Establishment of Optimal Protocols for Germination, Rooting and Elongation of four Moroccan Argan (Argania spinosa) Genotypes

Abstract

The establishment of several protocols to lift integumentary and embryonic dormancy is necessary to achieve and hasten the germination of argan tree [Argania spinosa L. (Skeels)], which faces several obstacles, including difficult climatic conditions, overgrazing and excessive harvesting of seeds for oil extraction threatening its natural regeneration. The present work aims to improve the germination and root power under greenhouse, In vitro and on petri dishes in four genotypes of argan tree namely Bouizakarne, Agadir, Admine and Ighrem. The germination under greenhouse is optimized after five pre-treatments of seeds: including the pulping of seeds, the mechanical scarification, the cold storage (4°C) for 1 month, the chemical scarification with sulfuric acid (95%) for 20 min and finally the chemical scarification with hydrogen peroxide (33%) for 24 h. The germination and the in vitro development of the argan tree are evaluated under the control of the medium effect (full and ½ strength MS) and the light effect. The results obtained showed that seed pulping was the most effective treatment under greenhouse with 66.66%. For in vitro culture, ½ strength MS medium recorded the highest germination rate (77.19%). Moreover, the argan tree was indifferent to light in triggering germination. However, light incubation improved germination on full strength MS medium more than on ½ strength MS medium. Yet, ½ strength MS medium incubated in the darkness revealed the highest percentage of germination in vitro with 81%. Thus, in vitro culture was shown to be the most favorable condition compared to other culture conditions. Moreover, it was not only attributed to the improvement of the germination rate but also to the reduction of the latency phase and to a good development of the in vitro plants. Indeed, it was not until day 4 that the kernels started to germinate with 18 days under glass. It was not until two months later that it developed a stem of 5.04 cm and a main root of 15.74 cm in length with possible adventitious roots. This was approved for all genotypes but was very remarkable in Ighrem the most recent genotype.