Inoculum of the take-all fungus in rotations of wheat and pasture: relationships to disease and yield of wheat.
A field trial was undertaken during 1984-86 to examine the behaviour of Gaeumannomyces graminis var. tritici inoculum with time and as affected by wheat and pasture rotations at a site in the Western Australian wheat belt. 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 2 yr 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 temp. and with soil moisture.