Some Consequences of Cereal Monoculture on Gaeumannomyces graminis (Sacc.) Arx & Olivier and the Take‐all Disease¹

Abstract

Studies were made of isolates of Goeumannomyces graminis (Sacc.) Arx & Olivier var. tritici J. Walker from different length crop sequences of wheat and barley following permanent grassland. Studies were done on the influence of crop ping intensity of soils, natural and steam disinfested, on disease expression from added inoculum. Efforts were also made to detect interactions between isolates and soils from the same and different cropping sequences. Investigation of variability in the pathogen related to virulence and specificity as well as to saprophytic traits.In general, mean virulence of isolates increased up to the point where approximately peak disease levels occurred in the field, and diminished subsequently. Host specificity of isolates from a monospecies system was also pronounced at this point whereas it was not evident in the first 2 crops ; it did not increase further after the 5th or 6th cereal of a single species. There was evidence of loss of competitive saprophytic ability in isolates from long sequences as against those from lst, 2nd and 3rd crops after permanent pasture. A differential sensitivity response from Gliomastix murorum (Cda.) Hughes var. felina (Marsh) Hughes was observed with isolates from 1 to a 3 year sequence compared with isolates from sequences of 4 to 8 years. Isolates from a 1st to a 3rd crop restricted colony growth of G. murorum in culture whereas those from 4th to the 8th cereal were overgrown by this fungus. Isolates from the 1st cereal after grass darkened considerably with age, those from a 2nd less so and those from a 3rd successive crop remained almost totally hyaline ; those from longer sequences darkened considerably but were very variable for this trait.The influence of soil from more intensively cropped cereal sequences, which was destroyed b steam disinfestation, was to depress disease levels from applied inoculum. This soirinhibitory effect set in between the first and 3rd cereal. 1965 66 67 68 69 70 71 72 73 74 Take-all Ructuatlons in a I 0 year barley succession.

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

“…Ggt in vitro aggressiveness was significantly higher for G 2 than for G 1 isolates (Lebreton et al ., 2004). Other studies demonstrated the association between changes in the pathogen in terms of morphological and pathogenicity characteristics and stages in Ggt epidemics (Cunningham, 1975; Bateman et al ., 1997; Chu Chou and Hornby, 1972, cited in Hornby et al. , 1998; Slope and Gutteridge, 1982, cited in Hornby et al.…”

“…Changes in the rhizosphere microbial communities have been shown to occur in soil after successive wheat cropping (Raaijmakers et al ., 1997) or different nitrogen fertilization (Sarniguet et al ., 1992) and contribute to TAD (Cook and Rovira, 1976; Sarniguet and Lucas, 1992; Raaijmakers and Weller, 1998) and soil suppressiveness to the disease (Sarniguet et al ., 1992). But changes in the characteristics of the pathogen itself (Cunningham, 1975; Slope and Gutteridge, 1982) or in Ggt population structure (Bateman et al ., 1997; Lebreton et al ., 2004) have sometimes been associated with the progress of take‐all polyetic epidemics.…”

Changes in population structure of the soilborne fungus Gaeumannomyces graminis var. tritici during continuous wheat cropping

“…The frequency of highly pathogenic isolates was high in G 2 group but there was no direct correspondence between aggressiveness and genotype. Some studies demonstrated the association between changes in the pathogens in terms of morphological and pathogenicity characteristics and stages in Ggt epidemics (Chu Chou and Hornby, 1971; Cunningham, 1975; Slope and Gutteridge, 1982; Bateman et al ., 1997). Bateman and colleagues (1997) demonstrated that perithecia were produced more abundantly on wheat roots seedlings inoculated with T 1 isolates than with T 2 isolates, which were more frequent before take‐all peaked in wheat sequences.…”

“…However, nothing is known about the dynamics of Ggt population structure under the effects of successive wheat crops and increases in populations of antagonistic microflora. One alternative or complementary hypothesis to explain TAD is that the frequency of Ggt weakly aggressive strains could increase during wheat monoculture (Tivoli et al ., 1974; Cunningham, 1975; Slope and Gutteridge, 1982). But, the epidemiological role of changes in Ggt population structure has not been demonstrated.…”

Virulence of Gaeumannomyces graminis var. tritici from fields under short‐term and long‐term wheat cultivation in the Pacific Northwest, U.S.A.

“…In contrast, a continuous supply of susceptible cereal roots might be the only chance for survival or maintenance of moderately or weakly virulent types. This could account for the observation ot Cunningham (1975) that average virulence tended to decrease slightly but detectably with prolonged culture of wheat or barley in Ireland. Nevertheless, even allowing for lOft moderately or weakly virulent isolates in our tests, the recovery of G. graminis var.…”