Prospects and strategies in controlling verticillium wilt of olive¹

Abstract

Control of verticillium wilt of olive currently depends on preventive measures. Since systemic fungicides are unable to prevent or control the disease, its control should primarily be based on cultural methods, including irrigation systems which restrict dissemination of Verticillium dahliae propagules by irrigation water and avoidance of intercropping with hosts susceptible to V. dahliae. Since leaves from affected olive trees contribute, through formation of microsclerotia, to the inoculum in the soil, pruning should be practised prior to branch defoliation. As for resistant olive rootstocks or cultivars, promising verticillium‐wilt resistance has been found in two rootstocks selected in California (US). However, these have to be tested under local conditions before they can be released to Mediterranean growers, while further search for other resistant rootstocks is needed. Soil solarization applied to individual diseased trees in established olive groves could substantially contribute to recovery or long‐lasting symptom remission in the treated trees. This effect is mainly attributed to the decrease or eradication of V. dahliae microsclerotia in the treated soil but also to heat‐tolerant fungal antagonists of the pathogen. Using herbicides to control weeds, and limiting soil rotovation, can restrict symptom development. Biological control can also be considered as a promising trend in controlling the disease by searching, testing and exploiting potential fungal or bacterial antagonists.

Reaction of selected apple cultivars to wilt pathogen Verticillium dahlia

“…To our knowledge, this is the first study that determines the level of apple resistance to Verticillium wilt and that can provide a control measure for the disease management in olives since commercially, resistant olive cultivars to V. dahliae are not available even though no considerable level of tolerance was recorded among olive cultivars. Some studies showed that very few olive cultivars have resistance properties (Wilhelm & Taylor 1965;Hartmann et al 1971;Schnathorst & Sibbett 1971;Tjamos 1993;Sesli et al 2010). In Spain, studies on olive resistance to Verticillium wilt (Ciccarese et al 2002;López-Escudero et al 2004) led to establishment of different levels of susceptibility among olive cultivars.…”

“…Chemical fungicides such as benzimidazoles did not provide sufficient control (Biris & Thanaassoulopulos 1980;Karajeh 1997). Post-planting soil solarization was fairly effective in controlling the disease but limited to regions that receive high solar radiation (Tjamos et al 1991;Tjamos 1993;Lopez-Escudero & Blanco-Lopez 1997;Karajeh & Al-Momany 2008). The management of Verticillium wilt is difficult and requires an integrated approach (JimenezDiaz et al 1998).…”

“…Verticillium wilt of olive is one of the most serious diseases affecting olive worldwide and in Mediterranean countries causing severe annual economic losses to irrigated olive trees planted with high-yielding but susceptible olive cultivars (Thanassoulopoulos et al 1979;Al-Ahmad & Hamidi 1984;Tjamos 1993;Naser 1996;Heale 2000;Tjamos et al 2000;Karajeh 2006;AlMomany 2010;Al-Taae & Al-Taae 2010).…”

“…Several approaches were used to control Verticillium wilt in olive groves including chemical control (Tawil et al 1992;Tawil & Abdin 1994;Karajeh 1997), post-planting soil solarisation (Tjamos et al 1991;Abu-Gharbieh et al 1998;Karajeh & Al-Momany 2008), solar chamber (Al-Ahmad & Duksi 1994;Karajeh & Al-Momany 2008), cultural practices (Al-Ahmad 1993; Karajeh & Al-Momany 2008), integrated control (Abu-Qamar & Al-Momany 2001, 2002 and biological control (Tjamos 1993;Karajeh & Al-Raddad 1999). Recently, disease control has essentially relied on preventive measures such as using disease-free plant materials and soils that are free from pathogens especially when establishing new olive groves (Karajeh 2006;Karajeh & Masoud 2006).…”

Scientific opinion on the pest categorisation of Verticillium dahliae Kleb

“…Damage caused by Verticillium wilt on olive production in the EU has increased during the past 30-40 years because of extensive irrigation and intercropping with V. dahliae-susceptible hosts, such as potato and cotton (Tjamos, 1993;BlancoLópez and Jiménez-Díaz, 1995;Levin et al, 2003). This effect has been reported for intensive as well as for extensive olive production (Cirulli, 1981).…”