The objective of this study was to understand and characterize the physiological and biochemical tolerance mechanisms of Argania spinosa under drought stress for selection tolerant ecotypes. Significant differences were observed among ecotypes in indices of leaf water status studied: stomatal conductance (g s ), predawn leaf water potential (Ψ pd ) and leaf relative water content. There was a significant decrease in these physiological traits with increasing degree of drought stress in all ecotypes. Drought stress significantly increased endogenous H 2 O 2 and lipid peroxidation. Moderate and severe drought stress increased significantly the catalase, superoxide dismutase, peroxidase, polyphenoloxidase and lipoxygenase activities, depending on time. Their constitutive activities were higher in inland ecotypes than in coastal ecotypes. According to canonical discriminant analysis, the inland ecotypes were essentially distinguished from the coastal ecotypes by the following physiological and biochemical traits: Ψ pd , g s , polyphenol oxidase, superoxide dismutase and malonyldialdehyde. Inland ecotypes seem to be more tolerant to drought stress than coastal ecotypes.

The present investigation was undertaken to characterise and to distinguish four contrasting Argania spinosa ecotypes in terms of drought tolerance by exploring the changes of leaf water status, osmoregulation and secondary metabolism. A. spinosa plants corresponding to four contrasting ecotypes (Lks, Alz, Rab and Adm) were subjected to drought stress. The results exhibited that there was a significant decrease in predawn leaf water potential (W pd ), stomatal conductance (g s ) and leaf relative water content under the influence of the intensity and duration of drought stress. Negative and significant correlations were recorded between epicuticular wax load (EWL) and residual transpiration rate. Electrolyte leakage (EL) increased significantly in leaves of plants under drought stress treatment compared to control plants. Furthermore, our data revealed that drought stress can induce shikimate and phenylpropanoid pathways in A. spinosa. A significant induction of phenylalanine ammonium lyase (PAL), shikimate dehydrogenase (SKDH) and cinnamate 4-hydroxylase (C4H) enzymes and an increase in polyphenol content were recorded, of which Lks showed the highest induction and accumulation among ecotypes. Accumulation of polyphenols was positively correlated with the SKDH, PAL and C4H activities. The strong induction of secondary metabolism in Lks might be linked to its better ability of drought tolerance. The proline and soluble sugar content in leaves of all ecotypes increased substantially in parallel with the severity of stress-induced. According to canonical discriminant analysis of our data, the four ecotypes were separated by the following physiological and biochemical parameters: EL, g s , EWL, soluble sugars and polyphenols.

Our study was undertaken to ascertain whether the change of the water status and the activation of superoxide dismutase and their isoenzymes in Argan tree can support edaphic drought tolerance and its recovery under rehydration. An experiment was conducted on four contrasting ecotypes of Argania spinosa plants: two contrasting coastal ecotypes (Admine (Adm) and Rabia (Rab)) and two contrasting inland ecotypes (Aoulouz (Alz) and Lakhssas (Lks)). Drought stress significantly decreased the leaf water potential and stomatal conductance in the four contrasted ecotypes. In terms of biochemical responses, significant accumulation of carbonyl groups, hydrogen peroxide and superoxide radical has been recorded in the leaves of stressed plants reflecting oxidative stress. In parallel, the activities of total superoxide dismutase (SOD) and their isoenzymes Cu/Zn-SOD, Cu/Zn-SOD and Fe-SOD were also found to have increased to scavenging ROS and protecting the cell against induced oxidative stress. The recovery kinetics of A. spinosa, as a response to rehydration, were significant and rapid. According to the traits having the most discriminating power, both inland ecotypes (Lks and Alz) showed a better upregulation of its protective mechanisms compared to coastal ecotypes (Rab and Adm). All these adaptive traits make the inland ecotypes as an elite resource of drought tolerance and might become the new focus of domestication research of argan tree in arid and semi-arid environments.

