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Major Genetic Changes in Wheat with Potential to Affect Disease Tolerance

First author: School of Biosciences, University of Nottingham, Sutton Bonington, Loughborough, Leicestershire LS12 5RD, UK; second and fifth authors: ADAS High Mowthorpe, Duggleby, Malton, North Yorkshire, YO17 8BP, UK; third (deceased) and sixth authors: John Innes Centre, Colney, Norwich NR4 7UH, UK; and fourth author: Rothamsted Research, Rothamsted, Harpenden, Hertfordshire AL5 2JQ, UK

Selection through plant breeding has resulted in most elite winter wheat germplasm in the United Kingdom containing the Rht-D1b semi-dwarfing allele, the 1BL.1RS chromosome arm translocation with rye, and an allele conferring suppression of awns. Near-isogenic lines (NILs) were used to test whether these major genetic changes have had any effect on disease tolerance. The ability of the NILs to tolerate epidemics of Septoria leaf blotch or stripe rust was measured in four field experiments over two seasons. Tolerance was quantified as yield loss per unit of green canopy area lost to disease. There was a trend for the presence of the 1BL.1RS translocation to decrease tolerance; however, this was not consistent across experiments and there was no effect of semi-dwarfing. The awned NIL exhibited decreased tolerance compared with the unawned NIL. There were significant differences in tolerance between the cultivar backgrounds in which the NILs were developed. Tolerance was lower in the modern genetic background of Weston, released in 1996, than in the genetic background of Maris Hunstman, released in 1972. The data suggest that certain physiological traits were associated with the tolerance differences among the backgrounds in these experiments. Potential yield, accumulation of stem soluble carbohydrate reserves, and grain sink capacity were negatively correlated with tolerance, whereas flag leaf area was positively correlated.