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 o f three years. In each year, first, third and continuous (ninth or subseque nt) wheat crops were grown on the same site so that epidemics of take-all d isease (causal fungus: Gaeumannomyces graminis var. tritici) were in, respe ctively, pre-build-up, build-up and decline stages. Fungi on pieces from th e upper parts of the roots, serially washed 20 times, were identified by gr owing onto agar media and allowing them to sporulate. Approximately 107 spe cies of 50 genera were identified, including some that were previously unre corded in Britain or on wheat. There was usually a trend (with statisticall y significant differences only in one year) for more fungal isolations per root piece with increasing number of successive wheat crops. Changes in pop ulations of several fungi were associated with number of wheat crops in one or more years but only Fusarium culmorum increased with increased number o f crops in all years. While individual fungi or the fungal community may be involved in take-all suppression or enhancement, then were no clear relati onships between either total numbers of fungal species or abundance of indi vidual species and the stage of the take-all epidemic. (C) 1999 Elsevier Sc ience B.V. All rights reserved.