changes in populations of several fungi were associated with number of wheat crops in one or more years but only Fusarium culmorum increased with increased number of crops in all years. While individual fungi or the fungal community may be involved in take-all suppression or enhancement, then were no clear relationships between either total numbers of fungal species or abundance of individual species and the stage of the take-all epidemic. (C) 1999 Elsevier Science B.V. All rights reserved.