Crown Gall Disease

Crown gall is a unique, tumor-inducing bacterial plant disease caused by the soil-borne bacterium Agrobacterium tumefaciens (family Rhizobiaceae). It is highly famous in molecular biology for its natural ability to 'genetically engineer' host plants by physically transferring a piece of its own DNA (the Ti plasmid) into plant cell nuclei. This genetic hijack forces the host cells to divide uncontrollably and produce specialized amino acids (opines) that feed the bacteria. Crown gall has an exceptionally broad host range, affecting over 600 species of woody and herbaceous plants globally, severely weakening their structural and vascular health.

Identifying Crown Gall is highly direct due to the distinctive, gnarled growths it produces. The primary symptom is the presence of rough, woody swellings or tumors (galls) forming on roots and stems near the soil line (the crown), though they can appear on upper branches and graft junctions. Galls start as small, soft, cream-colored swellings that rapidly expand, harden, and turn dark brown or black with a highly cracked, rough surface. As these galls enlarge, they disrupt the flow of water and nutrients, causing stunting, yellowing, and branch dieback. The identification photo displays a large, gnarled black tumor at the base of a rose stem, showing the typical cracked crown gall growth.

The life cycle of Agrobacterium tumefaciens is highly persistent in the soil. The bacteria can survive saprophytically in soil for several years without a host. They enter host plants through physical wounds caused by pruning, grafting, weeding, insect feeding, or winter cracking. Once inside, they attach to cell walls, transfer their T-DNA, and trigger rapid tumor growth. Spread is highly active in moist, alkaline soils and during warm summer months.

Managing Crown Gall is difficult because there are no effective chemical curatives to eliminate the bacteria once inside the vascular system. Control relies on strict prevention. For organic protection, apply the non-pathogenic competitor bacterium *Agrobacterium radiobacter* (strain K84) as a biological root dip on new transplants to block infection sites. Ensure all pruning shears and grafting knives are thoroughly sterilized in 70% isopropyl alcohol between cuts. Avoid making low physical wounds on trunks during weeding. Immediately dig up and destroy severely infected plants. For further advice, consult our Plant Disease Identifier Hub, or view profiles on Bacterial Canker, Fire Blight, and Root Rot.