Variability and selection of verticillium wilt resistant genotypes in cultivated olive and in the Olea genus

Abstract

Developing verticillium wilt resistant genotypes is currently a major objective in olive breeding. In this study, 6017 genotypes derived from 48 crosses obtained by open pollination and crosses between olive cultivars, wild olive genotypes and other Olea species and Olea europaea subspecies were individually evaluated for verticillium wilt resistance. More than 800 genotypes were identified as resistant to the disease based on the absence of symptoms. High genetic variability and wide segregation in resistance were observed. The inheritance of resistance was studied, and the best parents and crosses to breed resistant genotypes were identified. According to the results, verticillium wilt resistance in olive appears to be a quantitative trait. The results obtained by comparing the level of resistance between different crosses as well as by estimating heritability suggest that it is possible to breed for verticillium wilt resistance in olive.

Evaluation of Verticillium wilt resistance in selections from olive breeding crosses

“…In this sense, 'Frantoio' 9 'Arbosana' showed the highest proportion of R genotypes (38 %) while Changlot Real' 9 'Dolce Agogia' showed the highest proportion of S genotypes (81 %). These results are in concordance with previous studies (Wilhelm and Taylor 1965;Trapero et al 2015), which identified higher proportion of R genotypes in progenies from free pollination and different cross combinations including 'Frantoio' as parent. Different inheritance patterns against VW have been reported in other species such as cotton with no consensus on the genetic basis of resistance .…”

“…For each cross, white circle and triangle represent values for female and male parents, respectively out under controlled conditions in the present work. This procedure may represent some advantages compared to selection at the seedling stage previously reported (Wilhelm and Taylor 1965;Trapero et al 2015). On the one hand, the possibility of replication of plant materials, instead of one single plant per genotype, allows more accurate evaluation for disease resistance.…”

“…These results represent a higher proportion of resistant genotypes than previously reported in olive progenies from open pollination, although resistant seedlings were selected in progenies of different cultivars including susceptible parents such as 'Arbequina', 'Manzanillo', 'Mission' and 'Picudo' (Wilhelm and Taylor 1965;AriasCalderón et al 2015). Trapero et al (2015) found approximately half the proportion of R genotypes obtained in our work in the evaluation of a high number of genotypes derived from open pollination and crosses involving different olive cultivars, wild olive genotypes and other Olea genus. In our case, however, a different strategy was followed as the seedling progenies were first evaluated for agronomic traits and only those genotypes showing good agronomic performance were included in the inoculation tests.…”

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

“…This study used Frantoio olive as a resistance reference because of its resistance to D. V. dahliae and current commercial interest (López‐Escudero et al ., ; Barranco, ; Bubici & Cirulli, ; Arias‐Calderón et al ., ; Trapero et al ., ). 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 ., ; Cirulli et al ., ; Bubici & Cirulli, ; Gramaje et al ., ; Arias‐Calderón 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 (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, ).…”