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International audience; Secondary metabolites, such as phenolics, are plant defence substances. In the present study, the impact of Monilinia laxa inoculation under controlled conditions on phenolic content of apricot branches was investigated. A bi-parental hybrid population issued from Bergeron and Bakour cultivars (BerBa) and consisting of 192 hybrids was studied. The susceptibility of the BerBa population to M. laxa was evaluated by measuring the length of the necrosed tissues and the concentration of fungal DNA by qPCR in the branches 8 days post-inoculation. The results exhibit significant differences between the two parental cultivars in terms of necrosis length, which confirm their different susceptibility to the pathogen. A considerably high content of 2′,6′-dihydroxy-4′–methoxyacetophenone hexoside was found in branch tissues of Bakour (tolerant parental cultivar), amounting to 1.72 mg/g and 1.41 mg/g of fresh weight in non-inoculated and inoculated samples, respectively. The content of this compound in Bergeron branch tissues was several times lower, amounting to 0.24 mg/g and 0.14 mg/g of fresh weight in non-inoculated and inoculated samples, respectively. In the inoculated branches, scopolin was almost twice as abundant in the tolerant parental cultivar branch tissues as in the susceptible ones. In general, after inoculation a lower content of phenolic compounds was observed for hybrids with longer necrosed tissue. A Principal Component Analysis showed that at 8 days post-inoculation M. laxa concentration in the branches and the content of phenolic compounds, such as scopolin and chlorogenic acids, were negatively correlated. Additionally, the antifungal activity of pure phenolic compounds against M. laxa mycelial growth and spore germination was investigated. At a concentration of 500 mg/L, up to 40 % inhibition of M. laxa mycelial growth by scopoletin, up to 60 % inhibition by 2′,4′,6′-trihydroxyacetophenone and total inhibition by 2′-hydroxy-4′-methoxyacetophenone was observed. Scopoletin and 2′,4′,6′-trihydroxyacetophenone also inhibited spore germination by about 50 %. These results can serve to improve breeding programs aiming to develop apricot cultivars resistant to brown rot blossom blight.

International audience; The characterization of the largest worldwide representative data set of apricot (Prunus armeniaca L.) germplasm was performed using molecular markers. Genetic diversity and structure of the cultivated apricot genetic resources were analyzed to decipher the history of diffusion of this species around the world. A common set of 25 microsatellite markers was used for genotyping a total of 890 apricot accessions in different collections from the center of origin to the more recent regions of apricot culture. Using a Bayesian model-based clustering approach, the apricot genotypes can be structured into five different genetic clusters (F-ST = 0.174), correlated with the geographical regions of origin of the accessions. Accessions from China and Central Asia were clustered together and exhibited the highest levels of diversity, confirming an origin in this region. A loss of genetic diversity was observed from the center of origin to both western and eastern zones of recent apricot culture. Altogether, our results revealed that apricot spread from China and Central Asia, defined as the center of origin, following three major diffusion routes with a decreasing gradient of genetic variation in each geographical group. The identification of specific alleles outside the center of origin confirmed the existence of different secondary apricot diversification centers. The present work provides more understanding of the worldwide history of apricot species diffusion as well as the field of conservation of the available genetic resources. Data have been used to define an apricot core collection based on molecular marker diversity which will be useful for further identification of genomic regions associated with commercially important horticultural traits through genome-wide association studies to sustain apricot breeding programs.