Crown gall is a bacterial disease first discovered in New Zealand in 1900.  It has been found to seriously affect susceptible woody plants worldwide, causing a great financial loss in commercial nurseries where up to 80% of stock have been reported diseased.

 

THE DISEASE

Crown gall is a plant “cancer” caused by the soil inhabiting bacterium Agrobacterium tumefaciens.  The pathogen is responsible for nursery and orchard losses among stone fruit trees, grapes, apples, pears, nut trees, caneberries, clematis, hops, kiwifruit, persimmons, roses and many ornamental annuals, trees and shrubs.  It causes significant commercial losses worldwide.  Infected plants are usually weakened and unproductive due to their damaged root system and may die.  Galled nursery stocks are non-saleable.

              
The pathogenic Agrobacterium bacteria are present in most soils and can be spread by water, cultivation, insects, and by tools used in propagation.  Wounds on a susceptible plant may be colonized and infected by the pathogen, which then transfers T-DNA from its Ti plasmid into a plant cell.  This initiates formation of tumors or galls, which may become visible within three to four weeks.  Galls may reach a diameter of 3 inches or more and usually occur below soil level.  They can sometimes be found on stems and on pruning wounds.

Pathogenic bacteria may escape from the galls and infect other plants.  There are numerous strains of Agrobacterium, many of which are non-pathogenic and do not cause galls, although they may co-exist in galls with the pathogenic strain.  Also, small galls may be confused with wound callus or with insect damage.  Galls develop very slowly or not at all at temperatures below 10º C and above 35º C.

 

SYMPTOMS

The galls usually form on the roots or stems and have a rough, convoluted surface.  They  vary in size, often growing many times larger than the diameter of the roots or stem on which they are outgrowths.

Crown Gall