Factors Affecting Pseudomonas savastanoi pv. savastanoi Plant Inoculations and Their Use for Evaluation of Olive Cultivar Susceptibility

Abstract

Pseudomonas savastanoi pv. savastanoi causes olive knot disease, which is present in most countries where olive trees are grown. Although the use of cultivars with low susceptibility may be one of the most appropriate methods of disease control, little information is available from inoculation assays, and cultivar susceptibility assessments have been limited to few cultivars. We have evaluated the effects of pathogen virulence, plant age, the dose/response relationship, and the induction of secondary tumors in olive inoculation assays. Most P. savastanoi pv. savastanoi strains evaluated were highly virulent to olive plants, but interactions between cultivars and strains were found. The severity of the disease in a given cultivar was strongly dependent of the pathogen dose applied at the wound sites. Secondary tumors developed in noninoculated wounds following inoculation at another position on the stem, suggesting the migration of the pathogen within olive plants. Proportion and weight of primary knots and the presence of secondary knots were evaluated in 29 olive cultivars inoculated with two pathogen strains at two inoculum doses, allowing us to rate most of the cultivars as having either high, medium, or low susceptibility to olive knot disease. None of the cultivars were immune to the disease.

Epidemiology and Control of Plant Diseases Caused by Phytopathogenic Bacteria: The Case of Olive Knot Disease Caused by Pseudomonas savastanoi pv. savastanoi

“…There is a clear parabolic trend whose maximum value depends on cultivar susceptibility (Varvaro & Surico, 1978). Pathogen multiplication inside tissues of micropropagated olive plants can reach densities of 10 7 to 10 8 cfu/ knot (Rodríguez-Moreno et al, 2008), values very similar to those previously described with 1-2 years old seedlings by Penyalver et al (2006). The first reaction of tissue from the inoculated slit of a young stem is to renew or quickly increase cambium activity, although this depends on whether the inoculation takes place in winter, summer or spring (Surico, 1977).…”

“…In fact, some studies described the endophytic phase of Psv in olive plants as rare (Wilson & Magie, 1964). According to other authors, Psv could also present an endophytic phase, moving through the intercellular spaces and even in the xylem vessels and infecting areas close to the first infected zone (Penyalver et al, 2006;Schiff-Giorgini, 1906;Smith 1908Smith , 1920Wilson & Magie, 1964;Wilson & Ogawa, 1979). Further studies are needed to reliably assess the importance of this phase of Psv in olive knot epidemiology.…”

“…However, in Spain no significant differences were found between either leaves or stems with respect to the number of analyzed samples where Psv was isolated, detected by PCR, or regarding the average Psv populations over several years (Bertolini et al, 2003a;Quesada et al, 2007;Quesada et al, 2010aQuesada et al, , 2010b. Given that in such studies the Psv number were evaluated on stems after they were cut into pieces, some endophytic Psv could be also counted (Penyalver et al, 2006). Furthermore, both types of plant material (stems and leaves) should be analyzed from symptomless shoots to make the evaluation of Psv populations in the phyllosphere more accurate (Bertolini et al, 2003a;Quesada et al, 2007).…”

Differential Susceptibility of Olive Varieties to Olive Knot Disease in Istria

“…In the arid summer and cold winter the bacteria enter deeply into the inner parts of tumours and in that way to next year brings the 90% of its infection potential [17]. It is the causal agent of olive knot disease, a bacterial disease that affects olive trees mainly in Mediterranean countries, where climatic conditions often favour disease spread [13]. The minimal temperatures of 18-22°C are essential for the onset of the disease [7].…”

“…With age, the galls grow bigger and became hard, brown to black and corrugated, with a size ranging from a few millimetres to several centimetres in diameter [9]. The development of these galls is dependent on bacterial production of the phytohormone indole-3-acetic acid (IAA) and cytokinins [13]. Olive knot disease is considered an important problem for olive crops because of its effect on vegetative growth, olive yield and even possibly on olive oil quality through inferior organoleptic characteristics such as an unpleasant smell and a bitter, rancid taste [2,8,1].…”