Field evaluation of olive ( Olea europaea ) genotypes for resistance to Pseudomonas savastanoi pv. savastanoi
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ORIGINAL ARTICLE
Field evaluation of olive (Olea europaea) genotypes for resistance to Pseudomonas savastanoi pv. savastanoi Mazen Salman 1
&
Rachel Greenhut 2 & John Preece 3 & Louise Ferguson 4 & Daniel Kluepfel 5
Received: 1 October 2019 / Accepted: 1 April 2020 # Società Italiana di Patologia Vegetale (S.I.Pa.V.) 2020
Abstract Current commercial olive (Olea europaea) cultivars are susceptible to olive knot disease caused by Pseudomonas savastanoi pv. savastanoi. Here we report on the examination of the olive tree germplasm collection maintained at the USDA-ARS National Clonal Germplasm Repository (NCGR) in Winters, California for the incidence of olive knot disease. Over a two year period we evaluated olive knot disease incidence on 506 trees representing 144 unique accessions consisting of 104 named cultivars originating from the Mediterranean Basin, South America, and California, including several hybrids, and related subspecies e.g. Olea europaea ssp. cuspidata. All genotypes were replicated in four blocks with trees in these blocks ranging in age from 6 to 35 year old. The disease index was higher in 2014 (43.5%) than in 2013 (29.4%). The percentage of infection varied significantly (P < 0.05) between the different blocks in the study orchard. Eleven genotypes exhibited greater than 30% disease severity with Tragolea (Greece), Barnea (Israel) and Arbusana (Spain) being the most susceptible to olive knot disease. Eighty-six genotypes exhibited less than 10% disease severity with 17 genotypes of this group showing zero olive knot incidence over the two year observation period. Keywords Olea europaea . Olive knot . Resistance . Susceptibility . Germplasm
Introduction Olives (Olea europaea L.) are an important oil crop cultivated over large areas in many countries across of the Mediterranean Basin and in the southwestern and western USA. In recent years, cultivation of olives has increased due, in part, to the human health benefits of olive oil (Russo et al. 2016). Throughout its range, olive trees are affected by many pests and diseases (Abuamsha et al. 2013) including Pseudomonas savastanoi pv. savastanoi (Psav) which causes a disease
* Daniel Kluepfel [email protected] 1
College of Agricultural Science and Technology, Palestine Technical University-Kadoorie, Tulkarm, State of Palestine
2
Hi Fidelity Genetics, Durham, NC, USA
3
USDA/ARS Germplasm Repository, Davis, CA 95616, USA
4
Department of Plant Sciences, 3045 Wickson Hall, Davis, CA 95616, USA
5
USDA-ARS Crops Pathology and Genetics Research Unit, University of California, Davis, CA, 95616, USA
known as olive knot (Ercolani 1978; Gardan et al. 1992). The bacterium is a Gram-negative motile fluorescent pseudomonad (Gardan et al. 1992; López-Villalta 1999; Vuletin Selak et al. 2019) which can colonize the leaf surface of healthy olive trees throughout the year or can invade woody tissues through wounds and cause olive knot disease (Ercolani 1993). Symptoms of the olive knot disease are characterized by outgrowths on young stems, br
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