The argane tree is a remarkable essence by its botanical interest and its socioeconomic value. It is endemic species in the southwest of Morocco, where prolonged drought stress may occur. Although its tolerance has been commonly attributed to various mechanisms at the whole plant, the root system has a main role in the whole process of adaptation. We studied in argane tree plants the change in hydraulic conductivity, electrolyte leakage in root as well as root growth under drought stress and recovery. Our findings showed that the root hydraulic conductivity (Lp) value significantly decreased under drought stress treatment. This was associated with an increase of root electrolyte leakage, signaling the occurrence of an injury to root cell membranes. At root growth level, stressed plants managed to maintain their root elongation despite decreased root mass. After short period of rehydration, the argane tree plants exhibited a tendency of increased hydraulic conductivity during recovery after drought stress, suggesting that this root physiological response may be intimately linked to drought stress tolerance strategies. These results also could be important to contribute to selection of tolerant genotypes and develop argane tree regeneration programs in regions that suffer from lack of water.

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L'arganier est un arbre à usages multiples de grand intérêt socio-économique pour le Sud-Ouest marocain. Il est utilisé pour l'alimentation des hommes et du bétail, en médecine, en cosmétique, tout en permettant de lutter contre la désertification et l'érosion en produisant du bois à diverses finalités. Les peuplements naturels, en constante diminution depuis le XIXe siècle, sont menacés par diverses pressions anthropiques, de plus en plus fortes, réduisant les capacités de régénération naturelle de l'espèce. Dans ce contexte, le Cirad a été sollicité en 2006 afin d'oeuvrer concrètement à la réhabilitation de l'arganeraie, sous la forme d'un projet financé pour une durée de trois ans. Le but de ce projet est d'améliorer, par la recherche appliquée, la qualité de l'arganeraie à travers la production d'arganiers de qualité supérieure issus d'individus sélectionnés. Ceux-ci seront multipliés en masse au moyen des techniques de clonage les plus adaptées, en tirant profit pour les sélections de la grande variabilité existant entre les plants issus de graines, pour produire des populations clonales plus homogènes. Après deux ans de collaboration avec le Centre Régional de Recherche Forestière de Marrakech et l'Université de Marrakech, plus d'un millier de boutures de jeunes arganiers ont pu être produites dans le cadre d'essais de mise au point de la technique de bouturage de l'espèce. Ce matériel sera utilisé comme pieds-mères expérimentaux et pour des tests de comportement au champ, en comparaison à des semis traditionnels. Par ailleurs, sur les quatorze têtes de clones sélectionnées par les populations locales, huit ont pu être mobilisées pour amorcer la propagation en masse par bouturage, avant les tests au champ. Les techniques de multiplication végétative développées pourront également être mises à profit pour la production en quantité de plants à partir des semis issus des fruits récoltés sur les têtes de clones précitées, présumées de qualité supérieure. (Résumé d'auteur)

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The argan tree (Argania spinosa L. Skeels, Sapotaceae) is a genetic resource endemic in Morocco. Genetic diversity within and among 13 populations (130 genotypes) of argan tree was studied using AFLP markers. Having checked twenty combinations of labeled primers for regular genomes (500-6000 Mb) (EcoRI+3/ MseI+3 selective bases) and for small genome (50-500 Mb) (EcoRI+2/MseI+3 selective bases), we selected four combinations specific for regular genome able to produce a relatively high polymorphism and a low error rate (0.12 %). A total of 477 unambiguous peaks were amplified ranging from 70 to 500 bp. The average polymorphism information content (PICAVG) value ranged from 0.19 to 0.23. Marker index (MI) and resolving power (RP) varied from 21.23 to 28.82 and 27.63 to 44.92, respectively. Analysis of molecular variance (AMOVA) showed that 19 % of the genetic variation was partitioned among populations and 81 % of the genetic variation was within populations. This was confirmed by the coefficient of gene differentiation between populations (Gst=0.22), and gene flow was estimated to 1.709. The STRUCTURE analysis, principal coordinate analysis (PCoA) and Unweighyhed Pair Group Method with Arithmetic Mean (UPGMA) revealed that populations of A. spinosa were clustered into three genetic groups. The present results can be explored in the design of in situ and ex situ conservation and management programs.