Comparisons of isolates of the take-all fungus, Gaeumannomyces graminis var. tritici, from different cereal sequences using DNA probes and non-molecular methods

A mitochondrial ribosomal DNA probe (pEG34) that distinguishes two main restriction fragment length polymorphism (RFLP) types of isolate of the take-all fungus Gaeumannomyces graminis var. tritici was used to compare isolates from different host species. RFLP analysis confirmed that one type (designated T2), unlike the other type (T1), was associated more with barley than with triticale or wheat. RFLP analysis and other methods were also used to compare isolates of the take-all fungus from wheat seedlings grown in soil from first and second wheat crops. from wheat crops grown in longer sequences, and from oat crops grown as breaks from susceptible cereals. These provided samples from different stages of disease build up and decline in the take-all epidemic. Differences in frequencies of some characteristics were found at conventional significance levels (P less than or equal to 0.05): in a cereal sequence experiment at Rothamsted, U.K., isolates containing dsRNA were less frequent in T2 isolates than T1 isolates except in second wheats; perithecia were produced more abundantly on roots of wheat seedlings inoculated with T1 isolates than with T2 isolates, regardless of their origin. A weaker association (P less than or equal to 0.1) was also found: T2 isolates were often more frequent from second wheat crops, before take-all peaked in wheat sequences, than from other wheat crops or oats break crops. Collectively, the findings add only modest support to the controversial hypothesis that changes in the population of the take-all fungus occur during repeated cropping of wheat. The limitations of traditional sampling and assessment methods in such studies are discussed. (C) 1997 Elsevier Science Ltd.