‘Comment on Saumitou et al. (2017): Elucidation of the genetic architecture of self‐incompatibility in olive: evolutionary consequences and perspectives for orchard management’

Abstract

The new self‐incompatibility system (SI) was presented by Saumitou‐Laprade, Vernet, Vekemans et al. (2017). Evolutionary Applications based on 89 crosses between varieties in the olive tree. Four main points are not clear. We are examining here as follows: (i) the assertion that the self‐incompatibility system is sporophytic was not sustained by pollen germination data; (ii) surprisingly, the new model does not explain that about one‐third of pairwise combinations of olive varieties leads to asymmetric fruit setting; (iii) DNA preparation from one seed may contain two embryos, and thus, embryos should be separated before seed extraction; (iv) although effective self‐fertility in olive varieties was reported by many studies, the DSI model fails to explain self‐fertility in some olive varieties. Moreover, we cannot discuss result data, as science cannot be verified because variety names were encoded, this does not allow comparison of data with previous works. The DSI model on olive self‐incompatibility should explain more features than the model based on four dominance levels shared by six S‐alleles. Perspectives for orchard management based on this model may face serious limitations. An olive variety does not have a fifty percent chance of cross‐incompatibility, but surely fewer, and thus, the sporophytic system limits fruit production. Evolutionary perspectives of self‐incompatibility in Oleaceae should include data from the Jasmineae tribe that displays heterostyly SI.

Controlling for genetic identity of varieties, pollen contamination and stigma receptivity is essential to characterize the self‐incompatibility system of Olea europaea L.

“…The mating system of the Olive tree has remained a controversial issue in the literature, but many of the previously published studies have been based on a poorly genetically controlled experimental design. Given 1) the vast uncertainty around the genetic identity of vernacular varieties, 2) the massive risk of contamination associated with commonly used pollination protocols and 3) the importance of checking for stigma receptivity in controlled crosses [all important features that were not adequately taken into account in the studies cited by the Breton et al() comment], we are confident that the time is ripe for new standards to be set in the scientific community. We can only encourage authors of this comment as well as any other researchers having doubts about the actual existence of DSI and the absence of asymmetrical incompatibility reactions in Olive trees, to carefully assess reproducibility of the output data of their experimental crosses, to control for pollen contamination with paternity analyses and to use positive pollination controls of stigma receptivity.…”

“…Finally, according to the Breton et al () comment, the main objection against the existence of DSI in Olive remains its inability to explain the asymmetry reported by Breton et al. () and other authors (Farinelli, Boco, & Tombesi, ; Farinelli et al., ; Moutier, ; Spinardi & Bassi, ; Villemur, Musho, Delmas, Maamar, & Ouksili, ) in studies based on measurement of fruit set following reciprocal pollination between pairs of varieties.…”

“…As suggested in Saumitou-Laprade et al (2017), this discrepancy is probably due to several shortcomings in previously published analysis that lacked proper genetic control. In our view, the Comment to the Editor by Breton et al (2017) fails to take into account specific challenges associated with the genetic analysis of the particular biological material represented by Olive trees. Besides several inaccurate statements in their comment, we outline below three major sources of uncertainty in the studies cited by Breton et al (2017) that prevent conclusive evidence to be drawn about the rejection of our model for selfincompatibility system of the Olive tree.…”

“…This is indeed true. To understand the origin of this discrepancy, we analyzed 66 trees from the olive collection cited in Saumitou‐Laprade et al(), which includes pro parte some of the varieties cited in the Breton et al () comment (Breton et al., ; Farinelli et al., ). From these 66 individuals, we identified a total of 61 different genotypes using microsatellite markers and then matched these genotypes in the worldwide Olive World Germplasm Bank of INRA Marrakech assessed with the same markers.…”

Paternity tests support a diallelic self‐incompatibility system in a wild olive (Olea europaea subsp. laperrinei, Oleaceae)

“…In contrast, methods based on both intra‐ and interspecific stigma tests on a representative sample of olive cultivars indicated that Olea , Phillyrea, and Fraxinus share the same DSI system (Saumitou‐Laprade, Vernet, Vekemans, Billiard, et al, ). Some authors have, however, expressed doubts about these results due to strong divergences with their previous studies (i.e., asymmetry of incompatibilities in reciprocal crosses and pollen germination not sustaining DSI; Breton, Koubouris, Villemur, & Bervillé, ; Farinelli et al, ). Such disagreeing findings, thus, call for accurate SI tests on a homogeneous genetic pool, ideally on natural populations of O. europaea .…”