Armazenamento criogênico de sementes de feijão-caupi.

Abstract

Cryopreservation of seeds is the conservation of plant material in ultra low temperatures for long periods. However, for the technique to be effective cryopreservation is necessary to conduct studies regarding seeds. The objective of this work was to study the physical characteristics, water activity, the kinetics of cryogenic freezing at different temperatures and moisture contents, the determination of water content limit for cryopreservation, and cryogenic storage for six months seeds of cowpea varieties Cauamê and Potengi. To the physical characteristics determined the thousand seed weight by weighing batches of a thousand units in a semi-analytical scale, the dimensions with the aid of a caliper and the volume specific mass of the seeds by the method of measurement mass of water displaced; the bulk density was calculated by the relationship between seed mass and the volume occupied by these seeds; porosity, as the ratio between the bulk density and the actual density. To determine the equilibrium moisture content was adjusted to apparatus for Aqualab temperature 40°C and all readings for the seeds with 4, 8, 10, 12 and 14% w.b. were made by repeating this procedure, the adjusting device other storage temperatures of 30, 20 and 15°C. Seeds containing more than 6, 8, 10, 12 and 14% w.b. water were used for the kinetics of freezing, a thermocouple was inserted into the geometric center of each seed and another thermocouple inside the environment in which each reading was given at -20°C, -60°C to -150°C cryogenic counter and liquid nitrogen, -196°C. To limit the water content of the seeds were dried and/or humidified to obtain the levels of 4, 6, 8, 10,12, 14% w.b. then cryopreserved in liquid nitrogen to nitrogen vapor (-170°C) and at room temperature for a period of 5 days and submitted after slow thawing, the germination and vigor and finally tests, the seeds were cryopreserved for 30, 60, 90, 120, 150 and 180 days at 25°C, -20, 60, -150 and -196°C, and at the end of each storage period, seeds were subjected to germination and vigor tests. The dimensions, volume, sphericity and porosity of seeds of cowpea varieties Cauamê and Potengi increase with the increase of water content. With increasing water content, the actual density and the bulk density decreased by their values. The equation proposed by Sabbah was presented the highest coefficient of determination in relation to the other models used for the seeds of cowpea varieties and Cauamê and Potengi. The best percentage of germination of the two cowpea varieties were obtained when these seeds were cryopreserved in nitrogen vapor (-170°C) and liquid nitrogen (-196°C), with a water content of 8% w.b. Physiological quality (germination and vigor) seeds of cowpea varieties Cauamê and Potengi proved effective with the use of methods of cryopreservation, an increase in the percentage in relation to ambient temperature. Curves are exponential cryogenic freezing and not clearly distinguish the three typical phases; model Fourier satisfactorily describes the process for the kinetic freezing cowpea variety Cauamê at temperatures of -20°C to - 60°C and -20°C for Potengi range at all levels water studied the thermal diffusivity increases with decreasing water content at all temperatures and water contents.