In nature, Agrobacterium tumefaciens mediated infection of plant cells leads to P. crown gall disease in plants Q. hairy root disease in plants R. transfer of T-DNA into the plant chromosome S. transfer of Ri-plasmid into the plant cell

Agrobacterium tumefaciens causes crown gall disease (P) through transfer of T-DNA (tumor-DNA) from its Ti (tumor-inducing) plasmid into the plant chromosome (R). The T-DNA becomes integrated into the plant genome and causes tumor formation. Hairy root disease (Q) and Ri-plasmid transfer (S) are caused by Agrobacterium rhizogenes, not A. tumefaciens. Therefore, only P and R are correct for A. tumefaciens, making option B the right answer. Option A incorrectly selects S (which relates to A. rhizogenes), option C incorrectly includes Q and S (both A. rhizogenes features), and option D is incomplete.