  There is strong evidence in favor for zonal flow suppression of the
Ion-Temperature-Gradient (ITG) mode turbulence, specifically close to the
linear stability threshold. The present letter attempts to analytically
calculate the effects of zonal flow suppression of the ITG turbulence through
deriving a modified dispersion relation including the back-reaction of the
zonal flows on the ITG turbulence based on the quasilinear theory. The results
are manifested in a reduction of the linear growth rate and an increase in the
effective linear ITG threshold.
