Rate of decline of Gaeumannomyces graminis var. tritici inoculum and decomposition of residues from wheat cultivars

The rate of inoculum decline was determined for Gaeumannomyces graminis var. tritici (Ggt), a fungus causing take-all in cereals which survives saprophytically on crop debris during the intercrop period. Crop residues and Ggt inoculum in soil cores containing residues of six wheat cultivars from two fields were assessed in three experiments at intervals up to 7 months after harvest. At that time, for all cultivars, approximately three quarters of the original residue plant mass remained from crop residues where the stems were on the soil surface. The quantity of Ggt DNA per plant declined on average by 95% after 7 months, with most of the remaining inoculum residing in the stems and crown. Viable inoculum remaining in the plant residues was sufficient to infect newly planted wheat seedlings. It appears that after harvesting wheat exhibiting take-all, a period of more than 7 months is required to ensure inoculum in residues has declined sufficiently in soil to prevent reinfection of Ggt-susceptible cereal crops.