[OldRestorer]

Cyanoacrylate and baking soda is a great but is more for painted surfaces. It does bond really well though. you could use this for the lower half of the recommendation below.

The best thing is to first use thinned wood glue to fill the crack about 1/2 way. This will prevent further stress cracking of the underwood. Let it dry for 24 hours and then if you can, sand the surface and gather the sawdust. Mix one part glue to one part sawdust and fill the crack. I usually do this and then put more sawdust on top pressing lightly and leave it.
Next day, sand it flat and stain to best match, let dry and tone the way you like.

If you can at all close the gap with clamping that will help too. 

If you are going to top it off with tinted wood putty make sure it is Minwax professional putty. No cracking, no shrinking and no crumbling.

Oh and make sure it is not humid when you do this.

Pictures may change my personal recommendation.

Steve or Russel may have a better idea

Kirk