Ahmed Oukabli

Genetic structure and core collection of the World Olive Germplasm Bank of Marrakech: towards the optimised management and use of Mediterranean olive genetic resources

The conservation of cultivated plants in ex-situ collections is essential for the optimal management and use of their genetic resources. For the olive tree, two world germplasm banks (OWGB) are presently established, in Córdoba (Spain) and Marrakech (Morocco). This latter was recently founded and includes 561 accessions from 14 Mediterranean countries. Using 12 nuclear microsatellites (SSRs) and three chloroplast DNA markers, this collection was characterised to examine the structure of the genetic diversity and propose a set of olive accessions encompassing the whole Mediterranean allelic diversity range. We identified 505 SSR profiles based on a total of 210 alleles. Based on these markers, the genetic diversity was similar to that of cultivars and wild olives which were previously characterised in another study indicating that OWGB Marrakech is representative of Mediterranean olive germplasm. Using a model-based Bayesian clustering method and principal components analysis, this OWGB was structured into three main gene pools corresponding to eastern, central and western parts of the Mediterranean Basin. We proposed 10 cores of 67 accessions capturing all detected alleles and 10 cores of 58 accessions capturing the 186 alleles observed more than once. In each of the 10 cores, a set of 40 accessions was identical, whereas the remaining accessions were different, indicating the need to include complementary criteria such as phenotypic adaptive and agronomic traits. Our study generated a molecular database for the entire OWGB Marrakech that may be used to optimise a strategy for the management of olive genetic resources and their use for subsequent genetic and genomic olive breeding.

Anatomical and morphological study of apple (Malus x domestica Borkh.) flower buds growing under inadequate winter chilling

Summary Some apples cultivars produce low yields when grown in regions with inadequate winter chilling. Their unsatisfactory development is attributed to the lack of climatic adaptation which causes some abnormalities in bud differentiation. The development of reproductive spurs is erratic, leading to vegetative shoots, and the flower index is very low. The purpose of this work is to understand the flower differentiation problem. An assessment was made through morphological and histological studies, also an analysis of climatic data was performed in an attempt to identify the responsible factors. The number of chilling hours recorded was about 695. Defoliation was delayed and happened during the second week of January. Bud break was advanced by 10 d in comparison with the average period. The spurs density (12 and 23 spurs per m of twigs) was similar to the values observed in normal situation. The buds carried by these spurs evolved into vegetative shoots for all variety × rootstock combination used in this study. The average of this transformation was 47 and 50% for ‘Golden Delicious’ and ‘Starking Delicious’, respectively. A flowering index obtained was very low (1.3 kg per tree). Anatomical observations carried out on buds collected in October showed that differentiation was undertaken and the floral primordium was already formed with some abnormalities in flower development in later stage. At anthesis, internal structures of the buds showed primordia disorganized. Reproductive organs presented pistil abortion with low microsporogenesis. Xylem vessel elements were not observed at the base of the bud and vascular connection was not established. This problem in flower development occurred at this stage which was affected by external factors. The winter was characterized by periods of high temperatures which affect negatively the accumulation of chilling units. The mode of action of temperature, notably of chilling on the formation of flowering organs and vessels, remains to be determined.

Traditional agroecosystems as conservatories and incubators of cultivated plant varietal diversity: the case of fig (Ficus carica L.) in Morocco

BackgroundTraditional agroecosystems are known to host both large crop species diversity and high within crop genetic diversity. In a context of global change, this diversity may be needed to feed the world. Are these agroecosystems museums (i.e. large core collections) or cradles of diversity? We investigated this question for a clonally propagated plant, fig (Ficus carica), within its native range, in Morocco, but as far away as possible from supposed centers of domestication.ResultsFig varieties were locally numerous. They were found to be mainly highly local and corresponded to clones propagated vegetatively. Nevertheless these clones were often sufficiently old to have accumulated somatic mutations for selected traits (fig skin color) and at neutral loci (microsatellite markers). Further the pattern of spatial genetic structure was similar to the pattern expected in natural population for a mutation/drift/migration model at equilibrium, with homogeneous levels of local genetic diversity throughout Moroccan traditional agroecosystems.ConclusionsWe conclude that traditional agroecosystems constitue active incubators of varietal diversity even for clonally propagated crop species, and even when varieties correspond to clones that are often old. As only female fig is cultivated, wild fig and cultivated fig probably constitute a single evolutionary unit within these traditional agroecosystems. Core collections, however useful, are museums and hence cannot serve the same functions as traditional agroecosystems.

