Genetic mapping of sex and self-incompatibility determinants in the androdioecious plant Phillyrea angustifolia

The diversity of mating and sexual systems in Angiosperms is spectacular, but the factors driving their evolution remain poorly understood. In plants of the Oleaceae family, an unusual self-incompatibility (SI) system has been discovered recently, whereby only two distinct homomorphic SI specificities segregate stably. To understand the role of this peculiar SI system in preventing or promoting the diversity of sexual phenotypes observed across the family, an essential first step is to characterize the genetic architecture of these two traits. Here, we developed a high-density genetic map of the androdioecious shrub P. angustifolia based on a F1 cross between a hermaphrodite and a male parent with distinct SI genotypes. Using a double restriction-site associated digestion (ddRAD) sequencing approach, we obtained reliable genotypes for 196 offspring and their two parents at 10,388 markers. The resulting map comprises 23 linkage groups totaling 1,855.13 cM on the sex-averaged map. We found strong signals of association for the sex and SI phenotypes, that were each associated with a unique set of markers on linkage group 12 and 18 respectively, demonstrating inheritance of these traits as single, independent, mendelian factors. The P. angustifolia linkage map shows robust synteny to the olive tree genome overall. Two of the six markers strictly associated with SI in P. angustifolia have strong similarity with a recently identified 741kb chromosomal region fully linked to the SI phenotype on chromosome 18 of the olive tree genome, providing strong cross-validation support. The SI locus stands out as being markedly more rearranged, while the sex locus has remained relatively more collinear. This P. angustifolia linkage map will be a useful resource to investigate the various ways by which the sex and SI determination systems have co-evolved in the broader phylogenetic context of the Oleaceae family.

Study of the Bioecology of Aleurolobus olivinus Silvestri (1911) (Homoptera, Aleyrodidae) on olive Trees in Algeria

Aleurolobus olivinus is an insect of the family Aleyrodidae and the subfamily Aleyrodinae, considered as a secondary pest of olive trees, Olea europea, and has also been reported on Phillyrea angustifolia, P. latifolia and on Erica spp. It consists of a bio-ecological study, in particular of the life cycle that has been carried out on the branches of trees covered with a fine mesh net to avoid possible exchanges of individuals, while for the ecological study, leaf samples have been taken according to cardinal directions and branches 50 cm long according to their age, on 4 varieties of olive tree. The black whitefly generates two generations, one from April to September and the other from October to March. The life cycle lasts 79 to 98 days. Larvae mainly prefer the upper surface of the foliage in the South and Estet are abundant in autumn and winter and the varieties Zaiti (33.3%) and Sorani (27.4%) are the most infested compared to Terella and Khodeiri (21.8%) and (17.4%). It is the twigs of the year that are most attacked. The parasitism rate varies according to the month and season, it is 17% in autumn and 7.6% in winter while the monthly rate is 6% in May and 21.5% in November.

Seed germination of Phillyrea angustifolia L., a species of difficult propagation

Aim of study: The purpose was to determine the type of dormancy and the optimal germination conditions of Phillyrea angustifolia (Oleaceae) seeds.Area of study: Germination requirements of P. angustifolia seeds collected from wild plants growing in the province of Ávila (Central Spain) were studied.Materials and methods: Seed water uptake was measured. Seeds with and without an endocarp were germinated at different temperatures, and several treatments were tested.Main results: The lignified endocarp interferes mechanically with the emergence of the radicle, and the treatments that achieved the highest germination percentages were the total removal of the endocarp with pliers (84%) or the immersion in liquid nitrogen for 1 min (97%). Scarification with concentrated sulphuric acid did not significantly increase germination compared to the control seeds, and treatments with dry heat or wet heat were detrimental to seed germination. The optimum temperature for germination was 15 ºC. A pre-sowing treatment of soaking in distilled water for 24 h slightly increased germination speed. Neither cold stratification at 5 ºC nor soaking in a gibberellic acid solution improved seed germination. Research highlights: Phillyrea angustifolia seeds have physiological dormancy – that is, the embryo does not have enough growth potential to overcome the mechanical restriction of the lignified endocarp. The seeds do not exhibit physical dormancy, given their water-permeable lignified endocarp. Our results suggest that the optimum germination protocol for P. angustifolia would be the total removal of the endocarp or immersion in liquid nitrogen for 1 min, followed by immersion in distilled water for 24 h and then seed incubation at 15 ºC in light or darkness.

Habitat-correlated seed germination and morphology in populations of Phillyrea angustifolia L. (Oleaceae)

The broad aim of this work was to study intraspecific variation of seed germination in Phillyrea angustifolia L. (Oleaceae), a species with a hard (water-permeable) endocarp. Germination of seeds from six different wild populations was correlated with traits related either to seed morphology or to environmental parameters. Germination of naked seeds (seeds without endocarp) at the optimum germination conditions was similar among populations and individuals, but great differences could be detected regarding the germination of seeds with endocarp both at inter- and intra-populational levels. Differences among populations could be related to climatic parameters and to morphometric variables of seeds with endocarp. A higher germination was associated with populations growing in habitats with more severe summer (higher temperature, lower precipitation and a longer drought period) and producing elongated seeds (lower Feret ratio and roundness). Moreover, seeds from eight different individuals within a population were tested independently, and great differences regarding the germination of seeds with endocarp could be detected among individuals. Our results suggest that the morphological variation found in P. angustifolia endocarp is both under strong maternal genetic control as well as influenced by environmental factors, as indicated by the high variability among individuals within one population and the significant correlation between climate variables and seed germination among populations. Finally, it is emphasized that standardization of plant propagation protocols should take into account the degree of intraspecific variation of Mediterranean species.