Lower than the compensation of the other spouse. § 219(c)(2)(B):
(B) the amount of compensation (if any) includible in such individual’s gross income for the taxable year is less than the compensation includible in the gross income of such individual’s spouse for the taxable year.
If your wife has $200 reported in box 1 of a W-2 and no other compensation, she can contribute at least $200 to an IRA. If you have less than $200 of compensation, you, not your wife, is the one with the lower compensation and would be able to contribute from your wife's $200 whatever amount of that $200 your wife does not use to support an IRA contribution. If you have more than $200 of compensation, your wife could use your compensation to support an IRA contribution of more than $200 (provided you do not use all of your compensation to support your own IRA contribution).
