DISCUSSIONS
The results which implied the significant difference between studied cultivars to mechanical damage show the character of mechanical damage is one of the traits related to cultivar. In fact this character is related to seed coat characteristics that the more integrated seed coat and more lignin content, is more resistant to mechanical damage and if the seed coat be more thin and fragile, the susceptibility to mechanical damage will increase. Also the cultivar with larger seed size has more probability of mechanical damage. The results of many researchers studies particularly Verasilpa and colleagues (2001), Kryzanowski and colleagues (1995) also confirm this subject. On the other hand the extent of mechanical damage directly relate to seed moisture content. In fact there is an optimum level of moisture which causes the minimum mechanical damage. At moistures higher and lower than optimum level the extent of damage as seed crushing and bruising or breakage and cracks will be more. It can be concluded that on optimum moisture the soybean seed physical properties such as seed size, porosity and density are in the best condition for reducing mechanical damage. The results of Kashaninejad and colleagues (2007), Sosnowski and Kuzenyar (19910), Khazaie et al., (2009) studies also verify it.