Biomass production and gas exchange of winter wheat as affected by flag leaf inoculations with Septoria nodorum

summary Inoculation of flan leaves of winter wheat with Septoria nodorum (Berk.) Berk was more effective in reducing final grain weight when inoculation was at anthesis than when it was at flag leaf emergence, either during or following leaf expansion; grain number was not significantly affected by the timing of inoculation. The greatest senescence was observed with late inoculations with correspondingly lower flag leaf weight at grain maturity. It is suggested that flag leaves become more susceptible to S. nodorum with increasing time after emergence. Inoculation did not result in any significant redistribution of assimilate from stems to ears as it did not affect stem weight. The reduction in photosynthesis at high irradiance was proportional to infection‐induced senescence. Change in the total resistance to the diffusive flow of carbon dioxide was controlled by the mesophyll resistance, i.e. that remaining following subtraction of boundary layer and stomatal components.