The classification of isolates of Gaeumannomyces graminis from wheat, rye and oats using restriction fragment length polymorphisms in families of repeated DNA sequences

Abstract

Isolates of the take‐all fungus, Gaeumannomyces graminis var. avenae, which affects oats, wheat and other grasses, and of G.g. var. tritici, which preferentially affects wheat, rye and barley, contain a high proportion of repeated sequences. Total DNA from 57 fungal isolates collected from many locations and different cereal hosts, and scored for virulence on wheat, rye and oats, revealed many restriction fragment length polymorphisms. These RFLPs were observed either by staining the DNA directly, by hybridization to radioactively labelled total fungal DNA, or by hybridization with labelled wheat ribosomal DNA. With only a few exceptions, the isolates with the same preferred cereal hosts showed more similar patterns of restriction fragments than isolates that had different pathogenicity properties on cereal hosts, irrespective of the geographical origins of the isolates. This was even the case for R isolates of G.g. var. tritici that were virulent on wheat and rye compared with N isolates that were virulent only on wheat. Isolates were identified by hybridizing DNA from infected root samples with 32P‐labelled total fungal DNA. The restriction fragment polymorphisms involving families of repeated sequence can therefore be used as a predictive assay for host preference of an isolate, and have probably arisen by host selection of fungal lineages. The variation between isolates in different pathogenicity groups suggests that there is little gene flow between isolates that can infect different hosts, even though they can coexist in the same field.

Genetic evidence for differentiation of Gaeumannomyces graminis var. tritici into two major groups

“…The results demonstrated for the first time at the level of a large worldwide collection the existence of two major genetically different groups of Ggt that cause disease on wheat. There was a strong correspondence between G 1 (Lebreton et al , 2004), B (Freeman et al , 2005), R (O’Dell et al , 1992) and T2 isolates (Bateman et al , 1992) and between G 2 , A, N and T1. However, more N/R and T1/T2 isolates are required to confirm that these groups were consistently correlated with G 1 /G 2 and A/B types.…”

“…However, these group pairs were described with different molecular tools, at different geographical scales and on variable population sizes. Consequently, they were called, variously: T1/T2 (Bateman et al , 1992), N/R (O’Dell et al , 1992; Bryan et al , 1995), A1/A2 (Augustin et al , 1999), G 1 /G 2 (Lebreton et al , 2004) and A/B (Freeman et al , 2005). The group pairs differ in their RFLP profiles for T1/T2 (Ward & Gray, 1992) and N/R (O’Dell et al , 1992), in their nuclear rDNA sequences for N/R (Bryan et al , 1995) and A/B (Freeman et al , 2005), in their RAPD profiles for A1/A2 and N/R (Bryan et al , 1999; Augustin et al , 1999) and in their RAPD and AFLP patterns for G 1 /G 2 (Lebreton et al , 2004).…”

“…Consequently, they were called, variously: T1/T2 (Bateman et al , 1992), N/R (O’Dell et al , 1992; Bryan et al , 1995), A1/A2 (Augustin et al , 1999), G 1 /G 2 (Lebreton et al , 2004) and A/B (Freeman et al , 2005). The group pairs differ in their RFLP profiles for T1/T2 (Ward & Gray, 1992) and N/R (O’Dell et al , 1992), in their nuclear rDNA sequences for N/R (Bryan et al , 1995) and A/B (Freeman et al , 2005), in their RAPD profiles for A1/A2 and N/R (Bryan et al , 1999; Augustin et al , 1999) and in their RAPD and AFLP patterns for G 1 /G 2 (Lebreton et al , 2004). Isolates from these groups were collected from the same fields (Bateman et al , 1997; Lebreton et al , 2004; Freeman et al , 2005), from the same country (Augustin et al , 1999) or from several continents (Bryan et al , 1995, 1999).…”

Cultivar preference exhibited by two sympatric and genetically distinct populations of the soybean fungal pathogen Phialophora gregata f.sp. sojae

“…Competitive bioassays have been useful in detecting host preference or relative competitiveness in other pathosystems (Simpson et al ., 2000; Zeller et al ., 2002). Host preference in previously studied pathosystems is usually towards different host species (Pearson et al ., 1987; O'Dell et al ., 1992; Simpson et al ., 2000). The present study provides an example of differential host preference toward cultivars of the same host species.…”

Linear relationship between Gaeumannomyces graminis var. tritici (Ggt) genotypic frequencies and disease severity on wheat roots in the field

“…It is a haploid homothallic fungus probably existing as a series of clonally reproducing lines (Harvey et al ., 2001). Genetic difference between isolates existing in the same cereal crop implies little sexual recombination between isolates in the field (O'Dell and Flavell, 1992). Genetic differentiation among G. graminis populations and low genetic identities between geographically closed populations imply low levels of interpopulation gene flow (Harvey et al ., 2001).…”