Mosaic virus or wilt?

[superspeck]

My squash and cucumber plants can't seem to get growing, and some sort of disease is the cause. I've attached pictures. It's my first year gardening in this home, and everything is in containers with store bought potting soil.

The cucumber plants start out growing well, but then the stem yellows and leaves near the tip are stunted. Then the larger leaves near the base start to get yellow and splotchy.

Can anyone help troubleshoot this? It doesn't LOOK like the pictures I've seen of Mosaic Virus, but it might be. Which would be a shame, because wouldn't that mean that the dirt came contaminated?