Pre-breeding for resistance to Verticillium wilt in olive: Fishing in the wild relative gene pool

Characterization of resistance against the olive‐defoliating Verticillium dahliae pathotype in selected clones of wild olive

“…Wild olive genotypes highly resistant to D V. dahliae used as rootstocks can provide an improved means for the management of verticillium wilt in grafted susceptible olive cultivars that are agronomically adapted and commercially desirable (Jiménez‐Díaz et al ., ; Trapero et al ., , ; Arias‐Calderón et al ., ). In previous studies, it was concluded that wild olive clones Ac‐13, Ac‐18, OutVert and StopVert are highly resistant to D V. dahliae based on the development of incipient or no foliar disease symptoms, together with reduced stem vascular browning and reisolation of the fungus (Colella et al ., ; Jiménez‐Díaz, ; Bubici & Cirulli, ).…”

“…Because the amount of pathogen DNA in the plant should be representative of the number of potential fungal propagules, the symptomless reaction in Ac‐13, Ac‐18, OutVert and StopVert found in this and previous studies corresponds to expression of resistance, rather than tolerance, against D V. dahliae in them. Although previous studies have identified wild olive genotypes with a resistant phenotype to D V. dahliae (Colella et al ., ; Arias‐Calderón et al ., ; Trapero et al ., ), to the authors' knowledge this is the first time that symptomless resistance in wild olive has been demonstrated to correlate with the plant's ability to quantitatively reduce the extent of stem colonization by the pathogen. Mercado‐Blanco et al .…”

“…More importantly, a complete failure of positive reisolation of the pathogen occurred from stems of root‐dip inoculated Ac‐18 and sequentially inoculated StopVert, despite D V. dahliae DNA being quantified from all or some of the sampled stem zones, respectively. This partial or total failure of pathogen reisolation has also been reported in D. V. dahliae ‐resistant olive cultivars that developed limited foliar symptoms (Markakis et al ., ; Gramaje et al ., ; Arias‐Calderón et al ., ) as well as in resistant wild olives (Mercado‐Blanco et al ., ; Colella et al ., ; Arias‐Calderón et al ., ). This failure of reisolations is consistent with the aforementioned reduction in the amount of D. V. dahliae DNA, and may result from loss of pathogen viability and/or degradation in infected tissues over time, determined by expression of a non‐specific defence reaction (Pegg, ; Heinz et al ., ).…”

“…Wild olive genotypes highly resistant to D V. dahliae used as rootstocks can provide an improved means for the management of verticillium wilt in grafted susceptible olive cultivars that are agronomically adapted and commercially desirable (Jim enez-D ıaz et al, 2012; Trapero et al, 2013Trapero et al, , 2015Arias-Calder on et al, 2015). In previous studies, it was concluded that wild olive clones Ac- Bubici & Cirulli, 2011).…”

“…This study used Frantoio olive as a resistance reference because of its resistance to D. V. dahliae and current commercial interest (L opez-Escudero et al, 2004;Barranco, 2010;Bubici & Cirulli, 2011;Arias-Calder on et al, 2015;Trapero et al, 2015). Unlike the wild olive clones, incipient symptoms developed in Frantoio olives, with incidence varying from 20 to 60% depending on inoculation methods and experiments, which agrees with reports by other authors (Martos-Moreno et al, 2006;Cirulli et al, 2008;Gramaje et al, 2013;Arias-Calder on et al, 2015). Correspondingly, D V. dahliae DNA was quantified in all Frantoio stem zones, the mean amount being 129 to 339 times lower than the mean amount of V. dahliae DNA quantified in susceptible Picual olive, depending on the method of inoculation and experiment.…”