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Septoria tritici blotch (STB) is a major disease of wheat, reaching epidemic proportions in many parts of the world. In several studies, taller, later-maturing cultivars have had lower disease levels. This study was undertaken to investigate the genetic associations of natural field infection by STB with disease-escape mechanisms related to heading date and height components, mainly leaf spacing, in a population where height and maturity are not controlled by major genes. In field trials of a single seed-descent population of a cross between two nonsemi-dwarf cultivars, Apollo (with strong partial resistance to STB) and Thésée (susceptible), conducted over 3 years, there was a negative correlation between STB and heading date. There was no correlation between STB and distance from stem base to leaf 2; and there was an unexpected positive correlation between STB and distance from flag leaf to leaf 2, which contradicted the so-called ‘ladder effect’ postulated in STB epidemiology. No effect was detected of the presence of the 1BL−1RS translocation on STB levels. The largest single contributor to variation in STB levels was genetic variation between the progeny lines, and the narrow-sense heritability was 42%. These results suggest that breeders can select for STB resistance alongside optimal stature within the range of height which is adaptive in a particular environment. [ABSTRACT FROM AUTHOR]

More than 20000 wheat plants, derived from callus culture of immature wheat embryos were assessed for reaction to the take-all fungus (Gaeumannomyces graminis var. tritici) using a test-tube assay. Lines with less root and shoot blackening and more remaining green tissue than parental lines were identified in the SC3 generation. However these lines had more root and shoot blackening and less remaining green tissue in subsequent generations. The changes in reaction to the fungus may therefore have been epigenetic. The potential of this tissue culture derived material for breeding take-all resistant wheats is discussed. [ABSTRACT FROM AUTHOR]

Linear models were used to investigates the effects and interactions of treatments for the control of disease in multifactorial experiments on the dynamics of the take-all disease of wheat. Analyses were based on repeated measures of disease on second successive winter wheat crops in three successive seasons. The treatments were date of sowing, presence or absence of triadimenol-containing seed treatment, autumn nitrogen and chloride applications, timing of early spring nitrogen and total spring nitrogen applications. The effects of treatments were investigated on linear and quadratic trends of disease increase and on the integral amount of disease over time. Different disease variables were used to express disease relative to the total and diseased plant populations. The effects of treatments on absolute and relative numbers of diseased roots per plant were also analysed. During three seasons when disease was never severe, the effects of the treatments were shown to be variable. Late sowing consistently reduced disease during the early stages of epidemic (in the winter months). The effect of late sowing in reducing disease, however, persisted through to the end of the growing season in only one of the 3 years of the study. Autumn nitrogen application and Baytan seed treatment (containing triadimenol) also reduced disease in some seasons. The presence of an effect for either was dependent on sowing date and was most evident on the proportion of diseased roots relative to the diseased plant rather than the total plant population. [ABSTRACT FROM AUTHOR]