ABSTRACT:
Increased demand for livestock products is leading to research on more productive pastures adapted to different environments. Urochloa humidicola is a species adapted to low-fertility conditions and to environments occasionally subjected to temporary flooding and with highly dormant seeds at harvest. Mechanical and sulphuric acid (H2SO4) scarification are used to release these seeds from dormancy; although, there are several side effects. Hydrogen peroxide (H2O2) is linked to dormancy release in many crop species. The objective of this research was to characterize the dormancy release and H2O2 accumulation during one year of storage in dormant spikelets of U. humidicola cv. Llanero equilibrated to 4.5% and 50% relative humidity (RH) and stored at 20 °C, during which time the seeds had moisture contents (MCs) of 0.03 and 0.1 g H2O g-1 dry weight (DW), respectively. The seeds were evaluated initially and at 3, 6 and 12 months; the seeds from spikelets or just caryopses were evaluated. Germination and dormancy percentage, H2O2 content, superoxide dismutase (SOD) and peroxidase (PRX) activity were determined. The germination and H2O2 content increased mainly in the caryopses, and SOD activity increased. Moreover, dormancy and PRX activity decreased during storage. For the first time, it was shown, in U. humidicola cv. Llanero that dormancy release during storage is caused mainly by the accumulation of reactive oxygen species (ROS) in the spikelets even under ultra-dry storage conditions (4.5% RH), and this process could be accelerated by seed storage at a MC of 0.1 g H2O g-1 DW at 20 °C.
Key words:
Brachiaria; germination; oxidative window; ultra-dry storage; ROS