1" x 4" tongue and groove
Wheel chairs increase the psi due to smaller surface area. You need to have more supporting members and a thicker decking material. I would go with 5 total supports (two on outside and three evenly spaced in the middle; members should be 2” wide) and go with two layers of 3/4” plywood if used inside (outside would be pt 2” board). Those would support pretty much anyone. You also should think about transitions as well as maybe non-skid strips on the deck depending on the overall placement and usage.

You don’t say if it is inside or outside nor the length nor the pitch. These are important details as well as landing considerations.

This might help:
https://www.disabled-world.com/assistivedevices/ramps/ada-specs.php