Author : Khajorn Raoprasert

Summary : The recommended practice for long-term germplasm conservation of orthodox seeds is to store seeds with 5 + 1 percent moisture content under very low temperature. Reports point to further improvement in storage life by lowering seed moisture content below 5 percent (ultra-drying). This study explored the use of dessicants for ultra-drying. Three experiments were conducted to determine: 1) the moisture absorbing capacity of silica gel, calcium oxide, and hydrogel in equilibrium with several relative humidity (RH) at 26 degree C; 2) the equilibrium moisture content (EMC) under very low RH at 26 degree C of corn (Zea mays Linn.) representing starchy and large size seed, mung bean (Vigna radiata (L.) Wilczek) for starchy and medium size seed, kenaf (Hibiscus cannabinus) for oily and medium size seed, and chinese cabbage (Brassica pekinensis (Lour.) Rupr.) for oily and small size seed; and 3) desiccants on the viability of corn, mung bean, kenaf, and chinese cabbage seeds stored in sealed containers. Among the types of desiccants tested, calcium oxide had the highest moisture absorbing capacity, followed by hydrogel and silica gel. As regard to time to attain moisture absorbing capacity under the same RH within the range of 0-45 percent at 26 degree C, silica gel was fastest and hydrogel was the slowest. Under RH of 0, 5, 10, and 15 percent at 26 degree C, the corresponding EMC were 1.84, 3.23, 4.74, and 5.98 percent for corn; 1.87, 3.31, 4.90, and 5.98 percent for mung bean; 1.08, 2.61, 3.86, 4.37 percent for kenaf; and 0.91, 2.10, 3.02, 3.32 percent for chinese cabbage. Corn and mung bean seeds showed very small difference in EMC and chinese cabbage seeds had the lowest EMC. Corn, mung bean, kenaf, and chinese cabbage seeds were stored with silica gel or calcium oxide of pre-determined quantity to give an equivalent RH of 5, 10, and 15 percent in plastic aluminum foil laminate bags, 0.15 mm thick, kept at 26 degree C. After four months, corn seeds with initial moisture content of 9.14 percent had moisture .