Inoculum of the take-all fungus in rotations of wheat and pasture: Relationships to disease and yield of wheat

A field trial was undertaken between 1984 and 1986 to examine the behaviour of Gaeumannomyces graminis var. tritici inoculum through time and as affected by wheat and pasture rotations at a site in the Western Australian wheatbelt. Soil bioassays were carried out to determine infectivity and propagule numbers of the fungus ; incidence and severity of take-all were measured in wheat crops on the site.

Pasture supported inoculum levels as high as wheat, and in 1984 propagule numbers were greater in a field which had been in pasture the previous two years than in one in wheat the previous year. There were some positive relationships between propagule number and both incidence and severity of take-all, but few between infectivity of G. graminis and disease in the crop. However, more severe take-all was associated with higher propagule numbers, and less severe take-all with lower propagule numbers, when plots were sampled at the end of summer in 1984 and 1985. In 1984 both infectivity and propagule numbers of the take-all fungus were correlated with air and soil temperatures and with soil moisture.