Bouchaib Khadari

Genetic determinism of the vegetative and reproductive traits in an F1 olive tree progeny

The agronomic performance of fruit trees is significantly influenced by tree internal organization. Introducing architectural traits in breeding programs could thus lead to select new varieties with a regular bearing and lower input demand in order to reduce training and environmental costs. However, an interaction between tree ontogeny and genetic factors is expected. In this study, we investigated the genetic determinism of architectural traits in the olive tree, accounting for tree development over 5xa0years until first flowering occurrence. We studied an F1 progeny issued from a cross between two contrasted genotypes, ‘Olivière’ and ‘Arbequina’. Tree architecture was decomposed in quantitative traits, related to (1) growth and branching, (2) first flowering and fruiting. Models, including the year of growth, branching order and genotype effects, were built with variance function and covariance structure when necessary. After a model selection, broad sense heritabilities were calculated. During the first 3xa0years, both the mean values of vegetative traits and genetic factor significance depended on the shoot within-tree position. Dependencies between consecutive years were revealed for traits related to whole tree form. Whole tree form variables showed medium to high broad sense heritability values, whereas reproductive traits were highly heritable. This study demonstrates the existence of ontogenic trends in the olive tree, which result in traits heritable only at the tree periphery. A phenotyping strategy adapted to its architectural characteristics and a list of relevant traits, such as maximal internode length, is proposed. Transgressive effects suggest that genetic progress could be performed in future selection programs.

Ongoing domestication and diversification in grafted olive–oleaster agroecosystems in Northern Morocco

This paper analyzes sociohistorical and biological factors that shape olive–oleaster agroecosystems (hereafter OOAs), in northern Morocco and their continuing roles in olive domestication, diversification and food security. Forests are cleared and oleasters (wild olive trees) are preserved by farmers for their valuable oil and for use as rootstocks to graft olive. This practice is among those that have shaped olive domestication in the Mediterranean region. It contributes to the creation of forest-based olive agroecosystems and favors olive intraspecific diversityxa0that is highly adapted to heterogeneous mountain environments. Productions contribute to food security, short trade circuits, land tenure and cultural identity. Ethnobiological studies show a continuity of classification, naming and uses between selected oleaster types and olive varieties suggesting an ongoing domestication process. This is supported by genetic analyses which show a higher concentration of genotypes selected from seedlings that propagate through sexual propagation in OOAs as compared to areas where management of oleasters for oil and as rootstocks is absent. Photointerpretation of aerial images corroborated with field-based observations, show the impacts of exogenous projects since the French and Spanish Protectorate periods to contemporary projects of the state policy “Plan Maroc Vert.” We discuss the importance of OOAs for the preservation of on-farm genetic resources, food security and as models for future agroecosystems within the context of climate change.

Verifying the reliability of hybrid issued from the cross “Picholine marocaine clones X Picholine du Languedoc”

In order to verify the reliability of hybrid population issued from crossing between 3 clones of Picholine marocaine cultivar and the Picholine du Languedoc cultivar, the descendants and their parents were analysed using 35 microsatellite loci. No offspring resulted from self crossing of Picholine marocaine cultivar and 218 descendants among 220 analysed are legitimate. This study showed clearly a segregating population and may be used as a genetic material for linkage map construction and for phenotyping resistance traits related to Spilocaea oleagina disease.

How anthropogenic changes may affect soil-borne parasite diversity? Plant-parasitic nematode communities associated with olive trees in Morocco as a case study

BackgroundPlant-parasitic nematodes (PPN) are major crop pests. On olive (Olea europaea), they significantly contribute to economic losses in the top-ten olive producing countries in the world especially in nurseries and under cropping intensification. The diversity and the structure of PPN communities respond to environmental and anthropogenic forces. The olive tree is a good host plant model to understand the impact of such forces on PPN diversity since it grows according to different modalities (wild, feral and cultivated olives). A wide soil survey was conducted in several olive-growing regions in Morocco. The taxonomical and the functional diversity as well as the structures of PPN communities were described and then compared between non-cultivated (wild and feral forms) and cultivated (traditional and high-density olive cultivation) olives.ResultsA high diversity of PPN with the detection of 117 species and 47 genera was revealed. Some taxa were recorded for the first time on olive trees worldwide and new species were also identified. Anthropogenic factors (wild vs cultivated conditions) strongly impacted the PPN diversity and the functional composition of communities because the species richness, the local diversity and the evenness of communities significantly decreased and the abundance of nematodes significantly increased in high-density conditions. Furthermore, these conditions exhibited many more obligate and colonizer PPN and less persister PPN compared to non-cultivated conditions. Taxonomical structures of communities were also impacted: genera such as Xiphinema spp. and Heterodera spp. were dominant in wild olive, whereas harmful taxa such as Meloidogyne spp. were especially enhanced in high-density orchards.ConclusionsOlive anthropogenic practices reduce the PPN diversity in communities and lead to changes of the community structures with the development of some damaging nematodes. The study underlined the PPN diversity as a relevant indicator to assess community pathogenicity. That could be taken into account in order to design control strategies based on community rearrangements and interactions between species instead of reducing the most pathogenic species.

STUDYING THE GENETIC DETERMINISM OF OLIVE TREE ARCHITECTURE IN A F1 PROGENY 'OLIVIÈRE' × 'ARBEQUINA'

Tree architecture is of major importance for the agronomic performance of fruit tree orchards. It influences tree adaptability to cultivations systems, but also yields and fruit quality. In the present study, we aim at investigating the genetic determinism of architectural traits in the olive tree. A F1 hybrid population was created between two genotypes with contrasted architectures, ‘Oliviere’ and ‘Arbequina’. A phenotyping methodology was applied to analyze traits related to growth, branching and fruiting behaviour, that were measured during the first 4 years of tree growth. Taking into account the influence of tree ontogeny, the phenotypic variability was decomposed into genotypic and residual effects in order to identify the most heritable characters. Topological and geometrical variables showed relatively low to medium broad sense heritability values. The highest heritability values were found for the number of internodes and short laterals per growth unit, and the mean internodes length with H2 value greater than 0.5. Flowering variables showed high heritability values exceeding 0.6. A first QTL (quantitative trait loci) was detected for the number of lateral inflorescences, on the basis of a framework genetic map constructed with 44 SSR loci and 494 AFLP markers.