As usual, the answer is depends... some varieties have been bred to have more cold tolerance than others, wet cold vs dry cold makes a difference, etc. Also are you just concerned about the plant surviving or the fruit? If temps get below 50, it is likely to drop blossoms instead of setting more fruit. But it won't drop fruit that are already set. If the plants are protected and have been getting used to the cold gradually (a sudden cold snap when it's been warm is worse than gradually cooling temps), the plant should survive temps down into the upper 30's. I think the best protection is clear plastic over hoops or some kind of frame (so the plastic doesn't touch the plants), but row cover works too.