Crioconservação de sementes de acessos de feijão crioulo (Phaseolus vulgaris L.) cultivadas na região semiárida da Paraíba.

Abstract

The common bean (Phaseolus vulgaris L.) is one of the most consumed grains in the world. Its importance is mainly conditioned by its nutritional value, as it is the main source of protein for economically disadvantaged communities. The conservation of traditional varieties (landreces) is important, in the perpetuation of these accessions over time, and in what implies the production of varieties with more productive and resistant characteristics. In this sense, the objective of the Thesis was to evaluate the cryopreservation of P. vulgaris L. bean seeds, performing the physical and chemical characterization, determining the limit water content for cryopreservation, observing the drying and freezing kinetics and evaluating their physiological potential against cryopreservation and other types of storage. The experiments were developed in the laboratories of the Academic Unit of Food Engineering, belonging to the Center for Technology and Natural Resources - CTRN of the Federal University of Campina Grande, at the Brazilian Agricultural Research Corporation (Embrapa) cotton unit, located in the city of Campina Grande, Paraíba and in the laboratories of the Center for Research in Food Analysis (NUPEA) located at the State University of Paraíba UEPB Campus I - Campina Grande - PB. The bean seeds of the three accessions black, white (ovo de rolinha) and large blue (gordo azul) were purchased directly from local producers from several cities in the semi-arid region of Paraíba, associated with the Community Seed Bank (BSC) that integrate a network called Sementes da Paixão. Initially, the physical characterization of the three bean accessions was carried out, measuring the variation in the physical characteristics: length, width, thickness, mass of a thousand seeds, apparent specific mass, angle of repose and porosity, as a function of the water contents of 4, 6, 8, 10, 12 and 14% on a wet basis (w.b.), then the centesimal composition of the beans was determined (water, protein, lipid, carbohydrate and ash content). Drying kinetics were performed with beans with a moisture content of 25% b.u, at temperatures (55, 45, 35 and 25 °C) and the determination of drying curves, measuring the thermodynamic properties of heat transfer and water mass, as well as the freezing kinetics at four temperatures (-30, -80, -130, -180 °C) in bean seeds for the three bean accessions, obtaining the thermodynamic properties involved in this process (effective thermal diffusivity, activation energy, enthalpy, entropy, and Gibbs free energy) all seeds had a moisture content around 10% to 12% b.u. The determination of the Limit Water Content for Cryopreservation (TALC) was performed for each accession by humidifying and/or drying the seeds, at each pre-selected water content of 4, 6, 8, 10, 12 and 14% (b.u). Then, the samples were stored in nitrogen vapor at -180 °C for a period of five days, after which the samples were thawed and germination and vigor tests were performed to establish the best water content. Once the TALC was determined for each variety, samples with 200 seeds were deposited at four storage temperatures, 25, 10, -60 and -180 °C, in five time periods (0, 90, 180, 270 and 360 days) of cryostorage, after the storage periods the samples were thawed and subjected to germination and vigor tests. The physiological evaluation of the seeds over a period of one year confirmed the hypothesis that bean seeds of the studied accessions are tolerant to cryopreservation and support the highest germination and vigor rates when stored in liquid nitrogen vapor or at low temperatures. These results are relevant to the conservation of agro-sociobiodiversity in native seeds and may mediate the action and creation of protective measures for these traditional seed species with orthodox characteristics in times of climate change.