The report of Braun (1951) indicated that, though the gall bacterium (Agrobacterium tumefaciens) is necessary for the initiation of the disease and transformation of normal cell, the proliferation of the altered cell is independent of of the bacteria and their immediate metabolic product.

Hence, the tumor cells are transferable and when bacteria-free fragment are implanted into a healthy host, they can develop into uncoordinated crown gall tumors.

https://doi.org/10.1111/j.1749-6632.1952.tb39985.x

Try to extract the pathogen (if)/ plant extract, and reinoculate the healthy plant to confirm the reason reason if its physiological or pathological. What is the extent of infection on single plant and population?

i found also gall on the stem and root of pepper plant i suggest that the reason may be accumulation of an active compound