Secagem, beneficiamento e armazenamento de sementes de pinhão manso (Jatropha curcas L.)

Abstract

The objectives of this study was to investigate the effects of drying, processing and storage on physiological quality of physic nut seeds. The experiments were conducted at the Federal University of Viçosa. Three experiments were carried out using seeds of physic nut from the experimental farm of EPAMIG, located in the Janaúba-MG. In experiment I, the seeds with water content of 32%, were dried in the shade, the sun and forced circulation oven at temperatures of 33 and 43 °C until the water content of 9 ± 1%. The physiological quality of seeds was evaluated by germination, first count of germination test, electrical conductivity, accelerated aging, seedling emergence index and seedling emergence rate. The temperature of 43 °C provides faster drying of the seeds, which lasted 42 hours. On drying at 33 °C, the sun and shadow, this period was longer, with 54, 144 and 456 hours respectively. The drying in the shade provided immediate reduction in the physiological quality of seeds. The seeds dried in the sun or at a temperature of 33 °C did not differ regarding the physiological status and were better than those dried in the shade, however, germination was lower than those dried at 43 °C after 180 days of storage. The drying temperature of 43 °C did not affect seed germination and slightly reduced the vigor, even after 270 days of storage. As the highest temperature used did not affect seed germination, this suggests it was the time spent on seed drying crucial to its conservation. It was concluded that there was immediate and latent effects of drying in the shade on physiological quality of seeds of physic nut; seeds of physic nut can be dried at a temperature of 43 °C, and time spent drying must not exceed 42 hours. In experiment II, physic nut seeds processed in a pneumatic separator, and obtained two classes as the specific mass (heavy and light seeds). To obtain seed lots with different sizes, heavy and light seeds were screened in oblong sieves for large, intermediate, small and even non-size-classified seeds, providing eight treatments: heavy seeds not classified by size, large heavy seeds, intermediate heavy seeds, small heavy seeds, light seeds not classified by size, large light seeds, intermediate light seeds and small light seeds. The experiment design was a factorial 2 x 4 (specific mass x size) completely randomized with eight biological replications. Before the storage and twelve months of storage we assessed its seed quality with the following seed evaluations: germination on the 5th and 10th days after test settle, electric conductivity, accelerated aging, seedling emergence index and seedling emergence rate. There was significant effect of seed specific mass on physiological quality of physic nut seeds; heavy seeds showed higher quality than the lighter ones. Seed size showed no effect on physiological quality of physic nut seeds. We concluded that the specific mass of physic nut seeds influences on its physiological quality and heavier seeds have higher physiological quality than lighter ones. There was no effect of seed size on physiological quality of physic nut seeds. In experiment III, the seeds, with water content of 8,3%, were packed in cloth and plastic and stored for 450 days under laboratory conditions (no temperature control) air-conditioned room (18 to 20 oC), refrigerated chamber (10 to 12 °C) and refrigerated chamber (5-7 °C). At the beginning of storage and every 90 days, we determined the water content, germination and vigor of seeds. Reduction in the physiological quality of seeds of physic nut occurred during storage, regardless of the temperature and packaging. The seeds can be stored for 270 days at room without controlled temperature and relative humidity, in Viçosa-MG, both in plastic packaging such as cloth. From 270 days, it is recommended to use refrigerated environment, with temperatures ≤ 18-20 °C for seed storage, regardless of packaging used.