Symptom development, pathogen isolation and Real-Time QPCR quantification as factors for evaluating the resistance of olive cultivars to Verticillium pathotypes

Abstract

Verticillium wilt is the most serious olive disease in the Mediterranean countries and worldwide. The most effective control strategy is the use of resistant cultivars. However, limited information is available about the level and source of resistance in most of the olive cultivars and there are no published data using microsclerotia, the resting structures of Verticillium dahliae, as the infective inoculum. In the present study, we correlated symptomatology and the presence of the fungus along with the DNA relative amount (molecules μl −1 ) of a defoliating (D) and a non-defoliating (ND) V. dahliae strain in the susceptible cv. Amfissis and the tolerant cvs Kalamon and Koroneiki, as quantified by the Real-Time QPCR technology. The viability of the pathogen in the plant tissues was confirmed by isolating the fungus on PDA plates, while symptom assessment proved the correlation between the DNA relative amount of V. dahliae in plant tissues and cultivar susceptibility. It was further demonstrated that the D and ND strains were present at a significantly higher level in cv. Amfissis than in cvs Kalamon and Koroneiki. It was finally observed that the relative amount of the pathogen in roots was lower than in stems and shoots and declined in plant tissues over time. These data constitute a valuable contribution in evaluating resistance of olive cultivars or olive root-stocks to V. dahliae pathotypes.

Distribution and persistence of Verticillium dahliae in the xylem of Norway maple and European ash trees

“…Moreover, in the year after inoculation we were not able to detect or recover the pathogen in new xylem and only rarely in old xylem of recovered ash trees (Tables 3A and 4A). Similar results were observed for olive trees infected with V. dahliae, where reduction in symptoms was associated with a decrease in V. dahliae DNA in newly developed asymptomatic shoots (Markakis et al 2009;Mercado-Blanco et al 2003). Therefore, it appears that recovery correlated with the inactivation of the fungus in the xylem and impeding new infections (Hiemstra 1995a(Hiemstra , 1995bRodríguez-Jurado et al 1993;Sinclair et al 1981;Talboys 1968;Wilhelm and Taylor 1965).…”

Verticillium wilt in nursery trees: damage thresholds, spatial and temporal aspects

“…Apparently, recovered trees have not acquired induced resistance lasting until the next year. Recovery from disease is known to occur in trees, as a result of the formation of a new, uninfected ring of xylem vessels (Goud and Termorshuizen 2002;Hiemstra and Harris 1998;López-Escudero and Blanco-López 2005;Markakis et al 2009;Shigo 1984). However, the relationship with soil inoculum density has not been investigated before.…”

“…Nevertheless, recovery is an important aspect of verticillium wilt in established trees in gardens and orchards, e.g. of olive trees (López-Escudero and Blanco-López 2005) and for pathogen assessment (Markakis et al 2009). …”

Verticillium wilt caused by Verticillium dahliae in woody plants with emphasis on olive and shade trees

“…Upon this type of inoculation, the pathogen escapes the resistance mechanisms operating in roots (Chen et al 2004;Gold and Robb 1995;Heinz et al 1998), while upon root dipping the first fungal elimination that occurs in the roots may affect the distribution of the pathogen and progression of the disease. The type of inoculum used for root dipping may also impact colonization by the pathogen and disease progression (Markakis et al 2009). Also, there is a correlation between inoculum density and final disease incidence values (López Escudero and Blanco-López 2007; Bejarano- Alcázar et al 1995).…”