Abstract
Olive knot is an important disease in most countries where olives are commercially grown. In the spring of 2015, some galls were observed on the trunk and branches of 4-year-old olive trees in the north of Iran. The bacteria were isolated from galls and all isolates were gram-negative, aerobic, and capable of producing florescent pigment. Other phenotypic characteristics of the isolates were assessed. Pathogenicity tests were carried out on olive branches incubated with different isolates. Primary symptoms were observed after two weeks. Sequences of 16S rRNA and RNA polymerase beta subunit genes of pathogenic isolates were completely similar to Pseudomonas savastanoi pv. savastanoi (Smith 1908) Young et al. 1978 in GenBank. Based on the results from phenotypic analyses, pathogenicity tests and phylogenetic data, the isolates were identified as P. savastanoi pv. savastanoi. The host range of our isolates was specific to olive trees. None of the inoculated oleander (Nerium oleander L.), winter jasmine (Jasminum nudiflorum Lindl.), Japanese privet (Ligustrum japonicum Thunb.) and ash (Fraxinus excelsior L.) developed disease symptoms. No difference in disease resistance was observed between six studied olive cultivars. There was no olive tree or orchard around the studied orchard as far as more than one kilometer. As the disease agent listed in Iran’s foreign quarantine pests and diseases list, appropriate quarantine and phytosanitary measures were undertaken to eradicate the disease.
Highlights
Pseudomonas savastanoi Smith 1908) Young et al 1978 includes four pathovars; P. savastanoi pv. savastanoi, pv. nerii, pv. fraxini, and pv. retacarpa that cause knot or excrescences in olive (Olea europaea L.), oleander (Nerium oleander L.), common ash (Fraxinus excelsior L.), and Spanish broom (Retama sphaerocarpa L.), respectively (Caballo-Ponce et al, 2017)
Olive knot disease is one of the important diseases caused by P. savastanoi pv. savastanoi, which can cause significant yield losses
During the research which was conducted in the spring of 2015, we found knot symptoms on trunk and branches of 4-year-old olive trees in the north of Iran
Summary
Pseudomonas savastanoi Smith 1908) Young et al 1978 includes four pathovars; P. savastanoi pv. savastanoi, pv. nerii, pv. fraxini, and pv. retacarpa that cause knot or excrescences in olive (Olea europaea L.), oleander (Nerium oleander L.), common ash (Fraxinus excelsior L.), and Spanish broom (Retama sphaerocarpa L.), respectively (Caballo-Ponce et al, 2017). Savastanoi (here after Psv) causes olive knot disease. Olive knot represents a serious disease in many oliveproducing areas, which can cause a progressive plant decline that leads to reduction in the number of fruitbearing shoots and tree yield potential (Quesada et al, 2010). Olive knot disease seriously affects olive trees mainly in Mediterranean countries, where climatic conditions often favor spread of the disease. The development of these galls results from uncontrolled cell growth due to disruption in plant hormone balance. Gall appearance is dependent on auxin phytohormone, indole-3-acetic acid (IAA), produced by pathogenic bacteria (Kieffer et al, 2010). Several auxin biosynthetic pathways in plant galls forming bacteria have been described, which are mostly dependent on L-tryptophan as a precursor (Spaepen et al, 2007)
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