Genetic basis of control of Rhynchosporium secalis infection 4 and symptom expression in barley 5

10 Abstract The genetic basis of several different 11 components of resistance to Rhynchosporium secalis 12 in barley was investigated in a mapping population 13 derived from a cross between winter and spring 14 barley types. Both the severity of visual disease 15 symptoms and amount of R. secalis DNA in leaf 16 tissues were assessed in field trials in Scotland in the 17 2007/2008 and 2008/2009 growing seasons. Relative 18 expression of symptoms was defined as the residual 19 values from a linear regression of amount of R. secalis 20 DNA against visual plot disease score at GS 50. 21 Amount of R. secalis DNA and visual disease score 22 were highly correlated traits and identified nearly 23 identical QTL. The genetic control of relative 24 expression of symptoms was less clear. However, a 25 QTL on chromosome 7H was identified as having a 26 significant effect on the expression of visual disease 27 symptoms relative to overall amount of R. secalis 28 colonisation.