Helianthus annuus natural populations to increase the whole genetic diversity of domesticated sunflower: the concept of neodomestication

To broaden genetic basis of cultivated crop, seventy-seven Helianthus annuus natural ecotypes from North America were grown in Mauguio near Montpellier and crossed with three domesticated sunflower lines. The crossed F1 progenies were conducted in maternal lineage to maintain 10 plants per lineages in isolation for pollination and the intermixing was continued till G4 generation under low to hight selection pressure for some domestication traits. The G0 generation enabled to phenotype thirteen morphologic descriptors. Some traits: phenology, plant height, branching, oil content seed size and yield were evaluated though the G1, G2, G3 and G4 cycles. The studies of the first generations enabled us to release some main trends which are promising for the future of sunflower breeding. Indeed, we showed that the neo-domesticated materials gather adaptative traits from the natural populations. The first immediate effect of the intraspecific crossing between wild H. annuus and cultivated lines (G0 -> G1) was to increase 1000 seeds weight by 3.6 (9.7 g to 35.2 g), oil content by 20 % (26.8 % to 32.3 %), and to reduce apical, intermediate and basal branching respectively by 53 %, 40 % and 13 %. In the last G3 and G4 cycles, strong selection pressures were applied on the combined (1000SW*oil content) trait. Oil content increased by 3 % in G3 and continued by 11 % in G4. In the same time 1000SW after small decrease exhibits strong seed size increase + 13 % in G4 cycle. The other visible effect was clear evolution towards domestication traits, i.e., decrease of the different types of branching, reaching 76 % non branchy plants in G4. Qualitatively the different types of branching declined in the same way in G4 cycle: since 14 % plants were apical branched, 11 % intermediate and 17 % basal branched.