Genetic Characterization in Sainfoin (Onobrychis viciifolia): Inbreeding in an Outbreeding Species.

The legume sainfoin exhibits many characteristics favoring its use for ruminant nutrition. It is rich in secondary plant compounds such as tannins that support digestion and protect from gut parasites. Although its low nutrient and water requirements make it a valuable alternative for farmers, it suffers from low yield potential and limited interspecific competitive ability. Marker assisted selection could be a powerful tool to improve these traits in breeding programs. Our objectives are to (i) develop the first linkage map for sainfoin, (ii) identify genomic markers linked to phenotypic traits such as flowering time or tannin concentration and (iii) investigate the rate of self- and cross-fertilization. Four mapping populations based on pairwise crosses between plants with contrasting phenotypic properties have been established in the field and were phenotyped for tannin content, growth habit, biomass, plant height, time of flowering and seed yield. Genotyping was performed using Illumina sequencing and SRAP (sequence related amplified polymorphisms) analysis.

A high coefficient of variation for the tannin concentration (36%) indicated a good basis for QTL mapping. Preliminary analysis with SRAP markers revealed a high degree of self-fertilization (52% to 72%) in all mapping populations, which was in line with the strong maternal effect observed for most phenotypic traits. This is surprising because sainfoin is reported to be a self-incompatible species. The phenotypic results revealed a moderate superiority of progeny from cross-fertilization in plant height (p < 0.001), biomass (p < 0.001) and early flowering (p < 0.001). Self fertilization was also observed in sainfoin populations under natural conditions, but the degree was much lower with one self-fertilization event out of 15 individuals. The possibility to easily self-fertilize sainfoin without significant inbreeding depression may open the route for the development of inbred lines and hybrid breeding approaches.