The problems with converting Zadoks growth stages to DSSAT growth
stages emerge only before anthesis, as far as I can see. After
anthesis, both the Zadoks and DSSAT stages describe the various
filling stages of the kernel. Before anthesis, however, the Zadoks
stages track number of leaves and tillers visible in the field,
whereas the DSSAT stages define basically the daylengt sensitive
period.
One way to relate both scales would be (see the work of e.g.
Miglietta for this):
- final leaf number depends on the daylength at emergence and the
latitude of the location where the material was domesticated or bred;
- the rate of leaf emergence is a function of the ambient
temperature;
- the number of spikelets per spike is related to the time between
double ridge and terminal spikelet
 
This model makes some gross assumptions, but should be helpful in
converting things.
 
Good luck,
 
Anne Elings