Decreased capacity of take‐all fungus to oxidize manganous ions is associated with take‐all decline

Abstract

The phenomenon of decline of take‐all [a disease on wheat caused by Gaeumannomyces graminis var. tritici (Ggt)] is poorly understood. In this study, the capacity of Ggt strains, isolated from wheat roots grown in the field plots exhibiting various levels of take‐all decline, to oxidize Mn²⁺ ions was tested. Growth of all Ggt isolates on agar was increased by an addition of up to 100 mg'L^‐1 Mn²⁺ and was decreased by greater concentrations. The Ggt isolates oxidized Mn²⁺ to Mn³⁺ and/or Mn⁴⁺. There was a negative relationship (r=‐0.69) between the Mn²⁺ oxidation ranking and the extent of take‐all decline. A decreased capacity to oxidize Mn²⁺ causes a decrease in Ggt virulence and may result in decline in take‐all. This mechanism of take‐all decline is expected to act additively with other factors.