Large‐scale application of biological control of crown gall in Greece1

Abstract

Crown gall disease of cultivated plants, caused by Agrobacterium tumefaciens, constitutes a serious problem for the fruit tree, rose and grapevine nurseries in Greece. All three biotypes of A. tumefaciens exist in Greece. Biotypes 1 and 2 have a wide host range being responsible for the disease on fruit trees and roses while biotype 3 isolates have a narrow host range infecting grapevine only. All Greek isolates of biotype 1 and all but 3 isolates of biotype 2 were sensitive to biological control with the antagonistic bacterium A. radiobacter strain K84, but the biotype 3 isolates were insensitive to biocontrol. Experiments on the effectiveness of the method in artificial infections of seedlings as well as in naturally infested soils showed that the method is effective and can be applied without any risk of development of forms insensitive to biocontrol. The use of a lyophilized preparation of K84 with skim milk as suspending medium is recommended. The lyophilized antagonistic bacterium retains its activity and the final concentration (106 cfu ml‐) is adequate to protect treated plants from crown gall.