Abstract
The relationship between seed moisture fluctuation and development of seed with tortoiseshell-pattern wrinkles in a standing soybean plant was investigated. When the seed absorbed moisture after being dried to achieve a single seed moisture level of 13% or below, the seed coat became detached from the cotyledon. The moisture absorption rate of the seed coat immediately after moisture absorption was faster than that of the cotyledon. Subsequent repeated drying and moistening conditions caused repeated development and loss of tortoiseshell-pattern wrinkles, and the wrinkles gradually increased. These results suggested that when a seed absorbed moisture after being dried to achieve a single seed moisture level of 13% or below, the seed coat became detached from the cotyledon because of the difference in moisture absorption rates between the seed coat and cotyledon. Thus, it was assumed that further absorption of moisture caused development of tortoiseshell-pattern wrinkles. After that, although wrinkles temporarily disappeared in some seeds due to dryness during daytime, additional moisture, such as night-time dew, caused reappearance of tortoiseshell-pattern wrinkles. Subsequent repeated drying and moistening conditions caused repeated development and depletion of tortoiseshell-pattern wrinkles, leading to the loss of seed coat elasticity and establishment of permanent tortoiseshell-pattern wrinkles. These results imply the importance of harvesting plants immediately after seed maturation to prevent development of tortoiseshell-pattern wrinkles.
