Response of Some Olive Cultivars, Hybrid and Open Pollinated Seedlings to Pseudomonas savastanoi pv. savastanoi

Abstract

Olive knot disease caused by Pseudomonas savastanoi pv. savastanoi is spread in all olive cultivation area including Italy where it can cause significant yield losses. The aim of the present study was to screen in greenhouse some olive genotypes for resistance/tolerance to olive knot disease. In a first experiment, the olive cultivars Frantoio, Leccino, Moraiolo and Nostrale di Rigali were inoculated with 5 bacterial strains collected in Umbria (Central Italy) from cv. Frantoio. In a second experiment, 25 olive genotypes, in particular: three half-sib families [open pollinated seedlings of Ascolana (6 genotypes), Leccino (6 genotypes) and Moraiolo (3 genotypes)], three full-sib families [hybrid seedlings of Frantoio x Maurino (3 genotypes), Leccino x Maurino (3 genotypes) and Maurino x Frantoio (1 genotype)] and three olive cultivars (Frantoio, Leccino and Moraiolo) were inoculated with a bacterial strain which in the first experiment showed the highest virulence. Olive shoots were inoculated (5 inoculation sites per shoot) with a suspension containing 5 × 10⁸ CFU m1⁻¹. Symptom severity was evaluated about three months after inoculation, determining knot size and weight. The first experiment showed that, independently from the bacterial strains used, the cv. Frantoio was the most susceptible, followed by Nostrale di Kigali, Moraiolo and Leccino, which showed a knot weight which was 86% lower respect to the cv. Frantoio. The result of second experiment confirmed the cultivars Frantoio and Leccino as the most and the less susceptible, respectively. Among the hybrid and open pollinated seedlings, it seems interesting the Mo.6.105 genotype, which was more tolerant to the disease than cv. Leccino.