4 Answers

Recently planted seedlings go into a shock, and that represents a lack of "turgor pressure", meaning they are temporarily wilted.  They will improve if shaded a bit, did you plant in the heat of the day?  Was it windy?  Were they good and wet when you planted them, or dry, and then you watered them in?  Did you plant them promptly, or did they sit out of their pot and the roots dried out?  All of these lead to this problem.  Shade them and keep them wet, they should come around.. 

Too much water probably.

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An attractive female plant might solve the problem. How old is this tomato plant?