Efeito do armazenamento de criogênio na qualidade fisiológica de sementes de algodão e amendoim.

Abstract

Cryogenic storage of seeds is a way of preserving genetic diversity of plant species, however, for efficient storage of the seed, its physiological quality should be maintained for the longest period, which depends on prior knowledge of the physiological behavior of the seed during storage. The objectives was to study the physical properties, hygroscopic equilibrium moisture, kinetic of cryogenic freezing at different temperatures and moisture contents, the determination of water content limit for the cryopreservation and cryopreservation for six months of seed Topaz cotton and peanuts Havana. For the physical properties determined the actual volume and unity density of the seeds by the method of measuring the mass of water displaced; bulk density was calculated by the relationship between seed mass and the volume occupied by these seeds; the porosity, as the ratio between the bulk density and the unity density; specific heat, thermal conductivity and thermal diffusivity. seeds containing more than 4, 8, 10, 12 and 14% wb water content were used, at temperatures of -20 °C (freezer), -60 °C (cryogenic counter), -150 °C (counter Ultrafreezer) and -196 °C (liquid nitrogen) to the kinetics of freezin. To limit moisture content to cryoconservation of the seeds were dried and / or humidified to obtain the levels of 4, 6, 8, 10,12, 14% wb then cryopreserved in liquid nitrogen (-196 ° C) in nitrogen vapor (-150 °C) in cryo counter (-60 °C) at -20 °C and ambient temperature for a period of 5 days and submitted after slow thawing, the germination and vigor tests. For cryogenic storage, seeds were cryopreserved for 30, 60, 90, 120, 150 and 180 days at 25, - 20, 60, -150 and -196 °C and at the end of each storage period, seeds were submitted to the germination and vigor tests. It was found that one of the thousand seed mass, the water content in the seeds resulted in a high sphericity. With increasing water content, the unity density, bulk density and porosity decreased. The equilibrium moisture content of cotton and peanut Havana Topaz water are directly proportional to the relative humidity and decreases with increasing temperature for the same amount of equilibrium relative humidity. Henderson's model modified by Cavalcanti-Mata was best represented the hygroscopicity of cotton seeds and the Sabbah model for peanut seeds. The curves obtained for the freezing temperatures of -25, -60, -150 °C and -196 resemble the curve for freezing a material with a low water content where the kinetics of freezing is expressed by an exponential curve for thermal diffusivity results within the same water content, there is an oscillation of these values, but are a set pattern of increased or decreased, with a consequent temperature variation. The cotton seeds have a TALC from 6 to 8% bu -170 °C and 8% wb to 196 °C. The peanut seeds so if cryoconservated well at temperatures of -170 ° C and -196 °C for a range of water content of 10-12% wb cryogenic storage of cotton seed and peanut Havana Topaz increased the percentage of germination and seed vigor studied for 6 months.