The separate and combined effects of barley yellow dwarf virus and take-all fungus (Gaeumannomyces graminis var. tritici) on the growth and yield of wheat

The single and combined effects of barley yellow dwarf virus (BYDV) and the take-all fungus, Gaeumannomyces graminis var. tritici (Ggt) on wheat, cv. Condor, were determined in field and glasshouse trials. Before and after tillering, aphids with BYDV were fed on plants growing in soil with different proportions of dead and live inoculum of Ggt. Each pathogen reduced grain yield and increased the number of deadheads. In a number of cases, especially in the field, the combined effect of BYDV and Ggt was greater than a simple additive effect of either pathogen alone. Grain yield per plot and grain weight per head were each reduced, whilst the incidence of deadheads was increased, particularly following infection with BYDV after tillering. A possible mechanism to explain the interaction of the two pathogens is discussed.