The seed moisture content (MC) is one of the key factors affecting the seed longevity. It was generally recognized that a further reduction in seed MC below the empirical critical MC (5%) could induce harmful effect on seed viability. However, some studies have showed that there is no harmful effect induced by ultradrying in some seeds, and that the storability of ultradried seed is improved during past ten years. It was recently demonstrated that drying seed beyond the optimum MC provided no additional benefit to longevity and may even accelerate the rate of aging. Further researches on the determining of the optimum seed MC might lead to a debate regarding the various parameters involved. Because of the differences in chemical composition of seeds, seed MC can not reflect the actual state of water in seed. Studies on physical state as well as thermodynamic analysis of water in seed would provide theoretical bases for ultradry seed storage.
