بررسی امکان مهار زیستی بیماری لکه‌برگی باکتریایی گوجه‌فرنگی در آزمایشگاه و گلخانه

Tomato leaf spot incited by Pseudomonas syringae pv. syringae is a major economic disease in tomato fields and greenhouses. In this study, possibility of disease biological control was investigated by some strains of beneficial bacteria including Pseudomonas fluorescens and Bacillus subtilis, in vitro and in vivo. In summer 2016, pathogenic and benefit bacteria were isolated from tomato in West Azarbaijan fields. Identification of studied strains was performed using morphological, biochemical and physiological experiments. Molecular identification of beneficial bacteria was performed using universal primers of 16S rRNA gene (fD1/rP2). After amplifying 1500-bp fragment and sequencing, the sequences compared with those sequences in GenBank. Genetic identification of pathogenic strains carried out using universal primers of 16S rRNA and specific primers of Tom1/Tom2. The studied strain amplified 242 bp fragment. To primary screening, 100 µL of pathogenic bacteria suspension (1×107 CFUml-1) was spread on nutrient agar (NA) medium. Biological control capability of antagonistic bacteria was evaluated via secondary metabolites diffusion in agar procedure. For this, wells were created at a distance of 2 centimeters on the inoculated medium and 100 μl of beneficial bacteria suspension (1×107 CFUml-1) was poured in them. After two days, the diameter of the inhibitory zone was measured. The results indicated that diameter of inhibition zone was between 0 and 15 millimeters. Four P. fluorescens strains and eight B. subtilis strains were selected for greenhouse studies. Beneficial bacteria were attached to tomato seeds cv. Early urbana Y using 1% methyl cellulose. Inoculation of tomato seedling was done at the 4-5 leaf stage. Carborundum powder used for scratching the leaf surfaces, and then pathogenic bacteria suspension of 1×105 CFUml-1 sprayed on seedling foliage. After 21 days, the effect of antagonistic bacteria on disease reduction was evaluated compared to control. The surface area of spots related to the total leaf area was considered as a disease index. Based on the results, strains of Bs5, Bs27 and Pf7 showed the most effects on decreasing the leaf chlorotic spot created by pathogenic bacteria. These strains reduced 65, 40 and 27 percentage of the disease compared to the infected control, respectively. Pf95-1 and Bs32-M with a 5% disease reduction showed the least biocontrol effects. Additional studies on these strains are going.