I used X ray for seed quality and nothing happened (any type of mutation even physiological effects). Seeds germinated very well. In the lab where I worked everybody does and we never had problem because the radiation is very low. We worked with soybeans, beans, tomato, pepper, albergine, tabebuia, maize, etc.

Mutation will happen if you irradiate with gamma rays.

There is no study related to the effect of X-rays on plant seeds, but to the best of my knowledge, it desn't affect germination or other seed quality parameters, unless the seed is no longer exposed to the beam (less than 1hour). This also may depend on the scan settings (kV, mA).

Dear Alsayad,

X-rays are ionising radiations and can cause mutation. Therefore in the early days X-rays were used in mutation breeding and X-rays do induce mutations in seeds if high dose of hard X-rays are used. You can find hundreds of cultivars developed by X-radiation mutagenesis if you search the data base below:

http://mvgs.iaea.org/Search.aspx

Now gamma-rays and chemical mutagens like EMS are popular for mutation breeding. Dormant seeds are less prone to mutation as the cells are not dividing and chromosomes are coiled. Once you soak the seeds the cells start to divide and X-rays at lower doses can induce mutations and physiological damage as well. This at doses more than 50 Gy I would say but this depends on the species. For many cultivated species the optimal doses of X-rays for mutation induction are available in literature.

Now, about quality testing with X-rays. Again, I can say yes you can use X-rays for quality testing without damaging the cells, For this type of work they use soft X-rays. However, it is difficult to decide on the quality of a seed by X-ray radiography of a dry seed. Moistened seeds would give better results but still the doses used are low and the seed will germinate.

These different applications are possible because X-rays have a very high range of energy levels. Most X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz (3×1016 Hz to 3×1019 Hz) and energies in the range 100 eV to 100 keV. X-ray wavelengths are shorter than those of UV rays and longer than those of gamma rays. 

This is why we have multiple uses for X-rays: at airports for security check of luggage because the amount of absorbed energy depends on the density of the substances, so guns or wires can be easily  seen in the image. Similarly chest X-ray shows the bones and any pathology because bones are more dense than the soft tissue and we can capture the image. Now we have very sensitive instruments such as in medical imaging (CT Scan, fluoroscopy etc.).

I have attached 3 papers, one from one of the pioneers of mutation - Stadler, and two about seed testing with X-rays.