Philippe Baradat

Olea europaea (Oleaceae) phylogeography based on chloroplast DNA polymorphism

Abstract.Chloroplast DNA diversity in the olive (Olea europaea L.) complex was studied using PCR-RFLP and microsatellite markers. Fifteen chlorotypes were distinguished. We constructed a cpDNA phylogenetic tree in which five clades were recognised and located in distinct geographic areas: clade A in Central and Southern Africa, clade C in Asia, clade M in North-West Africa, clade E1 in the Mediterranean Basin and Sahara, and clade E2 in West Mediterranea. Cultivated olive clustered with Mediterranean and Saharan wild forms (clades E1 and E2). Strong genetic differentiation for cpDNA markers was observed between eastern and western Mediterranean olives, suggesting that these areas have represented different glacial refugia. Humans most likely spread one eastern chlorotype, preponderant in cultivars, across the western Mediterranean Basin. Its presence in O. e. subsp. laperrinei from the Sahara suggests a possible Mediterranean olive origin in an African population, which may have overlapped in the Southern Mediterranean during the Quaternary.

Combination of chloroplast and mitochondrial DNA polymorphisms to study cytoplasm genetic differentiation in the olive complex (Olea europaea L.)

Abstract.Four hundred and four individuals belonging to the species Olea europaea were characterised using mitochondrial DNA (mtDNA) RFLPs. Twelve mitotypes were distinguished. The combination of mtDNA information with cpDNA polymorphism (characterised in a previous study) led us to recognise 20 cytoplasmic lineages of which seven were found in the Mediterranean area (oleasters, cultivars and O. e. subsp. maroccana). In the olive complex, strong cytoplasm genetic differentiation was revealed (Fst = 0.73). Very strong linkage disequilibrium between cpDNA and mtDNA polymorphisms was observed, particularly in the Mediterranean subspecies europaea. This high congruence between genetic structure based on cpDNA or mtDNA sustains a low level of recurrent mutation in both organelle DNAs and, thus, the polymorphisms used in this study were pertinent to reconstruct olive phylogeography. In the Mediterranean area, genetic drift due to population regression during Quaternary glaciations, and founder effects associated with the postglacial seed dissemination, have probably contributed to the existence of a high genetic linkage disequilibrium between cpDNA and mtDNA polymorphisms. Thus, four Mediterranean cytoplasmic lineages, clearly distinguished both by cpDNA and mtDNA polymorphisms, most likely reflect four distinct relic populations during Quaternary glaciations. Finally, O. e. subsp. maroccana from South Morocco, which also displayed specific cytoplasmic lineages, should be considered as another relic Mediterranean population.

#Coffea arabica# hybrid performance for yield, fertility and bean weight

The performance of F1 hybrid plants derived from crosses between traditional varieties of Coffea arabica of Latin America with a “wild” collection of Sudan–Ethiopian origin were studied for yield, fertility and bean weight. Sudan–Ethiopian material possesses resistance to certain diseases, and possibly, better beverage quality. The objective of this breeding programme is to widen the very narrow genetic base of Central American coffee, even while increasing quality and productivity. The hybrid plants were obtained from two factorial crosses made and evaluated in two locations. They were compared in the two field trials using the six maternal lines as controls. Observations were taken on vegetative characters, annual and cumulated yield, dry weight of 100 beans, extent of early abortion as measured by the fraction of ‘peaberries’ and post-zygotic ovule fertility as measured by the fraction of mature no-floating berries in water (FF). The F1 hybrid population were compared to the populations of maternal lines for the aforementioned variables. An index-based selection was done in the hybrid populations employing three traits, yield, 100-bean weight and the post-zygotic fertility (FF). The performance of the selected hybrids was then compared to those of the best parental ‘control’ lines in each trial. The hybrid populations yielded 22–47% more than the maternal lines, but hybrids showed significantly more sterility than the parental control lines. Selection in the hybrid populations using the three selected traits led to significant genetic gain for yield and dry weight of 100 beans, and insignificant gain for fertility (FF). When selected on the basis of fertility alone, increase in yield and 100-bean weight were not obtained within the hybrid populations. By applying selection on yield and 100-bean weight, the selected hybrids produced 11–47% higher yields than the best line along with significantly higher or identical 100-bean weight and performed identically for fertility. The yield performance of hybrids between the Latin American material and the “wild’’ Sudan–Ethiopian material calls for further selection effort for improving beverage quality.

