Hi Mohammad,
 
Terminal spikelet point:
 
I did some field work last summer on some Canadian spring wheat cultivars.
For 3 of the cultivars (early-maturing) terminal spikelet initiation (TSI)
occurred between the 4th and 5th leaves, and for the late-maturing cultivars
it occurred between the 5th and 6th, regardless of seeding date.  More so
similar results have been observed under controlled environment studies in
growth cabinets.  Until enough of such experiment has been done with
different cultivars to emphasis the synchrony between TSI and number of
leaves on the main stem, I am afraid you may have to do a similar work on
your cultivars.
 
If this seems to be of some help, and you need some more details, do not
hesitate to let me know.
 
Good luck,
 
CHARLES.