That study is painfully flawed.
"Six trays containing the seeds of a garden cress herb were placed in a room without a WiFi router, and six trays were placed in a different room and next to two WiFi routers which, according to the girls' calculations,emitted about the same type of radiation as an ordinary cellphone, reports DR."
Did these rooms have the same sun exposure? Artificial light exposure? Temperature? Were the rooms adjacent? Were the wifi routers transmitting 2.4ghz band? 5ghz band? What's the transmit power set to? Are the electronics in the router properly shielded? Is there RF interference nearby?
If it was 2.4 and the rooms were adjacent they're getting blasted with RF, same with 5 but not as bad.
I especially enjoyed the "emitted about the same type of radiation as an ordinary cellphone". What "type" of radiation? EM, RF, or actual radiation? I'm assuming they mean RF, and if they do then yes same "type" but you've got higher EM coming off that router, and if one piece of electronic isn't shielded properly then it's not functioning properly and even more different.
I welcome further research on this, and maybe there is an effect, but this study is too flawed to draw any conclusions.
Sorry, I'm off my soap box.
Try switching your seedlings to the 5ghz band next time, it's less prone to interference