The correct option is A Agrobacterium
Biofertilisers are organisms that enrich the nutrient quality of the soil. The main sources of biofertilizers are bacteria, fungi and cyanobacteria.
Rhizobium bacteria are found in the nodules on the roots of leguminous plants. They form a symbiotic association with the higher plants. These bacteria fix atmospheric nitrogen into organic forms (they convert atmospheric nitrogen into ammonia), which are used by the plants as nutrients.
Fungi are also known to form symbiotic associations with roots of higher plants called mycorrhizae. In this association, the fungal partner absorbs nutrients from the soil for the plant, and the plant partner provides food and shelter for the fungi.
Cyanobacteria are autotrophic microbes widely distributed in aquatic and terrestrial environments. Many of which can fix atmospheric nitrogen, e.g., Anabaena, Nostoc, Oscillatoria etc.
Agrobacterium tumefaciens is a pathogen of several dicot plants. It causes gall tumours in the plants.