The Effect of Different Treatments on Seed Dormancy Breaking of Weed Stalked Bur Grass Tragus racemosus (L.) AlI

Stalked Bur Grass (Tragus racemosus L.) is an angiosperm annual plant with C4 photosynthesis pathway and stolon. It grows in hot and dry summers. This plant spreaded throughout the world from hot regions of Africa. It is regularly seen in barren lands or in between the generations with sequential initial stages with light-texture soils. Seed dormancy is in fact a physiological phenomenon which is observed in the seeds of most crops, pasture plants, medicinal herbs and weeds. Dormancy allows the plant to guarantee its germination and survival for long years and to survive through adverse environmental conditions through its spatial and temporal spread.
In order to evaluation dormancy break of Tragus racemosus L. seeds, an experiment was carried out based a Randomized Complete Block Design with four replications in research laboratory of Department of Agriculture, Birjand University during 2013. The initial experiments showed that the seeds of Stalked Bur Grass had initial dormancy and were unable to germinate at normal conditions, so that less than 5% of the seeds germinated. The studied treatments for breaking seeds dormancy included control (seeds disinfection by distilled water), wet chilling at 4°C for 1, 2, 3 and 4 weeds, treatment with H2SO4 at 97% for 20, 40, 60 and 80 seconds, treatment with KNO3 at 0.2, 0.4, 0.6 and 0.8% for 24 hours and treatment with Gibberellic acid (GA3) at 50, 100, 200 and 400 ppm. In this study, 25 seeds of Stalked Bur Grass were uniformly placed in petri dishes with the diameters of 9 cm on Watmann filter papers and were applied with 5 mL distilled water. The number of germinated seeds was counted on a daily basis for 21 days. In the end, germination percentage and rate was determined.
The results revealed that the effect of all studied levels of all treatments were significant on germination percentage and rate. The highest germination percentage (76%) was observed under wet chilling treatment at 4°C for 4 weeds and the lowest one (6%) was observed in control. The highest germination percentage under H2SO4 treatment was 41% obtained at the level of 80 seconds, under KNO3 treatment was 69% obtained at the level of 0.8%, and under GA3 treatment was 62% obtained at the level of 400 ppm. The highest germination rate (18.24 seeds per day) was observed at KNO3 treatment (0.8%) and the lowest one (0.91 seeds per day) was observed in control. In addition, the highest germination rate under H¬2SO4 treatment was 15.28 seeds per day obtained at the level of 80 seconds, under wet chilling was 13.25 seeds per day obtained at the level of 3 weeks, and under GA3 treatment was 12.08 seeds per day obtained at the level of 200 ppm. Wet chilling enhances the production of such stimulants as gibberellins. On the other hand, chilling treatment may reduce ABA amount or the sensitivity of embryo to ABA which can play a role in seeds dormancy breaking. KNO3 is likely to increase the sensitivity of germinating seeds to light acting as a complement factor for phytochrome which results in higher germination of the seeds. Most researchers believe that dormancy is broken by the balance between growth inhibitors like abscisic acid and growth stimulators like gibberellins. In addition, gibberellins activate a special signaling pathway that reduces abscisic acid in seeds and in contrast, auxins and cytokinins of the seeds are increased to a level enough for inducing dormancy break.
In the present study, the germinated seeds were counted for 21 days. The highest germination percentage (76%) was observed under wet chilling treatment for 4 weeks and the lowest one (6%) was observed under control treatment. The highest germination rate (18.24 seeds per day) was observed under KNO3treatment (0.8%) and the lowest rate (0.91 seeds per day) was reported under control treatment. According to the results it can be concluded that the dormancy of Stalked Bur Grass seeds belongs to physiological dormancy type.