Somaclonal variation are induced during tissue culture. As tissue culture is a routine practice for plant transformation (off course with exceptions) so one can say that during plant transformation somaclonal variation also occurs.  There are many reports available e.g. Agronomical and Physiochemical Characterization of Somaclonal Variants in Indica Basmati RiceS Rasheed, T Fatima, K Bashir, T Husnain, S Riazuddin- Pak. J. Biol. Sci. 6 (9), 844-848

Larkin, P.J., Scowcroft, W.R., 1981. Somaclonal variation—A novel

source of variability from cell culture for plant improvement.

Theor. Appl. Genet. 60, 197–214.

Yes! stress due to transformation can lead to soma clonal variation in the F1. This is not only due to transformation but also the stress during the regeneration process. The good part is like incase of maize if you successfully regenerate plant and get F1 seeds and plant , F2 plants are in most cases normal. See attached plus Kaeppler SM, KaepplerHF, Rhee Y, 2000. Epigenetic aspects of somaclonal variation in plants. Plant Mol Biol 43: 179–188 

Many mutations regarded as somaclonal variation appear to be caused by aberrant (aborted) T-DNA insertions. This leads to small insertion or deletions causing mutation that can't be linked to (complete) T-DNA elements.

@ Anirudha Sahu,

Except some model plants (ex. Arabidopsis), most plant genetic transformation with Agrobacterium are performed with tissue-culture methods. The sterile tissue-culturing medium environment is already encourage the occurrence of  somaclonal variation (SV) for explants such as callus, without even the infection of Agrobacterium. The infection of Agro can further stress the explants and induce more SV. However, I think it will be hard to determine which SV is due to environments and which are due to Agro infection.