The effect of endophytic bacterium Enterobacter sp. isolated from basil on growth stimulation and control of tomato seedling bacterial canker disease

Bacterial canker of tomato caused by Clavibacter michiganensis subsp. michiganensis, Cmm, is one of the limiting diseases of tomato cultivation. Because of the chemical control problems, biological control methods are used to control this disease in the recent investigation. Basil (Ocimum basilicum L.) is an annual herbaceous plant from the Lamiaceae family, and various endophytic bacteria have been reported from this plant. Also, many studies have shown that endophytic bacteria have the ability to stimulate growth and control many plant diseases. Therefore, in recent research, it was tried for the first time to test endophytic bacteria isolated from basil plant against tomato bacterial canker.

In this research, 16 endophytic bacteria isolated from basil. They were tested for their antibacterial properties against tomato bacterial canker in laboratory conditions using chloroform vapor method. Also, the effect of these bacteria on increasing total phenol and growth factors, including fresh weight, dry weight and seedling height were investigated. In the next step, the best bacteria in terms of growth factors were used to control bacterial canker, on tomato seedlings, under greenhouse conditions. Next, the physiological changes related to total phenol, catalase and peroxidase were investigated. Finally, molecular identification was done by PCR using universal 16SrRNA gene-specific primers ,27f and 1492r, DNA sequencing and BlastN in NCBI Genebank.

None of the endophytic bacteria showed antibacterial properties against bacterial canker under laboratory conditions. ReA1 isolate showed the highest growth stimulation and total phenol increasing compared to other bacteria therefore, it was used against tomato bacterial canker and reduced the disease by nearly fifty percent. Also, the growth factors were increased compared to the infected and healthy controls after inoculation with ReA1. In addition, the amount of peroxidase, catalase and total phenol increased in plants treated with ReA1 isolate compared to the control. So that the amount of total phenol, peroxidase and catalase, respectively from the highest to the lowest, was related to the application of ReA1 and Cmm, ReA1 alone, Cmm alone and the control without bacteria. ReA1 isolate was detected as Enterobacter sp. by DNA sequencing results.

Recent research showed that Enterobacter sp. strain ReA1 isolated from a plant belonging to the Lamiaceae family (basil) was tested on tomato plants from the Solanaceae family, which was able to reduce tomato bacterial canker disease without direct antibacterial effect. The main possible effects of this bacterium are related to the phenomenon of induced resistance in the plant and the increase of defensive and antimicrobial compounds in the plant. This control effect on the different plant species belonging to Solanaceae, the possibility that this bacterium could be used as a biocontrol agent on many kinds of plants and against a wide range of diseases. It also stimulated the growth of the plant, which makes possible the simultaneous use of this bacterium as a fertilizer and biocontrol agent.