Potato Surface Roots Enter New Soil

A few new roots (green) have this week entered the new soil (above the red line) - two are visible on the surface. I have been careful only to wet the soil surface by lightly spraying clean water. I'm not sure what this means, other than surface roots seem to have a determining effect on new root growth and direction. Looks like the potato plant is now finished with. Might be best to discard it anyway, since there is always a danger of virus disease build-up which might affect future plantings.