Isolation and Identification of the Bacterial Causal Agent of Pomegranate Knot Disease and Testing the Effect of Aqueous Rosemary Extract in Inhibiting Its Growth

Abstract

Pomegranate knot disease has recently spread on pomegranate trees in Syria. This study aimed to isolate and identify the disease agent that causes the formation of galls on the stems and branches of pomegranate trees. The pathogenic bacteria was isolated from newly formed galls on the infected pomegranate branches from different areas in Latakia Governorate, Syria. The isolated pathogenic bacterial isolates were grown on nutrient agar (NA) medium, and the cultural and morphological characteristics of the bacterial colonies were studied, in addition to some biochemical and pathogenicity tests were conducted. The effect of the aqueous extract of rosemary on the growth of the pathogenic bacteria was also tested in the laboratory on the nutrient medium using the disc diffusion method. Thereafter, the inhibition zone diameter around the paper disc treated with the extract at different concentrations was measured and the inhibition rate of the pathogenic bacteria was measured. The study of the cultural characteristics of the studied bacteria, biochemical tests and pathogencity test showed that the bacteria causing the disease is the same bacteria that causes olive knot disease (Pseudomonas savastanoi pv. Savastanoi). The results obtained also showed that the aqueous extract of rosemary at different concentrations (10, 15 and 25%) showed an inhibitory effect on the growth of the bacteria Pseudomonas savastanoi pv. savastanoi, where the inhibition rate reached 18.89, 20.11, 32.22 % for the three rosemary extract concentrations, respectively. In conclusion, this study showed that rosemary extract is a natural biobacterial pesticide that can be used in the future to combat the bacteria causing pomegranate knot disease.

Keywords:

Bacteria, pomegranate knot disease, Pseudomonas savastanoi pv. savastanoi, aqueous extract, rosemary, inhibition rate.