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University of Khartoum (2014)

Effect of Cryopreservation and Rehydration Methods on Seed Viability of Some Groundnut (Arachis hypogaea L.) Genotypes

Ahmed, Entisar Elilah Bakhiet Mohammed

Titre : Effect of Cryopreservation and Rehydration Methods on Seed Viability of Some Groundnut (Arachis hypogaea L.) Genotypes

Auteur : Ahmed Entisar Elilah Bakhiet Mohammed

Université de soutenance : University of Khartoum

Grade : Master of Science (MS) 2014

Résumé
A series of experiments were carried out to determine the sensitivity of five groundnut (Arachis hypogaea L.) genotypes (Sodari, Ghibaish, Barberton, ICGV121 and an Advance line) to desiccation under seven saturated salt solutions (H2SO4, KOH, K2CO3, NH4CL, (NH4)2SO4, KCL and KNO3) with specific relative humidity at 35ºC. Freezing in liquid nitrogen temperature (-196ºC) was done after desiccation to determine freezing sensitivity. The objectives of the study were to determine whether the variation in seed physical and chemical characteristics, dehydration rate and water desorption isotherms had an effect on seed viability. Also WC50 (water content at which 50% of seed viability is lost) and HMFL (high moisture freezing limit) were estimated to quantify seed desiccation and freezing sensitivity, respectively. Finally, the effect of different rehydration methods on the sensitivity of desiccated-frozen seeds was evaluated. The data were collected on seed physical and chemical characteristics, dehydration rate, desorption isotherms and water binding parameters. The equilibrium seed water content of desiccated seeds, germination percentages and rates of desiccated and desiccated-frozen seeds, WC50, water activity, water potential, HMFL and their correlations with other parameters were determined. Germination percentages of desiccated-frozen seeds, as influenced by rehydration methods, were also determined. Equilibrium mean water content in g H2O.g-1 dw was determined gravimetrically when seeds were oven-dried under 105ºC for 24 hrs. Water desorption isotherms and their parameters were obtained using the modified D’Arcy-Watt Model. Seed desiccation sensitivity (designated as WC50) was obtained using the Quantal Quadric response model. Freezing sensitivity was determined using high moisture freezing limit (HMFL). Desiccated-frozen seeds were rehydrated using pre-humidification and pre-heating in contrast to directly sown seeds. In the present study, the constructed desorption isotherm curves generally conformed to the expected inverted sigmoid shape with three distinctive regions of water binding sites characteristic of the orthodox seeds. This support the significant increases in seed viability (germination percentage) with decreases in equilibrium water content obtained in this study. However, the significant differences in germination percentages and rates of desiccated and desiccated-frozen seeds among the tested genotypes were associated with variation in seed physical and chemical characteristics. All seeds withstood low level of equilibrium water content (below 0.1g H2O.g-1dw) implying that they are not sensitive to desiccation and freezing as determined by sensitivity indicators (WC50, aw50, Ψ50 and HMFL). In this respect, Barberton, Ghibaish and Advance line showed less sensitivity to liquid nitrogen (HMFL value of 0.1g H2O.g-1dw) than Sodari and ICGV121 (HMFL values of 0.06 and 0.05g H2O.g-1dw, respectively). Correlation analyses indicated that equilibrium seed water content was positively correlated with seed germination percentage and rate after desiccation and freezing. Although WC50 was not correlated with all seed physical and chemical characters, it was positively correlated with HMFL indicating that the sensitivity of seeds to freezing depends upon its level of desiccation. Rehydration methods decreased the sensitivity of desiccated-frozen seeds especially when the initial rate of water uptake was slow to avoid the deleterious imbibitional injury. In conclusion, groundnut seeds under study are amenable to liquid nitrogen exposure ; hence they can be safely cryopreserved for long-term storage

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Page publiée le 16 septembre 2018