SELF AND CROSS POLLINATION EFFECTS ON POLLEN TUBE GROWTH AND FERTILIZATION IN SELF-COMPATIBLE ALMOND PRUNUS DULCIS 'TUONO'

Summary The inbreeding consequences linked to self compatibility in the cultivated almond, Prunus dulcis (Mill) D. A. Webb were evaluated histologically in the self-compatible cv. Tuono. Self and cross pollen tubes grow at similar speeds in the pistil of ‘Tuono’. The pollen tubes reach the style base 4 d after pollination. The gametophytic interactions did not help in reducing the occurrence, at this level, of inbreeding effects. The development of the embryo sac stimulated by two types of pollination is differentiated when the pollen tubes reach the style base. However, the fertilization process, marked by the fusion of polar nucleus and the elongation of the embryo sac, shows a delay in the case of the selfed ovule. The differentiation of the pollen sac is in fact realized for 20% of the ovules 5 d after self pollination. In this case 80% of the embryo sacs have unfused polar nuclei. For the same period, 80% of the crossed ovules have polar nuclei which are already fused. The type of pollination seems to have a potential effect on ovule viability of embryo sacs which suggest that the inbreeding effects are revealed after fertilization.

Differentiated dynamics of bud dormancy and growth in temperate fruit trees relating to bud phenology adaptation, the case of apple and almond trees

Few studies have focused on the characterization of bud dormancy and growth dynamics for temperate fruit species in temperate and mild cropping areas, although this is an appropriate framework to anticipate phenology adaptation facing future warming contexts which would potentially combine chill declines and heat increases. To examine this issue, two experimental approaches and field observations were used for high- and low-chill apple cultivars in temperate climate of southern France and in mild climates of northern Morocco and southern Brazil. Low-chill almond cultivars offered an additional relevant plant material for comparison with apple in northern Morocco. Divergent patterns of dormancy and growth dynamics were clearly found in apple tree between southern France and southern Brazil. Divergences were less pronounced between France and Morocco. A global view outlined main differences in the dormancy chronology and intensity, the transition between endordormancy and ecodormancy and the duration of ecodormancy. A key role of bud rehydration in the transition period was shown. High-chill cultivars would be submitted in mild conditions to heterogeneous rehydration capacities linked to insufficient chill fulfillment and excessive forcing linked to high temperatures. This would favor bud competitions and consequently excessive flowering durations and weak flowering. Low chilling requirements in apple and almond would conversely confer biological capacities to tolerate superficial dormancy and abrupt transition from endordormancy to ecodormancy without important heterogeneous rehydration states within buds. It may also assume that low-chill cultivars can also tolerate high temperatures during ecodormancy as well as extended flowering durations.

Morphological and molecular diversity and genetic structure of Moroccan cultivated almond (Prunus dulcis Mill.) beside some foreign varieties

In this study, 15 morphological traits and 16 microsatellite markers were used to assess the morphological variability and structure of 68 (33 local and 35 foreign) almond accessions (Prunus dulcis (Mill.) D.A. Webb). Extensive phenotypic diversity was found among the accessions, and results indicated a high variation in leaf and fruit traits. Varieties were separated into two distinct groups with a similarity coefficient of 0.761. Morphological traits were categorized by principal component analysis into five components, which explained 86.5% of the total variation. Nut and kernel traits were dominant in the two first components, accounting for 49.4% of the variation. By contrast, leaf traits accounted for 18.4% of the variation in the third component. The results of molecular analysis (Bayesian clustering approach) did not correspond to morphological groupings, and the second approach was more discriminate. The combination of both approaches revealed the richness among the collected plant materials, which will be useful in breeding programmes of this species.

