Specific features in the olive self-incompatibility system: A method to decipher S-allele pairs based on fruit settings

- Plenty of data from olive crosses based on fruit settings stayed uninterpreted because there are quantitative, whereas for all other species they are all or nothing. Researchers were disconcerted by such a situation.
- We tried to refer data to hermaphrodite flowers to compare varieties because inflorescence architecture is variable in flower numbers and % of hermaphrodite flowers between varieties.
- The method leads to explain all features in every cross and enabled us to release the S-allele pair for varieties.
- To make the method available to olive, researchers will contribute to increase knowledge on olive pollination to improve fruit production.

Olive fruit production is dependent on wind pollination, and recently sporophytic self-incompatibility has been advocated to function with six S-alleles. The aim here is to show fruit setting data gathered from literature can be interpreted and their standardization help to release firm conclusions on the S-allele pair carried by most varieties. Under a bag, fruit settings for mates do not allow to infer inter-compatibility of pairs of mates. Each variety displays a different number of flowers per inflorescence, and for a given proportion of hermaphrodite flowers, fruit sets per hermaphrodite flowers were calculated. Thus, broad fruit set data were standardized per 100 hermaphrodite flowers. The ratio fruit sets from self-pollination and fruit sets from crosses are commonly referred to fruit sets after open pollination, as the index of self-incompatibility (ISI) and the index for cross inter-compatibility (ICOI), respectively. Open pollination rate (OP-R) is considered to be the best rate of fruit sets for a variety. ICOI values were classified with the threshold at 0.6 to rank a pair of varieties as inter-incompatible and inter-compatible. Before, we have proceeded by trials and errors. Here we showed that rationale reasoning is efficient to analyze fruit settings. Computations on ICOI showed that matings that succeeded are more confident than matings that failed, because pollen efficiency appeared insufficient. Computations on ISI revealed high correlations between SI and co-dominant S-allele pairs as for SC and S-allele pairs sharing dominance relationships. Thus, the sporophytic self-incompatibility (SSI) model will help geneticists to unravel the S-allele series and to predict suitable pollinizers in olive orchards. Moreover, compensation for OP-R deficiency in orchards could be achieved by supplementing suitable pollinizers computed in silico.