根癌农杆菌（学名：Agrobacterium tumefaciens），农杆菌属，是一种存在土壤中杆状的革兰氏阴性菌 (Smith et al., 1907)，可导致140多种双子叶植物产生冠瘤.

Agrobacterium tumefaciens (updated scientific name Rhizobium radiobacter, synonym Agrobacterium radiobacter) is the causal agent of crown gall disease (the formation of tumours) in over 140 species of eudicots. It is a rod-shaped, Gram-negative soil bacterium. Symptoms are caused by the insertion of a small segment of DNA (known as the T-DNA, for 'transfer DNA'), from a plasmid, into the plant cell, which is incorporated at a semi-random location into the plant genome.