The only correct statement is (4) Host plant genes play an important role in influencing transformation frequencies.

Option-wise analysis

(1) T-DNA transfer occurs from left border to right border – Incorrect
T-DNA is delimited by left (LB) and right (RB) border repeats, but transfer is initiated at the right border and proceeds toward the left border. Saying “from left to right” reverses the actual direction.​

(2) The gfp reporter gene can never be used for selection of transgenic plants – Incorrect
GFP and enhanced GFP variants are widely used as visual selectable/ screenable markers, allowing direct identification of fluorescent transformants without antibiotics. Therefore it is wrong to say GFP can “never” be used for selection.​

(3) Transformation frequencies will decrease on over‑expression of virulence genes – Generally incorrect
Many studies show that constitutive or higher expression of certain vir genes, such as virG or virD1/D2, can increase transformation efficiency, not decrease it. Very extreme overexpression might be detrimental, but as a general statement this is not correct.​

(4) Host plant genes play an important role in influencing transformation frequencies – Correct
Agrobacterium-mediated transformation depends heavily on plant factors involved in perception, defense, nuclear import, chromatin remodeling and DNA repair; mutations or overexpression of specific host genes (e.g., VIP1, VIP2, genes controlling meristem activity, DNA repair components) significantly alter transformation frequency. Hence host plant genotype and gene activity are key determinants of how efficiently a species or cultivar can be transformed.​

SEO‑oriented introduction (for article use)

Agrobacterium-mediated plant transformation is controlled not only by bacterial virulence factors but also by host plant genes, which govern susceptibility, T-DNA trafficking and integration, and overall transformation frequency. While T-DNA actually moves from the right to the left border, GFP can be used as a visual selection marker, and overexpression of some vir genes often enhances transformation, it is the influence of host plant genes that is consistently recognized as a correct statement in this multiple-choice question.