Results of seven years of biological control of Agrobacterium tumefaciens in Spain1

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Abstract
Biological control of Agrobacterium tumefaciens using the K84 strain of A. radiobacter has been practised in Spain since 1979. Strain K84 is produced in Sevilla by the Agricultural Research Service and is mixed with peat. This formulation is authorized for use on stone fruits and roses, since results of various trials on rootstocks of these crops have shown that K84 is effective in controlling the disease in naturally infected nursery soil, as well as in experimental tests carried out on artificially inoculated soil. Results of biological control trials have shown that K84 has some effect on A. tumefaciens strains resistant to agrocin 84. Factors other than susceptibility to agrocin 84 influence the efficacy of biological control. This was demonstrated by using a K84 agrocin non‐producer strain which proved effective against both resistant and susceptible strains. Biological control on apple or pear is not yet authorized in Spain due to a paucity of data on field trials. However, initial pot tests showed good K84 activity on these hosts, against Spanish strains of A. tumefaciens. On grapevine, most of the A. tumefaciens strains that were isolated belong to biotype 3 and are resistant to agrocin 84. Because the disease is systemic on this species the use of K84 is not authorized.

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