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Grass species were grown in plots, as pure stands or mixed with wheat, after a sequence of wheat crops in which take-all ( Gaeumannomyces graminis var. tritici) had developed. Annual brome grasses maintained take-all inoculum in the soil as well as wheat (grown as a continuous sequence), and much better than cultivated species with a perennial habit. Take-all developed more in wheat grown after Anisantha sterilis (barren brome) or Bromus secalinus (rye brome), with or without wheat, than in continuous grass-free wheat in the same year, where take-all decline was apparently occurring. It was equally or more severe, however, in wheat grown after Lolium perenne (rye-grass) or Festuca arundinacea (tall fescue), despite these species having left the least inoculum in the soil. It was most severe in plots where these two grasses had been grown as mixtures with wheat. It is postulated that the presence of these grasses inhibited the development of take-all-suppressive microbiota that had developed in the grass-free wheat crops. The effects of the grasses appeared to be temporary, as amounts of take-all in a second subsequent winter wheat test crop were similar after all treatments. These results have important implications for take-all risk in wheat and, perhaps, other cereal crops grown after grass weed-infested cereals or after set-aside or similar 1-year covers containing weeds or sown grasses, especially in combination with cereal volunteers. They also indicate that grasses might be used experimentally in wheat crop sequences for investigating the mechanisms of suppression of, and conduciveness to, take-all. [ABSTRACT FROM AUTHOR]

In a controlled environment (15/10°C) (day/night) container experiment on winter wheat (cv. Avalon), eyespot incidence (percentage of plants affected) and number of leaf sheaths penetrated after 6 weeks increased with inoculum concentration (102−106 conidia mL−1) ofOculimacula yallundae(OY) orOculimacula acuformis(OA), but there was no difference between the two species. In an outdoor container experiment, seedlings inoculated with OY 2 weeks after sowing had a greater incidence of eyespot than those inoculated with OA, when assessed 7 weeks after inoculation. Seedlings inoculated with OA at 10 or 20 weeks after sowing developed more severe eyespot by maturity than those inoculated with OY. In an experiment at 15/10°C with seedlings inoculated with OY + OA 2 weeks after sowing, more leaf sheaths were penetrated by OY (3·0 per plant) than OA (2·3 per plant) 6 weeks after inoculation. Field experiments with winter wheat consistently showed leaf sheath production, leaf sheath death, and number of leaf sheaths infected or penetrated by OA or OY were related linearly to thermal time (°C days) after sowing. Depending on cultivar, season and sample, a new leaf sheath was produced in 116–216°C days; a leaf sheath died in 221–350°C days; and infection of a new leaf sheath occurred in 129–389°C days. The mean number of living leaf sheaths infected differed between samples, cultivars and seasons for both OY and OA. Regression analysis of the 1985/86 data suggested that OY progressed more rapidly than OA through the leaf sheaths, and that both the pathogens progressed more rapidly than the rate of leaf sheath death, but more slowly than the rate at which leaf sheaths were produced. It also suggested that OA progressed more slowly than the rate at which leaf sheaths died in 1987/88, but OY did not. [ABSTRACT FROM AUTHOR]

Effects of regular treatments with the fungicides carbendazim and prochloraz applied to whole plots divided into subplots with different initial population mixtures of carbendazim-sensitive or carbendazim-resistant Tapesia yallundae or T. acuformis were studied in successive crops of winter wheat from 1984/85 to 1999/2000. In unsprayed and carbendazim-sprayed whole plots, a stable coexistence of about 50% each of T. yallundae and T. acuformis developed within five seasons, but in whole plots sprayed with prochloraz or prochloraz plus carbendazim, the proportion of T. acuformis increased to > 80%. A discrete time difference equation model was derived from knowledge of the biology of eyespot and competition theory to describe the population changes. The model was fitted to the data from treatments where coexistence occurred [subplots in unsprayed (1985–92) and carbendazim-sprayed (1985–89) whole plots], using nonlinear least squares regression. The optimized value of the resource overlap coefficient was small, suggesting niche differences between the two species. Populations were nearly 100% carbendazim-resistant in carbendazim-sprayed whole plots by July 1985 (one season) and in whole plots sprayed with prochloraz plus carbendazim by July 1986 (two seasons). In prochloraz-sprayed whole plots, the proportion of carbendazim-resistant isolates decreased more rapidly than in unsprayed whole plots in the 1980s, but by July 1992 a shift in populations in unsprayed and prochloraz-sprayed whole plots towards predominantly carbendazim-resistant strains had occurred. [ABSTRACT FROM AUTHOR]

An experiment started in spring 1979 tested the effects of different treatments to perennial ryegrass, established as pure stands or undersown in spring wheat, on the severity of septoria diseases on the grass and in a following crop of winter wheat, sown in autumn 1980. Other plots were fallowed in 1979 and 1980 before sowing to winter wheat, also in autumn 1980. Septoria tritici was most severe in winter wheat after fallow and least severe in wheat that had been direct-drilIed after ryegrass. These effects were attributed to differences in amounts of available nitrogen, and consequent differences in crop growth, rather than to any differences in primary inoculum. Symptoms attributed to S. nodorum on the ryegrass were more common where the grass had been established under spring wheat than where it had been sown as a pure stand. They also tended to be more common where ryegrass had been inoculated with spores of S. nodorum than where it had been sprayed with captafol. Similar effects on symptoms attributed to Septoria spp. (mostly S. tritici) on the wheat were apparent in July. The results support the conclusion that the greater severity of septoria diseases that often occurs on wheat after grass than after non-graminaceous breaks, is probably due in part to survival of the pathogens on grass and, in some circumstances, on debris remaining from a previous wheat crop. However, other factors are also likely to be involved. [ABSTRACT FROM AUTHOR]

In field experiments with winter wheat in Hertfordshire, seed infection with Septoria nodorum and the incorporation of infected straw into seedbeds were often correlated with reduced seedling establishment and increased seedling infection. Artificially infected straw was a less effective source of inoculum than naturally infected straw, which gave rise to the most severe leaf symptoms in one season when heavy rain favoured the development of an epidemic. In an experiment where a severe epidemic did not develop, organomercury seed treatment was the most important factor increasing seedling emergence and grain yield, also apparently leading to decreased Septoria infection of the flag leaf sheath. Spores from lesions which developed after plots were sprayed with a suspension of pycnidiospores of S. nodorum were not always morphologically typical of that species. [ABSTRACT FROM AUTHOR]