Title: Pseudomonas from phosphate mine and tomato rhizosphere: Induced systemic resistance against clavibacter michiganensis subsp. Michiganensis (Bacterial canker)
Bacterial canker caused by the bacterium Clavibacter michiganensis subsp. michiganensis (Cmm) is one of the most feared diseases of solanaceous crops in the greenhouse as well as in the field, especially tomato and bell pepper. In Morocco, Agadir, is well known for intensive production of tomatoes. This production contributes to the national economy and represents 50% of Moroccan exports. In greenhouses, bacterial canker is destructive of tomato cultivated in this region but also worldwide. The chemical control is ineffective and has deleterious effects on the environment. Thus, biological control is considered an alternative, sustainable and eco-friendly strategy, especially by using antagonistic bacterial strains and strains able to induce resistance as indirect mean to overcome Cmm negative effects.In order to provide biocontrol agents against the bacterial canker of tomato caused by Clavibacter michiganensis subsp. michiganensis, we isolated fluorescent Pseudomonas bacteria from two biotopes Moroccan phosphate mine, and tomato rhizosphere soil. The aim of this work was to assess the potential of the isolated Pseudomonads as tools for plant growth promotion (PGPR effects) of tomato and biocontrol agents against of Cmm either by direct antagonism or indirect induced systemic resistance (ISR). The following seven isolatesPst4c, Pst94s1, Pst 96k, Pst124, Pst130 Bg22c and Bg23c were selected for their solubilization of insoluble Phosphate forms, potash (K), and insoluble zinc form (Zn). Antagonistic activities against Cmm by selected isolates were performed according to BOUIZGARNE et al.(2006) in addition to biofilm inhibition. The taxonomic characterization of these bacteria was performed by determination of phenotypic (API 20NE tests and other physiological tests) and genotypic traits (molecular 16S rDNA sequencing). Selected isolates were able to grow on root exudates and showed effective tomato root colonization. In greenhouse, experiments were conducted with on tomato seedlings in Agadir (Morocco) with the seven selected strains in order to induce systemic resistance mechanisms in tomato against Cmm. Results showed that Pseudomonas isolates solubilized the insoluble forms of P, K and Zn. In addition, they produce IAA in vitro. Tomato seedling treatment by the seven isolates resulted in enhanced soluble phenolic compounds. Indeed, in control seedlings, a production of 36,8 mg.g-1 was recorded whereas treatment with Pseudomonas Pst4c, Bg22c, Bg23c and Pst130 resulted in enhanced phenolic compounds in tomato roots up to 216 mg.g-1. Enhancement up to 5,4 folds was recorded in plants treated by Pst4c. These results are encouraging to consider the most efficient inducers as tools for biofertilzation as PGPR and controlling bacteria canker by systemic resistance.