Phenotypic biodiversity of an endemic wild pear, Pyrus mamorensis Trab., in North-Western Morocco using morphological descriptors

In this paper, we report on morphological diversity, ecology and flowering phenological records of an endangered and an endemic species of Morocco Pyrus mamorensis Trab. For this study, a survey was undertaken in North-Western Morocco (Mamora forest and Zaër region) whereby 67 accessions of P. mamorensis were sampled. A set of 33 genotypes of Pyrus spp. from the international collection INRA-Angers (France) of the genus Pyrus were also analyzed. The variability of the total of 100 accessions was assessed by twenty-six characters including fourteen qualitative and twelve quantitative traits. The results demonstrated high levels of morphological variation in the sampled accessions of P. mamorensis and established the relationships among the local germplasm using the UPGMA cluster analysis and the factorial discriminant analysis. Furthermore, we were able to distinguish three types of flowering in the Mamora forest: early, intermediate and late flowering type. Otherwise, the UPGMA classification comparing local accessions of P. mamorensis to the international collection led to the formation of four major groups showing the closest correspondence to their geographical origins: (1) The North African species represented by P. mamorensis, (2) The East Asian pea species, (3) The West Asian species and (4) The European species. These findings suggest the importance of implementing a conservation strategy preserving the genetic resources of wild pear in North-Western Morocco.

Bottleneck and gene flow effects impact the genetic structure of seed-propagated apricot populations in Moroccan oasis agroecosystems

In order to highlight the genetic status and origin of Moroccan apricot populations, trees were collected from ten oasis agroecosystems and analysed with AFLP markers. A total of 87 accessions and 12 cultivars grown in Moroccan orchards, including ‘Canino’ and ‘Del Patriarca’ cultivars, were surveyed and compared with in situ Tunisian and ex situ Montfavet (France) collections. Our results highlighted a narrow genetic diversity in the Maghreb region (Tunisia and Morocco) associated with a strong differentiation from the other groups, which supports a bottleneck effect. A similar model was illustrated at a finer geographical scale, i.e. the Draa Valley in Morocco. Genetic structure appeared as two major clusters subdivided into six sub-clusters in which Moroccan germplasm constituted specific groups in comparison with other Mediterranean apricots. Moroccan germplasm was classified into three sub-clusters, two of which were formed by genotypes related to ‘Del Patriarca’ and ‘Canino’, respectively. The present study highlights the wide Moroccan apricots diversity in traditional agroecosystems, and also suggests a substantial gene flow occurring from recently introduced cultivars (‘Canino’ and ‘Del Patriarca’) to local apricot populations, thus leading to local germplasm diversification through seedling propagation. If we consider its geographical position, the historical diffusion of the species and farming practices, Morocco could be viewed as an additional centre of secondary diversification for apricot. Understanding the origin and specificity of local apricot populations is crucial for managing local collections in regard to adaptive traits for arid and Saharan conditions as well as for introducing local genetic resources into current breeding programmes.

Identification of self-incompatibility S alleles in Moroccan almond (Prunus dulcis Miller) germplasm using PCR

Summary The S-genotypes of 70 Moroccan almond [Prunus dulcis Miller (D.A. Webb)] accessions collected from different geographical regions of Morocco were determined using PCR and agarose gel electrophoresis. PCR was carried out using seven pairs of primers that amplified different regions of the self-incompatibility S-allele. The results showed that the majority of Moroccan almond accessions had heterozygous S-RNase genotypes, with a total of 109 bands.The sizes of the amplified bands were compared with known S-alleles in almond varieties and labelled accordingly. Alleles S1, S3, S11, and S13 occurred at the highest frequencies (23%, 15%, 12%, and 16%, respectively). Alleles S4, S9, and S27 were not observed in the samples examined, and allele S24 had the lowest occurrence (1%). Moreover, the Sf allele, responsible for self-compatibility in almond, was identified in three local accessions for the first time.The application of PCR to study the diversity of S-alleles in almond germplasm is discussed.