Abstract
Clavibacter michiganensis subsp. michiganensis is a very important pathogen that causes bacterial wilt of tomato (BWT). Biological control of plant diseases is a critical tool for protecting the environment from chemical pollution. Twenty-five isolates of the genus Trichoderma were obtained from a healthy tomato root. Of the 25 isolates, KABOFT4 showed highly antagonistic activity that controlled the growth of C. michiganensis subsp. michiganensis (Cmm7) under in vitro conditions. The 5.8S ribosomal RNA gene and internal transcribed spacer identified the isolate as Trichoderma harzianum KABOFT4. The effect of this isolate as a soil drench and/or foliar application on bacterial wilt under greenhouse conditions was studied. The germination percentage of tomato seed treated with KABOFT4 increased by 36.7% compared to infected seed treated with only the pathogen Cmm7. Under greenhouse conditions, tomato seedlings treated with KABOFT4 as a soil drench, foliar and soil treatment, and foliar treatment had a 61.3, 26.7, and 40% reduced disease severity relative to the infected control, respectively. All treatments had a positive effect on tomato plants that presented as greater vegetative growth and accumulation of dry matter. The best fresh and dry weight was recorded when plants were treated with KABOFT4 as a soil and foliar application. Tomato plants treated with KABOFT4 also had increased total phenol and flavonoid contents in inoculated and non-inoculated plants compared to untreated plants. Under greenhouse conditions, T. harzianum strains can be used as an environmentally friendly way to manage the most economically important tomato disease. The results showed that a native endophytic strain of T. harzianum was a potent biocontrol agent against C. michiganensis subsp. michiganensis. Application of this strain to tomatoes in the greenhouse resulted in a decrease in disease severity and an increase in crop biomass.