Biological control of bacterial canker of tomato (Lycopersicon esculentum Mill.) by use of non-native strains of plant growth-promoting rhizobacteria

Tomato bacterial canker, caused by Clavibacter michiganensis subsp. michiganensis, is a serious tomato disease causing plant death and significant economic losses to the farmers. Several measures have been adopted to minimize the bacterial canker infection, but all have a limited success. This study investigated the growth-promoting and biocontrol activities of two potential non-native strains of plant growth-promoting bacteria (Acinetobacter sp. and Alcaligenes faecalis) isolated from the rhizosphere of selected medicinal plants and characterized by 16S rRNA gene sequencing method. The antibacterial assay was conducted on 21 potential PGPR isolates, followed by a two-year trial to assess the effects of two most effective PGPR strains on growth performance and canker disease incidence of tomato plants in the green house. Data on agronomic traits, number of wilted leaves, disease incidence, disease severity and percent disease reduction of the PGPR strains were collected and analyzed. The results of the antibacterial assay showed that Alcaligenes faecalis and Acinetobacter sp. exhibited higher inhibitory effects on C. michiganensis subsp. michiganensis with zones of inhibition of 38.00 mm and 19.50 mm respectively. In the greenhouse, Alcaligenes faecalis and Acinetobacter sp. delayed canker development and reduced the disease incidence by 28.4-47.4% and 30.0-50.0% in the first and second trials respectively. The PGPR strains also significantly (p <= 0.05) promoted the growth performance of tomato plants in the two trials. The study therefore showed the potential application of non-native strains of Alcaligenes faecalis and Acinetobacter sp as biological control agents of tomato canker disease.