Methods to Break Seed Dormancy of Rhynchosia capitata, a Summer Annual Weed

Dormancy of weed seeds is a significant feature contributing to their survival rate since it helps the weeds to avoid herbicides and other weeding practices along with unfavorable environmental conditions. We investigated the effects of different dormancy breaking treatments on the germination of Rhynchosia capitata, a common summer annual weed, which is emerging as a weed threat in Pakistan. Seeds were soaked in thiourea, KNO3, HCl, HNO3, and H2SO4, and they were also mechanically scarified (sandpaper). Results indicated that R. capitata seeds show signs of physical dormancy that is mainly due to the impermeability of their coat. Mechanical scarification and acid scarification (soaking of seeds in H2SO4 for 60 and 80 min and in HCl for 12 and 15 h) were very efficient in breaking dormancy and promoting germination. Seed soaking in HNO3 for 1 to 5 d showed little effect whereas various concentrations of thiourea and KNO3 were ineffective in breaking R. capitata seed dormancy. Treatment with sandpaper was very effective in breaking seed dormancy (Table 1). Results indicated that the germination of seeds that were mechanically scratched with sandpaper significantly increased to 100% as compared to HCl treatments. In addition, seeds mechanically scarified with sandpaper had the minimum response time (0.66 d) and mean germination time (2.16 d) when compared to all other treatments. When seeds were scarified with HCl (36%) for 3, 6, 9, 12, 15, and 18 h, seed germination significantly (p < 0.05) increased over the control (Table 1). Seeds treated with HCl for 12, 15, and 18 h had the minimum response time with 50% of the seeds germinating in all the replicates within 1.75, 1.13, and 1.20 d, respectively. Minimum MGT (2.94 and 2.95 d) was detected in seeds treated with HCl for 18 and 15 h, respectively. Both were statistically similar. Seeds treated with HCl for 3, 6, and 9 h had a significantly higher mean germination time than other treatments, but remained equal to each another. Maximum GI (7.75) was observed in sandpaper scarification and after 6 d when seeds were treated with HCl for 15 h. However, there was no germination in the control treatment. Mechanical constraint, including prevention of water and oxygen uptake, and retention or production of chemical inhibitors are some of the possible mechanisms that cause the strong inhibitory effect of the seed coat on seed germination (Taiz and [E. Zeiger], 2002). The results of various treatments in our study co