Survival of the take-all fungus in the presence and absence of susceptible grasses

Abstract

A field trial was conducted to compare the effect of depth on inoculum of Gaeumannomyces graminis var. tritici under grasses and bare-fallow. Soil was sampled from 0-5, 5-10 and 10-15 cm depths in March, October and December 1986. Sample bioassays were carried out to determine infectivity, propagule number and to evaluate the contribution of different sized particles to the total soil-borne inoculum. A pot experiment examined the conduciveness of the respective soil samples to take-all. Grasses were effective in the carry-over of the field inoculum of the take-all fungus. In grass plots, infectivity was similar at the three sampling dates, although propagule number increased with time. In fallow plots, infectivity and propagule number declined progressively. Inoculum level fluctuated with time in both treatments, mainly in the 10-15 cm layer, and was most stable in fallow plots at 5-10 cm. Infectivity increased with increase in propagule size and the larger propagules were more infective at l2°C rather than 20°C. There was no difference between the conduciveness of soils from each layer in fallow plots, but in grass plots conduciveness increased with depth. Infectivity and propagule number of the fungus at respective depths appeared to be related to organic matter, conduciveness and fertility of the soil.