Effect of a Single or Double Soil Solarization to Control Verticillium Wilt in Established Olive Orchards in Spain

Abstract

Four soil solarization experiments were completed in three commercial olive orchards infested with Verticillium dahliae in southern Spain. Three of the experiments used lines of trees and one used individual plants. Plantations had different initial inoculum densities of the pathogen. Initial studies indicated that highly virulent (cotton-defoliating) isolates of the pathogen were present in Marinaleda (experiment I), which represents the first record of such isolates affecting olive trees in Europe. Solarization treatments were applied to lines of trees for either one (single) or two consecutive (double) years. Solarization significantly reduced pathogen populations in the top 20 cm of soil for at least 3 years in relation to control plots. Pathogen reduction after the single solarization obscured effects of the second solarization treatment. Decrease of inoculum density in soil by solarization did not correspond to a similar reduction in disease severity. Disease severity was reduced only in orchards with medium or high initial inoculum densities. A second soil solarization treatment did not improve the effect of single solarization on Verticillium wilt control. In orchards with low inoculum densities, soil solarization did not result in significant differences in disease incidence and severity, but improved recovery of trees from the disease. Soil-solarized plots remained free of weeds, but tress in solarized plots did not show significant growth increase measured by trunk perimeter.

Verticillium wilt of olive: a case study to implement an integrated strategy to control a soil-borne pathogen

“…2a). When apoplexy occurs in young plants the death of the entire tree is very common (Blanco-López et al 1984;Rodríguez-Jurado et al 1993;Jiménez-Díaz et al 1998;López-Escudero and Blanco-López 2001). The 'slow decline' is characterized by heavy defoliation (green or dull-green leaves in this case) of branches (Fig.…”

“…The ND pathotype causes nearly the same symptoms in olive as D-pathotype infections, although at milder (defoliation of green leaves) or moderate (die-back, chlorosis or necrosis) levels. Similarly, it induces reduction in weight and, to a lesser extent, in height under favorable environmental conditions (López-Escudero and Blanco-López 2001;López-Escudero et al 2004, 2007aMartos-Moreno et al 2006). Differences in virulence seem to be consistent among olive cultivars (López-Escudero et al 2004, 2007aMartos-Moreno et al 2006;Dervis et al 2010).…”

“…Such trees are able to produce new vascular tissue that can completely enclose old necrotic xylem vessels, enabling new vegetative growth in affected stems and branches (Tjamos et al 1991;López-Escudero and Blanco-López 2001). Similarly, diseased but recovered plants usually produce suckers at the basis of the trunk.…”

“…Thus, an isolate recovered from cotton or olive displays cross virulence in both crops. The D pathotype is highly virulent and causes severe symptoms including wilt, chlorosis, defoliation, drastic weight and height reduction and, eventually, death of the tree (Blanco-López et al 1984;Rodríguez-Jurado et al 1993;López-Escudero and Blanco-López 2001;Birem et al 2009). The ND pathotype causes nearly the same symptoms in olive as D-pathotype infections, although at milder (defoliation of green leaves) or moderate (die-back, chlorosis or necrosis) levels.…”

“…Optimum temperature for V. dahliae ranged from 22 to 25°C which coincides with the most favorable temperature for the development of many Verticillium wilts (Garber and Presley 1971). Severity of VWO attacks is favored by air temperatures of 20-25°C during spring days, followed by summers with broader thermal amplitude but with day peaks not higher than 30-35°C (Wilhelm and Taylor 1965;López-Escudero and Blanco-López 2001). However, if during summer days temperatures are above 25°C for a prolonged period of time, both pathogen colonization and symptom development normally stop.…”