Can single conducting straight wire can radiate EM wave or we need two bend conducting wire similar to dipole antenna?
Monopole antennas are single wire antennas and are basically half a dipole antenna. They rely on a ground to most effectively radiate (like a dipole) but can still radiate without a ground. Think also about transistor radios tuned to FM - they use a telescopic antenna that is a monopole with a less than ideal earth plane.

If a wire is passing current there is a magnetic field distributed around it. If there is an associated driving voltage (to produce the current) then there will also be a distributed electric field surrounding it.

Electric and magnetic fields are the two components that combine to make a radiating EM field so a wire can radiate. It may not radiate effectively at a lot of frequencies but can do so very effectively if the wavelength of the signal is proportioned to the dimensions of the wire.