Condicionamento fisiológico de sementes de Urochloa brizantha

Abstract

Seed priming aims to attenuate the individual differences of each seed that composes a lot. On Urochloa seeds this technique may assist in the rapid and uniform germination and emergence. The aim of this work was to study the water absorption rate, performance of three lots with distinct vigor on Urochloa brizantha seeds, with the use of two different methods of priming using, for seed imbibition, water, PEG solution and urea solution, with or without seed drying after priming. Six different water absorption rates were performed:1- hydro-priming (distilled water) in moistened paper, 2- hydropriming (distilled water) by immersion, 3- polyethylene glycol 6000 (-1.5 MPa) in moistened paper, 4- polyethylene glycol 6000 (-1.5 MPa) by immersion, 5- Urea (150mmol/L) in moistened paper and 6- urea (150 mmol/L) by immersion; until the protrusion of the primary root. The evaluation was performed by the moisture content (kiln at 105 ºC for 24 hours) of seeds during the absorption. To evaluate the physiological performance with or without drying the completely randomized design in a factorial scheme 3 x 11 (three levels of vigor x without priming and ten priming methods), with four repetitions, was used. The treatments were: no priming (control), hydro-priming (distilled water) by immersion for 24 hours and in paper for 20 hours, polyethylene glycol 6000 (-1.5 MPa) by immersion for 24 hours and in paper for 24, 48 and 72 hours and urea (150 mmol/L) by immersion for 24 hours and in paper for 24, 48 and 72 hours. The germination, germination speed index, seedling emergence, emergence speed index, seedling length, vigor index and uniformity were evaluated. The seed lot of Urochloa brizantha of lower vigor absorbs a greater amount of water than the other lots of medium and high quality, both in moist paper and in immersion. Urochloa brizantha imbibition on wet paper prolongs phase II, using PEG solution (- 1.5 MPa) and urea solution (150 mmol / L) in comparison to water, to phase III with contents of 33% and 34%, respectively. The performance of the lots of Urochloa brizantha is variable for the different techniques. Conditioning in water immersion for 24 hours is suitable for batch of superior vigor, in laboratory and field evaluations. For the batch of medium quality, immersion in water for 24 hours is more efficient under laboratory conditions, and immersion in urea for 24 hours under field conditions. For the low-quality lot, the PEG immersion conditioning for 24 hours presents better performance of the Urochloa brizantha seeds. Hydrocondicionamento for 16 hours and immersion in water for 24 hours followed by drying, brings benefits to the germination speed of seed lots of Urochloa brizantha of different levels of quality. The use of physiological conditions with immersion and paper urea solution for 24 and 48 hours is favorable to the performance of Urochloa brizantha seeds in the field for high- and low-quality lots.