Effects of Pre-sowing Treatments and Abiotic Stress on the Germination of Ceratonia siliqua Seeds of Four Moroccan Biomes

Abstract

In order to improve the germination rate of carob seeds (Ceratonia siliqua L.), we studied the morphological characteristics of the fruits (pod and seeds, integumentary hardness and tolerance to abiotic stress of the seeds) of seven ecotypes of carob trees from four regions of Morocco. The fruits of its seven populations were studied according to seven discriminative characteristics relating to the pods (length, width, thickness, total number of seeds, total weight of the pulp, seeds  per pod and yield of pods per tree) and four discriminative characteristics relating to the seeds namely length, width, thickness and total fresh weight of seeds. Integumentary hardness was evaluated by pretreating the seeds with boiling water and 95% sulfuric acid. Similarly, we also followed the evolution of water absorption by the seeds during 4 days and we evaluated on these seeds pre-treated, effects of different incubation temperatures (10°C, 25°C and 40°C), their tolerance to different concentrations of NaCl, PEG6000 (0MPa, -0.5MPa, -1MPa and -1.5MPa ) and their reversibility. The morphological characterization of the fruits allowed us to group the populations studied into three groups. Soaking the carob seeds in sulfuric acid for 20 minutes improved the germination rate and time. The evolution of water absorption makes it possible to distinguish two phases. The first phase is obtained during the first 24 hours and characterized by a rapid penetration of water, and second phase which lasts over the last 72 hours and which is characterized by a slow entry of water. The optimum temperature for germination of seeds from all provenances is 25°C. The germination behavior of carob under conditions of osmotic stress demonstrated a highly significant treatment effect (concentration of PEG6000) on the rate and mean time of germination and revealed that this species is very resistant to drought. This study also showed that, salt has a depressive effect on the average germination rate, time and length of radicles. The results of the reversibility test showed that the germination of seeds transferred from osmotic stress and salt stress (-0.5, -1 and -1.5MPa) and from the temperature of 40°C. is totally inhibited. On the other hand, seeds transferred from a temperature of 15°C resume germination under optimal conditions. This study allowed us to select a variety with high yield and tolerant to various biotic constraints.