QTL Mapping of Flowering and Fruiting Traits in Olive

Abstract

One of the challenge fruit growers are facing is to balance between tree production and vegetative growth from year to year. To investigate the existence of genetic determinism for reproductive behaviour in olive tree, we studied an olive segregating population derived from a cross between ‘Olivière’ and ‘Arbequina’ cultivars. Our strategy was based on (i) an annual assessment of individual trees yield, and (ii) a decomposition of adult growth units at the crown periphery into quantitative variables related to both flowering and fruiting process in relation to their growth and branching. Genetic models, including the year, genotype effects and their interactions, were built with variance function and correlation structure of residuals when necessary. Among the progeny, trees were either ‘ON’ or ‘OFF’ for a given year and patterns of regular vs. irregular bearing were revealed. Genotype effect was significant on yield but not for flowering traits at growth unit (GU) scale, whereas the interaction between genotype and year was significant for both traits. A strong genetic effect was found for all fruiting traits without interaction with the year. Based on the new constructed genetic map, QTLs with small effects were detected, revealing multigenic control of the studied traits. Many were associated to alleles from ‘Arbequina’. Genetic correlations were found between Yield and Fruit set at GU scale suggesting a common genetic control, even though QTL co-localisations were in spe`cific years only. Most QTL were associated to flowering traits in specific years, even though reproductive traits at GU scale did not capture the bearing status of the trees in a given year. Results were also interpreted with respect to ontogenetic changes of growth and branching, and an alternative sampling strategy was proposed for capturing tree fruiting behaviour. Regular bearing progenies were identified and could constitute innovative material for selection programs.

Advanced olive selections with enhanced quality for minor constituents

“…for total phytosterol and tocopherol contents, and for the concentrations of stigmasterol, β-sitosterol and Δ 5 -avenasterol. Broad segregation in olive progenies has been reported previously for reproductive traits (Ben Sadok et al, 2013) as well as for oil quality traits such as fatty acid profile, tocopherol content and profile, polyphenols, and carotenoids . The most interesting variation identified in the present research consisted of increased levels of Δ 5 -avenasterol (30.7% of total sterols) in the selection UC-I-2-35 and tocopherols (263.2 mg·kg −1 fruit flesh) in the selection UC-I-37-69 (Table 3).…”

Recent developments in olive (Olea europaea L.) genetics and genomics: applications in taxonomy, varietal identification, traceability and breeding

“…Ben Sadok et al (2013) increased the number of markers mapped on the existing Olivière 9 Arbequina map (Khadari et al 2010); the resulting female map consisted of 25 linkage groups covering 1745 cM, while the paternal map consisted of 21 linkage groups covering 1597 cM and the integrated map of 26 linkage groups covering 2148 cM. This map is currently the most saturated map obtained for olive with classic molecular markers.…”

“…Usually, the high number of characteristics useful from an agronomic or economic point of view is quantitative traits and controlled by a high number of loci (QTLs) spread in the genome. Ben Sadok et al (2013) identified 12 QTLs on the genetic map based on Olivière 9 Arbequina (Khadari et al 2010), with small effects for interesting traits such as flowering; fruiting and production at whole tree scale. The highest part of QTLs was linked to alleles from the paternal cultivar Arbequina.…”

Transcriptomics and Biochemical Profiling: Current Dynamics in Elucidating the Potential Attributes of Olive

“…Apart from some specific motives in breeding for particular tree architecture in olive, little has been done on genetics, heritability patterns and QTL mapping (Hammami et al, 2012;Moriya et al, 2012). Nevertheless, no gene related to growth pattern has been mined in olive, which reflects how much space is available for the tools of genomics (Sadok et al, 2013). Genomics and its accessory techniques are providing new dimension to the researchers for exploring the genetic and molecular processes determining the growth habit in historically related trees (Hollender and Dardick, 2015).…”