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Influence of Ultra-drying with Desiccants of the Viability of Some Crop Seeds Stored in Sealed Container
Thesis Abstract:
The recommended practice for long-term germ plasm 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 five percent (ultradrying).
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°C; 2) the equilibrium moisture content (EMC) under very low RH at 26°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 pekin ens is (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°C, silica gel was fastest and hydrogel was the slowest.
Under RH of 0, 5, 10, and 15 percent at 26°C, the corresponding EMC were I .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, 2.6 1,3.86, 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, I 0, and I 5 percent in plastic aluminum foil laminate bags, 0.15 mm thick, kept at 26°C. After four months, corn seeds with initial moisture content of 9.14 percent had moisture contents of 4.12, 5.00, and 6.15 percent at 5, 10, and 15 percent RH, respectively. When stored with silica gel and with calcium oxide, the moisture contents were reduced to 4.29, 5.29, and 6.54 percent, respectively. In mung bean, moisture content decreased from 8.79 to 3.71, 4.78, and 5.71 percent when stored with silica gel and 3.68, 4.72, and 5.81 percent with calcium oxide. In kenaf, the decrease was from 8.19 to 2.83, 3.76, and 4.51 percent with silica gel and 2.48, 2.90, and 3.75 percent with calcium oxide. EMC was reached after at least 2-4 months, depending on initial moisture content and kind of seed.
Ultra-drying of seeds by packing them with silica gel or calcium oxide as dessicant did not induce any significant change in seed gennination and vigor within the four months of storage. However, mung bean seeds showed deep carcass across cotyledons, slow growth rate, and greater electrical conductivity. Corn seeds also showed slightly higher electrical conductivity. These were attributed to insufficient humidification prior to the tests, resulting in imbibition injury from rapid uptake of water by the still very dry seeds and not through ultra-drying injury. Hardseededness was observed in mung bean (2-7%) and kenaf ( 6-1 I%) as a resu It of ultra-drying.