DECREASED CAPACITY OF TAKE-ALL FUNGUS TO OXIDIZE MANGANOUS IONS IS ASSOCIATED WITH TAKE-ALL DECLINE

The phenomenon of decline of take-all [a disease on wheat caused by Ga eumannomyces graminis var. tritici (Ggt)] is poorly understood. In thi s study, the capacity of Ggt strains, isolated from wheat roots grown in the field plots exhibiting various levels of take-all decline, to o xidize Mn2+ ions was tested. Growth of all Ggt isolates on agar was in creased by an addition of up to 100 mg.L-1 Mn2+ and was decreased by g reater concentrations. The Ggt isolates oxidized Mn2+ to Mn3+ and/or M n4+. There was a negative relationship (r=-0.69) between the Mn2+ oxid ation 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.