(SRBIAU), Tehran-Iran 2Institute of Seed and plant Certification and Registration-Karaj-Iran 3Institute of Seed and Plant Improvement-Karaj-Iran

An experiment was conducted to evaluate soybean seed vigor in natural aging condition as factorial experiment based on completely randomized design (laboratory section) and complete randomized design (field section) with 3 replications in Seed and Plant Certification and Registration Institute (SPCRI), Karaj, Iran in 2012-13. The treatments included two cultivars of Williams and L17. The seeds were stored in controlled storage at recommended temperature and relative humidity for 6, 18 and 30 months and germination & vigor tests were conducted. The cv. Williams had significantly more germination percent compared to L17. The germination percent significantly was decreased by increasing the storage duration. Along with decrease of germination percent; the number of abnormal seedlings was significantly increased. Williams showed more resistance to seed deterioration that can be related to genetic attributes of this cultivar or structural characteristics such as seed coat, reserved matters, etc. The measured field characteristics were similar to measured laboratory traits. The higher primary and final seedling emergence, more accumulated emergence rate and also higher seedling emergence rate was related to cv.Williams. Approximately 25 % reduction in final seedling emergence was observed yearly by increasing the storage time. Higher reduction was recorded in accumulated emergence rat