Biological Control of Crown Gall Using Using Agrobacterium Strains K84 and K1026

Crown gall has been successfully controlled on a commercial scale for over 15 years by the use of Agrobacterium radiobacter strain K84. The continued success of strain K84 has been jeoparised by the possibility of transfer of the agrocin plasmid, pAgK84, to pathogenic agrobacteria, making them resistant to control. The construction of a transfer-deficient deletion mutant of pAgK84 has resulted in a strain (K1026) from which the agrocin plasmid (pAgK1026) can no longer be transferred to other agrobacteria. Strain K1026 controls crown gall as effectively as strain K84 and may be used to ensure that the danger of breakdown of biological control is minimised.