The spread of Glomus fasciculatum through roots of Trifolium subterraneum and Lolium rigidum

The lateral spread in a steamed lateritic podsol of Glomus fasciculatum (Thaxter sensu Gerd.) Gerd. and Trappe from localized inoculum was examined in two pasture species: Trifolium subterraneum L. (subterranean clover) and Lolium rigidum Gaud. (Wimmera ryegrass). Mycorrhizal infection was estimated 21, 28, 38 and 59 d after sowing at points 2, 4, 6, 8, 10, 14, 20 and 26 cm from the inoculum. 

The proportion of root length infected by G. fasciculatum at increasing distances from the inoculum could be best described by a Gompertz curve in both plant species at all harvests. Thus the curve had an upper plateau of the maximum percentage infection close to the inoculum, an exponential decline in the spread of G. fasciculatum and a lower plateau of infection. It is suggested that the pattern of spread of G. fasciculatum through roots of subterranean clover and ryegrass is related to changes in the amount of inoculum with distance from the point of inoculation, as well as over time. 

The rate of spread of the infection front was not constant. Thus it may not be appropriate to calculate mean rates of spread of mycorrhizal fungi over long time periods.