Effects of Some Environmental Factors on Germination and Longevity of Downy Brome (Bromus tectorum) Seeds

The effects of environmental factors on germination and longevity of downy brome seeds were examined in laboratory and field experiments. Downy brome could germinate in a broad range of temperatures (15/6, 20/10, 25/15, 30/15, and 35/20ºC). The germinability, however, was different depending on the temperature range and the results showed that the highest germination was occurred in 20/10ºC (91%) under continuous dark regime, while the lowest germination percentage was observed in 35/20ºC (5%) under light/dark conditions. Salinity showed significant adverse effect on germination of this weed, so that the highest germinability was at 0 concentration of NaCl (89%). Increased salinity levels significantly decreased downy brome germination and its germination completely ceased at 320 mM NaCl. This study indicated that increasing pH in the range of 4 to 8 resulted in enhanced germination percentage, while further increase of pH significantly reduced germinability. Another experiment in which seeds were after-ripened at different depths in the field showed that increased burial depths from 0 to 10 cm accelerated seed after ripening and the lowest germination occurred in the seeds which were placed on the soil surface.