Verticillium wilt of olive in Turkey: a survey on disease importance, pathogen diversity and susceptibility of relevant olive cultivars

Abstract

A comprehensive survey on the prevalence and incidence of Verticillium wilt of olive in Turkey has been conducted over 6 years (2003)(2004)(2005)(2006)(2007)(2008). Vegetative compatibility group (VCG) assessment and PCR-based molecular pathotyping were used to evaluate the distribution of the defoliating (D) and nondefoliating (ND) pathotypes of Verticillium dahliae in surveyed areas. Pathogen prevalence was 35% of all olive orchards inspected and incidence of the disease reached 3.1%. VCG1A was predominant (29.3%) and infected all major cultivars grown in Turkey. The other two VCGs detected (2A and 4B) were of minor relevance (4.9% and 0.9%, respectively). Disease incidence caused by VCG1A infections was higher (ranging from 1.1% to 6.9%) than that caused by VCG2A and VCG4B in 10 provinces (Manisa, Aydin, Kahramanmaras, Izmir, Mugla, Kilis, Denizli, Gaziantep, Mardin and Balikesir). However, VCG2A and 4B were more prevalent (and responsible for higher disease incidence) than VCG1A in three provinces (Hatay, Osmaniye and Bursa). Finally, VCG1A isolates were found in all provinces except Canakkale, and simultaneous presence of the three VCGs was only verified in Hatay province. An artificial inoculation bioassay (19 representative V. dahliae isolates included) revealed that VCG1A (13) isolates as a group were more aggressive and caused defoliation, whereas VCG2A (5) and VCG4B (1) isolates induced milder symptoms. Within a VCG group, virulence varied among isolates infecting the same olive cultivar and this virulence was also related to the differential susceptibility of the cultivars ('Manzanilla', 'Ayvalik' and 'Gemlik') tested. Molecular pathotyping allowed the identification of D (VCG1A) and ND (VCG2A/4B) pathotypes, which correlated with results from pathogenicity tests. Remarkably, the V. dahliae VCG1A/D pathotype population infecting olive in Turkey was molecularly different from that one previously identified in Spain.

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

“…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). The broad host range and apparent low host specificity suggests that V. dahliae populations contain low pathogenic and genetic diversity.…”

“…A survey in the Apulia region (Southern Italy) revealed that 16% of surveyed olive fields were infested with V. dahliae, and, more importantly, the pathogen was found in 50% of olive nurseries analyzed (Nigro et al 2005). Finally, a recent inspection covering 90% of the total olive acreage in Turkey revealed that V. dahliae was prevalent in 35% of all olive orchards inspected and that DI reached 3.1% (Dervis et al 2010). Reports are also confirming the presence of the disease in non traditional olive cultivating countries such as Australia (Sergeeva and Spooner-Hart 2009) or Argentina .…”

“…4). However, a correlation has not always been reported between VCG and pathogenicity in olive isolates (Tantaoui et al 2002), or a continuum of virulence has been found within the VCG1A/D pathotype group, revealing that severity of symptoms caused by some D isolates was not significantly different to that induced by ND isolates in artificial inoculation experiments (Dervis et al 2010). Thus, despite VCG assignment provides useful information on the diversity of V. dahliae populations, it could be insufficient to correlate genetic diversity with traits such as level of virulence or host specificity.…”

“…Other VCGs, either less prevalent or localized in well-defined geographical areas, have been reported as well (namely VCG3, VCG5, VCG6, VCGBr or VCGBa) (Bhat and Subbarao 1999;Bhat et al 2003;Joaquim and Rowe 1990;Strausbaugh et al 1992;Jiménez-Díaz et al 2006). Regarding to V. dahliae isolates infecting olive, only representatives of VCG1A, VCG2A, VCG2B, and VCG4B have so far been identified (Pérez-Artés et al 2000;Cherrab et al 2002;Tantaoui et al 2002;Tsror and Levin 2003;Bellahcene et al 2005b;Sanei et al 2005;Collado-Romero et al 2006;Dervis et al 2007Dervis et al , 2010 (Fig. 4).…”

“…Interesting examples pointing to an association between genetic groups and host specificity are: i) the predominance of isolates assigned to VCG4 in potato (Solanum tuberosum L.) infections in the United States and Israel (Joaquim and Rowe 1991;Strausbaugh et al 1992;Korolev et al 2000); ii) the aforementioned association of the highly-virulent, D-pathotype isolates of cotton (Gossypium hirsutum L.) with their assignment to VCG1A described in various areas such as Central Asia, China, Israel, Peru, Spain, Turkey and USA (Daayf et al 1995;Korolev et al 2001;Zhengjun et al 1998;Korolev et al 2008;Dervis et al 2008), in what may constitute an example of dispersal of isolates from an original focus of infected cotton genotypes; or iii) the prevalence of VCG2A and 2B isolates infecting artichoke (Cynara scolymus L.) in a defined artichokecultivating region of eastern-central Spain, with VCG2B being the most virulent in this host . Studies regarding to olive-infecting V. dahliae isolates, are indicating the following scenario: 1) highly-virulent isolates, inducing severe syndromes in olive, generally belong to the D pathotype; 2) all olive D-pathotype isolates have so far been assigned to VCG1A in all countries where this group/pathotype has been reported (Pérez-Artés et al 2000;Collado-Romero et al 2006;Dervis et al 2010); and 3) olive isolates assigned to other VCGs (namely, VCG2 and VCG4) have been characterized as ND pathotype either by pathogenicity testing or by PCR-based molecular pathotyping (Fig. 4).…”