The Antagonistic Effect of a Local Isolate of Trichoderma harzianum Against Olive Knot Disease in Syria

Abstract

Olive knot disease is considered one of the most important diseases affecting olive trees in Syria. The disease is caused by the bacteria Pseudomonas savastanoi pv. savastanoi (Pss). The aim of this study is to test the efficiency of the antagonistic effect of several extracts (ethyl acetate, hexane, and the enzymatic extract BIO-TH-WP) of a commercial isolate of the fungus Trichoderma harzianum on nutrient agar (NA), and also to test the direct effect of the fungus Trichoderma harzianum on inhibiting the growth of the bacteria Pseudomonas savastanoi pv. savastanoi grown on potato-dextrose-agar (PDA) medium. The pathogenic bacterium was isolated from infected olive trees in the Al-Kadmous area (Tartous Governorate, Syria). The antagonistic effect of different extracts of the fungus Trichoderma harzianum against the bacteria Pss was tested by the disk diffusion method. Paper disks were immersed in specific concentrations of the extracts (ethyl acetate, hexane, and enzymatic extract (BIO-TH-WP) of the fungus and placed on a Pss lawn and incubated at 28±2°C for 48 hours. Thereafter, the inhibition rate (%) of the pathogenic bacteria was measured. The results obtained showed that the inhibition rate reached 0.0, 33.3, 17.7% for the extracts hexane, ethyl acetate, and BIO-TH-WP, respectively. The use of the extracts on two year old trees led to a reduction of disease severity associated with an increase in the concentration of the enzymes peroxidase and polyphenol oxidase, 90 and 105 days after spraying with the enzymatic extract (BIO-TH-WP). The results obtained showed that ethyl acetate extract and the enzymatic extract BIO-TH-WP can be considered as a potential natural source that can be used for controlling olive knot disease.

Keywords:

Ethyl acetate, Trichoderma harzianum, olive knot disease, fungal extracts, biological control.