The Effect of Gibberellic Acid, After-Ripening and Eliminating Glumelle on Germination of Japanese Brome (Bromus japonicus Thunb.) Seeds

Japanese brome (Bromus japonicus Thunb.) is one of the most important annual narrow leaf weeds in wheat fields of Sistan and Baluchistan province. About 2 to 22 percent of yield loss depends on density and wheat cultivar. Fresh seeds of B. japonicus are classified on non-dormant or non-deep physiological dormant seeds. Treating by gibberellic acid is highly effective in both the embryo growth and seed germination processes in this type of dormancy. One of the important goals of germination and emergence studies in weed science is prediction of the dormancy longevity and germination time in field conditions. Therefore, the aim of this study was to evaluate germination properties of seeds at different times after physiological examination under the effect of gibberellic acid. An experiment was carried out as factorial based on randomized complete block design in 2013. Experimental factors were included six levels of 1- period of after ripening (immediately after harvest, 2, 4, 6, 9 and 12 months after harvest) and 2- pre-treatment by gibberellic acid for 48 hours in four concentrates (0, 100, 200, 300 mg lit-1). The effect of these factors was evaluated for two types of Japanese brome seeds; glumelle and nonglumelle. Samples placed into the incubator and temperature was kept on 20◦C in dark condition. Germination percentage, germination rate and mean germination time were recorded in every 48 hours. Analysis of data was performed using PROC GLM procedure of SAS (Version 9.2; SAS Institute, Cary, NC, USA). A three parameter sigmoidal model was fitted to the data using PROC NLIN of SAS to find the relationship between germination percentage and gibberellic acid concentration. The results showed that the effect of all experimental factors on germination properties was significant (P <0.01). Removal of glumelle, increasing the concentration of gibberellic acid and keeping more time after harvesting significantly increased germination percentage. The fitted model showed that the time to reach 50% of maximum germination in non-glumelle seeds was less than one month (T0> 1). In glumelle seeds, it takes about 6 months to reach 50% of its maximum (63%) in the 12th month after harvest. Germination rate increased from 1.7% per day in glumelle seeds to 15.5% per day in non- glumelle seeds. The duration of seed storage had a significant effect on its germination rate, so that at 12 months after harvest, it was approximately 15 times higher than harvest time. For the first three times after harvest; 0, 2 and 4 months after harvest, non-glumelle seeds showed a higher mean germination time than intact seeds, and vice versa, for the second three times; 6, 9 and 12 months after harvest. In this study, although the effect of gibberellic acid on enhancing germination was positive and there was significant differences among the four levels of this hormone, but its effect on glumelle seeds was higher than nonglumelle seeds. In other words, by removing glumelle, the effect of seed germination is reduced by the use of gibberellic acid. This experiment showed that removing glumelle and keeping seeds of the Japanese for 2 months and more have the greatest contribution to reduce non-deep physiological dormancy of this weed.