Hairy root disease

Hairy root disease is a pathological condition induced by the soil-borne bacterium Agrobacterium rhizogenes. The pathogen infects the host plant by transferring a specific segment of its DNA into the plant genome, which triggers the proliferation of adventitious roots and disrupts the normal hormonal balance of the plant.

The disease affects a wide range of important agricultural and ornamental species. Primary hosts include apple trees (Malus domestica), various rose cultivars, and red raspberries. In hydroponic and greenhouse environments, the infection can also impact vegetables, causing significant yield losses.

The diagnostic feature of the disease is the development of a dense cluster of thin, thread-like roots at the crown or on the main root system. These structures, known as 'hairy roots', lack typical root functions and often prevent the plant from developing a healthy root system, resulting in stunted growth and chlorosis of foliage.

Transmission of Agrobacterium rhizogenes occurs primarily through contaminated soil, irrigation water, and the use of unsterilized pruning equipment. The bacterium enters the plant through microscopic wounds in the root or crown tissue caused by insect feeding, nematodes, or cultural practices like transplanting.

Management of hairy root disease relies heavily on preventive measures rather than chemical control. Critical actions include:

• obtaining certified pathogen-free nursery stock;
• sterilizing all tools using appropriate disinfectants;
• maintaining good soil hygiene and avoiding root injuries;
• removing and destroying symptomatic plants to reduce the inoculum level.