Seedlings of Argan (Argania spinosa) from different geographical provenances reveal variable morphological growth responses to progressive drought stress under nursery conditions

To alleviate the combined effects of water and heat stress prevailing in drylands, the choice and introduction of appropriate plant species to these conditions is essential for the success of planting in rehabilitation projects. The argan tree (Argania spinosa) is a vigorous plant, admirably adapted to dry climates, with indisputable physiological and ecological characteristics that make of this tree an ideal plant to fight against erosion and desertification process, which seriously threaten arid lands. However, the geographical origin of seeds/seedlings represents a determining factor. In this context, we investigated the morphological responses of growth in two provenances of argan, the provenance of Tindouf PT' from Algeria and that of Agadir PA' from Morocco; under water stress conditions. The experiment attempts to evaluate the level of drought tolerance of these two provenances for selecting the planting material that copes and adapts better to hot arid lands. Argan seedlings of both provenances (PA and PT) were submitted to a water stress gradient (75, 40, 20, and 10% of field capacity), then morphological parameters (shoot height, number of leaves, number of spines, root collar diameter, length of taproot) were measured after 3, 6, 9 and 12 months of growth. All variables of morphological growth varied significantly (P<0.001) between water stress levels, seed geographical provenances and seedling growth ages. The overall of results concerning morphological parameters indicated that the increase of water stress induced in both argan provenances: a decrease in shoot height associated with an increase in length of taproot that resulted in the reduction of leaf numbers and radial growth but the increase the number of spines. The argan plantlets of Agadir have completely failed to tolerate water stress of 10% FC. Under water stress (40, 20, 10% FC), argan seedlings of Tindouf revealed higher growth results than those of Agadir. PT seedlings offset the water deficit by root elongation to ensure growth of the various components of the aerial part. PT seedlings were more resilient to drought stress as compared to those of PA. The highest growth results were obtained with 40% FC in PT seedlings, and with 75% FC among PA seedlings. It is recommended to use the PT seeds in planting projects under drought conditions, while PA seeds are more suitable under conditions of non-water deficit.