Effects of temperature and presoaking on germination, root length and shoot length of sesame (Sesamum indicum L)

In many regions of the world, sesame (Sesamum indicum L.) is planted during the winter following rice harvest These winter plantings subject the seed to cold and wet soils, with erratic germination and seedling growth. This study was initiated to evaluate two sesame cultivars for germination, root length, shoot length and root/shoot ratio at 8 days after planting as influenced by temperature and presoaking treatments. The presoaking treatments included soaking the seed for 2 or 12 hr in water or gibberellic acid (GA(3)) at 100 or 500 mg l(-1) in addition to an unsoaked control. After soaking, the seeds were evaluated for germination and seedling growth in growth pouches in growth chambers set at 15, 20, 25 or 30 degrees C. Germination was 100% for all treatments at 20, 25 and 30 degrees C. At 15 degrees C, all presoaking treatments, with the exception of the 2-hr soak in water, increased (P<0.05) the germination by 6-12% over the unsoaked seed. Further, soaking seed for 12 hr in either concentration of GA(3) increased (P<0.05) the germination to nearly 99%. No differences (P>0.05) among the presoaking treatments for root and shoot lengths were noted at 15 degrees C. At 25 and 30 degrees C, some reductions in root growth were noted from the 500 mg l(-1) GA(3) treatment at the 2-hr soak period when compared to unsoaked seed. Conversely, at 20 and 25 degrees C the 2-hr soak period in 500 mg l(-1) GAB stimulated (P<0.05) shoot growth over that of the unsoaked seed. The root/shoot ratio at 15 degrees C was increased (P<0.05) over that of the unsoaked seed by presoaking the seed for 12 hr in 500 mg l(-1) GA(3); however, no differences (P>0.05) were noted at 20, 25 or 30 degrees C. If sesame seeds are to be planted in cool soils (ca 15 degrees C), soaking the seed for 12 hr in 500 mg L(-1) GA(3) should enhance germination and increase the root/shoot ratio of the developing seedlings. These results indicate that the seeding rate could be reduced and the seedlings should be less susceptible to desiccation due to increased root development relative to shoot development.