1. Gene delivery into cereal crops through bombardment has become a routine now. It should be reasonably effective. However, there is a few concerns about this method, such as it frequently delivers multicopy transgene into plant cells (compared to Agrobacterium-mediated transformation). Transgenes integrating as a multicopy concatemers at a single locus is often observed as well. This has been well documented. Too many transgene copies in the genome can cause gene silencing.

2. There are a few cereal crops using Agrobacterium-mediated genetic transformation (ex. with immature embryos) with good results. You should check it out.