Efficacy of the Non-Pathogenic Agrobacterium Strains K84 and K1026 against Crown Gall in Tunisia

Abstract

The non-pathogenic Agrobacterium radiobacter strain K84 and its genetically modified (GEM) strain K1026 were tested for their effectiveness against local Tunisian strains and two reference strains (C58 and B6) of the crown gall bacterium Agrobacterium tumefaciens. Tests in planta were carried out on herbaceous plants (tomato and tagetes) and on some sensitive rootstocks (bitter almond, peach almond hybrid GF677 and quince BA29). In vitro tests showed that both K84 and K1026 were effective and that the difference between these strains was not statistically significant. On tomato and tagetes, strain K84 was effective against all crown gall isolates with the exception of the A. tumefaciens reference strain B6. GEM strain K1026 was very effective against all isolates from Tunisia and against the reference strains. Both antagonistic strains significantly reduced the percentage of galled plants as well as the number of galls per plant. Under field conditions, both antagonists controlled crown gall effectively. Best results were obtained on the bitter almond-tree rootstock. Antagonist effectiveness was less evident on quince BA29 and peach almond GF677 rootstocks. The genetically modified strain K1026 is of interest in controlling crown gall disease in Tunisia.