Selection for bean and liquor qualities within related hybrids of Arabica coffee in multilocal field trials

The success of a new variety of Arabica coffee (Coffea arabica L.) depends to an important extent on its liquor and bean qualities. Selection for these traits is however constrained by the prevalence of large genotype-by-environment (G×E)interactions in conjunction with the low genetic variability characteristic of this species. The aim of this study was to assess the extent to which key bean and liquor traits are affected by the environments and could be combined in order to improve the efficiency of selection for coffee quality in a narrow genetic basis set of hybrids obtained from a set of related lines and collectively representing the Ruiru 11 cultivar. Twenty-one full-sib families representative of this hybrid cultivar grown in Kenya in five sites exhibiting strong edaphic and climatic differences were used for the study. Rainfall amounts during various phases of berry development were used to explain the differences observed in the discriminating abilities of the locations for bean and liquor traits. The results showed that these families were best differentiated for bean sizes in the site where moisture supply was optimal throughout berry expansion and filling stages, whereas discrimination on the basis of liquor traits were best observed in the site where moderate moisture stress occurred during bean filling stage. The overall precision in prediction of family values was low for liquor qualities; but a much more efficient selection for large bold beans, optimally based on the AA grade was shown to be possible. Selection indices for family selection were computed to realize a trade-off between genetic gains in bean size and liquor flavour.

Molecular approach of genetic affinities between wild and ornamental Platanus

Apart from the wild species P. orientalis and P. occidentalis, the cultivated plane trees constitute a wide and heterogeneous group, with uncertain genetic status and largely debated names. The recent canker stain problem in Europe makes it necessary at the present time to consider the genetic resources and to determine the genetic bases of all these trees. To attain this objective, a genetic molecular approach was used to analyze 60 trees of P. orientalis and P. occidentalis,different London planes (P. hispanicaand P. densicoma), a few controlledP. occidentalis × P. orientalishybrids and particular trees from arboreta and old parks. Molecular analysis involved thirty RAPD fragments generated with nine primers, PCR-RFLP in the 5S RNA genes and mitochondrial polymorphisms revealed by RFLP method. Clones were recognized amongP. hispanica and P. densicomatrees. A Correspondence Analysis and a dendrogram constructed according to the genetic distances confirmed the supposed hybrid origin of P. hispanica and P. densicoma between P. occidentalisand P. orientalis. Contribution ofP. orientalis to their constitution seems more important than that of P. occidentalis. Mitochondrial DNA polymorphisms indicated that crosses occurred in both directions. Moreover, P. occidentalis as female parent led toP. densicoma whereas P. orientalis as female parent led to P. hispanica. Low prevalence of pure species individuals and confusion risks with hybrid trees even for old trees are highlighted.

Effects of wounding on the terpene content of twigs of maritime pine (Pinus pinaster Ait.)

SummaryAfter wounding the cortical tissues of twigs of Pinus pinaster, we investigated changes in diterpene resin acid content and the ultrastructural modification of secretory structures. There was an increase in total resin acid content in the cortical and woody tissues located near the wound. Not all resin acids responded in the same way, but in wounded tissues the amounts of isopimaric acid and of the group of dehydroabietic, levopimaric and palustric acids significantly increased. The composition of cortical tissues becomes closely related to that of woody tissues. The resin acid enrichment of cortical tissues is correlated with the reactivation of the epithelial cells of the resin ducts and the de novo synthesis of resin acids demonstrated by labelling with 14CO2.

A commentary on current approaches to forest population genetics

Some of the most frequently chosen approaches to forest population genetics as reflected in the present volume are discussed, and some topics possibly deserving more attention are addressed. Among the first are studies of self-fertilization as a characteristic of forest tree mating systems, gene markers as indicators of adaptive or phylogenetic differentiation, and methodological aspects of the measurement of genetic differentiation. The latter mainly concern generalizable methods of analysis and the involvement of gene markers in the determination of mating systems, detection of mechanisms of frequency dependent selection, and the incorporation of genetic profiles (characteristics of frequency distributions of genetic types) into population genetic analysis.