Wikipedia is not very complimentary about Rubberwood.
http://en.wikipedia.org/wiki/Rubberwood
The table has been made badly - no allowance has been made for natural shrinkage - the top of the table is fixed too rigidly to the base - the crack has happened because the rigid fixing resisted natural shrinkage across the grain.
Fixings like these allow for this movement by having elongated slots...
http://www.barncrest.co.uk/images/large/Angled_bracket.jpg
A single screw in one of the long slots, not too tight, lets things move a bit.
You should look to the way the top is fixed to the base.
You might leave it for things to get worse - remove the top and glue up the split under pressure from cramps - fill the crack with a proprietary filler product.
If your table has fixings like the one in the picture the single screw in the long slot may have been done up too tightly, preventing movement. Only one of the long slots should have a screw in it - the one that runs across the grain of the table top.
Good luck...
Peccavi
July 2009